engine and drivetrain Weird cooling system behaviour...

[BigDog]

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!

[albertamac]

time for a new rad cap maybe?

To the best of my knowledge, they have a psi rating, so that once a certain pressure is reached--> into the overflow vent.

I haven't had this problem on an o2, but I have needed to get a cap rated for a higher psi on a vehicle before to keep what your explaining from happening. Yours just may be worn out.

Maybe someone a little more sure of themselves can pipe in...

speaking of which, my 02 always runs hot, maybe I should get on that...

Mac

[BigDog]

I'll have to try that one. I'm running a 320i aluminium radiator, so it generally runs nice and cool, almost TOO cool. Gauge rarely makes it 1/2 way up, usually runs @1/3....

I"ll try the cap!

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BigDog

'76 2002

[toddman]

Your cooling system is indeed pressurized. As it heats and cools, coolant will expand and overflow out the vent. Generally if you bleed the system properly when you fill it with coolant to avoid air pockets in the system, there's enough space in the standard 02 radiator to expand/contract without spilling much fluid out. This time of year, I never see anywhere close to the half way mark.

BTW, In sammamish? Where? I am in renton, and just about to take my car out for a spin. The roads dried up in time for a nice little night time drive :-) We should organize a meeting for all the 02 seattle folks...

Toddman

[Guest Anonymous]

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

[c.d.iesel]

...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?

[BigDog]

I only use BMW radiator caps!!! Ha ha ha.

Actually I maintain the cooling system pretty well. I"m running a 320i Aluminium Radiator that I bought NEW from Max several years back when Paul was working there still. The H2o Pump is fairly recent as well, since I had one puke on me a couple years ago.

I"m going after the cap and thermostat today assuming I can find the parts at MY local dealer!

--

BD

[Tim_in_MD]

The p/n for the regular t-stat (80 deg I believe) is 11 53 1 253 249. I think it was under $30 but they did have to order it...came in within a couple of days.

HTH!

[BigDog]

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

[Guest Anonymous]

ive heard of a water pump gear(?) stripping off of the shaft.. maybe that was it.. interesting.. INteresting