Temp gauge dip and weak heat due to trapped air?

[nthach]

On the Ranger, I did the final cooling system flush, filled up with Prestone and replaced the thermostat. Now, there is heat but not as “strong” as before. Truck warms up fine. When I run the engine with the heat on, I do see the temp gauge dip from the middle down to the lower end of the “normal” range and creep back up. There is a new Motorcraft t-stat in it. Truck isn’t overheating. The heater bypass works fine, the heater hoses are hot, one is a bit cooler than the other.

I opened the radiator cap, I got a gush of coolant. I’m thinking of lifting the truck up or having it on ramps and running the engine with a no-spill funnel to try to purge out anymore air. I wanted to use an Airlift but there was still water in the engine block - no block drains, Ford wants you to knock out freeze plugs to drain the block. Any other things to check for?

 

[Lubener]

I was surprised how much better my heater worked after flushing the heater core, refilling it through the input side heater hose while the return hose being disconnected at the engine. If the new thermostat is "notched", any air behind it will pass and be burped out at the radiator.
Personally, I never change out a properly working thermostat. Just because it's new and OEM, does not gaurantee that it is going to work at 100%.

 

[bullwinkle]

A jiggle valve thermostat is always the way to go, it will allow air to work its way out. Drilling a 1/8" hole in one that doesn't have one helps too.