Hello all,
I am having an over heating problem with my race car. My coolant temps are hitting between 235* and 240* after about 15 minutes on track.

The weird thing is the oil temp never gets above 190-200*. I thought the oil temp was always supposed to be higher than the coolant temps.

I think I might have some air in the coolant system but with no bleed valves Im not sure how to get the air out.

My motor is a 350 stroked to 388 but there is nothing from the L98 left on it.

Is this more likely an air issue or a water pump going bad or something else? The car has no thermostat. And I ran it just like this last year and even when the temps were really high the coolant never got above 190.

Any suggestions?

 

Bump

 

I thought running with no T/stat alone could cause overheating. Theory being the coolant circulates through the radiator to quickly to cool sufficiently.

 

I have heard that also, but I was on track like that last summer and the temps were around 95* ambient and the car didnt overheat.

Im just trying to figure out if it is even possible for the coolant temps to be 40+ degrees hotter than the oil.....

 

Are you using a coolant mix or straight water? Water by itself will cool better but with straight water, it helps to have something in the coolant (like Water-Wetter) to provide some lubricant for the w/p.

If you did a recent flush, did you get all the air out of the system? It's possible that an air pocket is hindering the flow of coolant through the system.

Is the radiator clear of debris an/d or dirt? If airflow over the tubes is blocked, the ability of that part of the radiator to properly exchange heat will be diminished. Also, how old is the radiator? Stock radiators that are old will have tubes that are worn due to the flow of coolant. Thinner tubes will not provide as much heat transfer as newer tubes.

Did you add anything to the nose of the car that may have interfered with the flow of air into the radiator? Are the fans working?

Are you using the stock sending unit and gauge?? It's possible that the gauge is not reading correctly. Get a cheap mechanical temp gauge and see what it says.

 

I am using distilled water and water wetter. The radiator is clear of debris. My gauge is mechanical for both the oil and water temps.

Do you think the fan has a big impact on the race track? This car is a track only car.

Here is a pic

 

At speed, a fan should not make a lot of difference, especially if you are running in clear air.

The water pump could be on it's way out. Sometimes the impellers will rust or corrode especially with not rust inhibitors typically found in anti-freeze. Is it a stock L98 water pump?

If it's a custom electric unit, check for loose wiring, bad relay, etc.

If you think there may be an air pocket, try raising the front of the car high enough so that the top of the radiator filler neck is the high point in the system. Run the engine at about 1200 RPM at operating temp (180-190-ish) with the cap off. When any air pockets escape, you may see the coolant level drop.

If you have a closed system with an overflow bottle, watch for any bubbling that would indicate air going into the bottle.

 

Thanks for the responses. It is a stock L98 water pump.

Im going to drain out the coolant, put a fresh mix of distilled water and water wetter in and use one of those coolant funnels that puts a half gallon on top of the radiator cap.

If that doesnt work, I will look at other causes. The one I am most worried about is the tune on the car.

I had the car re-tuned back in March and it seems like it has run hot every since then. Im assuming the only thing in the tune that could make it run hot would be timing. And from what I have read its retarded timing that causes over heating, right?

I am thinking if my timing were retarded enough to cause overheating it would really be hurting power output and its not.....

 

So, which is it?

 

You got me there.

The water pump and the power steering reservoir are the only things I can think of that are left from the old L98.

 

Very nice!

 

We had the same problem with our race car a few years ago. When the car is cool take the cap off the radiator (or tank) and start the car. Watch the flow, it should be easy without a T-stat. Increase the rpm to about 3000 while watching it. If the level looks like it goes down and stops flowing, then when you back off, if it gushes out and starts flowing again, you're probably cavitating the pump. It just drills a hole in the water and it goes round and round in the pump but not through the engine. We had to change the blades to a turbine style instead of the paddle wheel and slow it down with a smaller crank pulley and a bigger pump pulley. One of the biggest results came from a free chunk of urethane about a yard wide and 4" deep. We stuck it under the car just behind the radiator like a little air dam. At speed, it creates a low pressure area behind the radiator and under the car and the hot air is pulled down and out instead of packing up under the hood. Engine driven fans with those flex blades just flatten out and turn into a big air plug at high rpm and block airflow especially inside a shroud! They may be OK for drags but not for roundy round or road race. I like electrics that will freewheel at speed and can be switched on for slow pace laps and in the pit area. But racing a C4, you probably already have that. Just a few ideas we did that worked for us.

 

Retarded timing will definitely cause an overheat. We
got the motor rebuilt on my late wife's '68 Firebird 400
vert, and on first fire up it overheated in short order
and started puking coolant. I was going to let it warm
up and then set the timing. It was retarded.

So go check the timing. That's easy.

 

Thanks again for the ideas. I will definitely check the timing.

I am running an electric fan. I will check the coolant levels at different RPMs to see if the pump is in fact cavitating.

 

Wow that is one sweet looking C4!

 

Thanks for the compliments. My favorite part about this race C4 is when I go out on track and blow by Porsche cup cars and many other extremely expensive race cars

 

That is an awesome feeling. Right on!!