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Old 10-06-2021, 17:49   #16
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Re: Perkins 4108 high oil pressure

Originally Posted by Lepke View Post
You can buy a mechanical oil pressure gauge for about $20. Screw it into the port the sender is in and then you'll have a real reading to talk about. A plugged oil line is extremely rare. I'd bet the gauge reading you saw is wrong and the engine has normal oil pressure. A mechanical gauge will verify it.

Engine oil pumps are closely matched in capacity to what the engine needs. So extreme pressures are difficult to achieve without a custom pump. The rear main seal on a 4108 is an old style rope seal. At high pressure they leak badly.
This. Use a proper diagnostic gauge. Iíve had gauges, aviation and marine, poop the bed and give wildly inaccurate readings.
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Old 10-06-2021, 19:04   #17
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Re: Perkins 4108 high oil pressure

I took my Perkins 4.108 out and had it rebuilt. I built a crib on a small boat trailer and ran the engine there before bringing it back to the boat. I didn't have but 10 psi on the oil pressure so the engine went back to the shop.

I can tell you that the pressure relief valve is responsible for 90 percent of the oil pressure. Too little spring force and you don't have enough pressure anywhere in the system.

I don't have a theory on how it could be too high though unless the needle valve got stuck somehow and is not relieving at all. It was just a spring, needle valve and some washers. I guess you could have a really really bad oil filter too.

I have small industrial pressure gages installed on my engine. I've always felt that the pressure indication is a bit of a false thing since you are not really reading the back pressure on the oil passages as much as you are looking at the performance of that pressure relief valve. Oil sending units aren't exactly calibrated instruments either, so I like the manual steam gages.

What does it look like under the valve cover? Are you getting oil up there? If the pressure relief valve is stuck I'm guessing it is spraying oil like a pressure washer into the valve cover. Other than going to the head, it mostly goes through the crankshaft oil passages and bearings. The rest of the lube is splash and drip on the way back to the pan.

As an aside or another data point, after my rebuild, I switched to synthetic oil. The engine did not like synthetic at all... oil consumption went way up, pressures where all over the place. I went back to Rotella 10W40 dinosaur blood and all is well in the kingdom once again.
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Old 11-06-2021, 05:22   #18
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Re: Perkins 4108 high oil pressure

The oil filter I’m using on the remote unit is NAPA Gold 1608, oil is Mobil Delvac 15w40 1300. Both are the same as what the previous owner (who I’m in frequent contact with, very capable and qualified guy) fitted and used with the setup.

I am definitely going to independently verify the gauge reading, I can’t do it until I’m home but will be doing that immediately upon returning. If the reading is correct I have a feeling that the issue is the oil pressure relief valve sticking closed. In that event, and kinda prophylactically until I’m home I’ll be changing oil and filter frequently to try and better lube the valve and give the engine a flush of sorts.

Thanks all for the speculation, consideration and advice.

Edit: I’ll take a look under the valve cover when I have a chance to do so, it doesn’t look particularly sprayed in there that I recall.
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Old 11-06-2021, 06:21   #19
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Re: Perkins 4108 high oil pressure

Sorry, 1806 not 1608. Typo there.
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Old 11-06-2021, 06:27   #20
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Re: Perkins 4108 high oil pressure

The pegged over gauge to me suggests that it is related to more electrical than the internal pressure relief valve suddenly going bad. Bad sensors happen.

You've never indicated that you observed the rear seals leaking when you observed the high pressure. Would agree w/the previous comment that more than likely you would see the the rr. seal w/that much pressure.

This can be a very frustrating repair to track down unless you use a multimeter to eliminate the gauge out of the equation. I've attached a write up on how to test the gauges. If the gauge checks out would replace the sensor.

The manual gauge screwed into the sensor port is the best way to find out what is going on, but will be generally a one and done for that piece of equipment. Don't remember if they were that expensive though, but believe a multimeter is a good investment in a tool that you will use often.
Attached Files
File Type: pdf Testing ENGINE GAUGES.pdf (290.9 KB, 6 views)
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Old 11-06-2021, 06:35   #21
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Re: Perkins 4108 high oil pressure

Originally Posted by Kevin Spacebag View Post
High oil pressure meaning pegged gauge. Not immediately and not constantly, so it’s not only the gauge (though could still be the sender, for sure).

That sounds more like a bad sender or circuit than an oil pressure problem.

In trouble shooting you want to follow TWO trains of though:
What is most likely?
What is cheapest/easiest to do even if unlikely?

Changing the sender and verifying the circuit is cheap and easy.

Even if unlikely do this first.

But also, still could be a flunky gage.

Maybe try this for $20.
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