INTAKE GASKET MAIN PAGE, PLEASE POST Q'S&A'S HERE!

Hey, So much information about the head/intake manifold gaskets here but they are all scattered. Please feel free to copy and paste useful information here. Let this be the main page for the gasket problems.


Okay, first off, I have a question. I am going to replace the intake manifold gasket on my 1998 Chevy Venture 3.4 tomorrow.
I know my way around things but this one looks pretty complicated.
Has anyone done it before and if so, what are the steps. Everything looks so crammed, I'm not sure what to take out first.
Please help me and others with the notorious gasket problems!
Much appriciated if replied to before wednesday, (im trying to get it done before the holiday's, parts stores are closed!!)
Thanks!

Did it myself. Followed the Haines Manual directions pretty much verbatum. My advice.
Have oil and filter for an oil change when finished. Coolant too.
Change the spark plugs with the manifolds off. Very easy job at that time.
Label ALL hoses and wires. I almost forgot one.

Charlie

Thanks for the advice, Im trying to locate the damn manual but its no-where to be found. At first, i wasnt sure if it even mentioned how to do this. But thanks to you, i know that it has the information i need.
My search for the book is now accelerated as i am trying to finish this today!
Thanks
PS. any special tools required?

Hey,
I started working on it today after getting the manual. The manual seems to leave off important steps, like how to remove the upper manifold. I couldnt get it off! Now, im unsure if it was the bolt under the egr or some kinda sensor infront of the distributor.
Please help, i had to put everything back together cuz i couldnt get the upper manifold off.
*do i have to pull the engine foward??
thanks!

I just wanted to let the forum know that the GM dealership has covered half of the expense. I have only owned the van for 3 months and i bought it at a non gm dealership. My total cost was 380 canadian taxes included.

I hope this is helpfull for someone

You hit a snag, stopped, & put it back together again??

I just wanted to let the forum know that the GM dealership has covered half of the expense. I have only owned the van for 3 months and i bought it at a non gm dealership. My total cost was 380 canadian taxes included.

I hope this is helpfull for someone

I lived in Ottawa and the GM dealership charge me CAD 1,200 to fix my intake manifold gasket!!! Even you pay half (i.e., CAD 380), the dealer charged the total cost for only CAD 760??? That is a big different between prices

I have step by step instructions, I can email you the attachment

olsen96, can you email me the instructions you have for the intake gasket change. thanks

fizzerbill@tampabay.rr.com

I have step by step instructions, I can email you the attachment
Olson can you please send me a copy of the instructions as I am just starting to get some leakage of coolant.
Thanks Alex

Since this looks to be a helpful thread, I'll pin it so it will be easy to find.

Please keep the questions and replies only to the actual repair procedure.
Please read all the posts here to see if someone has already asked the question before. Some vehicles (even though they are the same body style) have different procedures and tricks to getting the job done...so please post the year and engine size so you get the correct information

anyone have instructions for replacing the intake gasket on my 2002 venture? i cant locate a manual for it thanks

I have step by step instructions, I can email you the attachment

Could you please email me the instructions?

tcbchhbc@yahoo.com

I have step by step instructions, I can email you the attachment


If it's not too much trouble, could you email me the instructions or post them somewhere for download. I have a Olds Siloutte with the same leaks. The instructions should still apply. Thanks.
Rob

rkdenn@yahoo.com

Ok I'll post these instructions....I'm doing this off the top of my head, but basically anything you see in the way of getting the lower intake off must be removed or moved..
you know the basics..drain the coolant, disconnect the negative battery cable
1. air duct
2. throttle cables and mounting bracket
3. coil assembly
4. T/B hoses
5. egr valve
6. upper intake
7. alternator and bracket
8. fuel rail
9. P/S pump
10. studs for coil assembly
11. heater pipe
12. valve covers
13. lower intake

you will need to loosen the rockers and remove the pushrods
This is important! keep the pushrods in order..the intake and exhaust are different lengths and if installed in the wrong position will cause immediate engine damage when the engine is started!
clean everything up and install new gaskets
reinstall the manifold and torque to specs
reinstall everything.

