Deadpool86

I bought a 1981 corvette as a project car a little while back. It was running great for a few weeks when everything pretty much gave out all at once. The most recent problem now is that within 5 minutes of running (idling or driving) it seriously overheats. At the exact time this started, my power dwindled drastically. My max speed is about 55 and that is pushing it and extremely slow to get there at all.
Prior to that problem showing up I had these parts replaced: water pump, thermostat, fuel pump, altenator, and starter. The mechanics that looked at it did a compression test and claim that the radiator is fine. They are out of ideas as to what it could be. Does anyone have any suggestions? Mind you, that I brought up the parts I changed only for the fact that it could have helped cause a problem more than me saying that it isn't one of those things still. Oh and someone suggested the catalytic converter could be clogged, but found out it doesn't even have one. It's just a straight pipe

garygnu

they might not have bleed all of the air out of the coolant system..

CaseyJones

I assume you have checked the coolant level in the radiator (not the overflow tank) since this started happening. I would put money on a bad or stuck thermostat is the coolant is OK.

qwank

what kind of fuel pump did they install? low fuel pressure and a very lean condition could cause that. whats your timing set at? is the original computer, carb and distributor installed?

doorgunner

It is VERY difficult to get all the air out of some engine cooling systems....make sure that the heater control valve is on and allowing coolant to flow thru the heater core while you warm up the engine with the radiator cap off--BE VERY CAREFUL--coolant will spew out if the engine has air trapped in the system!

Once the temp gauge reaches 190*--the visible water in the radiator (I'm guessing the radiator cap is on the radiator on your year-model)should start circulating and belching out air bubbles.....add coolant as needed to fill the system (provided the thermostat isn't jammed closed)....it could take 60 minutes of running the engine/turning it off if it overheats to let it cool down to operating temp/running the engine again/etc. before all the air is removed.

And, like the other members said--other things could be adding-to/causing the overheating.....lean fuel mixture/incorrect timing/"jumped-timing/wrong style (standard direction) waterpump/etc.

Deadpool86

Wow. For a guy that's just learning about vehicles, that's a lot to check in on. lol. I'll check the cooling system for air and check in on the other things you have all mentioned and get back with you. I don't believe it is a lean mixture though. Some have mentioned they thought it might be running a slight bit richer. I'm pretty sure the water pump was replaced after the problem started so I don't believe it was that, but I'll check just in case I ended up trading one problem area for another in the process of trying to have it fixed. The mechanics did most of it themselves, but in the end it seems they didn't know much more than I did when they worked on it.

stumpshot

Pull the thermostat and see if the problem is fixed. Maybe your "Mechanics" put it in upside down or it's bad. If the "Mechanics" can't figure out an overheat problem, they don't need to call themselves "Mechanics".

Easy Mike

You don't need to check for air in the system. You need to check coolant level per your owner's manual. I agree with CaseyJones; this sure looks like a thermostat.

Kacyc3

Wouldnt a bad thermostat take longer than 5 min to over heat while full of coolant?(Ive never timed it) I know for a fact that my 406 over heats in 5 min when there is air in the system.

qwank

could be a cracked head too

1wicked55

Is it possible your mechanic put a reverse rotation water pump on your car.

This would make your engine overheat within a few min.

my 76 ray

Timing that is retarded will cause overheating and lack of power. Did your idle speed slow down when this started happening?

CaseyJones

Start with the simple stuff and work from there. It's cheaper, too. Thermostat. Radiator hoses. Timing. Vacuum leaks. Distributor advance not working. Carb adjustment. Compression check. Manifold heat control valve (passenger exhaust manifold of you still have them. The vacuum controlled valve between the manifold and pipe).

Then you can start throwing money at it. Just do the due diligence stuff first.

Are you losing coolant? With the car running at operating temp do you notice a stream of small bubbles in the overflow tank? Can you offer any other symptoms?

Easy Mike

maverickmk

That was my first thought as well.