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‘97 2.5 - oil leak frustration- identifying source

2723 Views 8 Replies 5 Participants Last post by  dave3d
Hi guys,

Writing this post from a place of utter frustration. Since early October I’ve been on a quest to rid my DSE of all oil leaks. Which has include renewing:

Rocker cover gasket
Engine oil sump gasket
Oil cooler pipes
Auto gearbox oil cooler & pipes
Gearbox sump gasket (new filter too etc)
New oil filter house gasket

Plus new water pump and viscous fan and a bunch of other little jobs!

Yesterday evening I went for a test drive to ensure everything was put back together correctly, which it was. But when I got home home black oil was ementating from or around the area near the oil filter housing block. It wasn’t a lot but progressively got heavier after another run out. It’s dripping down off the sump and onto the front diff. I had fitted a new oil filter housing gasket (STSC3337) which is a metal type. But, the leak appears to be above the filter mounting area - what is above the mounting area but not as high up the block as the rocker cover gasket? Should I have used additional sealer on the metal gasket? I torque’d all fittings per the value in the workshop manual.

I am so disappointed and the idea of going out there and taking it all to pieces again depresses me. Or maybe I had set my sights too high.

Does anyone one else know the M51 engine well, any pearls of wisdom to share? I maybe be down to just one leak now.

Encouragement needed ☹

1997 DSE auto - sold in Spain new.
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Never had anything to do with a diesel but near to the oil filter is going to be the oil pressure switch and possibly an oil pressure relief valve. Both these are known to leak on the V8, and I've had leaking oil pressure switches on other cars in the past too, so it might be worth having a look at those.
I have had my diesel for a long time but would not describe myself as an expert.
However talking generally, the oil leaks I have had in the past are :

- the turbo oil return pipe on the opposite RHS. Easy fix with new silicon hose and clips.
- oil cooler and pipes: the crimping of the hoses on the pipes is not very good even when new. Oil cooler connections never unscrew without shearing the pipes so a new cooler needed every time.
- rocker cover gasket: I removed the EGR and vacuum pump and fitted a blanking plate at the end of the rocker cover. The molded rocker cover gasket was a pain getting it correctly in place. I had oil leaks from the rocker cover as a result. It is easy to get it not seated right. I did it again by coating the gasket and rocker cover with a non setting sealant (red hematite) to hold it in place upside down in the cover while I bolted it to the head. I found this was the easiest way rather than fitting it to the head first.

From what you have said I would think your rocker cover gasket is the culprit. I would clean up the area with a petrol soaked rag so it is easier to see where fresh oil is coming from.
Also when you change oil filter it comes with several o-rings which you need to lube up so they don't pinch.
Also check the plastic cover for the oil filter housing that you tighten down with a big socket. It may have cracked if you have over done it.
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Thanks Richard and Dave.

spent the day on the leaks, I think test driving it yesterday spread oil all over the place making it tricky to identify where the source was.

I cleaned everywhere and re-torqued the oil filter housing bolts, all four, then ran the engine until hot. No oil at all appeared from above the oil filter housing or around it. My theory of oil coming down from above was wrong, as the rocker gasket is perfect - no leaks at all. I think that is problem 1 of 2 solved as it’s remained dry all day.

But...oil has appeared around the sump bolts directly under the oil filter housing!...problem #2.

I’ve checked and gently tightened the sump bolts, torqued to the correct value but still oil persists in coming from one bolt and running down the sump. I used a new gasket and the proper sealant, what do I do? Take the sump off and do it all again? ...guess so.
Clean everything, probably not an easy job, and then check after a short drive, you should be able to see whereabout it leaks from.
After more driving it’s the sump - and oil filter housing.

For this metal gasket (actual one pictured) is sealant needed too?

Auto part
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I have never needed to disturb my oil filter housing. It has never been off since new, 18 years.
As a general rule though, I always put a coat of non-setting sealant both sides of gaskets and then spread it out thinly between finger and thumb; whether it is a p38, lawnmower, outboard or motor bike.
As long as you don't put too much on it won't do any harm.
Can you see if the oil is passing along the bolt threads or from the gasket faces?
I have had my diesel for a long time but would not describe myself as an expert.
However talking generally, the oil leaks I have had in the past are :

- the turbo oil return pipe on the opposite RHS. Easy fix with new silicon hose and clips.
- ................................................
Dave, from where did you buy that silicon hose? any web link, please.

Sorry Kapila, I didn't make a note of where I bought it from or even what the size was. It was quite some while ago. It was a UK Ebay supplier though.
It was just a section of straight tubing, it wasn't a part specifically for a P38.
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