73 Beetle engine temperature drop?
My car will start up and run fine around town.
When running on the interstate the cylinder head
temperature will drop after a while and the engine
will lose power. I have noticed that when I turn the
heat on it only blows cold air when the cylinder
head temp has dropped. When I pull on the side of
the road the engine will warm up and drive fine for
a while and then start doing it again. When it
happens I will have the pedal to the floor and only
get 55 miles an hour when it will normally run in
the 80's.
What causes the engine to all the sudden run cold?