3.5l V8 Oil light flickering at high RPM

We're got an ex-ambulance LDV van with the LR 3.5l V8 engine fitted.
Had a bit of a freight yesterday when the oil light started flickering on the motorway. Pulled over to check oil level etc. and couldn't find anything amiss. Plenty of oil in. Only thing that was odd was an HT lead arcing onto the dip stick. Moved it out of the way and it stopped arcing, but still got the flickering oil light. Fine at idle, fine up to around 4k rpm, then starts flickering.
Would a worn pump generally give poor pressure at idle as opposed to high rpm? It's not done it before. Oil is as clean as the day it was changed.

First port of call would be the oil pressure relief valve - they are known to stick but only cost peanuts to change, if the valve is scored you've found the likely culprit. It is easy enough to remove oil pump, so pop it off and have a look, clean it up and reface the pump, put in new relief valve. If that doesn't do it new oil pump might be needed.

Don't forget to fit a new switch also.

Mine gets off road use but I fit a new oil pressure switch every 6 months or so usually, they just keep failing!

Have tried cheap/dear/aftermarket/OEM/you name it and always get issues.

I now have a mechanical guage fitted so I can keep tabs on the oil pressure at all times and especially when the oil light comes on which it often does when the switch gets wet, even after being replaced days earlier.

Anyway, that's a long way to explain why i recommend changing the pressure switch also

Ah, I did see them prv things on ebay earlier. I'll grab one and a switch and have a play.
Is it right that the pump is part of the timing cover on these? So belts off etc. to get to it?

Thanks.

What oil you got in there out of interest?

i go for switch..install gauge,then you know for sure..no guessing.

Not sure of the arrangement on the LDV, but if this is the standard 3.5l the oil pump gears are in the timing cover and the bottom face (the bit that gets badly scored) is bolted on to the bottom. The pressure switch is screwed into that bit. Its brass and has a blade terminal on it (with a wire attached). If you can get to it, you shouldn't even have to take the belts off.

My money would be on that first. If it only happens at high revs, it doesn't sound likely to be the pressure relief valve. that is when you have highest pressure and the valve should be open. When you drop down the revs if it is sticking open you would expect to lose pressure then I would have thought.

jonnyt said:

If it only happens at high revs, it doesn't sound likely to be the pressure relief valve. that is when you have highest pressure and the valve should be open. When you drop down the revs if it is sticking open you would expect to lose pressure then I would have thought.

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Exactly that I reckon. How many miles has it done? Could be the switch, if not I'd say it's the pump (happened on a mate's passat a few months ago, oil light flickering on motorway, plenty of oil, turned out to be a knackered pump). If not the pump it could be things wearing in the engine like bearings etc., increasing the tollerances, allowing more oil through = reducing the pressure, most prevalent at high speed/revs.

As has been said, fitting a pressure gauge is best.