Hi, i have a 1990 corvette with the l98 engine. I have a ongoing problem with the engine. It has been modified. Its a 383 stroker, that has been cammed with forged pistons and gapless rings(or so i was told when i bought it). i have assumed this was true just based on the performance of the motor etc. I have had the car since the end of the summer last year. It has not always overheated like it does now, this is why im posting about it here. I have replaced the water pump with a high flow eldebrok water pump, put a new thermostat in with a 160 degree opening point. The fans turn on at what appears to be a normal temp(about halfway on the coolant temp gauge) I even have a third fan on the front of the radiator. Today for example i drove the car early in the morning at about 8 am, and it was about 60-70 degrees out and it was still running hot. just drove it at about 3 and about 90 degrees out and had to rush it home after a short drive home because coolant temp was 260+ and oil temp was getting to abnormally high temps(not confident on an exact temp there). It has an aftermarket aluminum radiator as well. what could cause me to be running so hot? im full on coolant, full on oil. could i need a new radiator? if so how can i check that. i do have some problems where i run lean while accelerating, which i have read could cause overheating( i know this because the car had a air fuel ratio gauge put in and clear symptoms of running lean) I am a jr mechanic, so just asking for some help or advice on this. It could just run hot because it is a modified motor but it has not always run so hot so im just a bit confused on what might have changed or gone bad.
any help would be awesome

 

So are the fans running when its overheating? Does it run hot going down the road like 35+ mph?

 

Yes all three fans turn on and it still overheats, the ac fan, stock cooling fan and the aftermarket fan. And yes even when going decent speeds it will maybe cool a little but not nearly as much as i think it should. like maybe ten degrees. When the car is heating up the fans will come on and the car will just continue to heat up.

 

I'm guessing you checked the area between the radiator and A/C condenser? over time it will get packed full of leaves, paper, Polar Pop lids and whatever else you can imagine. if you haven't checked this, I would start there.

 

This may be a really dumb question on my part... but is it the correct water pump?

 

Yes, i have checked it for the debris, i have not gotten in to see if the radiator is blocked like the picture but i will look at that next. And as far as i know it is the right water pump because after i replaced it it did cool quite a bit better, and it fit on like a glove and i think i remember the one for the LT1 being a different shape than the one on the L98. The water ump was replaced shortly after i got it and this current overheating is a recent issue.

 

could always pressure test the system to look for leaks and maybe see if its properly bled and not getting air pockets. also could try going back to a OEM thermostat just to see if that could have an effect, is the fans shrouded properly? hopefully you don't have any passages blocked in the lines or engine or radiator.

 

One thing you can do is pull off a heater hose and start it up, it should pour out like a garden hose. The 90 up models have the pressurized expansion tank, so seeing flow can be hard.

 

Check that t-stat is opening at correct temp. Coolant temperature should pause when it hits 160F, fluctuate, and then rise.

Check that fans come on at correct temp. Main fans should be on at about 228F, the auxiliary pusher fan in front about 10F higher.

Check between radiator and condensor, usually this gets really plugged up over time. You actually need to remove the radiator to clean it properly as the pic above shows.

Check whether WP is weeping or not.

Make sure radiator cap is good. Look for any radiator leak under pressure.

If all that checks out, I'd do a full system flush and look for oil in the coolant, and coolant in the oil. A 383 makes more heat but it shouldn't overheat like that. A DeWitt radiator would be an upgrade but this issue needs to be investigated thoroughly first.

 

The radiator cap works just fine no leaks there. I don’t have much of a coolant leak, my next step I think is gonna be removing my radiator to look at it. My fans are on a aftermarket fan controller and they are currently set to come on quite early, and all three come on at once.(have them set this way to delay overheating in the case it needs to be driven. I can also make sure the thermostat opens at the right one as well.

 

Make sure the fan in front is pushing, not pulling. It also could be hindering air flow, try removing it and check your temps again. Retarded timing can make it run hot.

 

Blown head gasket ? Leave the radiator cap off and watch for bubbles. Look for water in the oil. Knock the center out of a thermostat so you have an orifice to slow down water flow . Make sure the thermostat you installed has a big enough hole. Are you sure your new water pump is moving water or coolant well ? Aren’t there Clockwise and CounterClockwise pumps ? Really odd it isn’t throwing a bunch of codes if its running that hot. Plugged up cats ? Running on all cylinders ?

 

The C4's were designed to run "hot" for cleaner emissions. We regularly see "new owners" who are shocked by the high temperatures at which the radiator fans turn on at. 228* (F) seems awfully Hot to some of us old folks.

The reason the Radiator cap was mentioned is because over time they have a bad habit of loosing pressure. At 16 pounds pressure the engine will go up to 261* (F) before boiling over. The lower pressures of a old radiator cap can cause overheating all by them selves. If it is over five years old replace it. It is cheap and it makes a huge difference.

How is the overflow jar? Does it have fluid go into it when heating up and does it pull the coolant back into the engine as it cools off? The Little Overflow Jar is a critical part of the cooling system. If it is not connected or has a broken hose going to it the overflow doesn't work. If it doesn't work then the Radiator will spit out coolant when it gets warm and then it will suck AIR back into the radiator in place of coolant. This is the beginning of trouble.

How much anti-freeze is their in your Coolant? 50/50 is common in colder areas, I use 70/30 where I use 70% distilled water and 30% anti-freeze in my engine's coolant. This gives me a bit of room to play and the extra water handles the heat better than anti-freeze. Be sure that you are not running "too much" anti-freeze as that leads to over heating as well.

Take a Infrared thermometer and verify the temperatures you are seeing. I have seen a LOT of lying gauges in my time.
Use the thermometer and verify that all eight cylinders are working and their temperatures are consistent with each other.

Under the nose of the Corvette should be a Black Rubber Air Dam. It is really important to have this Dam as it forces air up into the radiator at lower speeds.

How is the Catalytic Converter on your Corvette? Check it with the thermometer to be sure it is not clogged up or partially plugged up. You can remove the O2 and see how much comes out the hole where the O2 goes. It should be just a little bit like ~5 psi or so, if it starts flowing big time then you likely have a plugged or partially plugged catalytic or exhaust.

A plugged catalytic will make the engine run hot from the very start-up and limit performance as well. On a Corvette it is a bit harder but the temperatures should show it if it is bad.

You might want to replace the Oxygen Sensor as well if it is over 24 months/50k miles old. They start to lag when they get old and their signal strength weakens and this makes the computer use old weak data.

Add a bottle or two of the RED LINE "Water Wetter" into your coolant, it helps reduce temperatures as well!

Good Luck and Stay COOL!

 

On the ignition switch, ( i know, it’s under the dash) there is a connector with 3 wires on it. It’s the fan power.
for some reason, mine had been messed with by the previous owner, and it was just sitting on the ignition switch.
the fans were coming on *****-nilly, sometimes not at all.
check that connector and make sure it’s on good and tight and the wires are secure in that connector.
it’s right next to the large connector.
you may have to pull the seat to get all the way in there.
i had to.