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Old 21-06-2013, 17:13   #16
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Re: Perkins 4.108

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Originally Posted by westpole View Post
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?
YES. That is too low oil pressure.
Do as others have advised and attach a mechanical direct reading oil pressure gauge. If it reads the same, you have a problem.
What weight/viscosity oil are you using? If the water temperature you are motoring in is over 70 degrees F., you should be using 40weight CD rated oil.
I recently rebuilt a 4.108 for a customer whose fuel transfer pump was leaking diesel fuel into the crankcase. It thinned the lube oil until a connecting rod went through the case. He admitted to checking his oil and it was always up, he was checking diesel fuel in the oil, which does not lubricate the engine properly. Cost him $6,000USD
So, if you are not "making oil" and your oil pressure is that low, it may be time for a rebuild; new bearings, seals, gaskets, rings and a thorough check of the oil pump, piston rings, cam, crankshaft, cylinder liners, etc.

Good luck and keep the dry side up.
Tom - Love those Perkins
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Old 21-06-2013, 18:13   #17
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Re: Perkins 4.108

The Perkins 4-108 heat exchanger is undersized for the engine (and the engine itself is over-rated at 47HP or 50HP (commonly seen claims).

It's more like a 30HP engine.

I solved my overheating problems on my 1981 4-108 many years ago by fitting an oversize heat exchanger from a Perkins 4-154.

These engines are meant to run at 180-190F with fresh water cooling (circulating, not raw). The lower temps you have seen quoted are for raw water cooled models, where you don't want to get them so hot that the salt precipitates out of the cooling water.

Your oil pressure readings are way too low....bad guage or maybe other problems.

Mine, too, starts immediately and has a bit of smoke on startup.

I fitted a Walker Air-Sep to it some years ago and it's made a big difference in cleanliness of the engine room. Also, the negative crankcase pressure occasioned by the Air-Sep tends to reduce the oil leaks the 4-108 is known for. The engine seems to really like it!

Great engine....take care of it and it'll last many years.

Bill
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Old 21-06-2013, 20:01   #18
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Re: Perkins 4.108

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It's more like a 30HP engine.
Hmm, that sounds a bit low.

I have been running a CSY 33 with a 4-108 rated at 51 hp for a while, and have also ran sister ships, CSY 33s with the Westerbeke M30, rated at 30 HP and there is a big difference in power available.

The Perkins's 51 HP is, if I remember correctly rated at 4000 RPM, a bit much for normal running and the max continuous RPM is 3000, with less HP produces. Based on that one could conclude that the 51 HP is for emergency use only.
The emergency power has been useful a few times when transitioning rivers and Intercostal Waterways with strong currents and bridge tenders trying to close the bridge before we are clear. Had to floor the Perkins a few times and glad every one of the 51 HP responded, otherwise we would have been de-masted twice, not a good thing..
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Old 21-06-2013, 21:19   #19
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Re: Perkins 4.108

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Originally Posted by btrayfors View Post

you don't want to get them so hot that the salt precipitates out of the cooling water.
I have heard this before and I do not know where this idea comes from. Salt is more soluble at higher temps, precipitates at lower temps. In an open system where the water can evaporate or transition to steam, this makes sense, but not in a cooling system where there is a constant flow of liquid water.
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Old 21-06-2013, 21:28   #20
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Re: Perkins 4.108

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I have heard this before and I do not know where this idea comes from. Salt is more soluble at higher temps, precipitates at lower temps. In an open system where the water can evaporate or transition to steam, this makes sense, but not in a cooling system where there is a constant flow of liquid water.
I have seen it at the point of injection at the exhaust elbow. Pressure drop, exh temp?
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Old 21-06-2013, 22:22   #21
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Re: Perkins 4.108

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I have seen it at the point of injection at the exhaust elbow. Pressure drop, exh temp?
phase transition to steam at this point in the system, steam is highly corrosive/erosive and especially when mixed with NOx and SOx exhaust products makes acids, although a relatively minor change in cooling water temp I would think would have a negligible effect here.
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Old 11-09-2013, 17:42   #22
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Re: Perkins 4.108

I bought a new 4-108 (1992) in 1994 and it starts pronto , does smoke (but very little) on startup and runs at approx 180 deg with oil pres at around 40.
One caveat here guys - I notice the forum has folks from Miami to Hawaii to Maine. Keep in mind that you will not get the same running temp in Florida as you will in Maine (the water temp is quite different and these babies are water cooled.)

I burn Shell Rotella 15w 40. Says on the jug its made for Diesel Engines.
Pay attention to the owners manual. WHen these engines were made, fuel was very different (contained a lot of sulphur) and trhe oil was also different (not as much different as the fuel). Sulphur emissions laws has killed many older engines due to abrasive wearing and over heating. Read more at...
Ultra-low-sulfur diesel - Wikipedia, the free encyclopedia

This means that a good additive to replace the missing sulphur is required with these older babies.

I ran mine at 2800 rpm for about 5 years. My diesel mechanic cousin said a diesel must not be idled too much and should be run at rated speed or it will gum up. Many opinions about that !
Anyway - I was wasting diesel fuel (only got around 1.0 knot faster). I now run her at 2200 revs. I get 7.2 knots with a 17 x 13 (3 blade) on my 42 foot ketch (37 ft waterline - general formula for max speed is: SQRT of waterline x 1.25)
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Old 13-09-2013, 14:13   #23
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Re: Perkins 4.108

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Originally Posted by Guy View Post
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.
I would buy and temporarily mount a mechanical oil gauge just as an alternate means of verifying your reading. I've had oil sender fail, then oil gauge fail, then a brand new sender fail again, all within first year after a complete rebuild on Westerbeke 4-108. All the while i thought my engine was at 5 PSI at idle hot, and that I might have assembled something wrong during a rebuild/installation. Ive had a similar thread here with very similar advice.
Mechanical gauge finally cleared my confusion, as it showed 40-50 PSI on startup, then 35 PSI at idle hot, and 40psi under 3/4 load.
Getting yet another sender cleared the problem with readings on engine panel. Also If you have low oil pressure alarm, check the settings, but i believe it will sound at 5 PSI. You should install one.
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