My car is overheating when moving slowly or stopped. Once I get moving temp drops to below 200F, normal. As far as I know everything is good and the coolant system has never been appart, so I doubt any air is trapped. Once moving everything is fine...

Is there a typical failure? Burnt out fan motor, bad relay? All fuses are OK.

'02 Z06, 70k miles.

Thanks!

 

How hot is it getting?? Mine got up to 230 easy in stop and go traffic before I adjusted my fan temps.

 

My 02 runs anywhere from 210-225 in town .This seems high to me, How do you adjust your fan temp? The fan works but it doesen't seem to come on when it should..Thanks .....Pat

 

I am having nearly the same problem. Haven't had a boil-over yet, and the car is new to me, so I don't know what is normal. Last night was an 80 DgF evening and with the top down and the air off, the dash monitor said 198 F when moving, but would creep rather fast up to 208-210 F when stopped. I ran the AC earlier in 92 F heat with sun and it stayed around 210 to 215 F. The car has 56k on it and I can see that the system has never been touched.

 

BlueAngel, you never mentioned the temps that you consider overheating. C5s run at higher temps than you may be used to.

The stock thermostat is nominally a 190 F unit. Once the system heats up, the lowest temperature it will run is 185-195 F, depending on the individual thermostat. Below that temp, the thermostat begins closing to maintain that temp. My 02 runs at 194 when the thermostat is closed.
During stop and go traffic, or any other situation where there is low airflow through the radiator, the coolant temp rises if the AC is off (ie the fans are off.) At about 228 F (approximately, the temp varies slightly with model year), the fans (both of them) will come on at low speed. If outside temps are cool, this may be enough to lower the tamps. If the temps do keep rising, at about 235 F, the fans will go to high speed. The temps mentioned in many of the above posts are ops normal for an unmodified C5 cooling system.

If you have your AC on, the fans will run any time you are under 30 MPH and the coolant temp is over 165. If you turn off your AC, the fans will go off and your temps will rise just like was noted in k24556's post.

For C5 Pat, your system is working as designed. If you insist on changing the fan activation temps, it should be done with a programmer, either handheld like a Predator, or software, like LS1Edit or HPTuner.

 

Thanks Fdxpilot!. I think I'll rest easier knowing that the temps I'm seeing are really OK. Watching it climb is a little unnerving, when my gut tells me it should be steady. I think I'll check for cleanness and take it out in the heat this eveining and see if I ever get above the temps you mentioned.

 

Yea that used to freak me out to seeing it get near 230 but a diablo programmer fixed that!

 

I drove to the NCCC in Nashville today in 95F heat. Ran the air, and everything is just as fd-xpilot said as far as temp goes. I could feel the fans come on below 30 mph, and they came on high once. All is as he said. Thanks for ending my concern. On the highway, even in the heat it stayed a 198. Thanks for posting the explanation.

 

No problem. It seems a lot of folks get freaked out by temps in the 200-230 range, even though it's normal for the vette.

 

Always a good idea to check the upper front of radiator for leaves and trash that gets sucked up, never checked before You will be surprised.................

 

Sorry to be a couple of days getting back to this thread...

Temps were 250+, enough to have the AC shut down automatically and get the "coolant overtemp" on the DIC.

Checked for the usual debris in the rad, everything is nice and clean up there, no bags, leaves, racoons, etc.

Started the car up and noticed bubbles going in and out of the coolant tank. Shut it down, and the coolant level was low. Topped it up with water, ran it through a few idle-3k RPM circuits, shut it down and the coolant was low again. Topped it up again. Drove it for a bit, everything seemed fine, everything working normal, low fans on at 225F, high fans on at 235F, no more overheating.

Drove long drive home from Ottawa last night, 3.5 hrs. This morning I checked the level, it was low again. Topped it up before my 5hr drive to Michigan. Haven't checked it since.

In total I've added about 3L of water... quite a bit. I also replaced the rad cap since the original cap was letting a vacuum form in the system and not letting air in to replace it.

