Pegging Our Oil Pressure Gauge

Below are two emails I wrote to the Tayana Owner’s Group, which, by the way, is a great resource for Tayana owners, owners of similar boats, and those that dream of owning one. As they deal with some engine problems we encountered over the summer and can be instructive, especially about actually following instructions, I thought I would share them both here, slightly edited.

July 24, 2015

I should start off by saying I have very little knowledge of diesel engines or any engines for that matter. My experience stops with oil and filter changes, dealing with the alternator belt, and swapping out the impeller.

So, sitting on the hook in St. Michaels, Maryland, today, I turned on our engine, a Yanmar 3JH4E, intending to charge the batteries (something we have to do once or twice a summer when we are not moving too often). I usually put the engine in reverse at about 2000 RPM against the anchor. Today, as soon as I gave the engine the slightest bit of power, after putting it in gear, the oil pressure gauge completely pegged.

Initially, I shut it down, waited a few minutes, and tried again (my default action when I have no clue what to do). Again, I had the same result. However, I kept the engine in reverse for a while. Then, I moved the throttle ever so slightly forward. The RPM came up without the oil pressure pegging. I continued to do this over the next three or four minutes, eventually getting to 2000 RPM. Whenever I tried to just push down on the throttle, though, the pressure gauge would peg again. When that would happen, I would just back off and inch up again. So, now I am about an hour into charging with the pressure gauge holding steady.

I figure I will try again tomorrow and do an oil and filter change (last did one about a week and 10 engine hours ago). Beyond that and calling in a professional – something I am loathe to do – I do not have much of an idea how to proceed, but am game to try. If anyone has any advice and, especially, could offer a step-by-step troubleshooting list, I would be much obliged. I will certainly do some research over the next 24 hours and see what I can come up with on my own. Fortunately, I do have access to a car for the next two days, so I can run out to get a mechanical pressure gauge to run a test, once I figure out how to run said test.

Anyway, I appreciate your help. And I will let you know what the outcome is.

 

October 16, 2015

Back in late July, I had a problem with the oil pressure gauge on my Yanmar 3JH4E pegging. Not knowing anything about engines, I turned to the wisdom of the group here. Several of you gave me some good advice and shared your experiences. I figured I would share the eventual outcome of the situation.

Much of the advice from the list mirrored that from Nigel Calder’s Marine Diesel Engines,  pp. 128-132. Both sources recommended working through a five-step troubleshooting list starting with the gauge itself and working back to the sending unit. Further, all suggested it was probably not a problem with the engine as high pressure is only a remote possibility.

Being a bit thick-headed, inexperienced, and poor with directions, I jumped to the fifth step: testing the sending unit (and oil pressure) itself with a mechanical gauge. I purchased one from Harbor Freight for 25 bucks. Then, I spent the better part of an afternoon getting the sending unit off the engine and installing the mechanical gauge in its place. Then, we fired up the engine and found that the oil pressure was just fine.

Knowing that it was not a problem with the oil pressure itself and that we could now move the boat was a relief. But it obviously did not identify or fix our problem. So, I finally turned methodically to the troubleshooting list. I first checked the voltage from the gauge positive to a ground and found 12 volts; we passed there. Then I disconnected the sensing line from the gauge and the gauge pegged, meaning the gauge itself seemed to be working. Next, I confirmed that the gauge worked by attaching the sensing line terminal to the negative terminal, causing the gauge to read 0, which confirmed that the gauge was working fine. Then I tested the sending line itself and found it to be faulty. So, in a roundabout manner, I had identified the problem.

Rather than fix it at the time, we continued on with the last three weeks of our summer cruising, planning to replace the sending wire in the offseason. I am now getting ready to do just that. I do not expect to have any further issues, but if I do, I will post an update to the group.

Thanks to all of you who helped me out at the time. It was a relief to have some knowledgeable folks walk me through it. Calder had all the information, but reading about the process from multiple folks on the list allowed me to actually understand what he was saying in the book (which, when I read it over now, seems obvious enough, but was not at the time).

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