Hi

Here some documents regarding the intake manifold gasket :
Service bulletin : http://aklr.free.fr/envrac/SB-10001282-8175(Intake_manifold_gasket).pdf
Technical Bulletin : http://aklr.free.fr/envrac/GM_3.1_3.4_TB.pdf
Service buletin GM : http://aklr.free.fr/envrac/gmservbull.pdf
Sealing solution : http://aklr.free.fr/envrac/gskms15704.pdf

Christophe SALVAING

Web site : http://christophe.salvaing.free.fr
Family, Cars (Ford Aerostar LPG, Chevy Suburban LPG, AMC Pacer, Buick Roadmaster Estate Wagon, Pontiac Montana), Kitesurfing ...

Hi


Christophe SALVAING

Web site : http://christophe.salvaing.free.fr
Family, Cars (Ford Aerostar LPG, Chevy Suburban LPG, AMC Pacer, Buick Roadmaster Estate Wagon, Pontiac Montana), Kitesurfing ...


Wow, you own an AMC Pacer? I remember those. Don't see any around anymore, (at least in Central NY- they all rusted out like all the other cars LOL.)

Well, mine's leaking too. Its been doing it forever, though. I think its started using more antifreeze lately. Its not getting into the oil though. I heard its going out the exhaust, I don't know, but its going somewhere. I guess I'm gonna try to do it myself, does anyone have a copy of the Haynes manual, I'm having a hard time finding it, might have to order it. Or just go in and start pulling stuff out of the way on my own. It's my wife's '99 Venture.

Hello

Here is the part list for my mechanic I found within http://www.gm-v6lemons.com/gmservbull.pdf :

- short bolt 11588915
- long bolt 11588914
- threadlocker 12345382
- Fuel system - Fuel induction - Intake - Manifold gasket 3.4L 1997 - 2002 89017279

Do you thing a part is missing ?

Thank you.

Did it myself. Followed the Haines Manual directions pretty much verbatum. My advice.
Have oil and filter for an oil change when finished. Coolant too.
Change the spark plugs with the manifolds off. Very easy job at that time.
Label ALL hoses and wires. I almost forgot one.

Charlie

Charlie,

I just found out that my venture has this same problem. How long did it take you to replace the gasket and re-assemble everything?

And, if you don't mind my asking, how much experience did you have in auto maintenance prior to replacing this gasket?

I have been troubleshooting/repairing CNC machines for over 10 years, so I tend to think it wouldn't be too big a deal for me to perform this, but I certainly do not want to bite off more than I can chew.

Also, if anyone would be kind enough to email the instructions mentioned earlier to me, I'd greatly appreciate it. dnbphix@hotmail.com

I plan on picking up a copy of the haynes manual as well.

Thanks,
phix

I'm taking mine to a local private garage with a good reputation, they quoted me $436 (you know how that goes, it'll probably be closer to $500 actual). My local Chevy dealer told me $650 which isn't as bad as some places.

I had one garage quote me $1800. My usual mechanic quoted me $600-$800 USD. I'm still opting to do the job myself. My usual mechanic said it's not that difficult to do, just time consuming. He also recommended switching to standard coolant (the green stuff).

I'm planning on doing the job this Saturday (assuming I can get all the parts by then). I'll let you all know how it goes. I'm planning on taking digital pictures and documenting everything. I'll try to stick it all on my site for future do-it-yourself-ers, because we all know there will be plenty of them.

$1800?!? They just didn't want to do it. LOL But anyway, I'm looking forward to your pics and descriptions, I haven't fixed mine yet. Its not leaking into the oil, at least not in mass quantities, and I'm waiting for my tax refund. The wife is also looking for something to trade it in on, so if we find something before we get our refund check, it will be gone.

Hey Phix.
Took me and a friend the better part of a Saturday.
In the past I have done complete engine rebuilds but that was years ago. The experience I needed was knowing that the parts need to be PERFECTLY cleaned of old gasket prior to re-assembly. (mistake made on a Jeep head gasket years ago)
Figure on it taking all day and maybe two. Dont rush the job.
And a trick. The injector array is difficult to come off. Try to pop each injector separately then lift the entire unit. To re-install, allign all injectors and gently tap with a mallet on each injector. They pop back in. Go slow and stop if in doubt.

Hi all

A compilation of my own informations and Bengt Storberg advices(storberg@privat.utfors.se, thank you Bengt :))

Complete part list : http://aklr.free.fr/envrac/Intake_Manifold_Gasket_Part_List.xls

Instructions : http://aklr.free.fr/envrac/Intake_Manifold_Gasket_How_To.doc

Christophe

Christophe...

