Ever since I flushed the coolant, the upper radiator hose is full of air that I can't get out. It gets squished flat in the cold. I've tried running the engine with the degas cap loose, and I've just driven the truck hoping the air would work out over time, but it never does.

 

 

I've driven it in both hot and cold weather since the flush, on steep slopes and bumpy dirt roads. It comes up to normal temp, and does not overheat. The heater works. I don't think I've tried defrost... would that make a difference compared to regular heat?

 

 

Unless it is stuck or otherwise broken the thermostat always opens at temperature regardless of the heater control position. Changing the heater control position will have no bearing on his issue.

Sock, what makes you think (or how do you know) there is no coolant in your upper hose? If there is it sounds like your hose could be the highest point. Maybe loosen a clamp, rotate the hose slightly and try to refill your system. You may have to put a jack or blocks under under your truck ( I have no idea if your doing your work on a flat area or not) so the air can travel into the upper tank and then out of the system.

 

I don't see how it can be full of air myself. When and under what conditions is the hose flat?

 

Defrost has absolutely no effect on the thermostat, please don't spread that ignorance again.

It sounds like your coolant cap is bad. When the hose is squished does it go back to normal when you loosen the cap? If so, get a new cap and you're done. If the hose stay collapsed then you'll need to replace it, but that almost never happens.

 

I replaced the cap. That seems to have done the trick. The upper hose no longer squishes flat overnight, and I can hear liquid inside it when I squeeze it (couldn't hear any before) and the coolant level dropped a bit so apparently it has worked some air out of the system.

 

Thanks for the update.