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Old 03-06-2013, 13:04   #1
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Perkins 4.108

Sort of new at this boat diesel thing and was hoping for an opinion or two.
I have a 1981 vintage Perkins. It starts every time instantly. It blows a cloud of smoke but after two to three minutes no load 1500rpm most all of the smoke goes away and just a perceptible amounts remains. My oil pressure shows 35lbs at 2000rpm, 20lbs at fast idle but only 5lbs at slow idle. The water temp will climb to 200F when cruising at 90% throttle for any length of time but stays around 180 at 3/4 throttle.

Any thing unusual in these observations?
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Old 03-06-2013, 13:10   #2
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Re: Perkins 4.108

I don't get that much temp at 90% but I don't run at that. Oil psi sounds a little low. and the smoke is not to uncommon.
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Old 03-06-2013, 13:14   #3
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Re: Perkins 4.108

Sounds absolutely spot on to me!

Your 90% throttle "should" be a little cooler... Check dirty bottom, over propped, or cooling system maintenance ...

1. Raw water side, intake, strainer, impeller, heat exchanger, exhaust elbow
2. Fresh water side, water pump, T-stat, coolant level and condition, cap

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Old 03-06-2013, 13:25   #4
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Re: Perkins 4.108

Oil pressure should be between 35 and 45 all the time. 5 Lbs is not good. Maybe use a heavier oil. I would say do a compression check to see how rings are.
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Old 03-06-2013, 13:28   #5
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Re: Perkins 4.108

i normally idle my 1979 4-108 at about 700 rpm. i rarely go over 1700 rpm when running.

according to the perkins engine manual, normal oil pressure is between 30 and 60 lbs. i would be concerned at having oil pressure that low. normal temp is between 150 and 180, according to the manual. if you're running 200, i would check the coolling system, as happymdsailor said.

blowing smoke at startup is normal for this engine, but it usually disappears within less than a minute. the combination of smoke and low oil pressure would concern me, and i think i would look around for a good perkins mechanic to at least look the engine over. also, running at 90% throttle sounds like an engine killer to me, but that's just my humble opinion.

fwiw, my engine comes up to 60lbs oil pressure and 180 degrees water temp at idle or running at 1700 rpm.
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Old 03-06-2013, 13:43   #6
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Re: Perkins 4.108

Quote:
Originally Posted by S/V_Surya View Post
Oil pressure should be between 35 and 45 all the time. 5 Lbs is not good. Maybe use a heavier oil. I would say do a compression check to see how rings are.
You can have less than 35 psi at idle with a hot engine but 5 psi is low . Worn oil pumps and thin oil can make for low psi. The rings and the compression do not have a much to do with low oil pressure.
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Old 03-06-2013, 15:55   #7
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Re: Perkins 4.108

You should be running 30W diesel oil. If running 15-40w, you woud be getting lower pressure. I have about 15lbs at 700 when hot. Remember your oi and temp gauge could be off. I would ck the pressure with a mechinical gauge that can easily be scrwed in. Ck your water temp with an infared gun, which is cheap at Harbor freight. BTW I have 7000 hrs on my engine.
As an alternate, replace the thermostate...its cheap and easy.
A
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Old 03-06-2013, 17:38   #8
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Re: Perkins 4.108

I should have joined this sight three years ago! Great, fast feed back. I'm going to basically take all the advise starting with changing to the recommended oil, changing the thermostat, buying a HF infa-red gun, cleaning the raw water strainer and checking/replacing the impeller. That will take a couple of days and then I will take her out for an hour or so. If the pressure drops below 15lbs it will be mechanic eval time. Thanks for all the input.
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Old 03-06-2013, 20:44   #9
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Re: Perkins 4.108

dynamo1181 - beg to differ. i ran a batch of rotella 30w and the oil pressure / temperature were the same as when i ran rotella 15w40.

i took my thermostat out, on the advice of a REAL perkins mechanic. i'm always in warm climates. when i had cooling problems i took out the thermostat as part of my diagnosis. it turned out to be the fresh water pump. but the perkins guy advising me said don't bother putting the thermostat back in unless i was headed north (we were in the bahamas). it's been out two years now and i haven't seen any problems other than that it takes a bit longer to get up to operating temp....
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Old 03-06-2013, 23:06   #10
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Re: Perkins 4.108

Sniff your dip stick and put some of the oil between your fingers, and see if it seems too thin or smells like diesel fuel. A small diaphram leak can slowly dilute your oil with fuel.. Does the pressure seem better after an oil change, and slowly lower? This is just a possibility to check out.___Good Luck_____Grant.
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Old 04-06-2013, 05:11   #11
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Re: Perkins 4.108

Someone told me that an instant or quick starting diesel is basically confirming good compression, that hard starting is a common sign of poor compression.

FYI the smoke on starting is typically fuel that is unburnt due to cold cylinders.

The engine runs best at normal temps. That is why they spent the money to install a thermostat. I would suggest leaving it in place.
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Old 04-06-2013, 06:30   #12
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Re: Perkins 4.108

My 1985 4-108 idles at about 700 rpm. I generally set 2000 rpm when running. 5-6 Kts

My perkins engine manual say, normal oil pressure is between 30 and 60 lbs. Mine runs at 60lbs. Changed out to mechanical gauge as I felt I was getting false readings from the electric one. Your oil pressure concerns me. That's why I changed to a mechanical gauge, as I was seeing the same sort of numbers.
I run 40W oil. ambient temp and water temp rarely below 80F
My running temp is around 180.

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Old 05-06-2013, 22:59   #13
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Re: Perkins 4.108

worn main and rod bearing could also cause low oil pressure.
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Old 11-06-2013, 18:16   #14
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Re: Perkins 4.108

When doing your trouble shooting give yourself a hit list of possible faults then work through them one at a time doing the cheapest ones first and testing after each change to note the difference in performance.
Doing everything in one foul swoop can cost you unecessary cash and you may not know what cured the problem.
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Old 11-06-2013, 20:04   #15
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Re: Perkins 4.108

If it starts and runs without smoke after a bit of warm up don't worry about it. Just keep clean 30W oil in it, feed it clean fuel and keep the temp at 160 and 180. Low oil pressure at idle can mean a faulty gauge. If it continues after the oil change and after you've checked out the sender or installed a mechanical then yes, see a mechanic but for now do the maintenance and enjoy that engine. They are great.
kind regards,
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