I have noticed that both exhaust manifolds on my 1987 - 3.0L start to glow orange after 5~7 minutes at 2000 plus RPMs.

I gave it a complete tune-up consisting of plugs, wires, O2 sensor, gas and air filter, and pcv. I also changed all the injectors since I had a spare set. Also, the Cat Converter has been replaced.

The car runs great otherwise, but the glowing manifolds have me concerned.

Smog Machine readings are as follows:
HC:117 PPM; CO: 0.09%; CO2: 15.6%; O2: 0.1%; NO: 152 PPM all at 2500 RPMs.
With these readings, I'll probably fail my smog test later this year with the HC readings above 100 PPM.

What could be causing the manifolds to heat up so much?!

you put the correct cat convrt on? Or do you hav a turbo on your GA? the manifolds shouldnt be glowing really at all. Sounds like you hav a pluged up exhaust somewhere, hows the muffler? I hav seen glowing Manfs but they were turbo'd cars and running 10psi or above . Maybe someone else has had this hppen too.

I have to agree with Xeroinfinity, this is not normal, how is your fuel mileage? One thing to do is to remove the exhaust behind the cat and see if the problem still continues. If not then the exhaust is plugged behind the cat.

you put the correct cat convrt on? Or do you hav a turbo on your GA? the manifolds shouldnt be glowing really at all. Sounds like you hav a pluged up exhaust somewhere, hows the muffler? I hav seen glowing Manfs but they were turbo'd cars and running 10psi or above . Maybe someone else has had this hppen too.

I had thought that I had a plugged exhaust problem too, that's why I had it changed along with a new muffler after I noticed the manifolds glowing. I figured that the original Cat Converter and Muffler had served their time with 127,000 miles, so I had them replaced. Unfortunately, it did not cure the problem. They are aftermarket replacements from a local muffler shop.
No Turbo. The car is bone-stock.


I have to agree with Xeroinfinity, this is not normal, how is your fuel mileage? One thing to do is to remove the exhaust behind the cat and see if the problem still continues. If not then the exhaust is plugged behind the cat.

Mileage has not changed for many years. It remains at about 15~16 MPG with a combination (75%)city/(25%)highway driving.
I have not tried to disconnect the exhaust since it is new, and should not be plugged. There is plenty of exhaust coming out the tailpipe with a lot of force.

Even though you just replaced your o2 sensor, check it anyway. It sounds like you are running extremely rich.

is the converter and muffler on the right way? Alot of those items are directional==> one way. if either of the two are on backwards it might cause some backflow. Exhaust manifolds maybe plugged caused by bad gaskets.
Like skibum1111 said its running a bit right .

High NOx and HC readings indicate high cylinder temperatures and an incomplete burn. Have you had your EGR valve checked out recently?

Even though you just replaced your o2 sensor, check it anyway. It sounds like you are running extremely rich.

O2 Sensors are cheap enough, so I just finished replacing it with another new one (And a different brand: Bosch).
Still "Glowing"........................no change.

is the converter and muffler on the right way? Alot of those items are directional==> one way. if either of the two are on backwards it might cause some backflow. Exhaust manifolds maybe plugged caused by bad gaskets.
Like skibum1111 said its running a bit right .

I thought of that too, but keep in mind that the Manifolds were "Glowing" with my original GM installed Cat Converter and Muffler. The reason I decided to replace them was because I thought they were plugged. The replacements are doing the same thing as with the OEM Cat & Muffler.

Also, from what I can tell, the muffler is only able to go one way. As with the Cat Converter, it is a aftermarket universal fit. It has a air tube (that has been plugged since it does not fit my application) that is facing the front of the car. I have been told that this is the correct mounting. If I had Air Injection, then the tube would be used and would need to be mounted facing the engine.

My exhaust manifolds do not have gaskets. I remember this because I replaced the rear manifold several years ago because it had cracked. I was surprised to find no gaskets when I removed the manifold.

High NOx and HC readings indicate high cylinder temperatures and an incomplete burn. Have you had your EGR valve checked out recently?

I have checked it out. I removed it and inspected. Ports on the intake manifold and EGR are all nice and clean. I used a Vacuum pump to verify that it is holding, and that it has no leaks. Also, when pushing up on the diaphragm while engine is at idle, the engine will stumble and die.

I also pushed up on the EGR diaphragm while reving the engine to ~2000RPMs to see if having the EGR open it would cool the combustion chamber. But, it did not do anything. Manifolds still glowed.

Did you check your vacuum to the EGR valve. It should only receive vacuum above idle speed and below Wide Open Throttle.

Did you check your vacuum to the EGR valve. It should only receive vacuum above idle speed and below Wide Open Throttle.

A Mechanic friend was kind enough to bring his Snap On "Hand Held" SCANNER to check out my car/problem. He stated that glowing hot manifolds are usually caused by a Lean condition, possibly caused by a vacuum leak. Another cause is late timing ignition (which is unadjustable in my application).

The results of the Non-Driving diagnostics are as follows:

System is confirmed "Closed Loop" with no active or historical codes.
TPS: 0.56v and increasing steady with increase in throttle.
IAC: 25 @ idle
O2 Sensor: ~1.4 mV
O2 Mixture: going from "Lean" to "Rich" to "Lean"; Continually changing (which he said is good).
Ignition Timing: 24 BTC at Idle; increasing to 34 BTC at 2500 RPMs.
MAP Sensor: 44 C
MAF Sensor: ~4 @ Idle, gradually increasing while increasing throttle.
Knock Sensor: Off
Retard: 0 degrees.
EGR Cycle: Off
A/C Signal: Detects A/C On and OFF. OK

The results of the Driving Diagnostics are the same as the Non-Driving except for the EGR Cycle was going from ~43% and higher with different driving conditions.

