I just had my 88 L98 rebuilt to factory specs, 30 over. I've owned the car for 12 years and have done all my own wrenching until I felt it was time for a rebuild (212k). I still consider myself a novice so I have an open mind. Anyway, the work was done by a well respected shop on this forum so I want to trust them, but I know my car. I picked the car up yesterday afternoon and drove it to work. Almost immediately I noticed the temperature gauge was much higher than usual. For the conditions the temp shouldn't have been much over 200 but it went to 230+. The fans were both on. I called the shop and they said it was ok, and the shop owner would explain when he came back into the shop. I drove it home and in traffic it topped 240. My oil temperature sensor also showed high, 245+. My first thought was that there was air in the system, so I tried "burping" the radiator. I started the car with the radiator cap off and let it warm up. I expected to see coolant movement when it reached operating temp, but instead the level increased and started bubbling out of the radiator. Now too dangerous to put the cap back on, I shut off the car and about a gallon of coolant spewed like a fountain. So I refilled it and drove it back to the shop this morning. With 65 degree weather and no traffic it crept up to 230 degrees on the gauge. I talked to the shop and they said they noticed the gauge was high after they put the engine back in and thought it had always been like that. So they checked the temperature on the scan tool to read what the ECM was seeing and they said the ECM reads 15-20 degrees lower than the gauge. They told me my gauge is off. I of course don't want my dash telling me my car is always overheating so I'm having them replace the temperature sensor. I'm looking through my shop manual now and it looks like there are 3 coolant temperature sensors. 1 "Coolant Temp Switch" in the front of the intake manifold (page 6D5-1), 1 "Coolant temp SW" in the driver's side head near the alternator (6D5-3), and 1 "Cooling Fan Temp Switch" in the passenger head between 6 & 8 (6D5-4). There's also the "Oil Temp SW" on the drivers side rear below 5 & 7 (6D5-2).

So is the shop right? I'm thinking if the gauge shows hot for both coolant and oil, and the fans are both running, then 3 out of 4 sensors are saying the same thing and the ECM is seeing the wrong temp.

Your thoughts?

Ron

 

CTS ; Coolant temp SENSOR.
Sends temp info to the ECM as shown on the scanner ( typically taken as the "true" or more reliable engine temp )

Fan switch for the Aux fan in front of the radiator

Temp sender for the temp gauge

Above the oil filter
1 out 0f 4 ain't bad

EDIT
For what year ?
Early cars < '86 had the gauge sender and fan switch positions swapped in the heads as you describe from the manual

 

I would expect the car to run a little hotter as the engine breaks in. Everything is tight to start with.

Just keep and eye on things. How old is the radiator?

 

The engine and shop manual are 88.

The radiator is about 10 years old so I had them send it out to be tested. It tested good and re-used it (also removed all the leaves and crap between the radiator and condenser).

Thanks,

 

Did you try to bleed the air out? Is it losing coolant?

 

The anti freeze should not be like a fountain unless the overflow is full. It is supposed to be empty. That will cause high temps.When I bought mine it was doing that and I had to take 3 pitchers out of overflow and temps are perfect with 150000.
Good luck

 

If your engines getting hot enough to form a steam pocket, and yours certainly is, it would explain the antifreeze fountain. Try this, start the car, allow it to come up to operating temp, shut it off, walk away, and come back when it's cool. Now add coolant/water at the expansion tank (not overflow tank) I had to do this four or five times before all the air was completely expelled.

a new tight engines certainly do run hotter; and the oil should be changed after a twenty minute or so initial break in and then again after a hundred or so "easy miles" and in your case, where high temperatures and possible over heating has occurred, sooner rather than later.

finally, thermostats have been installed upside down before, or speaking from my own personal experience, after rebuilding a F word 460, the brand new Robert Shaw thermostat failed in the closed position. So you can never tell.

 

I know this is all basic stuff but it's usually the basics that trip us up!When they re-installed the distributor did they install it with no.1 cylinder at TDC and leave it at that? Most small block Chevy engines have 8 degrees BTDC as initial timing. Improper timing is a frequent cause of overheating on distributor equipped engines. Is the water pump new or did they re-use the old one? It might have been okay before the rebuild but things happen when parts come off an engine. Is the thermostat the correct one with correct temperature rating? The factory unit was 195 degrees but most owners and dealers changed them to 180 degree units. Check for manifold vacuum leaks. These can cause you to run lean and again, cause overheating. Did they hook up all the coolant hoses correctly? Fourth generation Corvettes are finicky about coolant flow. I know some of this seems kind of dumb but these are the same things that plagued a 1991 GTA that I owned which had basically the same engine as your car.

 

Try a cooler thermostat,but you will need the temps changed in the chip or a fan switch at the very least.

 

Check your hydraulic lifter adjustment. If they are adjusted a little soft the car will run pretty good but overheat. There are plenty of threads on here for the correct adjustment procedure.