Ok. This will be a rather lengthy post, but I need to give all the details so bare with me please. I've had over heating/air in coolant system plonked for like 2 months now. In the past 3 weeks I have replaced my thermostat (oem) intake manifold gasket and bottom radiator hose. After I installed these I bled the system following Billmans advice (always use his method). Maybe a week later the car over heats again and this time I break down and take the car to a reputable shop. The guy really knows what he's doing from all I know, and he's a good guy. Anyways, he discovers that my cap isn't holding pressure despite it having no visible signs of being faulty. So, replaced that, new coolant, bled the system, pressure tested the system and it didn't lose any pressure over something like a 5 hour period or so, he also tested for exhaust gases in the coolant as I was worried I may have a faulty head gasket. No exhaust gases in coolant. So, I'm happy, yay my car is fixed and it was all along a simple, inexpensive rad cap!.. Or so I believed. It's been a little over a week since I had this done and just a day or so ago, heat starts getting weak like it has before. It will only blow hot while I'm drive (60+) and blows cold as slow speeds or idle. I checked my bottom rad hose after letting the car warm up this morning and it was cold... Bingo! We have air in the lines I'm thinking. So the story now is. I'm not getting heat unless going fast, bottom hose is cold but my car is NOT over heating. Still should be air in the lines. My question is, how in the world am I getting air in my lines so slowly. It takes a week or more to accumulate these problems again. I'm so frustrated. There are no leaks or anything. Any advice is welcome since I'm at my ropes end with this problem. Sorry for the enormous post

 

You are getting air in there.

It is either leaking, or the HG is leaking under higher RPM and the idle test is not picking it up.

 

But there was no exhaust gases in the coolant?

 

I don't have milky coolant or oil. No signs of a bad gasket. But I guess it could fail in a certain spot to cause air in the lines but not let oil in the coolant. Idk. I figured there'd be exhaust gases in the coolant for sure if the hg is bad

 

Another important piece of info. I couldn't copy and paste this so I'll post of picture of it.

 

 

Also, if it was a bad head gasket it would cause these problems way quicker than a week or more time?

 

Also, if it was a bad head gasket it would cause these problems way quicker than a week or more time?

 

Bled the system. Definitely had air in it. Guess next step is replacing radiator, I'll try all I can before I do a head gasket

 

I'm going thru same thing mine started like yours now it over heats right after running temp and heat is cold as crap but I can bleed it and get super hot heat but as soon as I actually drive the car its cold heat and over heats but if I don't drive it it stays hot and will not over heat no mater if I let it sit there all day running lol