[suspect]

Is it necessary to drain the coolant when doing OFHG replacement? I’ve read about siphoning it out of the coolant reservoir so that the coolant level sits lower than the OFH. What happens if you don’t bother? Does it pour out of the OFH when you open it?

[tcphoto]

I believe that you should siphon a little out of the reservoir or it will make a bit of a mess, I'd checkout Zeitens YouTube channel to confirm it's a great resource. Just take a turkey baster and pull about a liter out and return when finished.

[jadams161]

No, it is not needed. When you pull the upper rad hose to the OFH it drains out what is needed. Remember to replace the "mickey mouse" flange while in there. Use real BMW gaskets and coolant.

[suspect]

Thanks guys. Taking a litre out of the expansion/reservoir was enough. Engine head flange (mickey mouse) already replaced.
A tip that helped was breaking the OFH bolt loose next to this flange using E10 spanner and then using a 12 point 8mm spanner to undo the rest of the bolt. Or use a E10 ratchet spanner if you can find one.

[feuer]

Originally Posted by suspect

Is it necessary to drain the coolant when doing OFHG replacement? I’ve read about siphoning it out of the coolant reservoir so that the coolant level sits lower than the OFH. What happens if you don’t bother? Does it pour out of the OFH when you open it?

Originally Posted by jadams161

No, it is not needed. When you pull the upper rad hose to the OFH it drains out what is needed. Remember to replace the "mickey mouse" flange while in there. Use real BMW gaskets and coolant.

Very accurate!