I have a 1985 corvette with a L98 and C5 conversion body kit. I recently rebuilt the motor and now it is overheating. The old motor overheated too but it quit after I made a new air dam that goes underneath the front bumper. My fan comes on, I dont have a air bubble in the coolant system, I have a 160 degree thermostat and the air dam is not bent or damaged. I have no idea why it is overheating. It does it in town and on the highway. Im frustrated and out of ideas. Can anyone help me with this problem? I can see coolant circulating and I dont have any garbage between the air conditioning condensor and the radiator. Please HELP!

 

Define overheating...These cars tend to run hot. The fans don't even kick until 225+

 

It runs at like 260+ on the highway. I want it to run at like 160 190 on the highway. It doesnt run hot in town or at a idle. At idle it runs 160.

 

Stop Running Your Car So HOT!!! 260+, are you kidding me? I'm supprised you haven't blown the thing up yet. Your air bubble might be what's causing it, or your thermostat is fused shut. If you can test the thermostat (by taking it out and boiling it to see if it opens) do so. If not, get that bubble out. Your thermometer inside the car takes the internal temp or the engine, not the radiator, so it may be that bubble getting into the thermometer which would give you a false and very high reading. If all that fails, get a bigger radiator capable of handleing more HP. But cross that bridge when you get to it.

 

You might scan it to verify the gage is accurate - compare the Coolant Temp Sensor to your Gage readout. They should be within 5 degrees of each other. If not, test the Gage by disconnecting the signal wire at the Sender. That should have it reading LO. Ground the wire and it should read MAX (usually 300). If that checks out, it needs a new Sender. If it doesn't, you will have to ohm out the wire between the Sender and the Display. You can also use another wire to jumper the Display to ground to test it's accuracy. If the Gage is faulty, you'll need a new Display.

 

Pull radiator and check for and clean out debree that is blocking air flow.

 

Also, Do you hear the fans turn on???

 

He said there is no air bubble so that would give him false hope. I do agree on the bigger radiator for more horsepower. Depends on the motor hes running.

That is a good idea! You can use a shop vac to suck up any debris. Get a auxilarry fan, replace thermostat in case it is stuck, flush the entire system, check the water pump for weeping ect.

Regardless, we need more information on the motor, how you know it's overheating, signs of smoke or boiling coolant ect.

 

In order for the fans to turn on at a lower temperature, you have to either have the PROM re-programmed or install a sender in the head that'll do the same thing.

I've seen the senders advertised for sale in some of the catalogs.

At highway speeds, the engine should not over-head due to the increases airflow over the radiator at speed.

I'm now thinking thermostat, radiator, radiator hoses, ignition timing or water pump.

Easiest to check the stat is to put it in a pot/pan of water on the range. Fire up the burner and use a meat thermometer to see the temp of the water while you watch the stat sitting in a pan/pot of water.

Any buildup on the interior of the radiator? You can remove the cap and see. With the engine at normal operating temp (stat open) and the cap removed you should be able to see the coolant flowing freely inside the radiator.

Are you using the correct water pump? Aren't the L98's' reverse rotation?

Any chance that one of the radiator hoses is being sucked shut?

How's the ignition timing? Retarded timing will cause the engine to run hot. Check the base timing and also check that the ECM takes over the timing chores once the engine fires. You can use your timing light to check that the timing advances as you wing the throttle.

Hope this helps.

Jake

West Point ROCKS!

 

One more thought; Use the packing method to be sure all the air is out.

Jake

West Point ROCKS!

 

Never heard of that, would you mind expanding?

 

I would start by running with no tstat for a litle bit and see what happens, then move to radiator. and so on.
good luck

 

The LT1 has two air bleed screws: ones at the stat housing and the other on the lower part of the TB. My Owner's manual says to open the bleed screws and pour in the 50/50 mix of coolant/water until it flows out of the bleed screw locations with no air exiting.

My manual also says that using other than a 50/50 mixture can cause inaccurate temp readings.

TPIS recommends this method. The packing method involves firing the engine and allowing it to reach a temp that the stat is open. You'd then carefully remove the coolant cap. Then reach over and open the throttle to bring the RPMs up to around 2000 or so.

When you do that, the coolant level will probably drop. While continuing to hold the R's at 2000 or so, add additional coolant mix until the little tank is full AND re-install the cap BEFORE letting the R's drop to idle.

I've use that method on a L98 several times and it works to get all the air out. I've never had to use it on my LT1, but I believe it'll work for LT1s too. Stat has to be open to allow full flow of the coolant through-out the engine.

Another thought: Any chance the stat was installed upside-down? That's happened before.

Jake

West Point ROCKS!

 

IMO if you're running at 160 at idle..I'd feel that the thermostat is ok...i'd lean more towards air flow being partially blocked (debri) through the radiator OR radiator partially plugged /blocked internally since problem occurs at highway speeds....I'm not sure how accessable your radiator is, but when it is running hotter...if you can get your hands to different areas of the radiator..try to touch different areas of the radiator and see if the temp. feels about the same..if you have hot and cold spots the radiator is likely plugged internally.

By the way the method of "packing" That Jake referred to works GREAT I've been using it for years on cars prone
to trap air in the system including ,but not just Vettes

PS If you have made a big horsepower increase you very well may need a larger radiator OR it may have made a previous problem more noticeable.

 

I would tend to believe the lower hose is collapsing.
1. Check to make sure the spring didn't rust away or fall out of the lower radiator hose.
2. change the gauge sender in the head at the rear of the right head.
If it's no good, your reading will be no good either.
3. find out if your fan seems to be running at normal full speed. If it's not you might need a new fan relay.
4. check your block to body ground wire.
5. make sure that when your aircond. comes on, the fan starts as well.

 

Ok I got it. I removed the all the bull crap plastic pieces in front of the radiator. then i bought one of those license plate grilles with the little holes all in it and cut the front of my bumper behind the grille out. ran a air duct from that hole to the radiator. Then relocated the air dam to a diff. location. The reason I relocated the air dam is because my car has that C5 conversion kit and the air dam was in a bad spot. All the hoses and the thermostat were replaced when I put the new motor in (500 miles ago) so i didn't replace all of that again just checked it. Now it runs 160-180 in town and on the highway. Thanks for all the suggestions. If anyone wants to see pics of what i did let me know and I will email them to you. The total cost of all the parts to make my new system work was about 100 bucks. It works great!

 

Congrats! Glad you sorted it out.

Jake

West Point ROCKS!

 

Now Enjoy The Ride