Oil pressure drop followed by engine knocking

Thanks. So why the gradual oil pressure drop at low revs then higher revs.

Does that sound like the oil pump failing? Should I replace the oil pressure regulator?

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Originally Posted by rar110

Thanks. So why the gradual oil pressure drop at low revs then higher revs.

Does that sound like the oil pump failing? Should I replace the oil pressure regulator?

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its not really RPM related its more engine load and speed of oil loss.

a hard working engine with only a litre or so of oil will take out the pistons

a lightly loaded engine with almost no oil will take out the bearings..

it happens due to the change of failure method of the lubrication system.

in the low oil level high load scenario you have enough oil to keep the pressure up so the bearings never really get to metal on metal on the bearings but the oil at the pistons is breaking down and unable to off load the heat from the pistons so the pistons suffer.

in the almost no oil but light load scenario the oil is getting areated so there isnt enough oil pressure (there might be on a gauge but its aerated oil so the surface area of oil in the bearings is no longer sufficient to support the bearing) but enough is being thrown to keep the piston cool enough that it doesnt fail catestropically.

the easy check is to test the oil then do a leak down test followed by vacuuming the cylinder. if it clicks when you put vac over a mid stroke cylinder most likely youve doe the bearing, if it fails a leak down its done the rings, bores and pistons.

unless you get insanely lucky and the noise is the lift pump its going to need a complete strip and rebuild.

Sorry Dave I was talking during the second break down with drop in oil pressure at low revs, raising revs at stand still increased oil pressure and warning light went off. Then over the next 1/2 hr needed higher and higher revs before oil warning light went out. There was no oil loss during this time. The oil level remained full on the dip stick, and oil still looks quite new, after refilling following oil pressure sensor blowing causing the first break down.

Here is a pic of the blown sensor.
https://uploads.tapatalk-cdn.com/202...dbde4bd6c4.jpg

Quote:

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Originally Posted by rar110

Sorry Dave I was talking during the second break down with drop in oil pressure at low revs, raising revs at stand still increased oil pressure and warning light went off. Then over the next 1/2 hr needed higher and higher revs before oil warning light went out. There was no oil loss during this time. The oil level remained full on the dip stick, and oil still looks quite new, after refilling following oil pressure sensor blowing causing the first break down.

Here is a pic of the blown sensor.
https://uploads.tapatalk-cdn.com/202...dbde4bd6c4.jpg

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Typically that would be failing main and big end bearings, as the tolerances expanded the flow rate of oil to maintain pressure is higher. to start with the relief valve closes up until its closed, after that the only way to maintain enough flow rate to keep oil pressure up is to increase pump speed which can only be done by spinning the engine faster.

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Originally Posted by AK83

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.

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yep, my TDi was similar.

And, yeah, no 'oilsafe' on a TDi unless the OP had an aftermarket thing fitted.

The oil pressure switch normally only needs less than 10 Psi to turn the light off. You may have had a low oil pressure problem for a while.
You will need to dismantle and inspect the engine to see what damage has occurred. I would be checking the conrods very carefully as they may be damaged. Crankshaft damage should be obvious . Cam bearings and oil pump to be checked carefully as well.

Good luck

Ian
Bittern

Quote:

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Originally Posted by rar110

Sorry Dave I was talking during the second break down with drop in oil pressure at low revs, raising revs at stand still increased oil pressure and warning light went off. Then over the next 1/2 hr needed higher and higher revs before oil warning light went out. There was no oil loss during this time. The oil level remained full on the dip stick, and oil still looks quite new, after refilling following oil pressure sensor blowing causing the first break down.

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As mentioned , the damage would have been done during the original event.
I suspect the reason your oil light needed more revs to stay off was simply due to the oil thinning as it warmed up. If you started it from cold it would probably stay off again ( not that I would if i didn't have to.
Unfortunately a rebuild on the cards .
Probably no consolation to you , but I have just returned from some semi extreme tracks, no damage to mine or 1 other , but one of the crew ( all D2's ) has managed to lunch 1x rear diff cross pin, 1x front right axle and 1x auto trans within 10 kilometres ,same car....unbelievable ( I suspect previous owner had been driving on road in diff lock for a while )
Bloody annoying for you that a simple part has caused such damage , I've replaced plenty leaking but luckily haven't had one let go.

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Originally Posted by discorevy

................
Probably no consolation to you , but I have just returned from some semi extreme tracks, no damage to mine or 1 other , but one of the crew ( all D2's ) has managed to lunch 1x rear diff cross pin, 1x front right axle and 1x auto trans within 10 kilometres ,same car....unbelievable ( I suspect previous owner had been driving on road in diff lock for a while )..............

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In the early days I drove my POS with an LT95 for about 1000 k's with the CDL on.

Had a slight vibe and some weird tyre wear, but no lasting issues.

Light wasn't working and it only got picked up when I took it for an alignment.

DL

Can anyone recommend a step by step guide for rebuilding the 300tdi? Thanks.

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Originally Posted by rar110

Can anyone recommend a step by step guide for rebuilding the 300tdi? Thanks.

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If you don't already follow Mike at Britannica Restorations on Youtube, you should.
He's got lots of vids on rebuilding them.