Oil pressure drop followed by engine knocking

**rar110** · 3rd April 2021, 11:39 AM

Looking for some advice on what has happened to the 300tdi in our 1998 D1.

First what happened (if relevant) was the oil pressure switch plastic top let go and emptied oil out into the engine bay. The motor seemed to quickly shut down automatically when it detected a drop in oil pressure.

We dropped out the remaining oil, replaced the switch, refilled with new oil and a new filter. The car started and ran fine for about an hour.

Then the oil light started coming on at idle, then soon after at higher revs, then at driving revs followed by en engine knocking sound. When the oil light stayed on knocking sound started I pulled over and shut down the motor ASAP.

I assumed the oil pump must have died and oil starvation has caused the engine knock. But would appreciate any other advice/suggestions about what needs to be done.

The motor is original, with 200,000km. I’m the 2nd owner and know the original owner. It’s had oil and filter changes every 5000km.

Thanks.

**alien** · 3rd April 2021, 12:44 PM

Possibly damaged a crank or big end bearing when it was starved of oil the first time.

**loanrangie** · 3rd April 2021, 04:35 PM

Agree with Kyle, it would shut have down because of near seizure as there are no electronic controls to protect the motor.

**Blknight.aus** · 3rd April 2021, 04:46 PM

I shall quote the from the book of lubrications

"he who is without oil shall throw the first rod"

Nulon 10/40.

**Tins** · 3rd April 2021, 05:08 PM

Sounds like it's rebuild time.

I'm curious about the OPS blowing out. Pretty uncommon, I would have thought. Could the PRV have malfunctioned?? Just speculating.

**rar110** · 3rd April 2021, 07:01 PM

The strange part is that after oil dump incident and refill, it ran as normal. No smoke, strange noises or loss of power.

So what am I up for, new bearings and maybe new crank. Is that it do you think?

**rar110** · 3rd April 2021, 07:06 PM

PRV? Pressure relief valve? Where is that?

**Tins** · 3rd April 2021, 08:21 PM

Originally Posted by rar110

PRV? Pressure relief valve? Where is that?

Hard to describe without pics, which I don't have ATM, but it is in the front cover, it comes in from the bottom. I stress that I was speculating, but if it did stick shut it may explain the pressure switch fail. I consider this unlikely, but I put it out there.

defender081.jpg

**AK83** · 3rd April 2021, 09:43 PM

Originally Posted by Tins

Sounds like it's rebuild time.

I'm curious about the OPS blowing out. Pretty uncommon, ....

Maybe uncommon, but not unheard of.

I had an XF Falcon same problem, not plastic IIRC, and also one of my earliest cars, can't recall exactly but it was either the Mini(72) or one of my first P6B's same issue.
Falcon was the most annoying out driving whilst at work.

My Tdi OPS leaked like a sieve too, but not enough to spill the engines guts out, just annoying constant large drips. I gooped it up with some orange coloured Permatex stuff, held for a few months.
Then of course on the Tdi, oil retaining things start to fail in procession .. oil cooler thermostat o ring, then vacuum pump core plug(orange good still holding OK) ... I got about about 18 months of respite, and finally the front main.

As loanrangie said, tdi doesn't have any way to stop motor if oil pressure fails.

**Blknight.aus** · 3rd April 2021, 11:56 PM

how they come to a halt depends on a myriad of factors,

if your running it lightly it will take out the big ends from lack of lube pressure then the mains before you get bore failure.

if you get it just in time, the big ends will be damaged but may not have fatally failed as the displaced bearing material squishes up against the side of the rod and the bearing journal on the radiusing of the crank keeping the oil pressure up and the bearing metal sort of in place. After a while the extruded material gets knocked clear and all of a sudden you've got catastrophic big end knock.

if you're lucky in this situation if your crank was on nominal size you can sometimes get away with a minimum undersize grind and max bearing sizes but thats the last build you get on that crank.

if your running hard it will take out the pistons as the lack of oil prevents adequate cooling before the oil pressure drops off.

If you catch it just in time there will be a build up of material helping hold the piston(s) in line in the bore, with new oil once thats "washed" away you get piston slap.

on the list of also rans is....

valves and rockers seizing and not reseating till the valve meets the piston and gets slammed home.

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