Do I need to drain the coolant before replacing the engine coolant temperature sensor on a 89 740 turbo?

There is no mention of it in the faq but I would imagine it to be the case.
I'd hate to drain it unnecessarily.

Thanks for the info

I just found out today it take a copper o-ring. I reused the old one.

We'll see.
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1989 740Ti 1986 240DL 1984 244GL

Have the new one ready with a little Anti-Sieze on the threads. Unscrew the old one, put your thumb on the hole, grab the new one, slide your thumb out of the way, screw it in. Coolant loss should be minimal.

Also make sure you leave the exp tank cap on and tightened down. This will help pull a vacuum on the line above and minimize the leak rate if you dawdle. If you take the cap off, you now have the exp tank acting as a source of head pressure for your leak!

someguyfromMaryland

Honestly, I was going to suggest removing the cap and having the wife apply suction to the tank while replacing the sensor. (I was afraid that would just open the flood gates to various comments.)