Low oil pressure

[Jakub]

So for almost a year I am trying to bring long term sleeper car to life. One of many but by far biggest problem was corroded engine block. I managed to get other block and do the swap. The car has 18.000 miles and condition of pistons, bearings, rings and other internals would be testament to that.

However, since engine block swap the oil pressure is running low. It used to be 80 at 2000 RPM now is 40, with just touch above control light on idle.
I use mineral 15W40, changed oil already and replaced the pressure senders so neither oil nor measuring instruments are at fault I think.

What did I do wrong?

[Michael]

The old oe sending units were calibrated for a different engine(maybe a different car gauge, I don't remember) and always read high (pegged at 80). A newer sender will read about where you are at, 45 to 50 at higher RPM, around 15 at idle when warm.

If you don't trust the gauge you can always hook up a tester to verify true pressure.

[Jonathan]

Any particular reason you're using 15W40 oil? That might be a little thin. I think halfway up the gauge is still a little low even for the replacement (i.e. better calibrated) gauges.

I started my car the other day and this is how the gauges looked. It was probably just above freezing that day. I also use 20W50 in my car. Manual says that's better suited for conditions always above 20 deg C. Well, that's normally the case when I drive it. My oil pressure needle will sit around 3/4's or so, but not pegged.

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[Jakub]

The oil is same brand, same viscosity as before incident. No matter if it’s new or old sender the measurement is same. The problem has to be within bowels of the engine.

Before I commit myself to taking engine apart again perhaps someone will have the answer.
Personally I have some suspicion where to look but will say nothing as not to suggest anything.

Below pictures, before and after engine failure, same road conditions, similar ambient temperature, warmed up engine.
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And this is what I suspect cause block failure in the first place.
When I’ve got a car there was huge mouse nest under manifold. Ammonia from their piss might have did the job.
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[DMC-Ron]

Jakub,
when you did the block swap did you transfer the oil pump? Broken spring on the pump pressure relief would cause a lower "top end" pressure.

Bypass at the oil pump pressure relief (relief piston not completely sealing closed) could cause lower operating pressure at all RPMs. But this would be true for any bypass in the engine as well (such as a main bearing).

Ron

[Jakub]

Thanks Ron,

I did transfer the old pump to new block. Can't remember about the spring but then again replacement was caused by block crack or rather hole, there was nothing wrong with the pump to the very end. I will put oil pump on my list of items to check when disassembling engine.

the hole was big enough to put finger inside water jacket,

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[David T]

Get a mechanical pressure gauge and install it right where the sender goes. You need at least 10 psi at idle and for every 1,000 RPM's you should see another 10 psi minimum. At 2,000 RPM's that would be 10 + 10 = 20 psi minimum. On a normal PRV it should be around 30, cold even more. Do not expect the dash gauge to give an accurate reading, it is good enough to say you either have pressure or you don't. The warning light is a better indicator. If it lights up or flashes, your oil pressure is too low. That is assuming the wire going to the sender (on the left side) is not grounding out because the insulation is burnt off.

[tommyrich]

There is an "easy to overlook" (I did) o-ring between the block and middle section of the engine (piece with the engine mounts). It is part of the oil pump passage. When I reassembled, there was very low pressure until the oring was installed. Just something to check...

[vwdmc16]

I'd see what a quality external oil pressure gauge says before tearing into anything. It's like getting a second opinion.

[DMCMW Dave]

There is an "easy to overlook" (I did) o-ring between the block and middle section of the engine (piece with the engine mounts). It is part of the oil pump passage. When I reassembled, there was very low pressure until the oring was installed. Just something to check...

I've seen that once. In that case, it was ZERO oil pressure. Really scary.