engine overheat and cold air -thermostat?

you may have another fault, such as frozen coolant.

Seen that, quite funny at the time as it was not my car and the owner was a bit of a non plussed divvy.

Was also funny watching the badly labouring engne trying to Kangeroo out of the engine bay.

PDH

Vert possibly thermostat or possibly head gasket feeding compression gases into the coolant and causing an airlock.

All was fine in that same morning, over the past few days, I have been noticing varying lengths of time for the heat to kick in, sometimes works well, other times, not so good. The temp guage has been also been rising to just below the red and then it drops dramatically to well below the normal mark. Have not paid attn to where it leveled off.

I assumed that it was the thermostat that was sticking and that was my explanation.

head gasket sounds expensive. I will start with the thermostat and rad flush. Any other advice to rule out the head gasket would be greatly appreciated. Some say to run the engine and tab on the thermostat housing.

Run it till it gets to operating temperature and switch off. leave it a couple of minutes then take the cap off the expansion tank. If you get a lot of escaping pressure and a kind of "glug glug" sound then I would definitely be looking at head gasket. Is the water level holding up?

Plain old rad leak can do that - had two cars now who barely leaked water but what did leak evap'd on the rad, then when they cool they suck in air which causes air locks and overheating followed by cooling just as symptoms state.

My method of diagnosis would be to look for leaks when hot, if none are found use rad-weld (ducks avoiding flames) and top up the coolant purely to see if it remedies the situation. If it does you have a leak of some sort and need to flush the radweld out of the system once you find it.

Leaks are somewhat more noticeable than a blown head gasket.

First remove the thermostate connect up again after flushing the system.

See how she runs then. If you are not lossing coolant then it was the thermostat. If you loosing coolant the headgasket is a possible.

Also check the waterpump. My transit was overheating and it turned out to tbe the water pump. However I still can't see anything wrong with the old one. My guess is the impellor loosens up when hot and wasn't moving enough water.

Some are not that much more noticable. My Peugeot used to leak from a pin prick in the hot end of the rad. It wasnt even visible - it evapourated before it became visible but sucked plenty of air in when it cooled. The only reason I found out it was leaking was the radweld test - it cured it until i flushed it again so i pressure tested the rad when cold and found it dripping out where previously it vanishe without trace, not even a mark on the metal.

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember snipped-for-privacy@tesco.net saying something like:

I had exactly that problem with a Transit water pump. The impeller was a loose fit on the shaft when the pump came out - pressfit crap.