So first things first, I have a 97 z28, M6. To give some background to this problem, I first will give some information about my previous cooling problems.
In the second week of September, the gauge would read red zone 5 minutes after the car being ran, so I bled it and air came out. Then I went to school, and had discovered that coolant was everywhere. It poured out of the reservoir, and was all over the ground. Later discovered that it was the Thermostat not opening, so I put a 160 lt1 thermostat from SLP. Car ran good afterwards. Then the 'flow valve control' thingy was leaking, so I replaced the hose from the water pump and the valve control thingy. Everything was good, until i went to school one morning, and the gauge went crazy, again. Popped the hood and opened the bleeders, and air. Like a lot, probably about 3 minutes worth, in 35 degree weather (which felt like a nice sunny day in Hawaii). All my hoses are good and tight. The car ran perfectly for about a week, and then this happened. My fans are working properly. I am starting to lean toward maybe the head gaskets? It cannot be 100% sure on the fact that there is coolant in the oil, but the oil level on the dipstick is higher than it should be. I am almost 99% sure that the oil level was correct before I started having these problems. Any ideas?

 

Is your pressure cap holding 18psi?

Have you pressure tested the cooling system?

Sounds like what is coming out of the air bleeders is actually steam. Are you running a 50/50 mix of ethylene glycol coolant and water?

You might want to use a test kit to check the coolant for hydrocarbons, which would confirm a head gasket leak.

 

The radiator cap is about 5 months old. It is rated at 18psi
I pressure tested the system in early september and it held in the 16-18psi range.
I am using a 50/50 mix from prestone.
I'll do some research on a test kit to test for hydrocarbons, because not pulling off the heads would make my life a tad bit easier as I am a young college student.

 

Radiator clogged?

 

A clogged radiator makes sense. The moron before me who owned it used some additive to stop a leak from happening. When I drained the coolant to do the water pump, the coolant was like a brown, honestly poop, looking color. So I think I'll see about cleaning it out, or end up just buying a new one. I'm guessing go with an AC DELCO?

 

Is your water pump coupling stripped and not turning your water pump causing engine to over heat in just a few minutes, like a very few minutes.

 

Stripped spline happened to me this summer. Car overheated in 5 minutes. Went to Electric pump.

 

I bet that stop leak stuff clogged up the steam pipe and fittings. Do you see any flow out of the return hose from the steam pipe at the radiator with the cap off? Check it cold.

 

1stZ28LT1 - I think that the water pump is working properly, I can't hear any "bad" sounds from it. I've only driven the car roughly 1200 miles since I put the new pump on.

ZZ- Before I installed the 160 thermostat, I bled the system. When I had the cap off, it looked like the coolant was just sitting there, not even recirculating. The 180 thermostat didnt suck down any coolant until I shut the car off, which i thought was weird, then it all seemed to work. Then i overheated again and put the 160 in, and hadno problems till recently.
Could this be a sign of the radiator being clogged and because of that, it can't reach the waterpump and consequently not cool the engine?
I'll recheck everything when i get home from school.

 

Odd thing is, GM recommends the stop leak pellets for these cars. From the factory service manual "D. Add two cooling system sealer pellets (GM P/N 3634621)".

I've never used them, and wouldn't.

 

These are alittle different than the bottle of miracle in a bottle fixes out there...2 pellets are not doing to do what an entire bottle of that crap can

 

If the coolant is just sitting there,I.m gonna go with the water pump.The water pump makes things move.Odd that it takes 5 minutes for the car to overheat.Usally takes 10 to 15 minutes.(spelling check here please).Most water pumps (from previous posts and my own experience ) last about to 80,000 mi or so.When you do the water pump,blow the system out as well.Hope this helps.

 

Forgot stuff I heard here.Make sure the thermostat is not upside down.Use a good quality 180 stat until you find this problem.Remember to disconnect the negative battery terminal while you are doing all this stuff.Make sure your coolant sensor works(it's on the radiator).My02.

 

Sorry I haven't been putting out any updates. I appreciate all of the input i have been getting! It's just that I am a college student, and I don't have much time right now. I plan on working on it this weekend, if the weather here in michigan doesn't decide to hate me.
I picked up a new radiator.
Fatdog2, As much as it seems possible that the water pump is bad, it has about 1200 or so miles on it, and it 'sounds' fine. Its not making any grinding noises at all. It honestly seems like the radiator is clogged, because it ran fine all summer, until i got back to my hometown. So it leads me to my radiator. I'm going to try and find the receipt for my water pump, and if a new radiator doesnt fix it, ill just get a free water pump.
I appreciate everybody's input

 

when the water pump went out on my 94 Z, the gauge went all over the place, up and down. The car had about 40k miles on it.

Had it replaced by Chevy with lifetime parts and labor warranty. Car has a 165k miles on it now. IIRC, I haven't replaced the pump. (knock wood)