htown81vette

My 1981 Corvette was losing coolant, so I figured it was the radiator and replaced the radiator with a 3 core aluminum radiator. Even when the stock radiator was half full of coolant the car generally would not over heat. Now just following the alum radiator install, the car will heat up to the thermostat temp rating (thermostat then opens) and stay at 190 deg, while idling. The problem is when I start driving it, the temp always zooms up to about 230 deg and even beyond sometimes. I brought the car back to the driveway and let it idle, and looked under the car for leaks. No leaks. The radiator is full, but actually it seems to be still losing water somewhere. Still, I am scratching my head wondering why it overheats so quickly, I ran it around all over the place with the stock radiator half full and it usually didn't overheat. Bear in mind I'm in Houston and the outside temp is 90 deg + but I would still think that an 3 core alum radiator with dual electric fans on all the time, the temp should stay rock solid on 190 deg. Anyone have any ideas on what is causing this?

Shark Racer

With my alum rad if I give just a bit of throttle to get the water pump spinning faster the temperature will drop quite a bit, just standing still.

I'd imagine you have an air bubble, when you filled the system was the front end raised? Did you have the heater running on full hot?

tracdogg2

Sounds like you have a cracked head.
Mike

Shark Racer

Pressure testing the radiator should diagnose this one, right?

htown81vette

That is my biggest fear is too. Actually, I'm not too fearful about it cause its a good excuse to buy some nice dart 180 cc alum heads. When life hands you a lemon, you buy new heads!

htown81vette

yes the front end was raised when I filled the radiator, I thought about the air bubble too. But I've added coolant a couple of times now, and keeps doing it. I guess I'll keep doing it, but starting wonder if its something more serious..I hear those 81 stock heads are notorious for cracking...

Shark Racer

Pretty much any of the iron heads on the C3s are, but especially the smogger ones. If it's ever been overheated, it's a high probability.

tracdogg2

Most likely you have 624 heads on the engine. These are prone to cracking just by staring at them. They always crack between the seats and only shows up when the engine is hot. Pressure testing the radiator won't show the problem unless you fill a cylinder and hydro the motor.
If you have plenty of anti-freeze in the engine your exhaust should have a sweet smell to it. You can also run the engine with the cap off. See if the radiator continues to blow bubbles in the coolant. But be very careful. If it burps you can get seriously burnt.
You can also pull the plugs and look for one that have been steam cleaned.
If you do pressurize the radiator do it with the engine running. Watch the pressure gauge. See if it keeps building pressure. If the crack is large enough you can force a misfire in the bad cylinder. Be sure to release the pressure before turning off the engine.
Mike

jordan89

Did you bleed the system?

OMF

Any chance the lower rad hose is being sucked closed when your driving it? How old is that hose??

htown81vette

Well there is coolant dribbling out of both sidepipes so I guess that answers that question. What I don't understand is that the motor has gotten way hotter than that, so those heads must have been cracked for some time now, which explains the reason why the radiator was always low on coolant, but the temps always stayed under control until I replaced the stock with the alum radiator. I guess the outside heat is just too much, seems like last summer during august I had the same problem. When the temps cooled down some it was not a problem. Guess its time for some new heads, might as well buy a cam too!

Indiancreek

Getting any exhaust smell in the coolant? Put it in gear and torque it up after its warmed up with the brake on. Have someone look for coolant from the exhaust. Pull your plugs and look for any signs of rusting.
Just a few things to help make up your mind.
Could be the heads might need resurfaced.

Shark Racer

How do you know it's coolant come out and not regular evaporation?

But I agree. Forget about diagnosing it, just install a 427 small block with some 15 degree heads and a big cam.

htown81vette

bingo

Jeff_Keryk

When engine heat quickly climbs, I replace the thermostat.

htown81vette

I just replaced that last year. But maybe I need to replace it again already? My thought would have been thermostat too, but it shouldn't need it.

htown81vette

Well i took the thermostat out to make sure it was installed correctly which it was, then I did the boiling water test, it opened, so i can eliminate that one..

Shark Racer

Looks like you have your answer.

http://www.dragzine.com/features/pri...eads-from-afr/

Cheap, too. For the cost of no more than 3 driver quality late C3s you could have an engine running these.

I really would like to see a review on these, especially in a 'vette.

htown81vette

WOW! Those are abit overkill for my little 200hp 350 I would think! I would need an engine that has the nuts to handle those heads. I'd be happy with just a set of 180 cc Dart heads, but I plan to upgrade to shortblock to a 406 someday, my question is this head (the Dart 180 cc) enough head for the 406, or should I go for the 200 cc Dart head with the thought in mind that I'll have a 500 hp 406" someday.

I would think a head that flows 400 cfm, I'd lose all kinds of torque midrange wise with my little turd of an engine. But there I go again thinking...

htown81vette

I don't know