Hamlet

Hi,

My problems began after I had a shop replace my A/C compressor and with it the water pump/thermostat was replaced. Before this I'm hard pressed to remember coolant ever hitting 220. Today it's about 90 outside and when slamming it back and forth on the freeway it got up to 250 degrees. I backed off after that but I'm sure I could provoke it further. It drops down to 220 or so quite quickly when letting up. A/C on tends to make it worse but it climbs steadily under load even with it off.

I've noted:
* Never gets over 210 idling.
* Doesn't spew coolant / oil not milky.
* Oil temp is following coolant temp pretty close.
* Fans are spinning.
* Gets up to temp quite quickly, 185 in 5 mins or so.
* Light load/slow speeds seem to work fine.
* Air duct is in place, except for the skid-thingies normally hanging under the car.

Done to far:
* Cleaned radiator and AC ditto using air/water. Seems reasonably clear.
* Replaced all idlers/tensioners.
* "Burped" it by the head air bleed line.

Fans engage temp has been lowered by previous owner, stage one is ~200 and stage two is ~210 I believe. Car is more or less stock '98 with 60k miles.

My own thoughts:
* Thermostat stuck half open/closed. What doesn't make sense if so is that engine gets up to working temp quite quickly.
* Radiator gone bad all of the sudden?
* Head gasket(s) gone, however doesn't seem to be the case (no oil stick gunk/coolant overflow).
* Shop filled it with some type of coolant the vette doesn't like. Dunno what is is but was supposed to be some "lifetime" fancy stuff, greenish color. Can't believe it would make that big a difference though.
* Lowered fan speeds causes fans to more or less always spin, maybe this obstructs air flow at speed?

I'm at a loss... dunno what to try next in order to pin it down. Also remember as far as I know everything was fine before the compressor was replaced (was in winter storage before the repair so can't remember if I floored it this hard before the repair this year). Any suggestions welcome!

Thanks,
Dan

Cutlassmaster

Sounds like you have air pocket. There are several ways to do it. Quickest might be to disconnect the hose at the coolant cross over under/near the throttle body. You can bleed the air out while running it if your careful of moving parts. Also make sure tank is full enough. Look down though the threads and stickies for other methods and overheating threads.
Chris

don hall

The cooling equation is quite simple..... coolant flow plus air flow equals cooling. Obstruct one, or both, and overheating occurs.
You knew that, and since you have checked/corrected the obvious
problem areas, the source of the overheating may be your t-stat:

"My own thoughts:
* Thermostat stuck half open/closed. What doesn't make sense if so is that engine gets up to working temp quite quickly."

That makes perfect sense.....a partially-shut t-stat will allow normal heating of the coolant in the engine, but not allow sufficient coolant flow to maintain a lower temp.

Remove the t-stat and place it in a pan of boiling water to see if it opens fully. If it doesn't, replace the t-stat.

4XLR8N

Since they replaced the thermostat and water pump both, either could be defective and thus the source of your issue.

That aside, my first thought based upon your description is an air flow issue, since the higher temps happen under load and when moving. I would double check that your center air dam is installed correctly. It is a critical piece for ensuring proper air flow through the radiator when vehicle is moving.

I am also concerned about "green" coolant? Your '98 should have Dex cool in it (orange/red color). These two coolants do not mix well - nasty things happen.

Hamlet

Thanks guys, I guess the thermostat is the next thing to try. I guess it's a matter of opinion but should I get a 160 degree one as my fan speeds are lowered? I won't drain the system before I have that $10 piece at hand if the old one is faulty.

About the coolant... it says PEAK on the receipt, a quick search seemed to indicate people using it in their vettes (C4 at least) with good result, but I must say it was a bit inconclusive. I'll check exactly what bottle it was but at least according to their site (Peak) it should be compatible... dunno?

Paul 75 L82

Here's the procedure to burp baby:

Start w/ a cold engine
Remove rad. cap
Idle for 1 minute
Install cap
Cycle RPM from idle to 3000 until coolant reaches 210F
Shut off engine
Remove cap
Start engine
Idle for 1 minute
Install cap
Cycle RPM from idle to 3000 until coolant reaches 210F
Shut off engine
Remove cap
Top off