DanielRicany

Hey guys. I have a 1985 Corvette with a Miniram, flat tappet ZZ409, 58mm throttle body, AFR 195 Eliminator Heads, 1 5/8" Hedman Longtube headers, 1.6:1 Roller Rockers, 3.75:1 rear gear, D.U.I. Distributor, MSD 6AL2 ignition box, miscellaneous and supporting mods.

I was having an overheating problem before around town where it would overheat when I had a load on it no matter how small. I had to pull over and the temp would come down. I fixed that by bleeding the hell out of the cooling system.

Now what happens is it seems like when I get on the highway in 4th gear and I do a WOT throttle run, the car begins to overheat until I either push the clutch or pull over.

New 180* thermostat, fan on temp is 210*, new American Eagle aluminum radiator, thermostat has two small holes drilled in it to bleed air, no leaks anywhere. No head gasket leaks, timing is advancing properly. Can't come up with any more ideas. All air dams are in place.

Thanks.

EDIT: Figured out it overheats only at a high RPM, not dependent on speed or load.

fredd1

Time for a new water pump maybe?

DanielRicany

Update: I took some kind of cover off the lower radiator hose because mine does not have a spring in it. I let the car get to 205*, and had someone rev it and hold it at 5k RPMs. The car shouldn't be going over 210*. The lower hose did not collapse and the temp climbed up to 220 before I had him let off. The fans came on at 210 and when he let off the temp came down.

C409

... ^^^ this ...... Pull your water pump off ... take the rear cover off ... and confirm that you have the correct rotation impeller on it .............

DanielRicany

Another Update: I took it out again and the same thing happened, so it's consistent. 4500 RPMs or more and it starts climbing up. Went to 238 this time. No overheating at idle, no overheating at normal driving, no overheating at WOT on low RPMs.

Thanks!

STL94LT1

From this thread and your previous threads I'm wondering if your ignition and/or cam timing is off?

BOOT77

Sounds like it's leaning out.

DanielRicany

The AFR gauge is reporting 14.7:1 when being held at those RPMs.

BOOT77

At WOT?

edit: what I mean is it overheating at WOT as it you run thru the gears or just if you hold it there part throttle?

DanielRicany

Either or. I can hold it and cruise at 4500 RPMs and it'll over heat. I can romp on it at 4500 RPMs and it will overheat. I can accelerate to and passed 4500 RPMs and it'll overheat.

BOOT77

Sorry I meant is the AFR 14.7 at WOT there or just when you hold it there part throttle.

DanielRicany

Oh, it's 14.7:1 under cruise and light throttle at that RPM and at WOT it's 12.7:1.

Cliff Harris

I read about this in another thread last week (same symptoms)...

Corvettes have a "reverse rotation" water pump because of the serpentine belt. If you have a "normal" water pump you will overheat.

DanielRicany

I tried going back to the previous spark plugs that I had in and it still overheats so it's not the plugs doing it.

I'm going to try bleeding it some more at 5000 RPMs, see if that helps it. If it doesn't, then off comes the water pump.

DanielRicany

Okay I bled it at 4000 and 5000 RPMs, and I also tried retarding the timing some. It still overheats.

Although, when I retarded the timing by 4 degrees, it took longer for the temperatures to get high.

Any ideas? Really would like to avoid buying a new water pump and having that not be the problem. Thanks!

STL94LT1

Are you 100% sure when you did the camshaft change that the timing gears were reinstalled correctly?

DanielRicany

They should have been. Wouldn't I have obvious symptoms of them being off? I heard that I would have no power, backfiring all the time, running rough, etc.

DinoBob

I vote water pump.

c4cruiser

As others have mentioned, remove the water pump to make sure that the impeller is moving water in the right direction. Also you can check to see if any of the blades are broken or if the shaft is holding the impeller so it doesn't slip.

Another thing to check is whether or not the belt tensioner is keeping the serp belt tight. If the tensioner is weak, the belt could be slipping on the W/P pulley. That will cause the W/P to turn too slow or possible not at all at high RPM. The tensioner has marks on it to show how much tension is being applied.

The problem is not with the timing or the tune. You have a water flow issue.

DanielRicany

I took a video of the water pump and the tensioner. The tensioner moves when I rev it. I don't know if that's normal or not? I replaced it about 8 months ago.

https://www.dropbox.com/s/k992jri415...164541_141.mp4