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Old 17-09-2014, 14:26   #16
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Re: Perkins 4.108 making oil

Thanks Guy, there were no perforations in the diaphragm of the lift pump that I could see, although I am far from a trained mechanic (as you can tell). I plan to have the injector pump removed and either rebuilt or completely replaced. Hopefully that will solve the problem, Your info on the differing internal pressures makes sense, and fits with the differing RPM idea. Thanks.


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Old 17-09-2014, 15:04   #17
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Re: Perkins 4.108 making oil

Interesting problem. So have you checked that the return line to the diesel tank is clear???. The external leak, might be due to a restriction in the return line, either at the tank or collapsed hose to the tank.

Increased back pressure could causes the seals to leak at the injector pump.

Agree that the lift pump either leaks or it doesn't.

You mentioned a leak at the remote oil fill and pressure at the dip stick. Is that as in oil seeping out around fill cover. If so verify that the crankcase breather is clear (hose from valve cover to air filter housing). If it is clear, you have a wee bit of blowby. It is slightly possible the excess crankcase pressure could cause the seals to leak in the injector pump (via oil return line from external pump)
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Old 17-09-2014, 15:07   #18
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Re: Perkins 4.108 making oil

The return from the chamber of the high pressure pump to the tank should be at low pressure, seems a leak would not be too likely. Is there a restriction in the return line that might explain the leak and cause higher internal presure in the pump, driving fuel past the seal into the crankcase? I might pull the hose and blow it out to be sure.
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Old 17-09-2014, 15:38   #19
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Re: Perkins 4.108 making oil

I have had this problem in a perkins (although it was consistent). It turned out to be a bad injector. That cylinder wasn't firing and the injector was washing the rings and fuel going into the oil. The engine seemed to run fine and I only discovered this by cracking off the injector nuts and noticing the one cylinder made no difference. A compression test showe one bad cylinder after that.
Coincidentally, a pushrod popped off the rocker arm also. either before or after the injector failure. probably related in some way. At any rate, you can see if a pushrod is off by removing the valve cover. I would crack those injectors and see if one cyl is not firing first. after the pushrod and injector were rebuilt the compression came back In that cylinder.
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Old 17-09-2014, 15:56   #20
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Re: Perkins 4.108 making oil

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Originally Posted by sanibel sailor View Post
The return from the chamber of the high pressure pump to the tank should be at low pressure, seems a leak would not be too likely. Is there a restriction in the return line that might explain the leak and cause higher internal presure in the pump, driving fuel past the seal into the crankcase? I might pull the hose and blow it out to be sure.
That sounds like a good idea
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Old 17-09-2014, 16:45   #21
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Re: Perkins 4.108 making oil

mike--sounds like what i was finding, despite words otherwise from my alleged mechanic, as i checked all he did, you are describing what i found.
take off both pumps. find a builder of same and have em done. injectors also.
check exhaust elbow for carbon. the next thing as mine deteriorated was the coloring of my fuel to black. oops. next was the flushing from system via exhaust a buncha black oily carbony stuff and some smoke, then runaway and seizure. two injectors were bad. all 4 have been replaced or rebuilt.
i should have had my injector and lift pumps rebuilt before i left usa, but i got a muuuch better price on them being rebuilt here and by a better mechanic.
as of now, both pumps and entire engine and all injectors are essentially brand new.
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Old 18-09-2014, 07:13   #22
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Re: Perkins 4.108 making oil

Thanks for all the great ideas folks. Much appreciated. I'll take a look at the return lines and make sure there are no obstructions. It is leaking at one joint, but that seems to be due to a dried grommet that Perkins uses. I've heard a few mechanics complain about them. I will look though.

Interesting idea about the bad injector, but you'd expect this to be a consistent problem, wouldn't you? It appears we are sometimes running just fine, with no diesel intruding in the oil, and then other times when we get a flood of diesel in a very short time. I hate intermittent problems...

I'm going to get the injector pump rebuilt or replaced, so we might as well test all the injectors as well. And I'll for carbon buildup at the exhaust elbow.

I'll keep you posted.


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Old 18-09-2014, 07:29   #23
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Re: Perkins 4.108 making oil

just a thought--- if you use an electric assist pump and keep it on during running of engine, you CAN bypass the lift opump, as i found i was doing.... might want to make a toggle switch for that, if you have one, so you can switch iot off during passages anbd general engine use and save it for the priming.

just a helpful hint from hell -ow -eeze
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Old 18-09-2014, 07:41   #24
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Re: Perkins 4.108 making oil

Mike,

I'm liking the restricted return and the leaky injector too... Albeit agreed that the intermittent occurrence is mind bogglingly FRUSTRATING!!!

You gotta admit though... You got one HELLA CLEAN crankcase if you can keep her in one piece until you figure this thing out!
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Old 18-09-2014, 13:11   #25
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Re: Perkins 4.108 making oil

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Originally Posted by HappyMdRSailor View Post
...You gotta admit though... You got one HELLA CLEAN crankcase if you can keep her in one piece until you figure this thing out!

So true! We've done more oil changes in the past three weeks than the rest of the five years I've owned the boat. The oil is actually looking very clean, compared to the sooty black I'm used to seeing.


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Old 18-09-2014, 13:37   #26
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Re: Perkins 4.108 making oil

Check your return line hoses. They can "break" internally causing a blockage. I've seen this happen to brake hoses. This would fit the intermittent problem.
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