89 Coupe, all stock

Symptoms
1. Temperature rises until I turn the car off.
2. Small fan in front of condenser will kick on at 225 degrees.
3. Temperature continues to rise.
4. I installed a switch for the fan behind the radiator.
5. Now, with both fans on, temperature still continues to rise. When
the temp gets to around 240, I'll turn the car off as not to cause
any damage.

Before this started, the car would reach 225, the fan would turn
on, and the temp would immediately drop to about 208, then the
fan would cut off.

Repair Attempts
1. Removed radiator. Had it disassembled, reamed out/cleaned
and reinstalled.
2. Installed new water pump.
3. Installed new thermostat.

Any Suggestions?

 

There could be air in the system.
Fill the over flow tank daily. Start the car and check to see if the coolant is flowing into the over flow tank.

Feel the upper and lower hoses at operating temps they should be close to the same temps. If one is hot and the other cold it could be the thermostat.

What thermostat is it, is it upside down?

 

:

 

When it first started doing this did you lose coolant in the radiator? I will guess since the radiator was out that it is clean in front of it.
Head gasket? Are you seeing white smoke at startup and maybe some surge at idle?

 

The thermostat is the Fail Safe type...guaranteed to fail in the open position. It is new. Only been one week.

The only white smoke I get is on the first startup in the morning. After that, no more smoke.

Coolant levels in the radiator and reservior look constant. No drop in levels and no coolant spot in my driveway.

Also installed new radiator cap and cleaned cooling fins on condenser and radiator.

 

Get a laser temp gauge and look for a hot spot.

 

Not a mechanic, but could the coolant temp sensor be bad? Does it really seem to get overheated?

What about the coolant to water ratio? Proper?

It seems that you have replaced/fixed the obvious potential culprits.

 

I'm suspecting the guage or the sensor. Can you verify that it is in fact getting that hot?

Greg

 

Have you burped that baby?

 

Gage readout is from the sender in the right head. You can test the accuracy of the display by disconnecting it - should read LO; grounding it should read MAX; however, that doesn't tell you whether or not the sender is faulty.

Main Fan Relay is grounded by the ECM when the Engine Coolant Temp Sensor - on the Intake, below the Throttle Body - indicates 226 degrees (a/c off); or when the a/c fan switch indicates a high side pressure of 230 psi (a/c on). To verify either, best to use a scanner.

Aux Fan is controlled by a switch in the left head. It grounds the Relay at 228 degrees.

Since your Aux Fan is coming on at an indicated 225 degrees, that switch as well as your Display seem to be working ok. For the Main Fan not to come on, suspect a Faulty Coolant Temp Sensor or it's wiring or ECM or the Relay itself. I'd look into to getting a scanner.

For the engine to overheat with both fans running (and from the factory - it only needed the 1 fan to stay under 226 degrees), the radiator full, the thermostat open, and no obstructions, I'd suspect the water pump, though I see you've replaced it. That leaves the head gasket - check #7 for coolant - rust on the plug threads or an electrode that looks different than all the rest. If it's leaking exhaust into the coolant, some radiator shops can pick that up with a simple test - though unless you have some of the old coolant, that may be difficult to do - depends on how well you flushed the block.

 

Exhaust in the coolant should show some deposits on the underside of the pressure cap.

 

Thanks for all the suggestions. I purchased a compression tester a couple of days ago. I'll closely inspect the plugs as I remove them for compressioon checks. I'll probably replace the sensor below the T/B just to make me feel good.

 

MY 88 is having the same problems , new waterpump, new themostat 185, new temp sensor, new hoses upper and lower, new fan relay. car idles to 235 when fan comes on still rises to 245 before i shut it down. no white smoke, checked the oil no water in it. thinking i might have air in the coolant system or maybe in need to reflush the system. my heater works fine and both hoses come to temp and fullness so i know coolant is going thru and themostat is open. any feedback would be helpful from the experts.

