No oil pressure at startup

[waterbound]

I've got a puzzle on my hands-Yanmar 3HMF fails to produce oil pressure at startup. I've replaced the oil pump after determining that it was a little out of tolerance (by spec). No change. I can spin the engine for about 20 seconds (using compression release) and it will produce oil pressure and run with constant 50psi. But let it sit overnight and same problem recurs. Any ideas, guys? Thanks in advance.

[a64pilot]

Change to a different oil fliter, one you have may not have an anti-drain back valve. If this is correct it means that at every cold start, you have to refill the oil filter before you get any oil pressure.
There are other possibilities, but this is easiest to eliminate.


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[waterbound]

Thanks A64pilot- Actually I've remote mounted the oil filter to a vertical position and low, keeping the filter full at all times.

[rwidman]

Originally Posted by a64pilot

Change to a different oil fliter, one you have may not have an anti-drain back valve. If this is correct it means that at every cold start, you have to refill the oil filter before you get any oil pressure.
There are other possibilities, but this is easiest to eliminate.


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That's my thought as well. Even if it has the valve it may have failed. A few dollars spent on a proper replacement will either fix the problem or eliminate that possibility.

[MarkSF]

An empty oil filter will typically cause a few seconds delay in building up oil pressure, not 20. The last time this happened on the Jaguar forum, and the symptoms were identical, the cause was a blocked pickup strainer.

[a64pilot]

Originally Posted by MarkSF

An empty oil filter will typically cause a few seconds delay in building up oil pressure, not 20. The last time this happened on the Jaguar forum, and the symptoms were identical, the cause was a blocked pickup strainer.

That of course requires removal of the oil pan, a loose pickup tube can also cause this, but we are back to pulling the pan again. Usually blocked strainer lowers oil pressure too as of course the flow is blocked.
I'm trying to start with easy stuff first. I'd hate to tell someone to pull the engine and pull the pan, only to find out they were using the wrong filter.
Oil pumps can also loose prime, usually it's old, worn ones that do, but he has a new oil pump, which often means somebody looked at that pick up tube and strainer?


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[gah964]

Originally Posted by a64pilot

That of course requires removal of the oil pan, a loose pickup tube can also cause this, but we are back to pulling the pan again. Usually blocked strainer lowers oil pressure too as of course the flow is blocked.
I'm trying to start with easy stuff first. I'd hate to tell someone to pull the engine and pull the pan, only to find out they were using the wrong filter.
Oil pumps can also loose prime, usually it's old, worn ones that do, but he has a new oil pump, which often means somebody looked at that pick up tube and strainer?


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and while we are talking blocked pick up screens we may as well talk about all journals' and returns ports ,oh boy you guys love these pigs got to love when that copper clogs things up.

[sailorchic34]

While the oil filter is low, if it does not have an anti drain back valve, oil in the engine will flow back to the oil pan via the oil filter. The longer hose run means the engine takes more time to fill the oil passages with oil. While the oil pump will generate pressure it has to get through the system before pressure builds. PLus flow rate is actually pretty low, so that longer hose to the remote filter is working against the OP

I would verify the oil filter is an anti-drain back type. Not all are.

[deblen]

Check the spring in oil pressure relief valve in engine also.

[tdoster]

Originally Posted by sailorchic34

While the oil filter is low, if it does not have an anti drain back valve, oil in the engine will flow back to the oil pan via the oil filter. The longer hose run means the engine takes more time to fill the oil passages with oil. While the oil pump will generate pressure it has to get through the system before pressure builds. PLus flow rate is actually pretty low, so that longer hose to the remote filter is working against the OP

I would verify the oil filter is an anti-drain back type. Not all are.

I would agree with that. Even though the remote mount has lowered the actual filter, the hoses are draining and the pump is working a lot harder to start the flow.

In Alaska, we were using block heaters with pre-oilers and had to actually seek out the drain back type to keep the oil in the pan heated until ready to run the pre-oiler. If you started one without the pre-oiler, it would take a scary long time to get the oil pressure up.

Bypass valve is also an easy thing to check, but probably not the culprit.

[cottonsail]

AutoMotorOiler Motor Oil Pre Oil System-Insta-Lube Kit and Engine Pre Lube System Insta-Lube Kit are pre-crank lube systems.

[John Boor]

Have you checked your oil pressure sender and your oil gauge.

John

[rwidman]

The real question is, When did this problem start? If it just started one day, there could be an internal problem. If it started right after the oil filter was changed or right after the remote filter was installed, the would lead directly to the problem.

[a64pilot]

Originally Posted by John Boor

Have you checked your oil pressure sender and your oil gauge.

John

I have seen the small hole in the pressure transducer clog before, taking a long time to show oil pressure.
A way to verify this is to see how slowly the pressure drops when you turn off the engine, it should drop almost instantly, if it doesn't, that may be the culprit.

[apacit]

I would check the sensor wiring. Mine came of once and the engine wouldn't start.