69patron

Greetings, I'll try not to sound too dumbfounded as I am a newbie!

I recently purchased a 69 base model 350/300 vette just about completely restored. I am having problems with it overheating when going under about 30mph or ideling, temps running 230-245+. At highway speeds temps is fine, typically temps 180-200. I have receipts (and know the guy well) from whom I boiught it from and it has a brand new radiator, temp sender, thermostat (180), water pump, and fan shroud. A thermometer verifys the temp, so it's not the display guage.
Intristingly, when it gets real hot, if I rev the engine for 30 sec or so the temp drops. Someone suggested if that happens the impellers in the water pump could be bad, but the water pump was replaced?
Any ideas??????Help please-
Andy

vettepilot68

You didnt mention a new fan clutch...I suspect this may be the cause.

big_G

I would check the fan clutch. If it is original, it may be weak. That would account for good cooling when moving.

BlueL36

You didn't mention the foam seals around the radiator. Those are needed to help the fan draw the air through the radiator and not around it.

69patron

I did forget to mention the fan clutch, That was suspected, thought to be bad and replaced.
Not too sure about the foam seal around the radiator, is that basically just a seal adjoining/between the shroud and the radiator?
I really appreciate the suggestions!

BlueL36

http://forums.corvetteforum.com/show...s&forum_id=119

lars

Andy -
The most common reason I see for low-rpm/low speed overheating is incorrect timing and timing advance. Before you start working on the cooling system, make sure you are set up right:

Set your timing for 36 degrees total (which will get you somewhere around 12 to 20 degrees initial) and make darned sure your vacuum advance control unit is functional: many are ruptured and defective. Replace it if it is not working. Hook the vacuum advance up to a direct manifold vacuum source (not ported) to pull the full advance in at idle. With this hooked up, you should see about 28-34 degrees of timing at idle and low rpm.

Inadequate timing increases engine temp drastically.

Easy Mike

Those seals are in there for a purpose. They force available air through the radiator where the cooling is provided. They tend to shrink with age and are often not replaced if the radiator has been removed. Without them, air leaks around the rad, instead of passing through it. As we all know, a Corvette needs all the available air passing through the radiator. Check the seals.

69patron

Thanks everyone,,,I'll check on those recommendations!

clem zahrobsky

there were some early model 350 corvettes that GM changed the diameter of the water pump pulley to get it to turn faster at low RPMs because these engine were running hot at low engine RPMs. someone here may have the old TSB about this.