Hi all I'm in need of your advice again, here goes;

Bought a 95 300tdi back in October which seemed a bit neglected at 170k and was leaking like sieve. Slowly worked way down with rocker gasket, inlet/exhaust gasket, new cyclone and oil cooler pipes. 250 odd miles later she started leaking by the flywheel housing so after a good Google and a bit of a cleanup suspected sump gasket / t-seals. When I stripped these out I found the mains to be worn so swapped big end and mains re torqued everything and refitted the sump. This tamed the leak but didn't cure it and in cleaning the mess up I noticed half of the bell housing bolts missing and it was cracked.

Round two consisted of engine out to fit a new bell housing, re sealed flywheel housing, new rear main seal and HD clutch. Everything back together and she ran sweet as a nut with no leaks (well from the engine at least).

Whilst I was at it I replaced the clock with a cheap oil pressure gauge just to try and keep an eye on things. It showed around 4.5 bar on a cold start and about 1.5 bar on a warm idle varying in between with engine speed. Whilst on the road test I noticed everything appeared normal at town speeds so braved the motorway and the pressure suddenly dropped to less than 1 bar promptly pulled off and everything returned to normal. Put this down to a loose connection on the sender wire as I didn't have any ring crimps and had just wrapped the wire around and tightened the nut.. Checked the standard warning light was working as it should and took the gauge with a pince of salt (first mistake).

Fast forward to the weekend and we set off for the Brecon beacons she drove down without missing a beat, ran around for the weekend seemingly ok except for the pressure gauge dropping at motorway speeds (60-65 at best). Halfway home stopped at the services for a break and all seemed fine. Pulled off and gauge working normally at low speeds dropped again on the motorway but down to zero this time however no standard light lit so figure the gauge wire must have come loose. Then a brief hesitation and she sounded like a bag of spanners. Fearing the worst dipped the clutch and headed for the hard shoulder and called the RAC.

45 mins later they showed and the knocking had gone and just as I started to think I'd imagined it, it slowly returned and back to a bag of spanners. Turned it off and had a quick look around and noticed exhaust gasses in the rocker and dipstick tube which has got me puzzled as to wether it's something I've fooked by doing the bottom end or if it's something else

Any advice or ideas welcomed, also is there anything that could cause oil pressure loss at speed but not at slow speed ?

And how goosed do you think my engine may be spun bearing from oil starvation or something else as surely this wouldn't lead to exhaust gasses in the rocker

Sorry for rambling

Sounds like something serious has happened. If the gauge is new and of a good quality, I would trust it more than your oil light. The Landy I just bough had zero oil showing in the dip stick a year ago. The previous owner drove it for another 400 km like that and when he started it the oil light was still off.

I have heard that there is still a bit of oil in the sump when the dip stick shows empty but can't confirm as yet.

Oil pressure and oil level are two different things anyway, that's why for an older engine, I would have an oil temp and oil pressure gauge on hand.

You should drain the oil to see if there is any signs of any bad shiny stuff in there. Pull the rocker cover and take a look there too.

Thanks for the reply. Oil level was spot on and had been all weekend. What's baffling me is what could cause the pressure to drop off at speed but seem ok at town speeds. Planning to drop the sump and have a poke around tomorrow eve. The pickup pipe was spotless and fitted with a new o ring

My dad always used to say that the oil pressure light was there to let you know it was fooked, because the pressure set on the was so low, the damaged is already done.

what grade oil did you put in?

smell the oil from the dip stick

oh and it was smoking and breathing heavily from the dipstick?

OP, as I said before, the oil pressure and oil level are different things. Surely if you have extremely low oil level the pressure will drop.

Since you have spot on oil level and wondering why your pressure was dropping, that can be caused by a few things like blocked pick up strainer in the oil pan, blocked oil passages, bad oil pump etc.

Only thing that can get fooked by putting in new bearings is if you put them in the wrong way round, blocking the oil holes, but thats unlikely.

When you did the bottom end did you check the oil pump for wear? Could the mesh over the pump be blocked so maybe when you're going faster its just not letting enough oil through relative to engine speed?

Barbados said:

OP, as I said before, the oil pressure and oil level are different things. Surely if you have extremely low oil level the pressure will drop.

Since you have spot on oil level and wondering why your pressure was dropping, that can be caused by a few things like blocked pick up strainer in the oil pan, blocked oil passages, bad oil pump etc.

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i was wondering if he is getting diesel in the oil, making it thin out at high temps

If he was getting diesel in the sump, wouldnt you see it on the dipstick being a higher level?

samc88 said:

If he was getting diesel in the sump, wouldnt you see it on the dipstick being a higher level?

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Yes but if he was a bit lower on oil and the diesel brought it back to the full mark he can't tell.

Another big mistake I see owners make is to put an entire tube of silicone on the oil sump surface when they are installing it.
The excess silicone blocks the strainer and then they wonder why they spun bearings soon after.

The OP will have to do some hands on diagnostics, the variables are many.

I tend to put a light smearing of hylomar both sides of the gasket to avoid that problem of chunks getting round the engine

Barbados said:

Yes but if he was a bit lower on oil and the diesel brought it back to the full mark he can't tell.

Another big mistake I see owners make is to put an entire tube of silicone on the oil sump surface when they are installing it.
The excess silicone blocks the strainer and then they wonder why they spun bearings soon after.

The OP will have to do some hands on diagnostics, the variables are many.

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esp if he has something up where it's passing stuff by the pistons and making it breathe heavily.

hard to say really without having a look

Hi guys thanks for your comments oil level was spot on and fresh 10w40, the strainer was spotless and tbf the silicone was used sparingly, was neurotic about checking levels every 50 miles or so and checked the standard pressure light was working as it should every fire up. Had convinced myself it was a dodgy pressure gauge wire loosing connection with the airflow at speed but seems it was working after all... It'd covered about 300 miles since the bearings had been changed when it let go.

Must admit I didn't check the oil pump when I was in there as did them on my back under the car.

Puzzling thing for me was it started back up again around 45 min later when the rac arrived with no knock although it started to return after a few min as it warmed up again while limping off the motorway so switched it off and waited for a flat bed.

Plan to drop the sump tomorrow eve and have a look, how's best to go about checking the oil pump or is it a pull the engine and check on the bench ?

trax said:

smell the oil from the dip stick

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What would I be looking for here diesel ?

trax said:

oh and it was smoking and breathing heavily from the dipstick?

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When I initially stopped lifted the dipstick to check level and noticed exhaust gasses coming up the tube so opened the filler and seemed to be excessive in there but she wasn't running at that point so hard to tell how hard it was breathing. Had only just had a new cyclone if that helps at all

yeah i was thinking diesel. try running it and remove the oil cap.. is it breathing really heavy?