Great information. But you listed a lot of parts I wasn't even thinking of prior to tackling this job. Are all necessary, ie 8 bolts?

Complete part list : http://aklr.free.fr/envrac/Intake_Manifold_Gasket_Part_List.xls

Anyway, this is the most comprehensive reply and I'm sure I'm not alone saying thanks for this information. I'm a former mechanic and I look forward to getting my hand dirty again.

mchristo63

By the way, are the rear spark plugs easy to get to when you have the intake and everything off?

I forgot to add an additional questions.... special tools? We all know how tight it is in there, what special tools if any are needed.

Also, Christophe offered a detailed explination of how to perform this task. But, it was mentioned in his commentary that you need to rotate the engine. Rotate the engine? Is the necessary? And if so... how hard is this to do?

A lot of you mentioned the Haynes manual and was wondering if what Christophe provided as instructions are also mentioned in the manual.

Thanks

I forgot to add an additional questions.... special tools? We all know how tight it is in there, what special tools if any are needed.

BEWARE OF THE NEW SEQUENCE AND TIGHTEN TORQUE ! !
http://aklr.free.fr/envrac/SB-10001282-8175(Intake_manifold_gasket).pdf
A lot of operation are provided in the Haynes manual but not easy to read because sequantial process is not in the same chapter.
New bolts are coated with threadlocker and not expansive
Change sparks is easy when all the stuff is open :)

Anyway, if regarding your own experience something is missing or incorrect please let me know

Have a good week-end ...

JAS
ps : good new for french owner : GM is finally developping a Chevy network here ...

BEWARE OF THE NEW SEQUENCE AND TIGHTEN TORQUE ! !
http://aklr.free.fr/envrac/SB-10001282-8175(Intake_manifold_gasket).pdf
A lot of operation are provided in the Haynes manual but not easy to read because sequantial process is not in the same chapter.
New bolts are coated with threadlocker and not expansive
Change sparks is easy when all the stuff is open :)

Anyway, if regarding your own experience something is missing or incorrect please let me know

Have a good week-end ...

JAS
ps : good new for french owner : GM is finally developping a Chevy network here ...
Yes that is great advice to change the spark plugs while you have easy access to them. One thing I'd like to add, and I've said before on some of these forums, is to use genuine AC Delco plugs, It's not worth saving a few bucks buying inferior plugs only to have problems a few days later and then finding out it is the plugs, and then having to go back in and replace them. The OEM Delco plugs are the best fit for operation in these vehicles and the other aftermarket ones are made for various vehicles with sometimes different specs.

Christophe,

Thanks for providing your step by step instructions. The Chilton book says "remove this, remove that" but doesn't explain what everything is.

I didn't have to rotate the engine forward either. I can see where it would have made removing the ignition coil easier, but I'm here by myself and don't really have the means to rotate the engine.

For anyone with rear A/C, if you don't rotate the engine forward, be sure you put the alternator back in BEFORE you put the upper intake manifold back on. Neglecting to do this cost me not getting it done last night. I'm guessing I've got about 2-3 hours left. I thought I was almost done, then realized that the alternator wouldn't go back in, and the Chilton manual's procedure for removing the alternator required rotating the engine forward. At that point, it was easier for me to take the upper intake manifold back off.

All I have left is reconnecting the plug wires to the ignition coil, reinstall the MAP sensor, connecting the wire harnesses and vacuum lines to the back side of the engine, reinstall the passenger side fender support and fuse rack, change the oil and add coolant.

I got it all done last night. It started right up with no obvious leaks.

I bled the cooling system for quite some time and everything seemed fine. This morning on the way to work, the temp gauge was all over the place again, so I'm hoping I still have an air pocket to bleed.

I'd rather be Venture-less than change the head gaskets.

Christophe and Charlie: Thank both of you very much for tips/advice in this forum. It helped a lot.

Well, I just got mine back from being repaired. Cost $525 including oil, filter, and spark plugs. I figured now was the time to get the plugs changed, even though its only at 80,000 miles. At least its finished for now. I hope it at least runs until its paid off. Other than the intake leak and that damn power door lock wiring getting wet problem, its been a very good van.

Well, I just got mine back from being repaired. Cost $525 including oil, filter, and spark plugs. I figured now was the time to get the plugs changed, even though its only at 80,000 miles. At least its finished for now. I hope it at least runs until its paid off. Other than the intake leak and that damn power door lock wiring getting wet problem, its been a very good van.
$525, wow you got off easy! Most of the people I spoke with have been quoted at least $800 and up ( way up for a few.) And I'm not sure if that included the spark plugs LOL.

