4.8 expansion tank - level sensor leak

[andrewwynn]

There is no good reason to replace the sensor if it's working and fits in the new reservoir. It's a Magnetic Reed switch good for millions of switches and isn't exposed to either environment or coolant.

[svvg]

Thanks for this. Understood and agreed. Just threw me initially as it was soaking wet - and the chamber/well that it clips up into was the source of my coolant leak. Just ordered a new tank from bmw. Arrives on wednesday.

Thanks for everones help!

[andrewwynn]

The failure can be anywhere. It seems yours failed somewhere in the level sensor cavity. My wife's failed on the rounded corner and was absolutely invisible until the system pressurized. It actually flexed the tank and I could see a hairline crack as well as the water streaming out, but when I opened the cap the tank shunk back to normal and made the crack invisible again.

Mine the tank failed on a seam. I don't have a level warning, my heat stopped working well that was my low coolant alert. I have a sensor my computer just isn't connected to it. I'm thinking of wiring up a simple led and resistor to make my own warning light

[svvg]

Sounds strange there’s there’s no low level warning. Maybe it’s been unplugged and the cable’s fallen down somewhere?

[wpoll]

Originally Posted by svvg

Sounds strange there’s there’s no low level warning. Maybe it’s been unplugged and the cable’s fallen down somewhere?

On some cars no level warning was fitted - low cluster pec perhaps.

[andrewwynn]

Correct: low cluster no sensor


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[svvg]

Just about to swap the tank over. I can’t find a good bleed proceedure for the 4.8 N62 though - and find conflicting posts re self bleeding system. Is anyone able to kindly provide a link/some info on best way to bleed the coolant on this engine?

Many thanks!

[740ilDuke]

Pelican has a write up.

https://www.pelicanparts.com/techart...ing_System.htm

[svvg]

Thanks - and yep, I had seen that, but it’s not for the 4.8 - and wasn’t sure if any differences? I’m not sure whether all models have an electronic thermostat? And the tank design is slightly different - although can’t imagine that makes much of a diffeence...?

Pelican also have a lot of stuff for the E60 which does have the n62 4.8 too, so can’t be massively different... when bleeding other cars I’ve set heater controls to hot and low fan, run the engine with the cap off amd bleed screw open. When bubbles stop coming out of the bleed screw I then tighten it and whack the cap back on. Get up to temp then let it cool and top up if needed... assume it can’t be that dissimilar...?!

[crystalworks]

^ That will work. But you will want to close the cap and bleed screw after doing that so you can rev the engine and dislodge any trapped air bubbles. Then re-open the bleed screw to let them out. You could probably rev the engine with the cap off as well, but I find that gets messy sometimes. Once you get full heat from the dashboard you can stop, let it cool, and top it off. It might take a few drive cycles and top offs to get to full as it continues to move the air over to the expansion tank.