Is your C4 running hotter than you like? Stock Idling its running about 235 before the main fan kicks on. Here is some info that I put together to help cool it down.

The normal operating temps for your C4 is about 190 while your driving. I hate my car being hot. Idling theres not MUCH you can do for it but if you add a better waterpump and a 160 theremostat, keep your radiator clean and in good shape and make sure your spoiler is well intact. Also cut open your lid and switch to a K&N. The better airflow the cooler it should run. Change your coolant regulary.


Main fan on/off:
Varies just a bit in exact temperature over the years, but it should come on anywhere between 225-228F (coolant), I say that because the in-car gauge is rarely so accurate for you to say its coming on exactly when the manual says it should.
The main fan will also cycle with the A/C running.
Aux fan (if you have it)-in front of your radiator and condensor, and it should come on just above your main fan temperature, say 228F, though in 85-86 it came on at 238F.

Stock Thermostats-
L98-195F (coolant)
LT1-180F (coolant)


Once the engine starts, your car will proceed upwards to the thermostat opening temperature, at which point it should hold steady as the stat cycles open and closed. At that time, the oil temperature will catch up with the coolant and usually passes it. This drags the coolant temp up towards the fan setting. Generally it'll settle at about 15-20F difference between the two.

Danger zone-if you have aluminum heads, do NOT allow the coolant to reach 250-260+, or you're risking a head gasket. That applies to both engines. A dino oil engine can handle oil temps 250 for short durations, but above this the oil breaks down and you need to change it sooner than usual. Synthetics can withstand 300F.



Things to do if you suspect the engine is overheating:

1.Check to see if the thermostat is working. Car temperature should stabilize momentarily at the thermostat opening temperature. If it doesnt, replace it.

2. Check to see if the fans are working. Let the car idle up to fan temperature and make sure they come on when they should. Try running the A/C to see the fan itself actually works at all, it should come on within a few minutes of running. Main fan relay is on the radiator shroud starting in '88, and earlier years have it just below the Master Cylinder on the wheel-well.

3. Check to make sure the WP is not weeping. There are weepholes in the WP that will leak when its bad. Its hard to diagnose otherwise.

4. Remove air bubbles in the system, and check for pressure leaks. Old caps lose pressure and should be replaced every 2-3 years when you should flush your system. Also check for small leaks in the hose between radiator and overflow/surge tank and make sure all hoses are tightly clamped. Some leaks dont happen until the engine is hot, you must be sure.

To burp the motor-for the L98 let the engine warm up with the rad. cap off, until the thermostat is open fully. While you are doing this, hold the engine at 2000rpm or the coolant will just bubble out. You can do it by yourself, but its best to have another person inside the car. Once the stat is open and the throttle is pressed, the coolant level will drop....fill it up and replace the cap. It may take 2 tries to get all of the air out. LT1 systems use a bleed screw next to the TB to allow air to escape.

5. Clean the space between radiator and condensor. The C4 is a vacuum cleaner and sucks things up through the nose, because the intake actually breathes in air after its passed through the radiator and condensor (not through the little air gaps in the hood or shroud). Debris passes above the condensor and settles in the space between it and the radiator. Once this is clogged the temps will end up about 10-15F higher. Dirt and grime will also cling to the fins in the radiator, and must be cleaned. KEEP IT CLEAN


Does the car still overheat?:
If you see any plumes of white smoke in normal operation, once the car is hot (ignore any light wisps of smoke on startup, it may just be condensation in the exhaust, especially when it gets cold at night), then you have a head gasket failure. If it doesnt do that and still continues to rise, then theres either a pressure leak in the system that you havent found or it could still be a head gasket. It doesnt have to look like a shuttle launch, but usually it does.

If the car is just running too hot for your tastes the only permanent fixes are a combination of the following,

1. Reset the fan temperature in the ECM, either from a chip or laptop tune for PCM modules. 195-210 will work.

2. Change the thermostat to a lower temperature, this applies more to L98s than LT1.

3. Add a larger radiator. DeWitts, Griffin, BeCool, etc. These will not help idle temperatures so much, but once you get moving the temps drop fast. I now see a 30F difference in coolant with the BECOOL on the interstate, even in the summer it keeps the coolant low (mine was 175F in 95F outside.

