oil circuit question

for about a year now the oil pressure light has taken abou 5 seconds to go out on a cold start up, I have put this down to a faulty oil flow non-return valve to the head being jammed/ faulty. I don't even know if the M30 has one of these though and I can't get any info out of the web on it either.

As I'm doing some other stuff to the oil filter head I have taken it off and its on my bench at the mo, I can't see any non-return check valve in there?? I can see the thermostat valve for flow to the oil radiator and the bypass valve for if the filter gets blocked.

Does anyone have any info on the oil circuit in the M30? My car is 1981 but had a replacement engine by a PO.

yeah, always used a genuine item, wouldn't think of doing anything else. Maybe I just have a faulty filter then as I think this problem started just after I put a new filter on. Hard to tell

I can't see where the valve would be in the filter though, surely its just a cylinder of filter paper around a metal core full of holes. Unless the filter paper is one way filter paper!!?

Having had a poke around I reckon maybe the filter bypass (pressure relief valve) is slightly leaky. This valve is there so if the filter gets blocked the filter will get bypassed and the engine will still get oil, albeit unfiltered. As such it directly connects the upstream side of the filter head to the downstream and a small leak would allow all the oil in the head to flow backwards through the filter head without needing to pass the filter (surely the resistance of passing through the oil filter paper is enough to maintain a reasonable hydraulic head?)

Will test by blocking off the bypass valve, a 2 Kroner piece just fits

that's good to know you are in the same boat with no ill-effects, I assume your cam is not wearing away like butter?? Surely this cannot be designed like this though.

My VW has a check valve (fitted inside the spin-on filter) which prevents the oil flowing back into the sump (through the filter) out of the head, ie on start-up the head is already full of oil and is pressurised almost instantly on start-up.

The M30 has a filter cartridge and so no obvious home for a nor-return valve, which is what led me to assume there must be some kind of check valve in side the filter mounting.

Maybe not then...

cheers for the roadfly tip, you're right this has been discussed at some length both for the earlier (pre E34) M30 engines which had a canister which hung downwards and for the E34 canisters (and presumably highlines?) where they point upwards.

consensus appears to be that the earlier filter canister heads came with a bypass valve (to allow oil to bypass a clogged filter) and later heads came with a bypass valve and a non-return check valve (which commonly fails). This is because the canister points upwards and so empties if the return flow is not checked.

The earlier canisters remain mostly full. 5 seconds delay on these engines seems to be within normal expectations. It is this article from the BCG tech articles that caused me to worry. Cos I've checked my sender and checked my banjo bolts and the pump delivers pressure fine.

http://www.normgrills.net/bcg/Engine_Service_FAQ.html#Anchor -Oil-49575

do you mean the banjo bolts with the circle groove cut in them (ie banjo bolt plus loctite)??

if so then that's the first thing I updated on my car when I bought her.

Update:

put the oil filterhead back on the car and replaced the oil pressure sensor with a VDO guage sender, same symptoms. I think its time to ignore it!! Once I get the VDO guages in I'll be able to read the pressure at the sender from start up anyway.

Would a thicker oil or a thinner oil be better for rapid oil circuit pressurisation?