Top Hose Doesn't Have Coolant: Airlocking?

[nightofstars]

How to treat & prevent airlock? This is kind of serious, we just don't know what to do & need this truck running:

We've changed the water pump, thermostat, heater core, head gaskets, and the overflow reservoir is full. Our hot/cold indicator goes above half on the word "Normal" in that gage so we installed an electric fan, after finding also the fan was moving too freely even when the truck was warmed up.

Does anyone know anything at all that can be done about this? No coolant in the top hose means the engine can't be run so we're beached and are really wondering at the serious nature of this & how to fix it fast. Why is this happening & what can be done?

[madpogue]

Thermostat stuck closed would be a first guess. Also, is the thermostat the right one, the right length so that the second disc on it closes the bypass when the main one opens?

[StrokerIH]

is the thermostat facing the right direction?

[BigFuel]

^same as above, T-Stat position. Easy to check if there is no coolant in the top hose. A lot of people might disagree but I will put the t-stat flange on a piece of wood and drill a tiny hole in the flange only. If it is a 4x2 the trucks natural unloaded rake will hold air in the heads. You need to lift the front of the truck so that the air will move to the front of the block and be pushed out.

[nightofstars]

At NAPA, they gave me the thermostat for this particular truck when ordered, so can you give any idea what size thermostat exactly is needed so I can be more specific?

The coolant is all new & I was also told today that often leads to airlocks that must be removed by removing the thermostat then reinstalling it, I am hoping this works. It seems something more should be done in that process somewhere?

Originally Posted by madpogue

Thermostat stuck closed would be a first guess. Also, is the thermostat the right one, the right length so that the second disc on it closes the bypass when the main one opens?

[BigFuel]

You probably have the correct t-stat (though wouldn't put it past a counter jockey to get it wrong, looking for a NAPA THM 371203). What StrokerIH and I are suggesting is that it was installed up-side-down.

About the air-lock, that's why I drill the small hole in the t-stat. Air pushing on the t-stat will not heat up the way a liquid would and in some cases (if there is excessive air) the t-stat won't open at all. The small hole will allow the air to creep past the t-stat and get the coolant right up to it. Still if it is a 4x2 then you need to lift the front of the truck so that any trapped air in the block will move to the front.

[madpogue]

All depends on whether the water pump might have been replaced by a previous owner; I know different years, different sources had different lengths. The key is to compare the new 'stat with the old one, for same dimensions.