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Old 12-04-2022, 09:24 PM   #1
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City: Seattle
Vessel Name: M.V. PATRIOT
Vessel Model: 1972 55 FOOT GRAND BANKS ALASKAN 3160 cats trade info advise and help on bot
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1972 cat 3160

These have been wonderful engines, they are in a GBAlaskan , The Patriot and I have done much in 10 years, purring all theru all conditions. my port engine now is dropping oil pressure when at an idle setting alarm off. If I chg oil, the pressure goes up to a nice 35lbs for a few 6 night trips, During this time the pressure starts dropping slowly until I need ot change oil again the great pressure,,, These have been non leakers! about the same time the oil issue came, I started seeing oil in the engine pan,, outside of this lose of oil neither engine has drop oil level from use. I have done reg oil changes and both have not used any I can detect, These are reman,s I didn't receive much history of when they were reman'ed

I need to learn, read, or any suggestions appreciated,,
Iol pump? how do I check?
but does this sound like main due to oil leak and pressure?
if front main? what would this mean for repairs?

hey all thank you for help,,
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Old 12-04-2022, 09:31 PM   #2
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First thing I would do is get an oil sample kit and use it.
Both Caterpillar SOS and Blackstone Labs can do a good job.
I use Cat.

You may have a fuel leak into the oil pan which will thin the oil out showing low pressure.
You will not likely be able to smell any diesel as the low suphur stuff stopped the sniff test years ago.

Different engine although of similar age but that is how I found out my injector seals had gone awry. And the oil test is whole lot simpler to do as a quick check than most other poking around. Of course if that does prove to be the case then the work after will be another matter.

\But get the test kit and use it because if it is fuel in the oil there can be serious damage done if allowed to go on for too long.
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Old 12-04-2022, 11:03 PM   #3
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What weight oil are you running in the offending engine?

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Old 12-05-2022, 12:52 AM   #4
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As C lectric refers to I'd see if you can get an oil test and specifically I'd look for fuel dilution. Assuming you're using a diesel engine oil, either 15W-40 or SAE 30, the viscosity of the oil itself will be relatively stable so a decrease in viscosity is most likely due to dilution with the very low viscosity diesel fuel. The simplest cause could be a bad fuel injector. I'd think the engine wouldn't run well but dropping one out of eight isn't as obvious as with a smaller engine.

Coolant leakage could also be a cause though much coolant would turn the oil milky. In any case a good oil analysis will help inform you what the root cause is.
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Old 12-05-2022, 01:21 AM   #5
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After an oil change you have good pressure, so it's not the oil pump or the oil pressure relief valve. You're probably getting oil in the diesel either at the injector pump or fuel pump.

Get the oil test to verify. If you have diesel in the oil, I'd start with the fuel pump seal. It's the cheapest choice. These engines were developed from a truck engine from the 1960s. There are some differences. I don't know if the fuel pump is the same. An injector service company may rebuild fuel pumps.
The truck version of the 3160 is 1100. The engine does not have replaceable sleeves. When your engine was rebuilt, the cylinders were bored oversize. It can be bored to .040" over. The 3208 replaced the 3160. It's similar, but not the same. Accessories like the fuel pump may be the same, but probably not internal parts.

The injector pump is different from the truck version. If that's the leak it would be best to take it to a shop that rebuilds injector pumps. Seattle Injector would be a good place to start. https://www.seattleinjector.com
But there are many good injector services in Seattle. Some might come to the boat, diagnose, remove and repair. It's not cheap.
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Old 12-05-2022, 07:40 AM   #6
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Doesn't the Cat V8 valley design provide a diesel piping leak to migrate to the oil? Boat diesel.com would be a good source for their archive history before tearing things down.

David on that forum is smart as a whip on anything Cat. A hands on Cat V8 grey beard mechanic would know the detailed piping for sure.
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Old 12-05-2022, 11:48 AM   #7
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The Cat guy on B.D. is dave all lower case and he has helped many.

My engine showed perfect oil pressure cold at idle. As the engine COOLANT warmed the pressure was where I expected it to be. Once run for a while I then noticed the oil pressure started to drop from abut 90PSI to about 70PSI.

Told me two things that I had known for a long time.

--1 THe engine oil takes a lot longer to really warm up than many people believe. Just because the coolant is up to temp does not mean the engine oil is.
--2 that I had fuel in the oil but it was still at a low enough % level the effects did not show up untill the oil was fully warmed or close.

I had changed the engine oil and it showed normal pressure as always. It took a bunch of hours for the dilution to raise its head as the fuel accumulated.

That's when I took the sample and it showed ~7% dilution initially meaning the dilution was slow to build so I didn't realize the implications untill after that oil change.
Your description of the symptoms raised my issue as your symptoms were almost identical to mine.

Get those sample kits and use them. If you have full pressure after an oil change, then slowly dropping pressure over about 40 or so hours AND full pressure when cold which drops as the engine warms up then you will likely find diesel fuel contamination in the oil. NOw is the time to take the samples , not soon after an oil change.

I don't know at what point the fuel contamination level becomes potentially damaging but I suggest you do not want to wait as the result could be a tear down of that engine. And to boot your engine is of the age, as was mine, that this is likely.

If the sample show nothing good, but don't wait.
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