4. Better water pump-Stewart, FlowKooler, etc. These affect idle temperature rises more than anything else, since they pull coolant in and push it out faster than the stock pump at idle. The car will still proceed upwards in temperature idlee, BUT SLOWER.

These are just some tips. Also replace your hoses AND clamps. Make a 50/50 mix of coolant AND DISTILLED WATER ONLY!!! NOT TAP WATER!!! TAP WATER EATS AWAY AT THE INSIDE OF THE RADIATOR AND RUBBER PARTS. DRINKING WATER IS BEST!!! Also use a reputable brand of coolant. I like PRESTONE. I hope this helps some of you out.

 

The main fan on my 85 project car has never worked. The auxiluary fan did at first but does not now. I replaced the fan relay on the drivers side wheel well and the temperature sensor in the block but did not solve the problem. I also removed the fan its self and tested it with jumper wires directly to the battery and it did work. I also cleaned the ground connection. I ran the car until the temperature guage reaches about 230 to 240 degrees but the fan does not start. Should the fan start if I turn on the air conditoner? What is the WP you mention . I would welcome any suggestions to help solve this problem.

thanks, jay

 

Your fan motor may be shot. Mine was on my 86 but I have only one fan. Try to turn the motor blade manually. Is it hard to turn? If so thats your culprit. What do you mean waterpump? The brand I suggest would be eddlebrock or Steward. Let the car warm up once it reach about 235 your fan should kick on if not turn on the air conditioner. I know it should be running now. If not then we need to pinpoint what is going on. It could be from what I know the motor or the fan relay. Are you not getting power to it? You said you basically jumped started it and it worked. Any wires damaged unplugged? I bet mech could help out hopefully he will see this post.

 

FUSE!!! ITS YOUR FUSE. That is blown i bet becuz if ur relay went bad it prolly blew out ur fuses

 

one of your fans is for your Air cond the other is for the engine , when you turn on the A/C the one fan should turn on to get rid of the heat the A/C creates. If the A/C is working correctly.

 

This morning I let the car run with the AC on. I had not done this before. As soon as it reached 238 degrees the fan started and then stopped when the temperature dropped to 218 degerees. Finally it works! Why doesent it run when the selector is in the heat & defrost position? Now to the auxiluary fan. When the car was shut off it used to keep running for a short period of time, but now it does not run at all. How and when is this fan supposed to work?

Your help is greatly appreciated, Jay

 

Well if it ran after the car was shut off it may have burned up the motr? Umm one of my wires came loose that connected to the motor. That might be it. Hmm I only have a single fan.I say rip the raidator and cooling crap out and make it air cooled like the VW.

 

on my 86, the fan should come on any time the A/C clutch is engaged, regardless of the engine temperature. and the a/c should never come on in the heat position, and maybe not the defrost either. If the fan is kicking on at 238, id say that is a little high, but then again your temperature readings may be off, as the sensor for the coolant temp is not the same one used to turn on the fan. On mine, the fan kicks on at 228 and continues until it drops to 212 or so.

http://members.shaw.ca/corvette86/Co...0View%2086.pdf

I want you to take a look at that. You said you replaced the sensor on the drivers side of the block (N13) but there is also another sensor on the passenger side (N5). i think that is the one you should take a look at as i believe that is the one that controls the fan to come on when the engine gets above that 228 range. Also there is a relay located infront of the radiator (N14) that also seems to have something to do with the cooling fan. Sorry i dont know the difference in functions of the relays and sensors.

 

Cooling fan is contolled by ECM based inputs from A/C request and coolant temp sensor readings. Raisin is right, the sensor on the left cylinder head is for temp gauge readings, the CTS for engine management is in front of intake ( I think), next to thermal time sitch for cold start injector. Have to check 85, but I think there are 2 relays for cooling fan system. I will check for you and get back.

 

what I mean to say is that the main fan only comes on when the selector is in the AC position and not at all when I slide it to heat @ defrost. I had only tried it with the selector in the heat position before. I will definetly replace the other temperature sensor (N5). My temperatures are to high. I wondered if there was another relay? Where is it exactly?

Thanks, Jay