Coolant and Thermostat

[BMWDriver]

Hey,
Apparently I've had another thermostat failure. It's still being replaced, so I'll know for sure if it's the culprit later - you just never quite know. Symptoms as reported by the mechanic is that the top hose was hot, while the bottom one was cool (could be other way around as far as my memory serves me) which would indicate the thermostat did not want to "open up".

Thermostat was replaced Feb. of last year. I wonder that the coolant has anything to do with it failing. I top it off with Prestone LowTox aluminum compatible, which is probably not what my usual mechanic uses. In fact, I have not done my homework on the subject properly now that I think about it.

Thanks for your input.

[bubba966]

Coolant choice does matter. But even crappy coolant won't kill a stat in 1 1/2 years. Either the stat was low grade (crappy off-brand), or was a stat that shouldn't have passed QC.

Or it's not the stat that's broke.

Or somethings jammed the stat.

[Ross]

My money is on a failed water pump, impeller loose on the shaft or broken.

[Ferret]

My money is on a failed water pump, impeller loose on the shaft or broken.

I agree with Ross on this one, this is exactly the symptoms that the M50 520i I did last month was showing.

The clue here is that the rad top hose is hot... this will only happen when the thermostat is open, and convection allows the hot water to rise to the top of the system.

Has your heater stopped working?

The pump isnt hard to do, though it's advisable to change the visco fan and pulley at the same time.

[BMWDriver]

The pump's broke. It had the unwanted plastic version and the impellers are broken. I'll see the broken pump when I get the car. Also the impellers tunred outside the engine, but were not turning when installed.

Somehow I'm not surprised; the owner who had it before me went for cheap jobs although not too much since it's in good shape overall.

The good news is that the metal's going in and will better handle my driving style.

[BMWDriver]

I'd think the pump would have failed too, which concurs with when it happened: after hiting some high revs. It is, after all, an old engine.

I can only hope it's actually the thermostat that failed, moneywise.

[bayviewsbb]

Hate being the bearer of bad news...
I replaced 2 'stats in 6 months...then replaced EVERYTHING and even had third 'stat drilled to stay open...but my 90 e34 535 still kept overheating. Took head off and gasket gone minutely on 4 and 6 cylinder... earlier compresson and blue dye tests did buggar all to show gasket failure... but if all your other cooling components are working ok, nothing left but the head..! Because if the gases are'nt getting out then on cool-down they convert to vapour and lock/stay in the system. 'Stat can't operate properly with air in system and will fluctuate/give false gauge readings 'till overheating occurs...

Bottom hose passes worked/heated coolant back into radiator to be cooled and pushed up and back out the top...Also suggest you run motor with rad' cap of to see if coolant discharging ok back into expansion tank. If sluggish, check outside hose for crap blocking/slowing discharge. If ok, (with engine off) check inside expansion tank hole with bit of wire where coolant empties, for plastic swarf left from making tank...,be amazed at the crap that builds up where the hose reduces down to fit the tank connector...(I've drilled this out to increase flow).

Good luck with finding the underlying problem
,
bayviewsbb

[citti2004]

my check engine light just came on yesterday , i went to autozone they ran the free test thing and said coolant thermostat- coolant temp. was below operation range. i have plenty of coolant.

[whiskychaser]

I dont know what this test involves but would guess they are just testing if your antifreeze is up to strength? I translate 'Coolant temp below operation range' as 'car hasnt warmed up properly'. Maybe clarify. Cant see where you are or what car you have. But as you mention Autozone I guess you are in the US. In which case try the stomp test for the CEL