So I've never had an issue with my Monte before today, when I noticed that the temp gauge was nearly in the red on my drive home from work. I turned the heater on and rolled down the windows, and that seemed to help. When I stopped, steam was coming out from the radiator overflow (only a small amount) and the coolant was violently boiling in the overflow and, by the sound, the radiator. The overflow has plenty of coolant in it (implying that there's no leak?). I took off the radiator cap, there's a little bit of brown stuff on it-could be buildup/a clog somewhere? I replaced the t-stat about a year ago and did a coolant flush then. I need to change the oil, was going to do that tomorrow anyway. Mechanic told me I have a leaking intake gasket in January that I haven't had the money/time to fix yet-could be related? Any help would be appreciated!

2003 LS with the 3400 engine and 150K miles, btw

 

Have you inspected your radiator cap? If the seal inside is all brittle and the disc is not moving freely you will need a new cap.

Have you noticed if your electric cooling fans are operating when your overheating?

You could always pull your T-stat for a test drive around and if it does not over heat your gold, or do the boil test with the T-stat.

Are the fins in your radiator free from an excessive amount of bugs and debris?

It almost sounds like it could just be a radiator cap for it to just fail like that, if you get a higher psi one it will raise your boiling temperature too.

Have you been able to determine if you water pump is still working, it sounds like your car savy enough with all the other things you have done, heater on etc. But do you notice any coolant spots below the car where the pump weep hole may be letting coolant drip? I know if you were just boiling over your engine cradle and such probably has coolant dripping from it, just looking for reasons for you.

 

I think, if you had a leaking intake gasket, that could cause your problem. Plus the brown stuff in the radiator says you may have oil leaking into the coolant. You may just need to buckle down.and get that leaky intake gasket fixed before it causes a more major problem!

 

I'm afraid you're right.

Zippy, I don't think the fans were operating, I let it idle for a bit and I don't think they ever came on (but it's hard to tell when the engine is on, because you can't really see them or hear them...any tips to make sure?)

Radiator is clean-I keep this car very clean.

Haven't noticed any leakage at all before.

Radiator cap could be it, I might get that replaced.

I'm sorry I'm not familiar with what you mean here? Do you mean remove the T-stat? Because I'm not sure how you'd drive after that...

 

Remove your cap and inspect it first before you buy a new one, the failure signs can be subtle, but look it over real good for hard brittle rubber and worn spring that fails to keep the system sealed.

You need to get at the right angle and perhaps use a flashlight and you can see if the fans have come on and even hear them. They will only come on after the engine reaches a set operating temperature. So look before you start your car as to where the fan blades are and then after you start it you will be familiar as to where to look. Fan failure is actually supposed to be the number 2 reason why engines over heat. Radiator cap comes in high on the list too.

Back in the day if ones car was overheating we would just remove the T-stat put the housing cover back an and drive without the T-stat installed. While in the long term it is not good for the engine in the short term it won't hurt anything. You can remove your T-stat and look at it, it should be closed when cold, no space between the small disc and housing. Put it into a pan of boiling water and if you observe the disc opening then the t-stat is good. If it fails to open then it will need to be replaced, about a $10 part. I don't know if these newer cars can actually drive around without the T-stat installed as I believe the T-stat has a rubber seal that comes into play preventing coolant from leaking out, in the old days we actually had a separate gasket. So I'm wrong about removing it and driving I would bet.

 

The Thermostat or Tstat could be the culprit you can remove it and drive the car with out it and have no problems.


The electric fans on the radiator will run if the thing is hot even if the engine is off, if not there could be a relay that controls them that has gone south.


I have a Pontiac Torrent that has the 3400 motor in it and it was doing this stuff. Took it to the Garage and they put in a new Thermostat and then went back cause of lack of heat they flushed the Heater Core supposedly fixed that.
However I finally got home for awhile and had been looking it over and found that it was a bit low on anti-freeze/water so filled that up and been monitoring all the stuff daily and it seems to be working for now???
Those pesky Tstat's can be a headache you can get a bad one cause who knows where they are made, I have known cases where the Garage put in several before a good one came along, rare but possible.
The thermostat will block the water movement until the engine heats up once the temp is reached from the thermostats setting from the Factory. it opens up and now you have the desired running temp.
Do not continue to drive once you are in the redline alert of the HOT on your gauges. Anything in that engine that is Aluminum will heat faster that most other metals. I had an issue with a (Ford mini Van) once that warped the heads. Once I saw it was overheating it was too late.
It is a good idea to keep the Maintenance up on the cooling systems. New Hoses, keep the radiator clean, every time you wash it check for bugs that clog the coils in the radiator and flush that material out, of the exterior.
You can probably youtube some information about this subject.


The intake gaskets are a headache on these V-6's and I have had several replaced you always have this Oil leak, I have never had an issue with a bad one that caused it to overheat, not saying is couldn't happen but I replace 5 of them on Cars I have owned 3800,3400,& 3100 engines. Make sure that you replace it with one that is better than factory minimum specs. Hope that helps some.


They say that all the stuff that goes in the car are supplied by the lowest bidder?????????????
So keep that in mind when something might go bad.

 

Quick update:

I don't think it's the T-Stat, started the motor up and the upper radiator hose got hot once it got up to temp (so coolant has to be flowing).

Figured out a good way to see the fans (needed a flashlight), and they did not come on while running the car, but I turned on the A/C and they both started right up-not sure if this means they're fine, or if a sensor or something could be the problem with them not coming on?

My coolant looks slightly discolored, and there appears to be some gunk in it-it's on the radiator cap, could possibly be dislodged rust? I'll try to post a pic later. I think my next move might be a coolant flush-is it better to put in the dexcool, or should I go with the standard green stuff? Pretty sure it's got dexcool now. Also going to change the oil, it's due anyway, I'll post back if it looks like it's got coolant in it.

I ran it for about 15 minutes this morning, and it didn't get too hot (slightly hotter than normal, but certainly not redlining). Of course, this was at idle. I have a scan tool but my brother in law is borrowing it at the moment, so I am just reading the temp guage-it's about one notch higher than normal today (yesterday it was just below redline while I was driving, I immediately pulled over and put on the heater to get it back down).

Supposed to be traveling tomorrow, so OF COURSE this happens today...

 

Check your owners manual for the proper anti-freeze recommendation.
My Dad was a Mechanic and I watched him work on cars a lot. So I am interested why you turn the heater on when it gets hot, it will give the liquid more path to circulate and there are coils in the Heater Core, something I am not familiar with? Sorry? Make sure your coolant level is up on the reservoir to the cold location when it is cold.
Also if debris gets into the Tstat that will cause some havoc, I think the fans should kick on when the car gets hot with out the AC on, you could take the relay from the A/C fans and replace it to the regular fans to see if that is the relay, they are a little square black thing looks like a printer cartridge, most likely in the line that powers the fans. Went out on one of my cars a few years back and I just replace them all. Good luck.

 

You turn the heater on because it kinda acts like another radiator, taking more heat away from the coolant in both the heater and the radiator.

 

LS8ARTum.jpg

That's what the radiator cap looks like. There's more gunk like that in the radiator, too.