Heat gets hot, goes cold, gets hot again

It just keeps happening. It doesn't constantly happen but on any given trip it will get cold and then return to hot within a few seconds.

Just replaced:

Head Gaskets (fel-pro)
LIM Gasket (fel-pro)
Thermostat (gates)

There are no leaks. The level is showing FULL. I properly bled the system and no air comes out when I turn the brass bleeder valve. It has been doing this since I purchased the car before changing all the gaskets.

The temperature will fluctuate from 195-205 and occasionally start rising (heat goes cold) and immediately drops from about 220 and the heat begins blowing hot again. I'm at a loss.

sounds like your computer is telling it open and close thermo to early. have you changed thermo sensor?

sounds like your computer is telling it open and close thermo to early. have you changed thermo sensor?

Are you referring to the engine coolant temperature sensor? If so, no. I've had no codes and the car warms up properly so I assumed it was alright.

sure sounds like an air pocket blocking coolant from flowing thru the heater core. Try bleeding it again, heater on full blast. You certainly wouldn't be the first to have to bleed a Grand Am repeatedly to clear out the air pockets. And, its a cheap option. Oh, and the computer can't "tell" thermostat to open, thermostat is a mechanical device that only opens/closes based on temp of coolant it's exposed to.
Hope this helps.

That's what I thought.

It appears to have been massive air pockets in the system. The procedure described on a major grand am site would not work, using the bleeder valve. I had to run the car with the cap off and heater on it's hottest setting. It took 3 times of blowing out massive air bubbles but for the first time since owning the car, the temp needle stays on 200 and doesn't not move. I couldn't believe it.

how you get that when it will show moter on dash not the check engine lite either the lite when you see moter on dash what will you do just drive it until you get home and see whats wrong?

typical of these to get air trapped in the system. a real pita to bleed.
though we have a procedure in the Tips and Maintenance (http://www.automotiveforums.com/vbulletin/forumdisplay.php?f=2148) subforum. :thumbsup:

Well, it got cold again sitting at a red light. Took off and it became hot again. Temperature didn't fluctuate though.

Bled it some more today and it seems fine. It's like there is never ending air in the system. Used the method described with the hose going into the coolant tank for about 15 minutes. There seemed to be less and less bubbles. I'm going to try it again in the morning for good measure.

I used a block tester and there are no exhaust gases going into the coolant and the headgaskets were just replaced.

I wonder... maybe you actually also dropped dirt or dislodged some and it plugged partially the heater core/radiator?

these newer models are a pain to get all the air out. Especially when the block or heater core is drained.
You'll just have to keep an eye on your coolant level. And keep your heater on as much as possible. ;)

Is the water pump in good shape?

the water pump is also something I suspect too...

also, maybe your new gasket ain't well installed or your engine block is disformed (I read it's common for the V6) causing the gasket to not seal well...

So far so good guys.

The water pump isn't leaking. I'm not losing coolant and I'm not getting exhaust gases into the coolant, so I'm not sure it's a gasket sealing issue. It could be though. One thing I've noticed is when completely cold, I remove the cap from the tank and a good amount of air escapes and the coolant level rises about 1/2"

I just can't fathom that combustion gases are entering considering I couldn't get a positive reading with a block tester.

Sounds very odd... when system cools off, it usually contracts, sucking air into top of reservoir. Mine will collapse the radiator hose when it's cooled overnight. If you're holding pressure after its cooled down, at least you know you don't have any leaks. But its still odd. Are you sure air is escaping? Could it be getting sucked in instead? (but then why would level go up?)
Anyway, sounds like you could have a coolant passageway blocked, and coolant boils in there and creates air pockets which block flow. Maybe a good chemical flush would clear it out....
Also, I've seen where some on this forum recommend drilling a few holes (2-3 mm) at the edges of the thermostat, and when re-installing it make sure one of the holes is at top-dead-center. This lets air bubbles get past thermostat better.
You could also check the smaller-diameter hoses going to/from the reservoir to make sure they're not clogged.
Hope this helps.

And I hate to bring up the Dexcool issue, but Dexcool works great until it gets a little air in the system, then it can create some oily/greasy residue. It also cant' be mixed with other (green) coolants. You say it's done this as long as you've had it, but how long is that? Are you still running Dexcool in it? Is there a lot of brown/yellow sludgy stuff in the reservoir?
When I got mine, it was clear that the prevous owner had mixed green coolant in with the original Dexcool. I switched to regular green coolant and also went with a 180-deg thermostat to keep things cooler. If you decide to switch from Dexcool, you have to really flush the system out pretty good, and clear out the reservoir as well.

I would suggest to be carefull about drilling holes in the thermostat as it could also damage it and also leave metal parts.

Using a lower temperature thermostat is also not a so great idea, it may make the engine stay cold and the "choke" can stay on, increasing the fuel consumption.

As for the water pump, it's not because that it do not leak that it's in good shape, you could have broken impalers or a broken shaft or loose one (basically they press fit the pulley, shaft and impalers).

As for the mix of different kind of coolant, some are incompatible and do make a mess.

Your car need dexcool coolant, I would NOT suggest to move to the green one. Yes the green is cheaper, but is incompatible partially with the cooling system, mainly dissimilar metal used around the system. Dexcool has been designed to not have issues, while the old green stuff has not. The result can be an accelerated corosion of the heater core.

The fact that your coolant rise when you open the bottle indicate a good air pocket in the system, which when you depressurise expend, and push away the coolant.

But in short, if you bleed the system, that everything work well and later on it still have air, then it mean that you have a leak.

When I got the car, the coolant was a little dirty but it was dexcool. I've only had the car 2 months.

I'm using Dexcool and it's as orange as it should be, with no sludge anywhere. What would symptoms of a bad water pump thats not leaking be? I have no overheating issues.

Right, it seems like air getting in would cause the coolant to drop when I remove the cap, not rise. Once I put the cap back on and do a cold startup, the coolant then returns to it's correct level. I'm leaning towards doing a chemical flush tomorrow.

chemical or back flush with plently of water... some say to use hot water. I personally didn't had to do that so can't suggest anything

I replaced the water pump as I already had a new one laying around. The old one was a GM part and looked to be much heavier duty than the replacement. It seemed very old but appeared to be in tip top shape. I couldn't turn the propeller by hand, not sure if it's suppose to be like that.

Flushed the system with tap water. I'm going to pick up the prestone materials tomorrow and do a nice chemical back flush

If I remember correctly you should not be able to spin the shaft on the water pump. But I might be wrong.

If I remember correctly you should not be able to spin the shaft on the water pump. But I might be wrong.

You should be able to turn the water pump by hand, it just won't spin freely.

get ur check yet?

http://www.topclassactions.com/close/14-gm-dexcool-engine-coolant

It's definitely not right. Not sure if it's a head gasket or maybe a warped head.

It doesn't completely overheat but will go up to about 220 at times. Even with a 195 thermostat in, the steady temp is 205 even when 30 degrees outside.

Thinking I'm just going to tear it down, take both heads in to the local machine shop and have them checked. I'll be sure to have someone else do the angle torquing. That was a very weird procedure having to hold the dial while turning.

FYI, the cooling fans (both) turn on at low speed at 220-deg, and go to high speed when ECT hits 230-deg. However, they also come on whenever A/C is on....

Got it all apart in 3 hours. The rear head gasket looked suspect. The heads have been dropped off at the local machine shop.

There was coolant in several cylinder. Not sure if it got there when removing the head or if it was already there. The walls are not scored or marked.