2000 grand prix 3100 overheat

[High Sierra 2500]

Hi, I have a customer's 2000 Pontiac grand prix se in my shop right now. The car has the 3.1 in it and 166K.

Came in for an overheating issue, customer was afraid to drive the car across town. I picked the car up and drove it to my shop.

Upon inspection, no coolant was visible in the radiator. Customer said he put coolant in the car a few weeks ago because it was low.

Next day I go to put coolant in the car, and it's full. Drive the car, runs fine. Drive it 75 miles without issue. Drove it on the freeway, left it idling for an hour, drove stop and go in the city. Nothing apparently wrong with it. Heat works, runs fine, does not lose coolant. No leaks visible with car on hoist, no vapors in exhaust, no bubbles in radiator. Ran errands with it for a week.

Drove the car back to the guy yesterday. He was going to drive me back to the shop when I dropped the car off. Halfway back (~4 miles each way) with him driving (normally) the temp gauge started climbing. The heat got cold. I pulled the radiator cap and found full coolant under pressure and the engine did not feel fully warmed up, although the t-stat seemed to be open. Drove the rest of the way to my house, checked coolant, no pressure in system, no coolant visible in radiator.

Today, coolant is full again, car runs fine again. Opened bleeds to see if there was air hiding in the system, none found.

So, where is all the coolant going that it is coming back? This one has me confused... Not sure what's going on here.

Thanks

[CrazyHorst]

My guess is that there's a restriction in either the radiator or heater core...which may not be consistent from day to day.

It seems like coolant is not "equalizing" in the system to a normal liquid level.

Also confounding the situation is that the coolant temp gage may read cold by virtue of being bathed in air rather than liquid at times.

The overall mileage of the vehicle would hint at lower intake gaskets...which could also be responsible for "sludging" the dex-cool and causing the issue mentioned above.

Easiest troubleshoot would be to drain the coolant and flush with a garden hose (etc) and make sure heater core and radiator are free-flowing.

[tblake]

When the radiator appears empty, how is the overflow level?

[High Sierra 2500]

Overflow level is typically below the "low" mark.

I also note an odor of coolant when the car is running now - No vapor, but I suspect we're looking at intake gaskets as noted above now. It's a 3.1, I've done a lot of them... But I never saw one quite like this.

[tblake]

I will also admit that is an odd problem. Does the oil cap and PCV valve have sludge on it like mine here?.....

http://www.automotiveforums.com/vbul...d.php?t=937651

Could you put a coolant pressure tester on it and pump it up to find out where its coming out?

[High Sierra 2500]

Well, more digging (this time out in the sun where I can see). Careful inspection... Didn't see anything like the usual 3100 intake failures I've seen before. Motor looked real clean (knocks a little, but no my problem). Still smell coolant though, and it keeps going low on coolant slowly.

Well... Keep looking... Heater hoses look kinda funky. Look down by the firewall where they connect to the core - gold goo on the connections, gold goo down on firewall and exhaust underneath. Apparently those connections have been leaking slow, dripping down onto the exhaust and burning off so it leaves no mark on the ground.

Must just be getting low and sucking air when you shut it off... Replace leaking hoses and see what happens...

[BNaylor]

Some knocking on the 3100 VIN "J" may be normal and considered piston slap as long as it disappears after a few minutes or until the engine is warmed up.

If you smell coolant in the cabin or through the vents then be sure to look underneath the passenger and driver's side carpeting. The heater core in the HVAC enclosure may be leaking which may explain where some coolant is going.

[High Sierra 2500]

Yeah, it has the piston slap, I'm used to that. It has just a little steady knock when it's warm. Not bad, and also not my problem as it's not my car.

I did look under the carpets - appears dry, don't see any leakage in the interior.

In further developments, seems that the owner filled the car with green coolant - doesn't mix so well with dexcool. So as of right now looks like the job will be replace heater hoses, flush cooling system, refill with dexcool.