E34 Collant Issue

[machinehead]

here's another thought.....the little pipe to the neck of the filler joins the radiator just below the top hose and the is water above this level as the rad bleed screw is higher and has been bled so there is no air in the rad when system is hot.

Could it be that the weight of fluid in the system isn't enough to balance out the level?

Is there something really fundimental I'm missing? on other people's car, when the filler cap is taken off does the level in the tank stay the same as when the cap was on, or does it rise when the cap is taken off?

ghead

[machinehead]

Anyone got any further ideas? any at all? before I shoot it....

[billB]

Machinehead

I need your help in explaining what do you mean by saying:
1. I'm still getting air in the expansion tank. Its like when the car is turned off and cools the water level doesn’t balance out and find its natural, even, level as the air in the tank is not escaping, caps open when hot not when cold!
2. I can only think that the aftermarket radiator doesn’t have the tube in the right place and is obscured by the cap. the cap does seal the hole ; again when hot ( under pressure it opens up)..see below.

My question is why is it important to balance and find the natural water level in your expansion tank? Is the car overheating? Is it loosing coolant? What is the exact problem the car has other than this balancing of fluids between the cap and the expansion tank? To sum: If the car is not overheating I won't worry about it.
Just in case I have misunderstood your post please read the following:

A. Please note that the expansion tank cap is like a spring-loaded valve "REACTING" to system pressure. As such it does not have to follow the laws of gravity in balancing the water level as implied above. Thus Its main function (other than the obvious) is to keep the RIGHT system coolant level at CERTAIN PRESSURE.

B. After market caps? Since PRESSURE is the main factor here I would make sure to replace it with an exact cap with the same pressure rating/setting.

C. Due to the relative cheap pricing on caps I refuse the aftermarket even if it was as good as the dealer's.

D. BMWs, at least the 5 series, don't run cooler than other cars in fact they do run on the hot side.

In short: When your cap is sealing coolant and keeping it under preset pressure; it is doing its job. Laws of Gravity do NOT apply here.

Regards
billb

[machinehead]

Hi, spoke to my BMW man today and he did a test on the gas to check its not exhaust gas, and he’s happy the head gasket is ok, which was one of my concerns.

New cap is genuine but not through a dealer. has same part number and manufacturer as the one I took off.

The only thought now is that as it did not do this before the rad was changed, that because the expansion tank is markedly smaller on the aftermarket one this is all it is. He’d never come across this exact issue but he’d said when he worked for BMW he’d seen some 5’s that constantly seemed to have a lower than normal level but were fine when the cap was removed.

The considered opinion is not to worry about it & just keep a check on the level.

Thanks for the help though.

[machinehead]

well, just when I thought that was that, yesterday and today it has started the same thing again. It has been fine for 4 day (~220miles) then yesterday and this morning, exactly the same problem.............