 

Looks like a basic cooling system problem and an issue of whether or not the gage is accurate. For the cooling system, the radiator could still be plugged up or there may be a bunch of debris between the condensor and radiator. You can have your old radiator cleaned at a shop or a new one isn't terribly expensive - $186 at the Last Detail - www.tld-corvette.com - Do make sure it's filled. Leave the cap off and when the thermostat opens, prop the throttle open a bit. Then fill it completely and put the cap back on before you close the throttle (though I have a feeling you've probably done this because when you don't, the Lo Coolant Light usually comes on). Also, when flushing, the only way I know of to get everything out of it is to remove the oil cooler hose at the filter and the knock sensor on the other side of the block. Don't do this, and you're leaving some water in it which is going to make a 50/50 fill a little difficult.

To solve the gage issue, verify the accuracy of the display (and it's wiring ) by disconnecting the sender on the right head - between #6 & #8. Gage should read LO. Ground the lead to the block - Gage should read 300. If you don't get either, there may be high resistance in the wiring - ohm it out between the sender and the Display Pin D4. If the wiring is ok, the Display probably isn't accurate. If you get the proper reads disconnected and grounded, you can try a new sender. First, though, you might want to see if the Engine Coolant Temp Sender is accurate. The ECM grounds the main fan relay as previously posted - 226 indicated by the ECT. Absent a scanner, spend 9 Bucks on a new sensor and compare how many ohms it reads across it's terminals with the one installed in your Vette after the engine has sat overnight. If close, the one in your Vette is probably ok. That leaves the wiring. Signal is yellow from Pin C10 at the ECM. Disconnect it at both ends and see if there's any resistance in it. With it plugged in at the ECM but disconnected at the sensor, verify that it has 5 volts at the ECM and at the connector (which is another way of verifying that there isn't high resistance in the circuit). If it doesn't have the 5 volts at the ECM, you probably need a new ECM.

 

i had a friend who would flush the radiator on his 5.0L mustang in the following way. he would drain the radiator by opening the lower stop-**** and then close it. the radiator would be filled with tap water from the garden hose. he'd then turn the car on and then reopen the lower stop **** while keeping the garden hose stuck in the radiator until everything came out clean for a minute or so.

it always seemed like a bad idea to me. i just didn't think the idea of running cold water constantly through the motor was all that great. i could never find anything anywhere that stated otherwise though. any thoughts?

 

I don't think cold water is a problem as long as the thermostat opens. If it doesn't, you're not flushing the block. However, with the method you've described, you usually only drain the water that's in the radiator when you turn off the supply. That leaves an unknown quantity of water in the block making it difficult to put in a proper mix and you really want it at a 50/50 ratio - distilled water to coolant; either that which you've mixed up yourself, or a store bought premix. Better to at least face it downhill and then drop the lower hose from the pump to get what you can out of the block and/or on the Vette, pull the oil cooler hose at the oil filter and the knock sensor. Capacity is about 2 gallons. Don't drain the block and you might only get a gallon of the right stuff back in it only it's going to be diluted by what you didn't drain out of it.

 

I 'powerflushed' mine by removing the tstat, reinstalling the tstat housing and disconnecting the upper rad hose from the radiator. Then mickeymoused some fittings, attached my garden hose to the radiator nipple... (also turned the pressure regulator on my house all the way up) and blasted it through till it was clear. Then I put the hose on the upper hose, blasted it backwards through the block till it was clear. I actually used a long poolvac hose to catch all the discharge water to drain it out to the driveway.

I switched this back and forth about 10 times until it came out clear instantly both ways. Those magic in a bottle fixes can't get all the crud out, but it helps to put one in there and run the car and let it do its thing to help break down the corrosion before powerflushing. Also if you dont have your hose connection secured on there good, it will blow off and spray everywhere. The cooling system is very restrictive.

 

A good thing happened today. After reading the reply by "Brother At Arms", I found that my heater is blowing cool air. Even with a coolant temp of 190 degrees. I don't know why its blowing cool but, It gives me a point to work from where as before I had none because I couldn't find anything out of the norm. I just may fix this car before the year is out.

Big *****