Overheating

Good Morning c4c5specialist,
It has been awhile. I'm the one you tried to help in the past with a high idle after a valve job. (1990 Corvette) It turned out, a large part of the problem was a couple of loose wires connecting into the computer box. It has never been perfect but it made a great improvement after reconnecting and messing around with these 3 wires and it has been running fairly good ever since. At the time while the engine was tore apart, the water pump was replaced just for the fun of it.
This is my newest and life threatening problem. Cruising down the road, everything was fine. I looked at my water temp. guage and it was like instant, It pegged out over 200+ degrees. The engine oil guage, no problem, it was a quarter on the guage. It never heated up. I thought it was just an electrical thing with the water temp. guage, it was so instant. In a couple of minutes I was home and the water was red hot and hissing. I hosed it down for 20 minutes. Any Ideas before I go looking for a garage. I'm kinda gun shy about going to a garage these days. Could it be the water pump, even though it is fairly new? It had a new radiator in before the valve job. There was plenty water at the time and it was so instant. Wishing you the best.

Have a great day,

semiD

[ChuckG]

My personal first stops would be temp sensor and thermostat.

Fan relays are another possibility.

Originally Posted by ChuckG

My personal first stops would be temp sensor and thermostat.

Fan relays are another possibility.

Thank you ChuckG,
Does the temp sensor control the water temp or does it only relay the temperture of the water to the gauge? Also the thermostat was removed and fans works fine. In the past if I stopped at a stoplight for any lenght of time the engine would overheat. A separtate switch was installed to turn on the fans whenever they are needed. If the water temp gauge ever showed halfway or 5/8s I could turn on the fans and instantly watch the water temp cool down. In one hand this cured up my overheating problem. On the other hand it puts a pretty good drain on the electrical system. I only used this when I was stuck at a light or in traffic and it truely does help keep the engine cool. Once the water temp heated up enough to open the themostat the heat just kept on going up until the water was boiling hot. Sometimes the fans could cool it down, sometimes not. If the fans were to come on say halfway on the gauge or sooner, I think there would be no problem but the fans don't come on until 3/4s+ on the gauge and that's just to late and to hot. I thought cold is better than hot so I removed the thermostat completely to stop the restriction to the water flow. I have been to the Chevy dealer, they kept my car for a week, saying everything was fine and charged me $500.00 for radiator work(which nothing was wrong) and when I got it back, It still had the same problem. The removing of the thermostat and installing the direct switch to the fans seemed to take care of the problem. My brain says water pump but it's a fairly new pump (less than a year) but I just don't know. When I'm cruising down the road water temp has never been a problem, ever. The wind seems to do the trick for cooling but not this time. Before I go to another garage and say replace the water pump and later find out it didn't fix the problem, I thought I should ask for some input first. I could probably replace the pump myself with a little proding.

Thanks for the input.
A wee bit more Please?

semiD

[ChuckG]

Something is wrong with the fan engaging, your description indicates. I'd idle the car in the driveway and watch what happens as it heats up. Could be as simple as a short in the fan or its connections means it operates only occasionally. From my read, it appears you have good airflow and a good radiator, and probably same for the water pump.

The temp switch reads water temp & relays that to the ECM to turn the fan off/on. They're cheap and do fail. Your ECM could also be failing in this task. Have you pulled any codes?

Another thought is the fan relay. Easy fix too. I replaced my relay and temp sensor, just out of concern over age. Noticed improved fan operation right away. I've replaced my ECM for similar concerns. That and many electrical parts, especially relays, were sub-par in the 80s. All cheap peace of mind.

I'm sure others have more detailed explanations on why one shouldn't remove the thermostat, but I've always heard it's a bad idea.

Were it me, I'd also replace the thermostat. Running the cooling system wide open prevents the car from reaching its normal operating temp and may confuse the ECM. It can also keep the engine too cold too long for the oil to properly circulate for extended periods and will greatly increase wear. Imagine start-up wear that lasts a half hour.

[aquaholic]

you mentioned that the water was red hot with the rad (i assume) hissing. did you ever check the coolant mixture to see what the freeze/boil points were? the hissing would lead me to believe that the water in the system was turning to steam. as just a simple and $5 check, i would go to the parts store and get one of those coolant testers with the needle on it and check your freeze/boil points. maybe your overheating condition is being caused by an improper mixture of water to antifreeze. an improper mix will cause any car to run hot at idle. just my 2 cents.

