New monovalve, same exact issues. I am now thinking my fairly new t-stat is bad and at times sticking open. When I have no heat the engine runs cool too. Even the exhaust smells harsh. It was installed last fall, but I think its worth a shot. Not sure where else to look. System is full and purged of air.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

I put in two new MTC monovalve inserts. Neither worked. I ended up buying the whole valve. I don't think they make the spring inside strong enough to stand up to the water flow. Total garbage.

When I previously replaced one with a Bosch (no longer available except from the dealer at stealer prices), it worked fine. One of the MTC inserts was too big to even fit into the opening. Even when replaced neither of the two worked.

In my case, the magnet must have been fine because I took the old Bosch insert out of another used valve and it worked. I mostly blame the MTC inserts. As an aside, I actually spoke to a person at MTC. He told me that he only had 2 returns in over 10,000 sales. Either he is miserably misinformed or they are not being returned because they are cheap. The problem is you get cheap.