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Old 22-09-2016, 11:10   #1
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Oil pressure. Optional or necessary?

I own a 1986 Catalina 27 with a universal m_18 diesel in it. My instrument panel only has tach, fuel, temp and volt gauges. There is what appears to be an oil pressure sender installed on the engine by the starter, but it doesn't seem to do anything because there's no gauge. I'm wondering it it is necessary to have an oil pressure gauge with the other instruments?
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Old 22-09-2016, 11:16   #2
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Re: Oil pressure. Optional or necessary?

I think, in general, the fancy panel option for an engine comes with a gauge, the cheapo option comes with it just wired to an alarm (light/buzzer).

Its certainly something you want to know about!
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Old 22-09-2016, 12:03   #3
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Re: Oil pressure. Optional or necessary?

You know I think it is very common for a sailboat to have no other instrumentation other than a tachometer, my 4JHE has a low oil pressure and I assume high temperature alarm, no gauges.
When you first turn on the key, you should get an alarm, this alarm should go off very soon after the engine starts, that is the low oil pressure alarm, I think what you are mistaking for a transducer is actually a switch that operates the low oil pressure alarm.
I will likely one day add a gauge, but the alarm is the one I consider the most important, unless your watching the gauge very often
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Old 22-09-2016, 12:19   #4
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Re: Oil pressure. Optional or necessary?

Definitely add a gauge, lets you know if the oil level is low (sucking air) or the bottom end is getting worn. If you're under way and the alarm goes off, the engine is already toast.
Strange but true, on my old Ranger pickup with the Pinto 4 banger, there was a low oil LEVEL float sensor that let you know if you were 1.5 qt low. You would think they would have added that to a $10k marine engine.
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Old 22-09-2016, 13:10   #5
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Re: Oil pressure. Optional or necessary?

The engine will not be toast just because the oil pressure warning sounds. Just like the gauge, it tells you that you have low oil pressure and better shut the engine down ASAP and find the cause. Depending on the load, an engine can run from less than a minute to several minutes safely without oil pressure. The engine could already be toast because of wear or just fine with a pinhole leak in the line that's allowed oil level to drop. The benefit of warning horn is that it will alert you as long as you can hear it. A gauge can show trends and actual oil pressure but, unless you look at it religiously, won't grab you by the ear and tell you that you have a problem. An ideal system would have both a warning horn and a gauge. Wouldn't start an engine without at least a warning horn.

As A64 pilot said, if you don't hear a warning sound when you turn the key on before cranking the engine that goes away almost immediately after the engine starts and you don't have a gauge, you don't have anything telling you if you have low/no oil pressure.
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Old 22-09-2016, 13:23   #6
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Re: Oil pressure. Optional or necessary?

Gauges are good tools to show pending engine problems, but alarms are probably better for people that don't view their gauges often. I have both.
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Old 22-09-2016, 13:29   #7
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Re: Oil pressure. Optional or necessary?

Interesting. First time I hear there is no oil light.

Upgrade. It is just a bulb. Cheap and useful.

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Old 22-09-2016, 13:39   #8
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Re: Oil pressure. Optional or necessary?

When I repowered went with the full meal deal panel. I am a belt and suspenders guy so panel has temp and temp alarm and oil Guage and oil pressure alarm. Also has voltmeter and tach. Also has light if hi amp Altn light.
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Old 22-09-2016, 16:42   #9
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Re: Oil pressure. Optional or necessary?

It is not necessary to have an oil pressure gauge.
However it is very necessary to have an oil pressure light and a working alarm. The low oil pressure light should be on when you switch the ignition on before starting and go out immediately the engine starts. It should then stay out while the engine is running unless there is a real low oil pressure situation in which case it should illuminate and sound the audible alarm. Then it is time to shut down and investigate.
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Old 22-09-2016, 16:56   #10
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Re: Oil pressure. Optional or necessary?

So I did a little experiment. I removed the sender wire and attached it to a ground. i then started the engine, and, to my surprise, a light illuminated and an alarm sounded. Very relieved to know that i have some ability to know about my pressure. No doubt it'll save my a$$ some point down the line.
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Old 22-09-2016, 18:14   #11
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Re: Oil pressure. Optional or necessary?

An oil pressure SWITCH if wired correct will give you an alarm. Useful and on your engine easy to install if not there already.

A sender for a gauge might take up the only port to sense pressure on a small engine.

A gauge will show trend....if you see the pressure going down over a long time you would check filters etc. Almost never happens.

If you hear a shrill alarm it usually suggest that there is no oil pressure and that is usually an end game. However your small diesel would fair well with any oil in the pan by the splash oil as the engine turns. Just shut it down as fast as possible.

If you check your oil level on a regular basis you will likely never have a problem.
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Old 23-09-2016, 09:37   #12
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Re: Oil pressure. Optional or necessary?

how does the phrase "seized engine" sound to you?
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Old 23-09-2016, 10:11   #13
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Re: Oil pressure. Optional or necessary?

I haven't seen them all of course, but all I have seen, the light is for alternator charging, and the audio alarm is for low oil pressure, they both should be on before starting the engine of course.
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Old 23-09-2016, 11:11   #14
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Re: Oil pressure. Optional or necessary?

Based on mechanics I've talked to, an equally important gauge to have is an oil temp readout. If you do not run the engine hot enough (hard enough) to get/keep the oil hot, all manner of bad things can happen. I guess that's why Yanmar says that if you do not regularily run your engine in the 80%+ range of RPM, then you need to run it up to red line for 15-20 minutes after every 6-8 hours of operation at lower RPMs. We're running a Yanmar 4JH-TE; cruising at +3000RPM just doesn't feel right, so we go to 3500-3600RPM every 6-8 hrs of operation. FWIW
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Old 23-09-2016, 11:48   #15
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Re: Oil pressure. Optional or necessary?

Oil temp is important, on aircraft piston engines 180F is generally considered to be the temp where you will cook off the moisture in oil. However you can use an IR point and shoot thermometer on the oil filter to determine your oil temp. Not much to be gained from watching it. Once you determine a cruise RPM that gets the oil hot that is all you need. I bet it's a lower RPM than most think, usually you don't have to run the snot out of them to get them to operating temp, usually just a decent load, not RPM will get you there. Gauges are nice, but I believe on average most boats don't have them, yet very few engine failures happen, and on most of them it's from a lack of preventative maintenance.
I will probably one day T in an oil PSI gauge on mine, after I do some other more pressing projects first.
On mine 1500 RPM gets it fully warmed up, maybe even lower.


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