Rebuilt the motor.
New Hoses.
New Thermostat. Drilled 1/8" hole for bypass
New Radiator
New Sending units.
New Water Pump


Vette will run up to 245-250 degrees. By the time the fans kick in at 228 it is too late, then it goes to 250. I installed a mechanical gauge to verify that the dash gauge was correct, it is not, it will read another 10-15 degrees higher yet! The cooling system has been bled several times. Not sure where to go. This car is non-stop problems. I am at the point I have twice as much in it as it worth (going on three times as much!!) I'm not much of a quitter though. The car will learn to like me.

 

Is the thermostat openning? Is there a chance it has a blown headgasket?

 

You are saying when the fan comes on it dose not lower the temp? What dose it run up to if the A/C is on from start up? I would pressure check the system I know you said rebuilt motor but sounds like there is a leak some where

 

I have not charged the A/C yet.

 

I checked to make sure the thermostat was opening. It seems to work properly. Can anybody recommend the best way to check the cooling system to see if there would be a blown head gasket?

 

If you have a blown head gasket you should have seen leaking or water in the oil by now.

 

Not always, go to your local NAPA store and get a block tester kit and follow the instructions.

 

I would have the cooling system pressure tested by a radiator shop..."If" you have a cooling system leak it could be anywere..Did you visually inspect your A/C coil carefully for any kind of blockage when you had the radiator removed? Is your exhaust obstructed? how is your ignition timing? These are a few to think about..

 

Cant tell you how many tens of thousands that thought has cost me over the years. Welcome to hell.

 

my 90 does this to. it jumps to like 240'ish then the thermostat opens finally. I've verified the temp with a mechanical gauge as well and it shows what the dash gauge is showing.

Mine just had head gaskets done as well so that isn't the problem and it holds pressure fine as well. I think it has a huge air pocket somewhere that don't want to come out!

I find the air pocket idea to be true because if the coolant was getting to 240-250'ish inside the block and my fans thermal sensor is on at 228 and off at 208 then why wont the fans come on when internally the coolant appears to be at this temp. However after my thermostat finally opens the first time the next time the coolant temp sky rockets to 240'ish the fans do come on.

when my car was on level ground it never did this but since I got it up on car ramps it always acts like this. Or could this just be a coincidence? Another possibility could it be the lever style pressure relief radiator cap? I noticed even when shut off when this hot no coolant ever enters the overflow. After I did the head gaskets seemed to cool just fine then all of a sudden it started doing this.

another thing I considered around about the time this started happening was plugged cats which I punched all of them. However something I found odd was this car even with punched cats is still very quiet (has stock mufflers) I am almost wondering if this used catback exhaust being it came from a guy who lived up in the mountains possibly some rodents got into the mufflers. Because when the car had the front Y-pipe loose at the exhaust manifolds it cooled differently as well. My mufflers are the type where one of the outlets is fake .... But even so without cats I would have thought it would be noisier then it is kinda sounds like a non performance car with a restrictive exhaust by comparison my 82 trans am with cat and stock type muffler is twice as noisy as my corvette now.

 

I have a 90 and if I'm cruising with no traffic lights or stop and go my temp is fine. Now if I'm in traffic or even if I'm cruising up a mountain road, the temp goes way up. Not sure if thermostat is sticking or fans are not kicking in. Unfortunately I'm more of just an oil changer mechanic so if I do take it somewhere I don't want to get screwed! Any thought about the car problem?

 

Pressure check the cooling system to determine a blown head gasket.
Have you checked for debris, leaves, dirt, dead birds, etc, between the AC condenser and radiator?

 

A blown headgasket will cause steam out your exhaust and a dropping coolant level and blue colored spark plug insulator, and wet plugs too. I think your problem is that you haven't yet got all the air out of your cooling system. When you drain the coolant totally, like to replace the radiator, you lose the coolant in the heater core. It is difficult to get all the air out of the heater core and I recently had my OEM radiator replaced and continued to get the low coolant light. This will also cause high coolant temps. You need to burp the cooling system several times repeatedly in order to get all the air out of the heater core. You MUST rev the engine to about 1500 rpm in order to see the coolant drop when looking into the rad filler, then fill the radiator, close the cap and THEN let the engine rpm back to normal idle. After, "burping" my cooling system, I drove the car about two miles and returned to my mechanic and he slowly removed the rad cap (damn dangerous because you have to remove slowly enough to not let the coolant boil out) and I stayed in the car and raced the engine to 1500 rpm while he filled the radiator and back out for another 2 miles. After the second burp, I no longer have air in my system.

 

Yep--thanks

 

The entire cooling system is new. Including radiator. No obstructions or debri. Have tried burping the system several times. If the car is being driven down the road, it does not heat up. Just when idling. Going to try an Ecklers sending unit to turn the fans on quicker.

 

I don't think that will work on a 1990-up. those are for post-90 cars. I believe cooling control is done through the coolant temp switch found at the front of the intake manifold and then the relays are switched on by the ecm.

I pulled the plug from my cylinder head and used a thermal switch to ground both fan relays which really works good and draws a hell of alot of air. But you wont find a low temp sensor like ecklers sells anywhere on the car. But to add it there a pipe plug between 1 & 3 plug wires on your 90, just remove that pipe plug & thread in the thermal sensor and run a ground wire from that to your relays and then the ecm wont have any control over fan operation.

if you need the ground wire colors on the relays let me know.

 

just replace that pipe plug with one of these and use it to ground your relays. I think this is what you saw on ecklers.

 

Every Corvette will heat up some if you are sitting or at very low speeds. Sounds like your thermostat may not be opening up all the way/sticking.

 

Everything being good and all, I would have to guess that there is a lack of pressurization in your system somewhere....a pressure check is in order as previously suggested. Have you tried a water wetting agent? It might help....I run some in mine.

 

I haven't tried the water wetter. Read a few horror stories. Still waiting for the Eckler piece to try that. I also picked up some Kingsford fluid and a new Bic. That might be the only cure. I truly own the Vette from hell.