Overheating 300tdi: New thermostat

Hi

My 94 300tdi 90 with 200k on the clock was running perfectly on my 40 mile commute to the farm and back with no overheating on the local lanes (never exceeding 50mph) but it would overheat when on the A12/14 when at a constant 60mph after around 30 milles.

So I flushed the system using forte cooling system flush and back flushed the rad and fitted a new thermostat (genuine part)
the old thermostat looks like it wasn't closing fully.

But now it will overheat on the local lanes on my trip to the farm and back which it didn't do before, I also only seem to be getting intermittent warm air from the heater... i.e it works on the was to work but not on the way home?

Any ideas what to check and where to start? Ive had the head tested and that is fine (block test)


Thanks
j

intermittent warm air sounds like an airlock to me, how id you bleed it??

Yep, sounds like an airlock if the heater isn't working as it should.

My "neverfails" solution is to lift the front of the vehicle (jack or ramps), unscrew the plug on the top of the thermostat housing and the flick the heater pipes to make sure the airlock moves. Takes a matter of minutes.

Well the airlock has been removed and the heater is working, but only blows air when I am driving above 30mph, is that normal?

But it still overheats to around 3/4 on the temp gauge, the rad looks fairly new and has all its fins, front and back.

If the bleed screw on the thermostat is removed with the engine running there is a good flow of coolant being moved around. Any other ideas?

Thanks
James.

Silly question but have you checked that your water pump is working as it should!