Originally Posted by ChuckG

Something is wrong with the fan engaging, your description indicates. I'd idle the car in the driveway and watch what happens as it heats up. Could be as simple as a short in the fan or its connections means it operates only occasionally. From my read, it appears you have good airflow and a good radiator, and probably same for the water pump.

The temp switch reads water temp & relays that to the ECM to turn the fan off/on. They're cheap and do fail. Your ECM could also be failing in this task. Have you pulled any codes?

Another thought is the fan relay. Easy fix too. I replaced my relay and temp sensor, just out of concern over age. Noticed improved fan operation right away. I've replaced my ECM for similar concerns. That and many electrical parts, especially relays, were sub-par in the 80s. All cheap peace of mind.

I'm sure others have more detailed explanations on why one shouldn't remove the thermostat, but I've always heard it's a bad idea.

Were it me, I'd also replace the thermostat. Running the cooling system wide open prevents the car from reaching its normal operating temp and may confuse the ECM. It can also keep the engine too cold too long for the oil to properly circulate for extended periods and will greatly increase wear. Imagine start-up wear that lasts a half hour.

********************************
Thank you ChuckG,
You got me thinking with your first message. So I started the vette and turned on both fans with the direct switch. I let it ldle for 20 minutes. It was perfect. Water temp showed about 1/4 on the gauge. It never overheated. Now I know the water pump is working fine? and both fans are working fine. I'm thinking now, that at the time of the overheating, I did not turn on the fans with the direct switch and if the relay didn't turn the fans on when it reaches a certain temp, the heat just kept on going until it pegged out on the gauge. Now I'm thinking it's one or both of the relays that plug in next to the radiator???? I quess I could idle the vette without turning on the fans with the direct switch to see if it heats up after awhile and if it starts to go past 3/4s on the gauge without the fans starting up. I can turn it off real quick and hose it down. Then I think for sure it could be One or both of those relays and that is a cheap fix. (THANK YOU LORD) Funny thing is I replaced both less than a year ago when I had the valve job done. I'm chewing on the other thoughts that you gave me. How do I get the fans to turn on sooner (automatically), say 1/2 way on the gauge?? What is the coolest thermostat I can get? (160*?) Getting my vette to heat up has never been a problem, Keeping it cool is my quest and for the last 6 months I thought I had it worked out. I feel 3/8's on the water temp is the best and when it starts to hang out on the halfway mark I start to worry. The Chevy dealer said it was perfect and just fine when it was on the 5/8's mark but they did nothing in figuring out the real problem and left me hanging in the wind.

Thank you so much for your input,

semiD

Originally Posted by aquaholic

you mentioned that the water was red hot with the rad (i assume) hissing. did you ever check the coolant mixture to see what the freeze/boil points were? the hissing would lead me to believe that the water in the system was turning to steam. as just a simple and $5 check, i would go to the parts store and get one of those coolant testers with the needle on it and check your freeze/boil points. maybe your overheating condition is being caused by an improper mixture of water to antifreeze. an improper mix will cause any car to run hot at idle. just my 2 cents.

Thank you aquaholic!!
Yes it was red hot and the sounds it was making was all internal. You could hear the crackling and hissing inside the engine. Nothing external. All internal.
You know it could low on antifreeze. It uses a tad bit of water here and there and I always top it off with water, not antifreeze. I will for sure check this out. I repied to ChuckG'S input and where I at.

Thank you so much for your input, I truly appreciate it,

semiD

[aquaholic]

good luck brother. hope you get it fixed cause summertime is here. be careful not to get that temp running to low. 195 seems to be about normal. if you get that car down in the 160's it may start to run rich which will cause you a whole new set of problems.

[c4c5specialist]

HI there,
It would also be suggested to check for debris at the front of the radiator/condensor.
Also, if you turn on your AC, does your fan turn on?
Allthebest, c4c5

Originally Posted by c4c5specialist

HI there,
It would also be suggested to check for debris at the front of the radiator/condensor.
Also, if you turn on your AC, does your fan turn on?
Allthebest, c4c5

Ahhhhh!! That's right, I forgot, when the A/C is turned on,the fans come on. Will that tell me if the relays are working? I've been thinking maybe I turned the fans on with the direct switch(which I think I know you are against??) and then off. Maybe the power surge did something to the relays?? If everything turns out fine, I will truly be at a lost as to what happened. It's nice to hear from you again!! Thanks for your input c4c5 specialist.

Have a great day,

semiD