I have an '86 with a L-78 and I just had the dash rebuilt so I know its working. around town the oil temp goes up to 235 and the water temp stays around 205. when driving on the interstate. the water temp runs around 200 and the oil temp goes up as high as 239.

after reading the post on this board I say this is normal. but what concerns me is when going gown the interstate the service engine soon light comes on and stays on.

if I stop the car and shut it off for a couple of minutes, the service engine soon light doesn't re- light when I re-start the car.

the engine has had the oil, antifreeze, spark plugs and air filter. changed.

the engins runs smooth but starts a little hard when hot, so i think the injectors are due for a service / replacement.

the engine runs smooth as silk.

what do I need to do if anything.

John

 

You should pull the codes to see were it leads you.. But if it only happens on the highway I would first look at the egr..

 

Read the codes and make appropaite repair/adjustments.

I don;t think there is a code for oil or water temps...besides, yours are exactly what they should be in another brutal summer...

 

It's been over 100 a few days here in Atlanta, with a RealFeel of the low 110's. Until I sprung a leak this week, my temperatures NEVER got over 220. They would slowly cylce from 195 to 205, just like they should. At the hottest part of the day, in my black '90, I would possibly creep up a bit while driving hard. My car ran hot when I got it, and I replaced the radiator with a new (still stock-style) radiator and heater core. tested the radiator cap and pressure in the system. Not a problem with heat until this week where I developed a leak around my T fitting (that goes from the water pump to the upper reservoir and down to the oil cooler, assuming you have that option).

When people say it's "normal" to run at 230, they may be correct about how it runs 20 years past new, but it certainly didn't run that way new. Especially if you're using a proper mixture of anti freeze and if you're using something like water wetter (I don't, typically, and right now I have straight water in the tank).

I'd suggest doing a pressure test (you can borrow the kit from AutoZone or the like) and checking your radiator for crap in it. The oil temperatures could be normal if you don't have an oil cooler. But don't listen to the "car still runs, must be okay" on the heat. The engine wasn't designed to run that way. Think about it: these cars are often race cars. You think a race car that runs at 60% above normal operating temperature at 70 mph sounds right? Doing 150 should be pushing your temperatures high, not normal driving.

 

You have the classic symptoms of a error code 32 -- EGR system inoperative.

Check for codes per this web site:

http://corvettephotographs.com/c4vettes/codes.htm

See what the codes are telling you here:

http://forums.corvetteforum.com/1576116036-post35.html

The ECM commands EGR by sending a ground to the EGR solenoid mounted on the thermostat housing. That solenoid applies ported vacuum from the throttle body to the EGR valve, which opens. The hot exhaust gas flowing through the EGR pipe (arcing over the passenger side valve cover from the exhaust manifold to the intake manifold) causes the EGR temperature switch to close. If this switch does NOT close the ECM will set error code 32. ALL of the EGR system has to work or you will get this error code.

The ECM only commands EGR during cruising conditions so that's why the SES light comes on while driving.

 

 

I will try to replace the ERG valve. I just got the service manual so it will be the first job I tackle after I changed spark plugs yesterday.

the radiator was flushed and pressure tested OK and I had a new water pump installed just after buying the car. the water temp seems to be doing what you describe cycling between 195 and 205 but the oil temp climbs to over 235. I do not have the water oil cooler.

I plan on calling the auto parts store for an ERG valve unless there is some other place that charges less then $75.

thanks for the advice , I'll keep you posted.

John

 

It's quite normal for oil temperature to run 20 degrees higher than water temp.

 

JGalfo,
It may not be the EGR valve.
There is a temp sender on the EGR tube that grounds the wire any time the temp gets hot on the tube.
It has been my experience that the vacuum line that opens the EGR valve breaks, or has a leak, and it can't pull the EGR valve open.
When that happens, the tube stays cold, the sensor stays cold, and the ECM thinks the valve didn't open.
Sometimes the EGR solenoid connector falls out of the EGR solenoid, shutting off the vacuum as well.
Don't condemn the EGR valve just yet without doing some research.
Also, the egr valve has a calibrated vacuum leak so that it will close after the vacuum is shut off in the closed mode. If the leak wasn't there, it would just stay on till the engine gets shut off.
So if you suck on the EGR vacuum line, it will exhibit a leak. And it's supposed to.

 

thanks for the advice.

I drove the car to work today and the air temps were in the 80's and 90's. the water temp never went over 200 and the oil temp never went over 215. the service engine soon light never lit up either.

I guess I will just watch it and read the service manual for a couple of days.

John

 

That's why I said earlier that the whole EGR system has to be working for it to pass the test. That's also why I described the whole system and how everything interconnects so you can look at the individual parts and see which one(s) are bad.

In my case the EGR solenoid failed and was not opening the EGR valve. The EGR valve was frozen and did not work after I replaced the EGR solenoid.

 

Its better to check codes than to just start replacing parts.