Gentlemen
if the radiator fill cap is not the highest point in the cooling system will the air still bleed or will air remain trapped and possibly cause overheating?
Thank you.

How does one fully fill such a system in the first place?

If the radiator fill cap is say the second highest point - then the first had better be an overflow bottle . . .

What sort of arrangement do you have?

WHAT ENGINE

bcowanwheels,
The engine is a 1974 Chevy 250 inline. The engine is in the factory position, the radiator is stock with a "corner fill" that puts the fill cap lower than the top of the radiator, lower than the top radiator hose inlet, and lower than the thermostat housing. The over flow bottle is in the stock position lower than the top of the radiator.

Yes Mr. Stock 49, how does one fill such a system in the first place?

regards,
ken

Ken,


I have the same radiator type. My setup does not use an expansion/overflow tank. Your may be a later add-on too? All it needs is a dump hose from right below the radiator cap. The "expansion" space is the air pocket trapped inside the radiator when you fill it up. Any excess coolant will be spit out of the overflow tube when the engine gets hot. Once it's purged, no more comes out on subsequent heat cycles and the air space is automatically the right size.
I added an overflow tank on mine just the same. I'm no tree huggin hippy but I don't like running coolant to the ground either.

And like you I didn't like having a pocket in the radiator.

Nova,
Thanks. What's happening is that I moved the temp sending unit to the head and the readings I get there go from 210 to 230F. The climb and drop reading there is erratic which leads me to believe that there is not a steady stream of water there but rather an air pocket. My fan control temp switch is located in the thermo housing where it was before I moved the sending unit. My fan used to come on when the water temp at the thermo housing reached 190 to 200F. Now it does not come on unless I override manually. And then the temp at the head does not drop.

ken

our setups sound very similar, my temp gauge sensor is at the head too, and fan switch is at the thermo housing. I too saw 230F on the gauge and did not like it. That part does run hotter than the thermo housing. I wonder if the fluctuation is the thermostat opening and closing..... doing it's job. But the fan switch should work the way it did before, so if it now doesn't come on, maybe you are right and it is no longer in contact with coolant. Does this happen at idle? Gets better as soon as you give it steady gas? with higher rpms the water pump may be able to move more water and put the thermo switch in constant contact with coolant.

When my fan comes on, the head temp starts going down almost immediately. My switch is adjustable. (Fact I did not know until I started pokin around it and saw a small screw... I bought it assuming it was not adjustable since the mfg specs did not say anything )

You may also have a water pump problem, is it relatively new? Need to make sure it moves enough water.

The way I purge air from just about all cars is with the help of a burp funnel made by Lisle: http://www.amazon.com/Lisle-24610-Spill-Free-Funnel/dp/B001A4EAV0 I think I used it with my Nova too? been too long. It allows bubbles to come up higher than the radiator, and then fluid in the funnel replaces the air without letting new air in.

On the older Chevy's the radiator cores run north and south - inlet tank on top/outlet on the bottom - the thermostat is well south of the upper tank in the radiator:

whereas in an early 70's Nova there is a lot less clearance:

with the upper water hose running more or less horizontally to the inlet tank. But top of the head (water jackets) are lower then the top core tubes (running east and west) in the radiator core - no?

Is your engine somehow sitting higher? An air pocket in the radiator is one thing. Air in the top of the head another.

Really old engine, it should get good care