Potential M52 Head Issue

[Bener 13]

Hi all, 

I've got a really tidy 1997 E39 528i. It's just gone over 100,000km and it's worth looking after (in my opinion).

My issue is that I may have a head issue - I've replaced water pump, thermostat housing, radiator and fan clutch. 

I got the local euro mechanic to do the radiator and fan clutch last week, and it was fine for a week. Then it overheated again on a short trip (not off the scale, but up to the red).

I tested the viscous fan and I could stop it fairly easily with a rubber stick, I'm not sure if that's a valid test but it didn't seem to be that hard to stop. Mechanic reckons it's all good. 

The problem is I'm losing water slowly. I checked on the day it overheated and it was down near the bottom of the reservoir. I really can't see anywhere else the water would be going. I had an idea that it may have been an air lock type scenario (I know they are hard to bleed) but it doesn't make sense that it's losing water. It still seems to be dropping a bit, although it's really slow. Temp has been fine.

Mechanic came and did a Co2 test on it (one of the hand pump things with the blue liquid) and seemed pretty confident it wasn't the head. It has no other symptoms - running mint, no oil in water or water in oil, no smoke. I've had cars with bad head gaskets before and it was a mess!

Anything I'm missing or any suggestions? I can't think of anywhere else the water could be going. And is a head job even worth the cost? If it was a few grand I would consider it but I'm not sure what I would do if it's much more.

 

[hqstu 780]

Was the car overheating before these components were replaced?  Is it still overheating now?

Is the radiator drain plug installed fully?  It may be not be quite right and dripping out under pressure so the moving car and undertray hides in from dripping on the ground?

The new thermostat may be a dud?

The fan clutch is either engaged or not. Centrifugal force throws the viscous fluid away from the "clutch" area and the blades free spin.  It's only when hot (air moving through radiator) and the bi-metallic strip bends does it open the valve and the viscous fluid enters the clutch galleries and locks up the fan (to a point, say 2500rpm or so).  You can hear it when it does...  However when the car is cold and off and the fan clutch has been sitting then viscous fluid drains down around half of the clutch area and the blades feels "stiff" when rotating by hand, but once engine is running the centrifugal force moves it away again and the fan can be stopped by hand.  Don't try and stop it when the fan is "roaring" and air is moving, that would be a bad outcome...

[Bener 13]

>>Was the car overheating before these components were replaced?  Is it still overheating now?
Yes it was, and after the last top up it's stopped overheating.

Will take the bottom cover off and check the plug. Thanks for the info!

I just did that fan test (people say use a rolled up newspaper) because they're meant to be a failure point on the E39. I actually though when the clutch was fully engaged it would be unable to be stopped.

[Eagle 1514]

You haven't specified whether it was pressure tested?

If you have the engine tray on you probably ain't going see nothing dripping. Lots of coolant hoses hoses which can leak like ones under the manifold

[BreakMyWindow 1870]

Yeah engine under tray off and a pressure test. 
 

Can you smell any coolant while driving? 

[Bener 13]

Yep it's been pressure tested with no issues.

Also, no coolant smell. Thanks for the advice, I've got a bunch of things to check now!