1986 coupe, aluminum heads. Stock.
Sitting still temp continues to go up, even after fan comes on. Drive and temp goes down to "normal" temp (195, in my case). It got up to 246 sitting still, and it was still rising. This is something new, I just started seeing.

Any ideas on what may be the problem?

Oh - I had a blown fuse two weeks ago for the fan. Replaced it and the fan comes on like it should.

 

Are you sure the fan is turning fast enough and there is no debris between radiator and A/C condenser??

Is the coolant level ok?

Does coolant surge through the radiator when you reach over and crack the throttle?

Is the A/C on when you are checking coolant temp?

Turn on the heater full blast and see if coolant temps come down.

 

Have you replaced the thermostat?

 

Don't know about fan speed - looks and sounds normal.
Haven't cleaned out debris in about 3 years - I'll check it out.
Coolant level is OK.
AC currently not working - no refrigerant.
I'll check with the heater on.

Thermostat is 6 months old (180 deg).
Water pump is about a year old.

 

The thermostat is not the problem.

The main fan between the radiator and engine is controled by the memcal (chip) in the ECM. Stock temperature for the fan to come on is 227*. The fan will cut off at 217* stock. This is if you let it idle up to those temps. There is a fan relay on the driverside inner fender. The digital readout on the dash is controled by a coolant temp sender in the left head between #6 and #8 spark plugs.

You may have a secondary (aux) fan infront of the radiator that you can see if you look under the front bumper. Some C4's came with them and some not. That fan is controled by a sensor in the driverside head between #1 and #3 spark plugs. The on temperature for that fan is 235* stock. Note: (on 85 vettes the location of the coolant temp sender and aux fan sensor is just opposite from what I described).

That being said you, know what to look for with the fan situation. Make sure it comes on and goes off at those temps. This is if the chip is still stock.

The ONLY thing a thermostat does is control the warm up time and minimal operating temperatures. I bet it takes a little longer than it should to warm your engine up. On the highway your temperatures should be around 170* with that 160* t-stat. The stock degree t-stat for the L98 cars is 195* and for the LTx cars is 180* stock.

Take the radiator cap off when cool and start the engine and let it get to the same degree as the t-stat. The t-stat will open and let coolant circulate through the engine block. This is usually where the air is trapped. You will notice the coolant level in the radiator cap opening being to lower and may see bubbles. Fill the coolant as need. Let the engine get to where the main fan cuts on...watch for overheating. Now rev the engine to 2,000 rpm for a few minutes and check the coolant level again. After this the air should be out of the system. If you need to know more let me know.

Here is a test I did so you know what to look for:

 

On the 86s the secondary fan (if there is one) is tied to the A/C and won't come on unless the A/C is on. You can jumper a couple of leads on the A/C circuit but that just turns the fan on permanently and there are more efficient methods.

1. Make sure that the system is topped off (and the overflow tank is full as indicated) and is free of air.

2. As mentioned check for debris between condenser and raditor and in front of condenser.

3. Have the radiator cap pressure checked.

4. If the cap is working properly be sure that the overflow system is working properly.

 

You're half right. If the thermostat doesn't fully open when it's supposed to, it restricts coolant flow to the radiator. Restricted water flow=less cooling. That would explain the higher engine temps at stand still.

 

A place to start would be: pull the radiator and completely clean it and straighten out any and all cooling fins. Second would be to do a complete cooling system flush and replace with 50/50 distilled +coolant.
Check the two hoses and replace the radiator cap.

The above is for starters.

 

Just so there is no confussion, the secondary fan on an 86 is controlled by a temp switch in the drivers side head.

 

 

The stat has nothing to do with it. Once it is open, it's done.



Good luck with THAT test. With the cap off (cooling system not under pressure) the coolant will boil LOOONG before it reaches the fan on temp.



WRONG!

RACE ON!!!

 

Tell that to my '86. It will be glad to hear that.

 

You may have a defective fan switch or wire between it and the aux fan relay, but that wasn't the way it was built. Just check the wiring schematic in your FSM to confirm that.

RACE ON!!!

 

Is there a different way to get the air out of the system on 84-91 Corvettes? There are bleed valves on the LTx Corvettes. The radiator cap opening is the only way *I* see to get air out with out breaking a seal.

 

The last car I checked with this problem had plastic bags blocking 75% of the radiator.

I've cleaned lots of leaves out of mine twice already. Last time I installed some adhesive weatherstrip under the condensor to keep it clean.

 

Just do what you suggested. Run the engine with the cap off until the fan comes on. Let me know how that works out for you.

RACE ON!!!

 

The fan will come on after all the water boils out. Once the oil cooks and the bearings start smoking, enough heat will get to the airbound fan switch to close it.

 

To answer some of the questions:
I don't have an auxilary fan.
My ECM chip turns the fan on at 195.
My thermostat opens at 180. I verified this.

Letting it idle in the driveway and checking things out:

I found that the fan doesn't always come on when it should. Sometimes it does and other times it doesn't
I found that if it should be on (based on coolant temp) and it isn't - tapping on the relay turns it on.
I may have just thought the fan was on when it wasn't. It's hard to hear in traffic with my exhaust.

I just replaced the relay.

I'm going to clean out between the radiator and condensor coil this weekend. The last time I did this was 3 years ago.

I'm optimistic this may get rid of my problem.

Thanks for the help, guys. Lots of useful info.

 

the only way I know of getting the most coolant in your car, is take off the radiator cap, start it up cold, open the throttle a little bit and run the engine to about 1300-1500 RPM, the water pump flows more coolant, compressing the air in the heads, etc.
add the coolant while the level is low with the engine revved up, and put the cap back on quick. Then let go of the throttle.
If the cap is any good, you will vent hot air with a little coolant into the overflow tank, and when it cools off, the recovery valve in the cap opens when the coolant in the engine cools off, drawing in the rest of the coolant it needs over several heating and cooling cycles.
In order for this to work, the overflow tank hose must be good, and the clamps tight.
watch your driver information panel, and make sure the low coolant sensor light doesn't come on, and you know it's full.
The information panel is coordinated with the radio, so that the radio squawks or chirps when a fault light comes on (factory Bose radio)