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Date: 12-13-05 07:09
From: BigDog in Sammamish, WA  
Subject: Weird cooling system behaviour...  
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Figure this one out... So the other day I notice the temp gauge moves more than normal. Seems everything is fine, then I notice it's HOTTER than usual, not screaming off the charts, just hotter than normal. Then a while later it's back to normal. Weird. So I check the coolant level and find I"m down to about where the top hose comes in. I filler up and get on with my driving about. Check coolant next day, and yes, it's down there again!!!
I figure got a leak someplace. I look and look, re-do a couple hoses for good measure, and yet, it does it again! I can't figure where it's leaking, so I put a plastic bottle on the overflow vent, and sure enough, it filled up! So now at least I know WHERE the coolant is going, the question is WHY is it doing this?????
With the fluctuations in temp I think maybe my thermostat is failing? Closing when the motor is hot, re-openning when it gets hotter??? Does this make sense at all???
No noise from the H2O pump at all, no squeeky belts, no howling bearings, it seems to be working nominally.
Coolant looks fine, no signs of unusual stuff in there, no large quantities of oil or anything else. No sign of coolant in the engine oil or in the valve cover.
No chance it's burning any coolant, the plugs look good, and with the temps this time of year you'd see the condensate coming out the tail pipe for certain!
I'm baffled, I think the thermostat maybe the cause? Anybody have similar excperiences???
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BigDog
'76 20002 Maybe trying a new thermostat tomorrow!
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Date: 12-14-05 02:34
From: CharleyII
Subject: Re: shot in the dark...
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check the rubber seals on the rad cap. if there's a crack/tear in the the release valve seal (the small one) it allow your system to depressurize which will effectively lower the boiling point of the coolant and it'll just vaporize. the disapearing coolant trick :)
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Date: 12-14-05 06:39
From: c.d.iesel in South West Connecticut - Darien = The Right Coast
Subject: Weird cooling Science !
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...well - if your filling
up a catch bottle off of the radiator over flow
hose?- then you either have a thermostat
that's causing the motor to really run too hot
and the pressure is climbint too high, AND your NON-BMW
radiator cap is alowing the over flow at possible too low a pressure.
IF there are no other coolent leaks like from hoses, water pump, heater core, replace the thermostat and radiator cap.
How old is the water pump?
How old is the radiator?
 _________________ 1976 BMW 2002 #2743711(sorry I sold it 12/25/06)
1986 BMW R65 650cc twin 19k miles
1964 BMW R27 250cc single 15K miles
2002 BMW 325xiTouring 29k miles
1984 MERCEDES-BENZ W123 300D Turbodiesel-188k miles fein-DIESEL
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Date: 12-14-05 06:03
From: BigDog in Sammamish, WA
Subject: Well, the verdict seems to be...
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Must be the water pump has died. I didn't really notice a lot of movement when I had the cap off, and with a new thermostat and cap, same behaviour, if not a little worse thanks to the pressure addition from the new cap....
The last water pump I had die, went out with a bang, seized up, smoked a belt, this one just appears to have puked...
Oh well, so much for the cheap and easy stuff, now on to H2O pump replacement.
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BigDog
'76 2002
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Date: 12-15-05 01:24
From: Guest
Subject: Re: Well, the verdict seems to be...
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ive heard of a water pump gear(?) stripping off of the shaft.. maybe that was it.. interesting.. INteresting :)
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