All is normal, except for the glowing manifolds. And it has him as baffled as everyone else.

We also tried to spraying Carb Cleaner all around the intake manifold, vacuum lines,etc. to see if we had a vacuum leak. Non detected.

Hooked up a Vacuum Guage and got 15~16 mmHg. He says it a bit low. Should be 18 mmHg, but doesn't think it too bad. Can someone check their own car and let me know what you get?!?

We do not know what normal timing is. Since it is not adjustable, my manual does not show timing setting. Does anyone know the specs??

icepick: From what you were describing through the diagonostics, it doesn't sound like you timing is off. It pretty much sounds like everythign is normal.... We do "have" a 87 3.0L, as well but so far i'm coming to a dead end as well for the exact timing on the car. But some symptoms of incorrect timing tend to be; Check engine light, chattering noise from engine, sluggish no power, and sometimes they run hot. I presonally though it was the cat as well, but you've got me stumped on this one as well now. I'll keep looking though for any timing info...

icepick: From what you were describing through the diagonostics, it doesn't sound like you timing is off. It pretty much sounds like everythign is normal.... We do "have" a 87 3.0L, as well but so far i'm coming to a dead end as well for the exact timing on the car. But some symptoms of incorrect timing tend to be; Check engine light, chattering noise from engine, sluggish no power, and sometimes they run hot. I presonally though it was the cat as well, but you've got me stumped on this one as well now. I'll keep looking though for any timing info...

Since you have an '87 with a 3.0L like mine, can you check your vacuum (if you have access to a vacuum guage). Tell me what your readings are at idle once it's warmed up.

By the way: THANKS! to everyone for their suggestions/help.

Unfortunetly i can't check the vacuum pressure on our 87, due to the fact i don't have a pressure gauge, and currently we don't have the car in our posession, it's at our local garage, due to a blown trans so i don't have access to the car. As far as the timing specs go, all i could find was the same thing as you, that it's electronically controled and not able to be manually adjusted, other then refer to service manual. I'll check my haynes manual when i get home and see if there is anything in there as well for you if you haven't done this already.

Icepick, your timing sounds pretty well dead on. Anything as old as '87 that still has 15-16" of vacuum is in good shape. Are you 100% positive there is no exhaust restriction? Maybe a birds nest?

Icepick, your timing sounds pretty well dead on. Anything as old as '87 that still has 15-16" of vacuum is in good shape. Are you 100% positive there is no exhaust restriction? Maybe a birds nest?

I am now 100% positive! I just got finished driving my neighbors crazy.

I decided to remove the exhaust pipe at the rear manifold (directly below the O2 Sensor). Basically open exhaust. Loud as hell, but after suffering through 10 minutes of 2000 + rpms, the exhaust manifolds started to glow.

I'm starting to think that this might be normal maybe?!?!?? Maybe never noticed this before. Afterall, the exhaust manifolds are kind of thin steel, not cast.

Sure would be nice if someone else with the same year car and 3.0 L engine would rev their engine to 2000 rpms for about 10 minutes to see what happens to their manifolds.

Calling all cars, calling all cars..............Anyone with a '87 - 3.0L engine!! Please rev your engines to about 2000~2500 RPMs for about 5~10 minutes and tell me what happens to your exhaust manifolds.

I am going nuts.........................

I can reassure you that they don't glow being reved at 2,000 rpm, ours never glowed like that. The last time we drove ours, i had to look under the hood due to a trans leak, at night, and everything was normal with no glow.

I have an idea, it's a bit of a longshot, but i guess it could be possible... The exhaust manifold itself, maybe breaking down the metal maybe getting thinner, with all the exhaust heat coming through, it's going to heat up much faster and hotter.... Would anyone else care to agree or disagree with me on this?

I can reassure you that they don't glow being reved at 2,000 rpm, ours never glowed like that. The last time we drove ours, i had to look under the hood due to a trans leak, at night, and everything was normal with no glow.

I have an idea, it's a bit of a longshot, but i guess it could be possible... The exhaust manifold itself, maybe breaking down the metal maybe getting thinner, with all the exhaust heat coming through, it's going to heat up much faster and hotter.... Would anyone else care to agree or disagree with me on this?

I drove the car on a highway that gradually climbs. I have kept the engine at ~2500 RPMs and driven about a mile at night. I pulled off to the side and quickly opened the hood to find a very low glow. I also drove up a steep hill full throttle for about three blocks, and quickly pulled over and opened the hood to find a slite glowing manifold. In both instances, it cooled really quick (about 20 seconds or less).

If I wasn't really looking for the glow, I would probably miss it entirely, especially if I take a bit longer to open the hood and look in, or if I wasn't looking for it specifically.

The only time I can get the manifolds glowing hot red/orange is while standing in front of the car reving engine. I still hope someone with a '87 - 3.0L will stand in front of their car and rev it to ~2500 RPMs for about ~10 minutes and tell me what happens.

I kind of like your theory on the metal getting thinner, and it heating up faster and hotter, but I really don't know what to think about it........You would think that if it is thinner, it would crack or break, or develope an exhaust leak?!?!

What kind of fuel are you running? I would get a emissions test done on it to make sure you are not running to lean. Just a thought.

His exhaust readings indicated a rich mixture. I wonder if the exhaust valves aren't opening too early. Does that engine have a timing belt or chain?

There is also the possibilty that the mainfolds are cracked and the exhaust is going out of these cracks and super heating the manifolds.