Date: 25 Jul 2006 12:41:06 GMT
From: John B <>
Subject: Re: Cooling System Dilemma - '92 900i

On 25 Jul 2006 05:32:51 -0700, wrote: > Advice needed...I have been having overheating problems. This part: > > > > which sits right over the alternator, started leaking. I pulled it out, > and it seems there was some kind of passive valve in there that ain't > there any more! I assume it blew forward, in the direction of the Hi, The part you're talking about is the heater bypass valve, which is only present on 1992 and up 900s. It's supposed to improve flow to the heater core when the car is at an idle, though I'm not exactly sure how it works. > straight hole. This goes into a metal pipe that takes you to to the > back of the engine (front of the car) and goes into the motor. I > checked the pipe, it is clear. Is it stuck somewhere in the block, or > did it blow through all the way to the radiator? As I understand it, coolant flows from the cylinder head through the elbow hose, then through the metal pipe, and ultimately into the heater core. So it seems unlikely that any part of this valve could have ended up anywhere near the radiator. > > The car is cool as long as I don't take it on the highway. That makes > me think there is a partial blockage somewhere, but enough water gets > through for low speed driving. Were you having the overheating problems before this valve started leaking? It could be that the leaking valve is unrelated to the overheating, or that the leaking valve is preventing the system from maintaining pressure. > > Where should I look? Also, I sealed up the part in question with blue > RTV and plan to drive it a few days until I can replace it. It the > missing valve the whole problem, as it prevents proper flow? If so, > what about the lost valve? It had to go somewhere! > I suggest you get yourself a new bypass valve (which you'll need anyway) and compare it to your failed valve to figure out what parts may have escaped. Also, this is probably a good time to drain/flush your cooling system, replace the top hose (thermostat housing to radiator), check the function of the radiator cooling fans, and replace the thermostat. Depending on the milage, you might also consider preemptively replacing the radiator. Doing all these things should fix just about any cooling system problem, I think. John -- Posted via a free Usenet account from

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