Expansion tank empty twice in 4 days.

[NoSmokeNoPoke 24]

I’ve only just recently bought my 535D and had a warning on the dash to top up coolant. Any filled the expansion tank and drove for about 400miles and again it’s empty. Is there any common issues with these that I’ve missed? It’s only done 110k. Is it possible a fill of the expansion tank wasn’t enough to fill the system to the required level? At what level does the warning in the dash alert... 

 

thanks in advance. 

[Mashed Potatoes 528]

It would go off when the bottle is low. It's either an air lock or a leak. More than likely a slow leak if you've had nothing major done to the engine recently. A pressure test will show any kind of leak in the system. Stick some cardboard under it when you park up overnight and see if there's any wet patches on it in the morning. Just make sure it's hot when you park it up, a pressurized coolant system will give off more of a tell tale if there is a leak then a stone cold one.

[LukeH 46]

Egr cooler is a favourite to leak on these, and also the connection on top of the cooler.  It might not be that obvious at first but I've had a few of these leak in the past so worth checking. 

[NoSmokeNoPoke 24]

Thanks guys. 

[Mad4it 1]

I have a similar issue but I noticed dried coolant spray on the top hose. Upon inspection radiator cowling wet from the top down (RHS when viewed from the front). Today I removed the bonnet catch panel and the top radiator cover. The leak is from the join in the vent pipe. I will either try recrimping the original clamp or replace with a fuel line clamp as a temporary fix until I get a new vent pipe assy from main stealer.

Will update tomorrow on the "fix"

[711jrp 328]

As said egr cooler, I also had the heat exchanger leak, it's under the oil filter and the leak shows up as coolant on the n/s engine mounting.

[Carl-e34 518]

If no external leaks ....  How about the heater matrix ?

[Mad4it 1]

As promised,  update on the coolant vent pipe leak and attempted temporary fix. Put an additional pipe clamp on the very end of the rubber hose pictured in previous posting. Might have gotten away with it if I hadn't attempted to fit the small diameter pipe back in the cowling clips. Tride to replace the plastic pipe with copper brake pipe but pipe needs to be about 7mm OD. 2nd option was 2 x 8mm plastic in-line connectors and a 7.6mm bore fuel injection rubber tubing and fuel line clamps (14mm). The in-line connectors came with 12mm clamps. just big enough to go over the OE hoses but too small for the new repair pipe.  So far it is proving to be watertight. Enquiry placed with Cotswold BMW last night to order a BM OE replacement. 

[NoSmokeNoPoke 24]

EGR cooler pipe was split on mine. All good now.