Yeah, I'm considering myself lucky. But I do live in a rural area and this was a private garage. The mechanic was familiar with the procedure and had done several other 3.1/3.4's. He knew things about the procedure I had looked up online, so I felt comfortable going with him. Even my local GM dealer quoted me "only" $650, another private garage quoted me $560.

One of the steps is to drain the coolant. One question though how does one drain the coolant? I think it comes out from the bottom of the rad but I can't figure out how to turn the draincock. What I believe is the draincock is a white nylon? plug on the bottom driver's side facing the engine. I can barely get my hands up to it and will be limited to what tools I could use but I can't figure out what to use to turn it? I thought at first it was a butterfly type with the wings broken off but I think I need a sort of screwdriver. Does anyone know what shape (philips, torx, slot.....) and what direction to turn (assume CCW to loosen) and how much to turn it?

I just jack it up, remove the lower hose, and drain it into a bucket.

Yeah I thought of that too...............But last fall when I was going to replace the fluid for maintenance purposes I remember not being about to get that off either. I think it may have been the difficulty in getting to it or that the clamp was rotated such that I could not get it off. In any event I am irritated that I cannot simply open the drain and I wondered if anyone knows how to do it.

I understand. Those factory clamps are a bitch, you have to use pliers tot get them off, instead of a screwdriver like aftermarket clamps. If I remember, it wasn't that easy for me either, the first time, I had to work the hose back and forth before it came off. But I've had bad experiences with the plastic drain petcocks the newer vehicles have, they use a rubber O-ring, which often breaks when you try to open it. Thats why I switched to removing the lower hose. Older vehicles, which I am more used to working on, had a brass/metal drain petcock, which didn't have rubber O-rings that failed.

One of the steps is to drain the coolant. One question though how does one drain the coolant? I think it comes out from the bottom of the rad but I can't figure out how to turn the draincock. What I believe is the draincock is a white nylon? plug on the bottom driver's side facing the engine. I can barely get my hands up to it and will be limited to what tools I could use but I can't figure out what to use to turn it? I thought at first it was a butterfly type with the wings broken off but I think I need a sort of screwdriver. Does anyone know what shape (philips, torx, slot.....) and what direction to turn (assume CCW to loosen) and how much to turn it?

Here is a link for a diagram of the valve (below). Looks like a quarter-turn. I am NOT sure what kind of screw driver or wrench you use.

Radiator Drain Valve (http://www.my-chevy-venture.com/radiator-drain-valve.html)

I tried to find it on my van, but I believe I would have to take of the plastic shield to get a look at it.

Good luck,

Here is a links for a diagram of the valve (below). Looks like a quarter-turn. I am NOT sure what kind of screw driver or wrench you use.There are several different types of plugs, depending on when the plug was made. Early plugs could use a large blade screwdriver to tighten it, but that screwdriver could not be used to losen it due to the "security screw" like feature. I have no idea why they put it on there. Instead you could use a phillips screwdriver in the center hole. My first plug was like this and was always a bitch to get out and easy to round out if the plug was stuck.

A later revision still could use a large screwdriver to tighen it, but replaced the phillips center hole with a hex hole for an allen wrench. This worked better as it wasn't as prone to round out, but is still a pain. The center hole also had a square area so you could use a 1/4" ratchet. This style plug is the one that you linked too. I've used this style up until I snapped off the little pin last week.

The third style is just like a wing-nut. It just has two large tabs that can be turned by fingers, or more likely a pair pliers.

If you are going to replace your drain plug, expect to remove your radiator. I had to the first time to remove the original plug as it was corroded/stuck in there. There also is a little plastic tab that snaps down when installing the drain plug to help prevent it from coming completely out when you open it. This tab is nearly impossible to see and even more impossible to move while the radiator is in the vehicle.

The picture you show isn't for our radiators though, or at least not my '98. On mine you give it about a 3/8 of a turn clockwise, pulling out as you turn.

My venture Van 2002 also have this probelm. I just bought this Feb. And the wanrranty is over just last month. Could you send me stuff how to repair it.
zhaogzhi@yahoo.com. thanks.

