Here what I did and what happen. Just rebuilt 351m to 400, I fill radiator with just water tighten cap and started engine up. When warm and thermostat open up about 1 1/2 gallon of water pour out the over flow hose ( at radiator) which I had stuck in a bucket. I shut off the engine and when cool down it suck the 1 1/2 gallon of water back in, "note" temperature reading just into normal during this time. I thought my radiator cap was bad and got a new one at 13 lb, but the same thing happen again. My auto parts man said i had a air-lock in cooling system and told me to turn on the truck heater in the bronco rev engine to 1500 RPM for about 2 minute than shut engine off and let cool down and repeat several times. I did this and notice when warm and while water was flowing from over flow tube from raditor into bucket that their was air bubble in the bucket. About the fourth time the air bubble stop but still 1 1/2 gallon of water went into bucket."Note" temperture gauge always show normal reading, Question? can I trust the temperture gauge giving me a true reading if their a air-lock. Also truck heater in bronco did not blow hot air or warm air. Heater hose from water pump was hot right up to the fire wall but return hose from the engine block was just warm. I remove both heater hose from engine and was able to blow air through them and heater core using my lungs. Also I was told it might be a plug radiator,so I disconnected the lower hose from radiator and put the garden hose in the top fill and ran water and it pour out the botton radiator hose just as fast as going in the top. Help!!!!!!!

 

I had this problem with my brother-in-law’s 68 cougar. What we did was fill the rad half full then start the engine, then slowly fill the rad to about 2" from the top, the water will come up a little then go back down, it will take about one more gallon after this. Leave the cap off during this. Good luck, some engines are a pain about this.

 

Thanks for the input F1001978, I'll give it a try. Question? what were your symptom that lead you to believe you had a air lock, were they like mine pushing a lot of water out the over flow. I may add that my water pump is brand new not a rebuild and feel that it not pumping water do to a air lock I guess. When engine is warm up( running about 1500-2000 rpm) the top of the radiator is hot but cooling fins ( middle Section) and bottom are cool to touch which makes me believe that water is not moving through radiator. When I shut the engine off the whole radiator become very hot which make me think that the engine fan while running forcing air through tha radiator keeping middle and lower section cool. If their was water moving through radiator while engine was running it seems to me It wouldn't be cool to touch. Im afraid that I might over heat my engine do to this air lock if that is the case. temp gauge read normal but can I trust it do to air-lock. Help!!!

 

I was reading an article in 4-Wheeler magazine awhile ago about starting a new engine. What they said was the biggest mistake that people make is when filling the cooling system. They said if you fill it with a t-stat in place you will get air trapped in the cooling system and cause hot spots on the cylinder walls. They said simply install the lower radiator hose, remove the T-stat and housing and fill thge radiator until water runs out of the intake manifold freely. That will prevent air in the system then re-install the T-stat and housing. Your system is BURPING trying to get the air out, and until it's all gone it will continue to do so. Good Luck, let us know.

Shew Ain't Revved Ti'll The Rods Are Thrown!
Al

 

Those are the same symptoms his car had. We tried a new water pump, at least 5 different thermostats and even tried leaving it out. Nothing helped until we tried filling the radiator the way I described. I think what happened was the radiator was almost even with the top of the motor so air was trapped, then when the motor was running the air moved to the water pump keeping it from pumping. The motor would heat up really quick but the radiator would stay cool, the water in the motor would boil and push the rest of the water out.

 

Thanks guys for the input, heading for the shop for round three. Starting to question my self if I put the head gaskets on backwards, looking at old head gasket notice small hole on one end and large hole on the another where water jacket matches up, gasket were mark "front" but maybe I experience a real brain fart or something LOL, thanks again.

 

If u are having air problems in the cooling systems, u have to run the motor cold with the rad cap off. Wait till u see the water drop, add more, and keep running till water comes out. U have to be fast with the cap, or water will spill everywhere. Only do this if u are having trap air problems. Normal is to do the same, but not to wait till water comes out, but run it till the water stops going down, of till the motor starts to warm up.