2 coolant related questions:

1) I bought my 09 MCS several years ago with 9k miles on it, under factory warranty + extended maintenance which expired about 6 months ago. I have no reason to believe that the coolant has ever been touched. I notice, though, that the coolant appears very green in color, and not blue as Pentofrost NF is. Did MINI ever use green coolant? I plan to do a flush anyway, and replace with blue, but should I be concerned about compatibility? Here is coolant from my MINI (red cup) compared to some Pentosin G11 (Pentofrost NF):



2) I have a leak which is likely coming from the thermostat housing. I'll verify this weekend when I dig under the hood. Typically, does the entire t-stat housing need to be replaced, or just the seal? I plan to do a flush while I'm in there. Is there anything else I need besides the T-stat housing and/or seal + coolant?

Thanks

MINI OEM coolant is mostly blue in color, with some hints of green (pic below).
It is possible that over time the blue pigments wear off and green color starts to dominate, but equally possible that what you have your cooling system is not OEM cooling fluid.

At this point, the worst thing you can do is not flushing the old liquid out.
I would just can a gallon of OEM MINI fluid and use it to flush the cooling system. I'm not sure how close it is to Pentosin G11 chemistry, so sticking to OEM fluid (not that expensive) is the safest bet.

You replace the entire T-stat, as the plastic housing is prone to cracking and the t-stat itself to sticking with age.

If you want to really take care of your cooling system for good, I would also replace the water pump. They also start leaking north of 60K miles. This way you will not be touching your cooling system for a long time. However, water pump is on the opposite (passenger) side of the engine, and doing it is a separate project. The only thing in common with t-stat swap is coolant flushing.

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Thanks for that, afadeev! I was under the impression that the factory Mini coolant was Pentofrost NF/G11, but I guess maybe I'm mistaken. Your photo does look slightly greener than my G11 which is a very pure blue.

Still, from what I'm reading, G11 is a safe/good/compatible alternative. I admit, I have several liters of it leftover from my VWs, so I'd like to use it if I can. What's the total capacity? 5-6 liters?

Regarding replacing the water pump... I'm reading here that the pipe between them WILL break (looks like at the H20 pump side) when removed and so it should be replaced. True?

Thanks.