Originally Posted by Swerve
Sounds more like air in the coolant system. the air bubles can collect around the temp sensor blocking the heat transfer.
A coolant cap that doesn't hold pressure can cause this. Test/replace that, and spend some time bleeding ALL the air out of the system and see if that fixes the issue.
im almost 100% sure theres no air in the system, im sure my dad knows what hes doing.
after all, he does have an ase master cert.
i plan to replace the cap and t-stat soon, as of right now the SAS is priority #1.
it seems to be ok right now because its warmer out, but if i turn the heat on it drops down, so does the mpg.
so im still leaning towards the t-stat being stuck open, if the cap was bad the overflow bottle would "overflow" wouldn't it?