E39 temperature fluctuation diagnosis

[jeffbebe 1559]

Background:

Short drive today and in the last couple of kms home the temperature gauge started showing much higher (close the red) temperatures but only on heavy acceleration (e.g. up hills). Once idling gauge returned to its normal central position. I've never noticed this before and am certain it's not normal.

About a month ago I replaced a the upper radiator hose and fixed a small leak where a small hose had split (not sure the name of the hose). No noticeable coolant leaks anywhere. Had a bit of coolant splashed around but that was from before I fixed the radiator hose. When I replaced I topped up coolant and bled it; since then the coolant level has not dropped noticeably.

Have noticed a little bit of water on the ground near the front right of the car when it's parked but it doesn't seem to contain coolant so I assumed it was from the A/C unit.

I don't know much about this stuff but figured that if its was a cooling system problem then the temperature increase would be permanent not just on acceleration. Any ideas? Faulty sensor?

Sod's law it happens just before I have to head to Perth for work for a few days so I'll have to stew about it wondering if it's gonna cost an arm and leg 'til I get back!!

[BM WORLD 1283]

water pump?? thermostat??

[euroriffic 609]

I'd make sure you don't have an air lock. M52's are a pig to bleed! Did mine on my steep drive with the front jacked up aswell just to make sure.

[yng_750 247]

sounds like an air lock

best case your coolant was normal temp and ran away from the sensor on acceleration allowing it to heat soak from the block

worst case you coolant was overheating and accelerating was the only time it touched the sensor

e39 can be troublesome seriously recommend getting it properly checked out as the costs otherwise if it blows can be stupidly high

[BM WORLD 1283]

air in the system could be from a sleight leak ,

water gets forced out under pressure then as the system cools it sucks air back in

then next time you drive it the coolant system will find it hard to keep at normal temp.

could be slight leak around water pump seals , thermostat housing , side tanks on the radiator etc etc

[jeffbebe 1559]

Thanks, gents. It's due for a warrant in the next couple of weeks so I'll just take it to mechanic early and get him to check this out at the same time.

[jeffbebe 1559]

Couldn't find any leaks. My mechanic's checked everything and anything and couldn't find any issues - plus the problem hasn't returned. Guess it may have been a bit of air trapped in there - fingers crossed it was a one off.

All the checks has uncovered a few other issues... Choice.