Hey guys. I've got an '06 R50 and I'm pretty sure I need to replace the thermostat. Does this mean that I need to replace the expansion tank as well?

 

No. Not unless the expansion tank is leaking.
Leaks around the thermostat gasket and the thermostat housing are common.
Always replace the gasket with the thermostat (they're sold together anyway).
Get the newer version gasket if possible (clear rather than opaque) as it's supposed to be more reliable.
Change the thermostat housing if a leak or oozing there is noticed. New clips on the hoses you took off
to change the housing would be a good idea as well.
Consider changing it even if not ($45 and you'll already have the part off to change the thermostat).

What thermostat symptoms are you having? Running too hot or too cold and under what conditions?
If too hot make sure your radiator fan is working properly (both the low speed and high speed function).

 

When I'm driving, and come to a stop, the fan kicks on and the engine temp starts to go up. When I get moving again, the temp goes back down. I turn the heat all the way up to draw heat from the engine and it's blowing out cold air. Sometimes it blows out hot air, sometimes it's cold.

 

Thanks for the help btw

 

When you say the engine temp starts to go up, do you mean the temp gauge
is low and creeps up toward halfway, or on halfway and going higher, or are
you talking about the temp of the air from the vents?
The first (low gauge readings) would make me think of a bad thermostat (stuck open, always sending
coolant to the radiator), but it's puzzling why the fan would go on at a low temp unless
the a/c is on (to help with defrost) as well.
The second (high gauge readings) would make me think of a bad thermostat (stuck closed),
or a bad water pump impeller that doesn't flow at idle.
Happens with VWs with plastic impellers but not sure about MINIs.

 

It's the temp gauge. It'll be at halfway and then start to climb when I come to a stop.

 

I assume the reservoir (expansion tank) is filled at least to min.
Open the filler cap when cold (transmission side of engine) to make sure it's not low there and not filling from the reservoir.
The low speed of the fan should come on before the gauge begins to climb,
and the high speed setting of the fan should definitely be on when the gauge begins to climb.
Does the front of the radiator get hot?

Assuming all these are true, possiblities I can think of are thermostat not opening, water pump not doing well.

 

I've checked it while it was cold, and the coolant is around the minimum level. The low speed of the fan does come on before the gauge goes up. I'll have to check the front of the radiator when it happens tomorrow. Fingers crossed that it's just the thermostat and not the water pump.