My venture Van 2002 also have this probelm. I just bought this Feb. And the wanrranty is over just last month. Could you send me stuff how to repair it.Just go buy the Haynes manual. It's less then $30 and it will save you several hundred with just changing the intake gasket alone.

I lucked out and got my gasket changed under warranty. One problem I did have that might be worth mentioning...when I received my van back, it was running rough, and I could hear a vaccum type noise. It wound up being a broken injector o-ring. They replaced them all.

Seems like they should have caught this before returning the van to me. Too many young techs I guess.

Good news. My vehicle has been reparied and under warranty. Thank you every body in this forum. I feeel this forum is very good for me.

I just wanted to let the forum know that the GM dealership has covered half of the expense. I have only owned the van for 3 months and i bought it at a non gm dealership. My total cost was 380 canadian taxes included.

I hope this is helpfull for someone

My 2000 Venture with 43,000 km had a intake AND head gasket leakage. My dealership replaced both gaskets free of charge (labour and parts) on warranty even though my Venture was not covered anymore. The only condition was to proof that the van had been serviced correctly and that was the case; all the oil change and service was done at Chev dealer.

After replace the intake gasket. My low engine oil ligh is still on. Is the oil too full?

My 2000 Venture with 43,000 km had a intake AND head gasket leakage. My dealership replaced both gaskets free of charge (labour and parts) on warranty even though my Venture was not covered anymore. The only condition was to proof that the van had been serviced correctly and that was the case; all the oil change and service was done at Chev dealer.
I wonder if the dealership would have been so generous if the oil changes and/or services were done at a non-GM dealer? I have seen dealers give customers a hard time about warranty coverage on covered repairs if the customer had the vehicle serviced elsewhere,even though you are not required to have items like oil changes,preventative maintenance care, etc. done at the dealer while the vehicle is under warranty.

I wonder if the dealership would have been so generous if the oil changes and/or services were done at a non-GM dealer?The funny thing is that oil changes and to some extent coolant changes aren't a contributing factor to the intake (and head) gasket leaks. You could change your oil (or coolant) every 10 miles or 10,000 miles and the leaks are still going to form. The flaw is in the gaskets and engine design, NOT with lack of preventative maitenance.

The funny thing is that oil changes and to some extent coolant changes aren't a contributing factor to the intake (and head) gasket leaks. You could change your oil (or coolant) every 10 miles or 10,000 miles and the leaks are still going to form. The flaw is in the gaskets and engine design, NOT with lack of preventative maitenance.

Yeah pay them in small increments (per oil change) or in one lump (after a failure).

Funny how they will stand behind their product if you keep paying them after purchasing the vehicle.

I wanted to pass on what I did to get the dealership/GM to pay for the repairs to our Van. Same issue oil and anti freeze missing dealer diagnosed as failed intake gaskets. We got the usual ridiculous quote to fix it and I called GM regional and pitched a fit. The Bottomline to use here is simply. If GM had done it right the first time they would not be using a different(improved gasket). GM tried to tap around it but the gent I was dealing with finally admitted that I was correct. If this probalem was due to normal wear and tear then it would be one thing, it is not is due to deficent materials being used which inevitably must be replaced at some point in the vehicles life. This IS the fault of the manufacture and not the owner/operator wear and tear. Total cost for our work was about 350.00

I wanted to pass on what I did to get the dealership/GM to pay for the repairs to our Van....Total cost for our work was about 350.00So you got GM to pay for the costs but it cost you $350?

I wanted to pass on what I did to get the dealership/GM to pay for the repairs to our Van. Same issue oil and anti freeze missing dealer diagnosed as failed intake gaskets. We got the usual ridiculous quote to fix it and I called GM regional and pitched a fit. The Bottomline to use here is simply. If GM had done it right the first time they would not be using a different(improved gasket). GM tried to tap around it but the gent I was dealing with finally admitted that I was correct. If this probalem was due to normal wear and tear then it would be one thing, it is not is due to deficent materials being used which inevitably must be replaced at some point in the vehicles life. This IS the fault of the manufacture and not the owner/operator wear and tear. Total cost for our work was about 350.00

Unfortunately, the rep I talked to didn't budge, even after giving her this logic. The crazy thing is, when I first called and talked to the GM rep she said there's a good posibility that they could help, but I had to take it to my local dealership to verify that it's the lower intake manifold. After the dealership verified the problem was indeed the lower intake manifold gasket, I called the rep back and give her the news. She placed me on hold to call the dealership and when she returned she politely refused to help at all (even though my van only has 40,000 miles on it). Even after I mentioned the TSB, and all of the complaints on the Web, she still refused to help. Went back to the dealer, paid the $45.00 fee to have it looked at, and drove it to my mechanic. The savings is a little over $100.00, and I prefer to use the local reputable shop ($773.00 - local vs. $919.00 - dealership (both quotes include oil and coolant change)). With all the problems I've had with this van I think I'll invest in a extended warranty.

