axl911

The thermostat in my E36 BMW failed in a open position. Would have been very bad for me if it had failed closed.

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anthony

Syd B.

I still think you should ask your mechanic to explain why he thought you required a new oil thermostat. I'd be very interested in what symptom he saw in the absence of overheating that would lead him to this conclusion.

Michael Delaney

There are "fail safe" thermostats available for most cars. Of course these are for water pumpers. But they fail in the open position. A good idea.

Bob Krantz

Like Adrian said, it fails closed because the initial (cold) position allows for faster oil warm-up. (Running with cold, thick oil for too long can be almost as bad as "overheated" oil.) From personal experience, the failure comes from corrosion, either of the bi-metallic spring or of the sliding piston within the cast aluminum housing that lives below the oil tank--you know, the thing with the drain plug. The design flaw, as I see it, is that this is the low point in the system (needs to be, if it is also the drain) and so collects the water and other nasty stuff that condenses in the oil tank. Some of you, especially in cold climates, might notice a bit of water when you start draining the tank. When I was in Alaska, I started to periodically drain the water by just cracking the plug open half a turn, and letting capillary action wick the water out. My educated guess is that the acid-rich water will eat through the spring before Porsche envisioned.

Bob K
1989 C4

ps. If you replace an early 964 thermostat, be warned that the casting is different and will require different rubber hoses as well.