small block burp!

My son just had his 327 rebuilt. Runs great with a hotter cam,ign.high flow waterpump and a new alum radiator. The problem is the temp guage is all over the place. I'm told there is air in the cooling system. Is there a way to burp this baby?

 

http://www.denlorstools.com/home/dt1/page_6847/remove_trapped_air_from_cars_cooling_system.html

look at this maybe it will help
i know it isnt SBC related its just for information purposes only

 

Never had a problem with SBC doing this. Except for the heater core in my 50 truck. Are the radiator, engine, etc. in original locations? I had a rad shop put a petcock in my heater core-bleed it once in the winter, I'm done. You can raise the front of the car, but sometimes have to get WAY up there.

 

try taking the top hose off and filling it up with as much fluid as you can. cap it off with your hand or a plug and squeeze the hose alot..see if yuo can burp the air back out the bottom hose..(thru the radiator)..or jostle the car a bit than put it up on some jack stands in the front..
i have never had this problem with an SBC before but i do know its an issue with the LT-1 engine..they have a provision to remove the air out of the system thru a small valve on the water pump.

 

Thanks guys. Ya I have never had this problem on the 283's I've done but they were not souped up like the kid did. He drives it back and forth to work and keeps a good eye on the temp. I'll have him try the old hose squeese!

 

whose radiator did you use?

 

You may have to drain a little off. I typically loosen the heater hose if so equipped. Or when I fill it from the get go, I have the thermostat housing off and fill it JUST to the top but not over. If you have an aftermarket intake you can use the temp sender hole that is on top or if it is set up for crossflow from front to back cooling, just ease open a line.

Mike

 

Mityvac makes a tool for getting the trapped air out of cooling systems.

 

What kind of car is it in? The radiator cap has always worked for me. I've never heard of a trapped air problem except here on the HAMB. If it's in some kind of low slung sectioned ride with a built in plumbing trap, then I can understand having a problem getting the air out, but most everything should be self venting.

If you have trapped air that gives you an intermittent false temp. ga. reading then the air must be moving or it wouldn't be intermittent. If it moves it will find it's way to the top of the system. 98% of the time that is the radiator cap.

If the gauge is electric, I'd be looking for a wire with worn insulation causing a short or a loose terminal. A mechanical gauge will show fluctuations but but not rapidly.

Maybe some day I'll find that Chevrolet engine that traps air but until then my experience tells me to look for a different solution to the gauge problem. I couldn't possibly count the number of times that I've had to drain and refill the cooling system for many many reasons and never encountered trapped air that didn't vent once the thermostat opened. JMHO.

 

Tommy do LT-1's count as a chevy engine?
they have a provision for getting the trapped air out..built right into the pump..
now i would agree if you ment or qualified it as a non LT-1 Chevy engine..

 

Thanks everyone! I forward this to the boy.

 

i have had this happen to me. if you drill 3 1/8" holes in the thermastat. around the outside lip the air will come out.

 

I think that's the key right there...if air IS trapped in the engine, an intermittent or changing reading on the gauge would indicate that the air is moving around. (Sender is submerged...sender is surrounded by an air bubble...submerged...air bubble.) If the air is moving around, then it should eventually find its way to the top of the cooling system, which should be the cap.

I also agree with Tommy that the problem could very easily be the gauge, whether it's electric or mechanical. If it's electric, it could be a loose ground, shorted gauge, chafed wire, or the temp sender is bad. If it's mechanical, it could be a bad unit, or if it's old, the mechanism could be sticking.

The other thing I would check is the thermostat itself. It could be opening and closing erratically. Try replacing it.

Finally, is he running an electric or mechanical fan? If it's an electric fan, it might not be coming on or switching off too early. If it's mechanical, and a clutch fan, it could have a worn out/failing clutch. Both of these would present a problem in slow and stop/go traffic, while the radiator would start cooling again while driving at sustained speeds, as air will flow through the radiator on its own, without the fan pulling it through.

I also drill a small hole in the flange of the thermostat--it makes initially getting air out of the engine block easier.

-Brad

 

He said it was a 327.

 

Air bubble and boiling...nothing new. Run it, pull cap, add what you need, it'll puke anything over that, and when it does it has reached its' level. Had the same in my Hot Rod years ago, and haven't had a bit of a problem since...I've had it for 13 years!

 

Try a high volume thermastat. Regular thermastats now made for FI not carbs. They stay closed a lot longer, and causes the temperatures to really vary. I run a Robert Shaw, but NAPA and Advanced have good heavy duty or high volume thermastats also.

 

All you do is take the cap off when its cold and leave it off and run it till the stat opens. when the water starts to flow let it run throw the pump for min and the air will come out . Put the cap on and you should be all set . Air bound is the what its called