Heater loses temperatures at speed

[R1cardo]

Heats up fine but loses warmth when you get up o to speed, so above 50ish. Any suggestions?

[BenHar]

Thermostat.

Ben

[R1cardo]

Thermostats has been replaced

[ChrisHC]

Perhaps the water pump, which is a bit of a weakness on the 6 sylinder cars in my experience.

[flybynite]

Heats up fine but loses warmth when you get up o to speed, so above 50ish. Any suggestions?

What engine?

First thoughts for me, especially if things have been replaced is bleeding? Have you bled the system properly? Nose high, heater set to hot etc etc?

[R1cardo]

325i. Thermostat was done at a garage, so presumably was bled correctly.

[flybynite]

325i. Thermostat was done at a garage, so presumably was bled correctly.

E30 M20s can be a pig to bleed correctly so unless they have experience of E30s then I wouldn't assume anything.