I have been experiencing problems with my 05 Monte overheating sporadically. I have replaced my hoses, radiator, water pump, thermostat coolant temperature sensor, belt and tensioner. My oil is not cloudy and it passes a pressure test every time.
When I allow my car to hear up slowly before I drive it it does not overheat. My heat works fine at this point. However, when I start it and drive it immediately it inevitably overheats after about 3 miles. The heat also fails to work. The coolant won't drain into the radiator and when I bleed it only vapor comes out. I assume because there is not any or enough coolant in the system.
I am replacing the thermostat and gasket one more time but I'm afraid it won't be enough. Opinions please.

 

Some times air will get into the system and that will cause it to overheat.


The other thing that can be an issue with the V-6's is the upper and lower intake manifold gaskets. I didn't think this was an issue at first and with my one SUV I couldn't get through the McD's drive through with out it going to overheat and the Fans kicked on and it was nuts. Had the Gaskets changed and Wa-La it was all taken care of.

 

What engine? Air is in the system so I agree there. Could be warped heads on a 3400, gasket issue on either 3800/3400, leaky heater core, simply air in the system, ect.

 

"Warped heads"? It's funny how so many people on this forum defended the 3.4 when I said it was a piece of ****, and now I run across this....

 

Never had one? Fantastic engines that do run for a long time. The Achilles heel seems to be those aluminum heads on the iron block coupled with overheating; and GM's crappy LIM gaskets but I've seen those in 3800s too. Truly a weak point, but on the driver to keep up maintenance. I'm somewhere around 180k miles original engine and transmission and I've heard much higher than that. I don't expect I'll have any problems for quite some time. Also I do want to differentiate and make clear I am referring to the LA1 3400.

Of course 3800s are legendary for a variety of reasons.

 

I've bled the air out. I replaced the heads last year. Just did the thermostat today. She's still not acting right. I'm going to try blue devil and pray I can make it a few more months.

 

I am sure a lot of people will knock it and I've heard people on the fence about blue devil brand specifically, I have personally used a bottle of steel seal with success on a 3400 engine'd car I purchased some time ago.

I wouldn't recommend simply putting that in the system with existing coolant. I would put only distilled water and just that with maybe the t-stat out to allow it to pass easily. Just a few things I did to get it to take all those years ago.

 

I'm really at my wits end with this car. I love my car but I feel like every time I fix one thing something else goes out. I have heard good things about blue devil but honestly I don't even think it's the gasket. If it happened all the time that would make more sense but it only tries to overheat when I drive it immediately after startup or if it's running well and then I turn the car off and turn it back on while it's still warm. I've had multiple mechanics from shade tree to ase certified stumped as to the cause.

 

Well intermittent overheat? Are you sure it is overheating then? You said the heat goes out. Does it always go out or only when it's over heating? Did you ever mix dexron coolant with another coolant (orange coolant with another color like green). Also letting it idle may not overheat the engine since it isn't labored; then driving it, the load on the engine causes it to overheat. Is this true every time? If so I wouldn't call it intermittent.

I still have a feeling that if it is overheating and you are showing all of these signs, it is something to the effect of a warped head(s), then again you said coolant doesn't drain into the radiator, can you elaborate.

Remember not to mix those liquid sealers with any antifreeze. I think they may say it's ok, but I wouldn't trust it personally as I haven't done it/seen it. I have personally seen 2 3400s (though not in a Monte Carlo) have sighs very similar to this and in the end, we tried that steel seal which worked,so I recommend that but it's up to you.

I wish you the best and I hope you get this repaired; it's terrible to have a vehicle down around the holidays.

 

Overheating while not getting heat just screams of an air pocket IMO