Hi guys,

Looking for some input from the knowledge.

After a fortnight standing this BMW has developed a fault with the oil pressure. Basically it drove fine for 40 minutes or so then the oil light and stop engine signs illuminated. A quick check of the oil revealed it to be like water. So much so you couldn't take a reading from the dipstick.

I changed the oil and the car drove fine, maybe a couple of hours worth this time. Unfortunately the problem returned. I'm fairly sure the pressure was low as the car got hot and the top end rattled.

Does anyone have any suggestions on what to check? I should add that the bottom end doesn't knock or rattle. I'm thinking a sticking relief spring on the oil pump, but I also think there may be a nrv and such like on the filter housing.

Thanks on advance.

A lot of these engines had new bottom ends due to bore wear, on occasion the oil pump chain drive nut is not tightened up properly during the rebuild, it can then work loose. The sump needs dropping to check this.

If the oil filter has not been changed for a long time it may have broken up.

I have have had a look on the Bimmer forum but can't find to much about it. Agree with the above as a possibility. BMW had the nikasil problem pre 2000. Maybe join their forum. They seem a good bunch.
Bimmerforums uk.

Hope you don't mind. I have posted you question on the BMW forum. I will keep you informed.

Cheers

Frog

Reply 1,
There is some sort of pressure relief valve in the filter housing IIRC

Cheers for the input guys! And thanks for posting it Frog.

AP1, I don't think it's going be that nut. The car has been with us for > 100k. Quite interesting about bore wash, I thought it was only the V8 units of that era that suffered.

To add a little more to this, the thin oil I mentioned was a mystery. The car's oil was about 8k old and looked fine (checked almost as frequently as the coupé ). So something has happened in that fortnight to thin the oil. I also did the filter which was split in two, again I assume what ever thinned the oil also attacked that?

could it not be some sort of headgasket problem or something else causing oil and water to mix?.

i have seen a car before where the headgasket was gone and the oil turned to watery crap. you could check your coolant to see if it is low or mixed with oil

Should clarify, there's no water in the oil. It was extremely thin and ran like water.

I think these have a water cooled part to the oil filter housing which may cause the water under heat to be injected into the oil:

Usually it works the other way around though.

If its the paper element oil filter housings then its easy to squash the filter or incorectly fit them causing a rattle on the top end and illumination of the oil pressure light.

Further to this,blocking of the oil strainer was common on early engines.

What colour is the oil? And are there any other symptoms ie smoking

If the oil was very thin it's either getting very hot or it's fuel contaminated, does the oil smell of fuel?

This is the oil filter housing:

http://www.bmminiparts.com/DiagramView.aspx?DiagramId=156791&MOSP=47539

If it was fuel to that extreme then the car wouldn't run right.

I would guess the oil is thin due to excess heat caused by a restriction.

The relief valves in the oil filter housings are prone to failing and paper from the element itself can be forced Into the system causing the same loss of pressure.
The oil pressure switch is near the housing around the back iirc so might be worth checking the pressure live.

Re the thin oil. Just had mine serviced yesterday and the oil has only been in for appx 3000 miles and when that came out I was shocked how thin it was. My mechanic says that this is normal as the oil they use is very thin to start with. This I saw when the new oil went in.

From what I gather the Nikasil issue will cause low compression and a lumpy idle. Chances are though that if the car didn't suffer in the early 2000's then it never will as the cause was sulphur in the fuel which has now been considerably reduced.

The oil specced by BMW is a 0W-30 so as other have said it is meant to be thin, especially when hot.

You could have a clogged filter or partly blocked sump pickup. Has the sump ever been off? Excess sump sealant can often find its way into the pickup.

If you do undo the oil filter cap, be careful how you do it. I was lacking in tools and used a large adjustable spanner, which subsequently slipped and put a hole in the PAS fluid reservoir.

BMW lists various different oil thicknesses for the M52+M52Tu, these are:

0w30, 5w30, 5w40 and 0w40.

Castrol Edge (SLX) 5w30 is commonly used by dealers.

We've been using 0w-30 for well over two years now as the main engine oil (Excludes M power and early 123d as a rule of thumb)

Have you actually checked the oil pressure? It maybe only be a sender/lamp problem. If you do have low pressure it will be a problem with the oil pump or bypass valve.

It's nearly impossible for the oil to just thin out that much overnight.

All oil looks as thin as water once its gets hot, it does not mean its not at the correct viscosity. 0w30 is a sturdy oil type, it will thin out much less than most others, 10w40's for example.

Thanks for your input guys. However the decision to break it has been made. Brother didn't fancy spending any more on it. He's already spent thousands.

Scuderia, the pressure was definitely low. Top end rattle and excess heat. Plus the oil was thin when cold. I have my suspicions about what has happened, but I think damage will have been done even if I manage to restore warm oil pressure.

My old 328 used to rattle like hell on idle.
Never did get to the bottom of it.
Prob best choice as there not worth much these days.

I'm gutted for my brother, it was a lovely car. Full respray, new suspension and a mint leather interior. And the best bit, a manual gearbox with great ratios for the engine. But enough was enough, an engine rebuild would be too far, this is worse than a vanos rattle.