2004 3.4 Monte Carlo Heater/Heating Issues

[Brandy R]

Hello Everybody,

I have been looking around the internet trying to find a solution to my problem but I haven't found anything about my specific situation.

My 2004 3.4 Monte Carlo started overheating as soon as I got into my hometown, four hours on the road, for Thanksgiving last week. Upon pulling over and checking everything out my coolant level was pretty low, so I filled it back up. Since then the coolant level hasn't dropped any, at least not noticeably. The first time I drove the car after adding the coolant the temperature gauge rose to almost where the warning light would have come on and then dropped down to the normal operating level. The rest of the time I was on vacation the temperature gauge never went higher than what I was used to seeing.

Two days after I returned to where I currently live I started noticing problems again. I was on my way into work and turned on my heater once the gauge started registering a temperature, and unlike usual it was blowing out cold air. In the mean time the temperature kept rising almost to where the warning light would have come on and then it dropped to lower than the normal operating temperature. During the temperature drop the heater started pushing out warm air but as soon as the temperature was done going down the air was cold again. This kept going on for a while until eventually my heater started working steadily.

As I continued driving I noticed that as long as I was moving at least 30mph or so the temperature stayed normal, but as soon as I was in slow traffic or at a light it would rise back to almost where the warning light would come on. At that point it would drop down a good bit and then repeat the cycle if I was sitting in one place long enough.

I replaced the thermostat last night thinking that was the problem, but after I took it out for a drive it was still doing the same thing. My car hasn't actually overheated since it happened last week which makes me think something is working, just not properly, and as I said earlier the coolant level has been holding since I filled it back up. If anybody could help me figure out what the problem is I would really appreciate it.

Thank you all,
Brandy

Sorry for giving you all my life story by the way, haha. I didn't mean for this to be so long but wanted to make sure I gave all the potentially crucial details.


Edit: I forgot to mention that my car is throwing some error codes but I didn't think it would have much to do with the car overheating considering what they were for. P0401 (EGR flow insufficient), and another stating that an O2 sensor wasn't functioning properly.

[Tech II]

Well, obviously, you have more than one problem....another problem is you.....you are driving around with codes, and don't fix them....you are driving an overheating car, and again, you don't fix it, you just add coolant, and could potentially cause an overheating problem that could warp heads, and create bigger problems....

The fact that you had to add a lot of coolant tells me you have a leak....when you have a leak, you create an "air pocket" in the engine....this air pocket is what prevents coolant flow throw your heater core, and is why your air is cold out of your registers....some times the air pocket will move when the thermostat opens......kind of like self burping itself.....with the air pocket gone, coolant again flows through the heater core, and you have heat......but eventually, because you are leaking coolant, another air pocket will form, the car will overheat on the gage, and you will not get hot air out of your registers.....the answer is simple....fix the leak....if you don't, you are asking for major problems......

You can rent a pressure tester, and see if you have an external leak, like a radiator, radiator hoses, heater core hoses, heater core, water pump, etc.

More often than not, with the 3.4 engine, the culprit is usually the lower intake gaskets......look under your throttle body with a flash light and if you see coolant collecting in the depressions on top of the engine, that is your problem....

let me warn you though, the vehicle should be checked, professionally, by a good Tech.....I have seen many a lower intake gasket replaced, and because the car overheated badly, it also took out the head gasket, usually #1 cylinder......if not properly checked, and is diagnosed just as an intake gasket problem, and the head gasket was bad, you will be doing the same job all over again, and then some.....

And get those other codes checked out and fix too...