Hi there,

I own a 1996 Monte Carlo 3.1L. it has 130k miles on it and has had the head gaskets replaced within the last 8 years. I have a fairly new water pump as well as a new rad.

I am at a loss right now and in need of some advice. My car has been having intermittent over heating problems recently. On top of that it has also had a few instances of it being under powered. typically these things occur at different times witch leads me to believe that they are separate issues.

I have noticed a few things before it overheats. First the engine will start to get hot (according to the thermostat) while I am stopped or driving slow. When I step on the gas the temp with instantly drop back to normal levels. this will go on for about 10 minutes, after witch the gauge will ping on the red and then the "HOT" light will come on. When it overheats I notice all of the coolant backs out of the engine and I end up with a ton of air in the engine. I have also noted that during these moments the heater completely stops working. As a temp fix for the overheating, I typically pull over and open the bleeder valve and let the air out. This fix can last anywhere from an hour to days. I have also noticed that it happens less when I put it in Overdrive.

As for the car feeling under powered. It has only happened a few times and been in the morning. Along with it being under powered, it also has a valve knock and or rough idle. Typically to fix this I turn off the engine and wait a minute or two and then when i start it up it is fine for weeks.

So far I have changed the oil, topped off the coolant, checked all of the fluids, changed the two main coolant hoses in the front of the engine, and checked the plug wires.

I will be working on my car again this weekend so any suggestions/advice would be greatly appreciated.

 

This may be a silly question, but have you verified the radiator fans are working? Any check engine codes?
You say the heater stops working leads me to suspect air getting into the cooling system, which means water escaping. The most common culprit in my experience is intake gaskets leaking. If no obvious sign of coolant on the ground , I'd bet on lower intake leaking.
You shouldn't be needing to top off coolant regularly unless it's leaking somewhere.
But that will cause the temp gauge to be erratic and air pockets in the system cause heat to not blow hot

 

I would have to agree with Aerocoupe on that. The intake manifold gaskets are always a problem and when they need to be replaced they will make for some serious overheating. You should here the Fans kick on when this all occurs if not you may want to have that checked. it would appear that the thermostat is working if you have flow of the antifreeze, I think there is an anti freeze that could have issues with these motors, I am thinking you need to run the Red and not the Green. What my technician's told me for mine. There is also a small spoiler under the front of the car that may have been broken and not allowing air to get in, also check the Radiator in the front to make sure Bugs have not blocked the Air flow. You may have a waterpump that isn't working properly also. you said it was new but that doesn't mean its working, the noisy engine is typical but try a synthetic oil, or an additive that may help.

 

Hi,

Thank you for the response. I have verified that both radiator fans are working.
The only engine code that I have ever gotten is for a misfire in cylinder 2 (I do not remember the exact code off the top of my head) but I have not had it for quite a while. I will add the lower intake gasket to my list of things to check on Saturday.

On top of the Intake manifold gasket, I will also be checking:
-The water pump
-Replacing the coolant
-Checking the Coils

If anyone can think of anything else that would be awesome!

*I would also like to mention that I have not seen any coolant in the oil and vice versa. Which I know is the dreaded sign of a head gasket problem.

 

Another sign of a head gasket issue is white smoke from the exhaust (which is actual steam from coolant getting into a cylinder.

Since you keep bleeding the air out of the system and more is coming back, it's coming from somewhere. My first advice, get the radiator pressure tester form the auto parts store (typically it's a free loan-a-tool). This can let you pressurize the entire system. Look and listen for a coolant leak.

I'm concerned with under power, a cylinder mis-fire and this air pocket. I did have a 3100 blow a head gasket and have a slight mis-fire when it was started cold, after that no issues. But it kept getting an air pocket and I did pull over multiple times to release that air from the bleeder. Multiple attempts to pressure test the cooling system did not reveal any leaks. The issue was that compressed air from a cylinder was getting into the cooling system from the failure in the head gasket. Changed it and all problems were resolved.

Before jumping to that, check out some other items and rule out those things first.

 

Hi there,

Just a little update.
I completely dissembled the Intake Manifold and got to the gaskets.
They were in really bad condition (I will post pictures when I get the chance.).
I also discovered that there was coolant in the oil underneath the front valve
cover. But no sign of oil in the coolant when I drained the system. On the right
side of the gaskets there were large melted holes that were letting coolant into
the engine. As well as a hole on the lower right side of the gasket next to the
bead of silicone. Honestly I don't know how my car ran, especially after seeing
the gaskets. But all in all it is going well, considering I have never done this
before. I will be finishing it this coming weekend. Hopefully this fixes my
problems.

Thank to Aerocoupe86 and drivernumber3 for pointing me in the right direction!

-Ryan

 

It's pretty common on those 3.1, 3.8s hell any engine really once they get some age and miles. I've always believed the coolant the manufactures starting using in mid 90s was the culprit. Never seen intake gaskets fail so much until about that time. I could be wrong I guess.
Anyhow glad you found it.its not a hard project, just take your time

 

The culprit is plastic/nylon gaskets. Dex is still to this day blamed on the gasket failures. I have seen 3100 engines that never used a drop of Dex (not even from the factory) suffer this failure. One was my own '94 Grand Am, twice the LIM gaskets failed in 215K miles.