As a Venture owner myself, instead of an extended warranty, may I recommend a different Make and model.

As a Venture owner myself, instead of an extended warranty, may I recommend a different Make and model.

Hehehe... I wish. I still owe too much on this to get rid of it. Stuck with three more years of payments. :banghead:

What's the symptoms of a leaking lower intake manifold? (exept the obvious of a puddle under the van)

Does a leaking intake manifold gasket impair performance?

What's the symptoms of a leaking lower intake manifold? (exept the obvious of a puddle under the van)Actually, a puddle doesn't form a lot of the time. The usual indications of a leaky intake gasket is oil in the coolant. Check in the oil cap for a slightly runny mayo-like substance on the top inside of the cap. There may also be some visible just inside the valve cover. If you see anything white-ish or light brown with that consistancy, you likely have the leak.

If you have a leak forming a puddle on the ground, I would be more suspicious of a coolant hose or fitting leaking at first. A head gasket also could be at fault but the #1 cylinder is often the problem cylinder.

Does a leaking intake manifold gasket impair performance?The leak I beleive is on the right side of the manifold were the fluid cross over the engine through the block. While it can leak out to the outside of the engine, I beleive the more common failure mode is to leak into the engine. The antifreeze mixes with the oil and lowers the lubricating properties. A little probably won't do significant lasing damage, but left unchecked, and it will eventually lead to problem (read: expensive). More then one person has reported broken cams and other problems. There probably wouldn't be a noticable performance drop, depending on the size of the leak though.

Luckily, the leak didn't mix with the oil. You could actually see the leak coming from the passenger front side of the lower intake. It's in the shop and should be fixed this afternoon. I was just curious if the leak could cause the van to run rough if the coolant was finding it's way to the combustion chamber.

I was just curious if the leak could cause the van to run rough if the coolant was finding it's way to the combustion chamber.Yes if it found it's way in the combustion chamber it could. However it is nearly impossible for the intake gasket to allow coolant to enter the combustion chamber. What would be much more likely would be a faulty head gasket or a cracked head. Definitely keep an eye on it. As I've said elsewhere, I had a intake gasket that needed replaced and a week later had to do my head gasket.

Yes if it found it's way in the combustion chamber it could. However it is nearly impossible for the intake gasket to allow coolant to enter the combustion chamber. What would be much more likely would be a faulty head gasket or a cracked head. Definitely keep an eye on it. As I've said elsewhere, I had a intake gasket that needed replaced and a week later had to do my head gasket.

Thanks for the input. I got the van back last night and it's running great. They did a pressure test and said it was the lower intake manifold gasket. Wouldn't the pressure test show a bad head or head gasket if that were the case?

Thanks for the input. I got the van back last night and it's running great. They did a pressure test and said it was the lower intake manifold gasket. Wouldn't the pressure test show a bad head or head gasket if that were the case?Possibly but not guaranteed. It's possible that the leak only forms when the engine is hot or cold, when things have expanded or contracted as much as they can. The early stages might not show the signs under one condition and would on the other. When my head gasket went south, I initially did a pressure check on all 6 cylinders and there weren't any abnormal readings indicating an obvious leak. It quickly deteroriated though and while I didn't do one when I knew what the problem was, I'm sure it would have been blindingly obvious.

Also, a pressure check really only measures how much pressure the cylinder can build up over a few quick strokes of the piston. It would probably have to be a significant leak to make a difference with just a regular pressure check. A leak down test however would be more indicitave of a problem. With the leak down test, the cylinder is put in TDC to ensure the valves are closed and the cylinder filled with compressed air. A special gauge measures what the pressure in the cylinder is as well as the incoming air supply pressure is. The difference is how much is "leaking" out somewhere. By pressurizing the cylinder over a longer period, a problem is easier to diagnose. A faulty head could leak bubbles into the coolant, eventually showing up at the radiator cap.