308 cooling system airlock

Have you tried lifting the back end (or front end) of the car up?

 

Sounds like thermostat is not opening. And sometimes you may have to bleed it several times.

 

Water pump?

 

I didn't realize you have good pressure in the system.
Check out Birdmans tips for proper filling procedures and cooling system info.

http://www.birdmanferrari.com/service/coolant/coolant_troubleshoot.htm


http://www.birdmanferrari.com/service/coolant/coolant_bleed.htm

 

Perhaps I misunderstand your issue, but the system isn't pressureized by the water pump, it pressureized by the expansion of the water as it heats up. You could easily have full system pressure without the water pump running. The hot water in the block will cause the whole system to be pressureized, even up at the cold radiator. Eventually the water in the block will boil and burp probably-still-cold water out the tank/radiator cap.

If your car had the thermostat bleeder I'd run the car with open and see if it is just air around the t-stat. I always drill a little hole in the top of the flange of the t-stat to prevent an air pocket from causing issues.

 

100 ys ago working on 308's......On 308s the radiator bleed screw is lower than the tstat housing. I always refill a system at the overflow tank. Then run the car with the cap off and don't think about putting the cap on until I start seeing warm water start to rise visually in the overflow tank which indicates warming water that is expanding. Then once I confirm that I'll cap the system and bleed at the tstat housing then the radiator bleed screw then back to the tstat housing and I'm done. Hope that helps.

 

Along with the raise the rear of the car idea...

I made myself a rising tube to increase the pressure:
1) remove the filler cap from the expansion tank
2) find a plastic pipe (household waste uVPC) that is a good fit inside the neck of the tank, if necessary wind electrical tape around the outside until it is a better fit.
3) make it as long as will fit under the engine cover, while still being able to fill it with water
4) now fill pipe to top with water...

You now have 18" extra water pressure at the rear to help push the water through.



I then refined this idea.
1) I cut the valve from an old inner tube and trimmed the rubber into a circle that was a nice fit in the filler neck
2) then cut a wood plug to fit inside the neck of the header tank with the valve inside.
I could then hold the plug and valve in place, attach an airline (set to 10psi) and pressurise the COLD water. As soon as I let go the plug would jump out and loose the pressure, but I could top up the header tank and by holding this in place I could drive water through the system, top up and drive through repeatedly until the air lock was gone.


NOTES:
DON'T FORGET TO SET YOUR HEATER(S) TO FULL HEAT... there are water valves there as well which can encourage airlocks if closed.
Some 3x8 thermostat housings have a bleed screw on them.


David
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your water pump could have a bearing going out allowing air to get into the system which in turns pressure to build up in the radiator and making the water temp to go up,alot of times you won't see this happening or hear the bearing squell,but air has a funny way of finding places to go,I would replace the water pump and the termostat and you'll be good

 

The factory did not go through any of these gymnastics to fill the cooling systems on the production line believe me. Also the mechanics that have worked on these cars since the early seventies have not earlier. It's very simple, open the radiator bleed screw, take out the bleed bolt in the thermostat housing. Pour water in the filler until it runs out the radiator bleeder then close it. Continue pouring water until it comes out the thermostat housing bleeder then cap it off. Continue pouring in water until the tank is about half full and cap it off.

Thats all there is to it.......Really.

If that does not work either the directions were not followed or there is something wrong with the cooling system.



Quit trying to make something so simple so hard.

 

Not possible.

 

Sounds to me like your tstat is not opening. It would be wise to replace the tstat with an engine rebuild anyway (if you just re-used the old one). Make sure it's not in upside down, although I think that it's tough to install it upside down! I suppose it's possible the wpump isn't pumping coolant around the system but that's highly unlikely - if the pulley is rotating then the impellar should be rotating and pumping.

 

Did you test the t-stats on the stove before installation?

 

is the engine running during this whole time Brain

 

I expect Brian will answer no. I figured out to do it on my own just as he explained. When the air is out, its out. Whether its running or not makes no difference, in fact it might make it slightly harder.

My 77 does not have a T-stat bleeder, and I have never had any problem bleeding it.

 

That has a hose at its highest point that goes uphill directly to the coolant header tank so there should be no way for it to air lock unless the car is plumbed wrong.

 

No.