Low oil pressure question

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Low oil pressure question

Postby melissar » Sun Aug 12, 2018 11:01 am

Looking at a GB with older (1974) twin Lehman 120s and have a couple questions about oil pressure. Both engines are around 3000 +/- hours. The boat consistently runs about 30+ psi on the starboard engine, 20+ on the port side. (Gauges are inaccurate, these readings are taken at the engines by an experienced mechanical surveyor.) We have oil analyses that show nothing unusual from 5 years ago and 6 months ago and expect a current report this week (although for the current sample, only have 10-15 approx hours since oil change.) We don't expect the new analysis to show any changes. Current owner says boat isn't using oil and we have no reason to doubt that assertion. Engines run well, no knocking or pinging, no scary smoke or sheen, etc. I'd really appreciate thoughts from those of you more experienced than we are -- would you be confident, cautious or run?
Fleur de Lys, La Center WA
Grand Banks 36-427
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Re: Low oil pressure question

Postby melissar » Mon Aug 13, 2018 9:48 am

Anyone?
Fleur de Lys, La Center WA
Grand Banks 36-427
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Re: Low oil pressure question

Postby GB42-267 » Mon Aug 13, 2018 12:35 pm

I'm a bit confused, you make the statement that the gauges are inaccurate. Are they reading 30 PSI and the other 20 PSI, or are corrected pressure readings taken by your mechanic 30 & 20 PSI ?
If the accurate readings are 10 PSI apart, you should suspect a problem somewhere. 30 PSI is within the normal range for these engines, but 20 PSI is on the low side and warrant further investigation. I would consider between 32 - 35 PSI to be normal and indicate a tight running engine. It could be a simple thing as a restricted oil sender port or as bad as excessively worn bearings, you can't tell without tearing into the engine.
the most recent oil sample probably won't show anything, but if there is any significant variation from one engine to the other with such low hours, expect problems. On the other hand, you should consult the mechanic you hired for the survey, he should be able to give you a solid advise on what he see, or at least some pointers.
Bjorn M
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Re: Low oil pressure question

Postby Tom Overs » Wed Aug 15, 2018 5:02 am

Are these readings at tick over or when the engine is heated and running.
20 psi at Tick over isn't anything to worry about and could be caused by several different things up to and including main bearings.

For clarity.... My engine on start up reads 20 psi and will slowly increase to 35psi (running) once the engine has warmed up. I have no idea why but its been doing this since it was rebuilt many years ago.

I would change the oil filters (get good quality ones) run the engine to full temperature 1500 revs and see if they change.

Start with the simple things first.

These engines were used in many different types of equipment with different cam shafts oil pumps and even pistons and con-rods, it is possible that one of the engines has been changed at some point.

Tom.
GB32-390
"Little Ship"

Born to cruise...........once forced to work!
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