My question now is, what's the next typical failure mode for a leaking cooling system? Hose? Head gasket? Engine is internally BONE stock '02 LS6 with ~70k miles. I don't see an puddles under the car, but I'll check again after work today...

 

I had a '89 Camaro with the 5.7L V8 and I was constantly adding water and antifreeze every few weeks. I knew I had a leak, but I NEVER, EVER saw any antifrieeze dripping or puddling under the car. I checked EVERYTHING! I replaced the water pump, thermostat, new thermostat housing, new radiator cap. Checked every hose, clamp, and any evidence of leaking antifreeze, nothing This went on for about 18 months and it was driving me crazy. On one particular hot day in the middle of the summer, I popped the hood with engine running and I saw steam coming out on the front part of engine on the passenger side. I had a failed intake manifold gasket, that leaked only when the engine was hot. Replace the gasket, no more leaking antifreeze. Took me about 10 hours to fix, but it was very satisfying to finally find and fix the problem. Ended up having the same problem on my truck about 7 years ago.

 

 

Well I can sleep a little better knowing that the temps are normal. I did clean the rad Unbelievable the crap that was in there.I topped off the coolant Saturday And I see it's about an inch lower today (Mon.) I can't find any leak or steam anywhere. I'll keep aneye on it. Thanks Guys ....Pat

 

OK, I checked the coolant level again last night and it was still full, so that was after a 5 hour drive. Feeling pretty confident now that there is no leak, maybe the bad rad cap was just letting steam out and over time the water in the coolant was just evaporating?

In total I added about 3L of water to get it topped up... that seems like an aweful lot. What's the coolant capacity of these cars?

Also, there was always coolant in the overflow tank... does this mean I was driving around with 3L of AIR trapped in the engine where coolant should have been? If so, how likely is it that my heads were full of air?

With traditional "green" coolant, I'm under the impression that the coolant itself does not evaporate, only the water does, so if you have an evaporation problem you can just add water and all is well. Is the same true with the "red" Dexcool coolant? Should I be flushing the system and replacing it all with fresh stuff?

 

My coolant dropped about a half a litre, I topped it up again and drove 150 miles it hasen't moved so I'm guessing air

 

The capacity for a M6 car is 11.9L or 12.6 quarts. For the A4, it's 11.6L or 12.3 quarts. The .3L difference is the size of the trans cooler tube that's built into the A4 radiator.

The manual says to always add 50/50 mix Dexcool and water. If you go over 50/50, you raise the boiling point, but also raise the freeze temperature. 100% Dexcool freezes at -20C or -8F. The manual advises never to go more than 70% Dexcool. At 50/50, the boiling point is 128C or 262F, and the freeze point is -37C or -34F.

The fill procedure in volume 2 of the 1999 shop manual runs like this:

1. Fill the system through the surge tank opening

2. Fill half the capacity of the system with 100% DEX-COOL(r) coolant

3. Slowly add clean drinkable water to the system until the level reaches the base of the neck

4. Start the engine

5. Idle engine for 1 minute

6. Install surge tank cap

7. Cycle the RPM, idle to 3000, in 30 second intervals until engine coolant reaches 99C or 210F

8. Shut off the engine

9. Slowly and carefully remove the surge tank cap - open it until you hear hissing, then wait until the hissing stops. Then remove the cap

10. Start the engine.

11. Idle engine for 1 minute and fill surge tank to 1/2 inch (13mm) above COLD FULL mark on the radiator surge tank

12. Install the surge tank cap

13. Cycle the RPM, idle to 3000, in 30 second intervals until engine coolant reaches 99C or 210F

14. Shut off the engine

15. Top off coolant as necessary, 1/2 inch (13mm) above FULL COLD mark on the radiator surge tank

16. Rinse away any excess coolant from the engine and compartment

17. Inspect the concentration of the coolant with a coolant tester

Oh, and make sure the surge tank isn't leaking. My son had a devil of a coolant leak - turned out it was a crack in the tank on his ten year old Taurus.