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Old 07-14-2013
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Yanmar Oil Pressure Pegged

I have a 1992 Yanmar 3GM30F motor with ~670 h on it. The past few times I have fired it up, the oil pressure gauge pegs around 85 psi for about 5 minutes then drops to ~50 PSI (mid gauge). Throttle up and the pressure rises some (10 PSI).

Oil level is fine, changed filter at end of last season on the hard. I don't think it is the gauge or pressure sensor since they do end up operating once the oil/motor warm up. My gut feel is it it is the oil pressure relief valve unit.

Next w/e I will change the oil filter again to see it is a plugged filter (doubt it). If I have to change the oil pressure relief valve, is this a simple job? Is the piece costly? It's located in the Oil Filter house base, correct?
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Old 07-15-2013
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Re: Yanmar Oil Pressure Pegged

What weight oil? If it is too heavy (viscous) the pressure will build up in the manner you are seeing until the oil heats up.

If the weight is right I think it's more likely your pressure sender is "off" than the relief valve is at fault.
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Old 07-15-2013
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Re: Yanmar Oil Pressure Pegged

Quote:
Originally Posted by fryewe View Post
What weight oil? If it is too heavy (viscous) the pressure will build up in the manner you are seeing until the oil heats up.

If the weight is right I think it's more likely your pressure sender is "off" than the relief valve is at fault.

I am using the same oil I have used since day 1, Rotofella (sp?) 30 Wt. If Pressure sender is "off" wouldn't it not work once the motor is warmed up? When the motor is warmed up, the gauge appears to read fine.

Thanks for the response.

DrB
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Old 07-15-2013
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Re: Yanmar Oil Pressure Pegged

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Originally Posted by DrB View Post
---

Oil level is fine, changed filter at end of last season on the hard. ---
Did you change the oil as well? Oil can degrade over time as well as from usage.
Doubt that that's the cause of your problem though.
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Old 07-15-2013
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Re: Yanmar Oil Pressure Pegged

I'd pull the sender and clean it as a first step.
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Old 07-15-2013
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Re: Yanmar Oil Pressure Pegged

Quote:
Originally Posted by fryewe View Post
I'd pull the sender and clean it as a first step.
If you can get a mechanical gauge as a test you might try that before ripping into the engine pressure relief valve. Some oil filters, maybe all, have pressure relief or by-pass valves. Maybe try a different brand and make sure they meet the engine specs.

Paul T
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Old 07-16-2013
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Re: Yanmar Oil Pressure Pegged

When troubleshooting anything try to split the system in half and isolate the problem to one side (of the half) or the other. In this case the problem could be in the engine that the pressure IS too high, maybe caused by blocked passages? Or, it could be indicating too high caused by the pressure monitoring system (sending unit or gauge, etc.). I'd split the system between those to systems, the engine and the monitor. As stated above, get a mechanical pressure gauge and put it in where the oil pressure sending unit was. if you get the same indication, you know it's in the engine. If your nearly due for an oil change I'd start there though. Or if the problem showed up right after you did one, replace the oil filter (may be a defective pressure bypass in the filter).
What did the pressure used to be? Used to be 55 then dropped to 20 after 5 min? In other words is it a 30 PSI even gain? If so I'd look at wiring, might be getting extra resistance into the monitoring system from a poor connection.
Good luck.
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Old 07-16-2013
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Re: Yanmar Oil Pressure Pegged

Your first test is to get a mechanical oil pressure gauge and remove the oil pressure sender and put the gauge in its place. Get a true and accurate reading and then you can go forward.

This little cheap one from Harbor Freight is only $24.99 and it will do you just fine.

Engine Oil Pressure Test Kit



You can see the various little fittings that will include the one you need and you just pull the sender and screw the tester in the place of the sender. If you determine that the pressure is actually high you need to find where the obstruction is before you run the engine too much, check the pressure regulator and hopefully that will be it, also change the oil and filter. Let us know if you have any questions or when you discover the issue and fix it, what it took to get it right. My guess is that it is the sender or the gauge.

Side note, you can replace the original Yanmar gauge and sender with a Teleflex sender and gauge. You do have to replace both, because the sender from Yanmar is proprietary and will not talk to other gauges and the gauges will not talk to other senders. If you decide to replace the gauge and sender with the MUCH less expensive Teleflex unit the cost of the two, sender and gauge will be less than the Yanmar sender alone.
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Old 07-17-2013
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Re: Yanmar Oil Pressure Pegged

It's almost sure to be the pressure sender. My engine starts at 45 psi cold and when hot drops to nothing. A little rev up and it goes back up and stays then drops again and so it fluctuates.

I have driven for hours with the gauge just above zero and the proof for me that it's the sender is that the buzzer works off a different sender and even when pressure is effectively zero, the buzzer doesn't go off and the engine runs just fine.

I'll get round to a new sender one day . . . .
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Old 07-17-2013
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Re: Yanmar Oil Pressure Pegged

Electrical oil pressure sending units typically work by changing the resistance in proportion to the oil pressure. As the oil pressure rises the resistance, in OHMs, goes up. This change in resistance may not be linear. The path of current is likely from the negative terminal of the battery and negative bus through a ground wire to the engine block. Then through the oil pressure sending unit where the resistance is varied with the change in oil pressure. Continuing out a single wire to the oil pressure gauge and finally out through another wire to the positive bus and to the positive side of the battery. Any poor connections along this route will add resistance to the circuit and show up as a higher then normal reading. This, of course is simplified and your system may be different. Don't be surprised if you remove the sending unit to check the pressure and it is ok, then reinstall the sending unit only to find the problem went away.
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