I think I'm answering my own question but I'm delving outside my comfort zone!
So back in May I bought a damaged repairable 2011 Caddy 1.6TDI, non runner 81K genuine miles (MOT and condition back it up). What a bad decision that was. The damage was the easy part but the reason it wouldn't start was a dodgy earth to the starter.....
Anyway damage repaired take it for a run, fine for 15mins but then got the low oil pressure light. Did a few more short journeys and the dreaded glowplug light...That turned out to be 2 x failed injectors, sorted that then it dumped all its coolant. So a new radiator has been fitted, however the low oil pressure light comes on when warmed-up. Got a pressure gauge and plumbed that in, 24psi when cold (should be 29psi) and quite a lot less when warm!
Have removed the sump this week with a view to replacing the oil pump but there is evidence something wasn't right before. The oil pump is powered by a toothed belt from the crank. Took the oil pump off and it looks fine, no worn lobes and makes a nice squelchy sound. Belt looks fine with no teeth missing...Hmm its a DAYCO belt dated 2017 (van is 2011). So me thinks the oil pump is probably recent. So that must mean the big-ends / main bearings are worn??
I'm tempted to take the "big-end" caps off and see the state of the bearings, I assume if the crank isn't scored but if the big end bearings are then I can possibly just replace them (That might sound naive!!). I guess I will have to put the caps back in their original position / orientation and replace the bolts (assume stretch). If they look fine then I guess it could be the main bearings, but I assume they can't be replaced without removing the engine?
I do realise that the low oil pressure could mean that the top end inc turbo may have some future issues but I also realise that buying a second hand engine can also be a gamble let alone the fact that I don't really want to go to the extent of swapping it time/lack of experience...edit1 AND MONEY!
Be grateful for your thoughts.
edit2: It doesn't smoke when running and yes there were some bits of fine metal when the oil was changed.
I've subsequently watched some You Tube vids and both bearing tasks look doable. Noted that a couple of the big-end bearings do have minimal side to side movement which seems normal, not sure if the other two are sticking. None have any upward movement.
have you tried a compression test to eliminate worn or damaged rings?
scs
Thanks scs.
No I haven't..But I've started at the bottom thinking faulty oil pump = low oil pressure and wondering if worn crank bearings could be the cause.
Diesel engines usually have fairly robust bottom ends due to the high compression diesel engines have. I do know of a diesel engine that required an engine rebore at fairly low mileage although that was a Vauxhall.
scs