heaters blowing hot then cold
 

I have recently changed the thermostat on my 93 scooby turbo. I thought that id bled the coolant through the system correctly but if i go for a drive the heaters are hot to start with then if i sit at traffic lights the heaters go cold then when i drive again they go hot. im gonna drain the system again could anyone point me in the right direction of correctly bleeding the coolant system???

You have to idle the engine with the pressure cap off the header tank.

Wait til the rad fan comes on, then top off the header tank, re-install the rad cap.


Fan ON, means the temp is high enough for the thermostat to be open, and this means circulation that purges the air. Have a cloth on hand, the header tank will burp a few times underway.



Did you install a genuine thermostat? I ask because the Tridon aftermarket jobs are shallow enough to mount the wrong way round. Genuine only fits one way.

tried bleeding off the way you said and so far it has worked heaters been hot all day. I have noticed that the two pipes from the rad feed and return are under a bit of pressure so i have had a sniff test done today and all was well is this pressure possibly still a little trapped air in my system?