Surplus MEP-002A up and running but strange oil pressure fluctuations.

[BadBrad1]

Surplus MEP-002A up and running but strange oil pressure fluctuations. RESOLVED

Ok got most issues figured out but have now experienced something that has me kind of flummoxed. When I acquired the generator it had a bad oil pressure switch in it which I simply jumped out as I awaited arrival of a replacement switch. Well got the switch installed today and fired it up and it ran about 6 -7 minutes and then just shut down....WTF is going on! I restarted it and same thing happens runs for a bit and shuts off...so I am kind of pissed did I get a bad switch?? So I start it again and am standing there with a meter clipped to the switch and it shuts down again but this time I am right there and see the oil pressure drop on the gauge... Now what the **** is happening. So I get the jumper out, jump out the oil pressure switch and restart the generator and watch the oil pressure gauge.

It runs for 5 minutes or so showing solid and steady oil pressure at about 26 lbs. then it starts to drop. In about three -four seconds it drops to around 15-16 lbs then in about the same time interval, 3-4 seconds ,it comes back up to 26 lbs and sits solid and steady for about another 5 minutes then drops again in the same manner as before and comes back up and continues this weird cycle. As the motor warmed up the time between drops seemed to lengthen a bit and the pressure drop lessened to about a 5 lb drop and rise.

During all this the engine RPMS did not fluctuate nor did the sound of the motor differ as the oil pressure cycled.

Obviously the oil pressure drop opened the pressure switch which is adjustable from about 14-20 lbs. so it is working as it should.

Needless to say this has me a bit concerned and puzzled..it's almost like something is opening up dropping the oil pressure then closing and then again opening and closing in a cyclic manner.

Any ideas out there?? Some kind of check valve or pressure valve malfunction??

 

[CDR]

What the oil temps?

 

[Keith_J]

Check out the -34 TM, there is an oil pressure relief valve and a thermostatic valve on the oil system. Otherwise, it is oil pump time.

 

[m16ty]

I'd guess a weak relief valve. Seems to me that maybe after the oil warms it gets thinner and doesn't put as much strain on the weak relief, that would explain why it goes longer after warm up.

This is just a guess but that would be the first place I'd look.

 

[Ratch]

Oil level good?

 

[lxawolf]

Oil level good?

+1 It may sound crazy but this could be as simple as low oil?

 

[glassk]

The high temp cut out switch (sw4) is in same line, are the shutters working, few minuites is about right without cooling for it to cut off from temp,... just a thought

 

[cuad4u]

Do you have the "right" diesel engine oil in it and not something like 5W-30 gasoline engine oil? Light weight gasoline engine oil may be thinning out too much when the diesel engine gets up to operating temperature. I think we are all grasping at straws to find a simple answer. As others have said, if everything else checks out it is either oil pump replacement time or oil pressure relief valve replacement time.

 

[BadBrad1]

Thanks for the responses, it had fresh oil in it when I picked it up so not sure of the oil weight that is in it. I am going to do a oil change and check out the filter bypass check valve and thermostatic oil valve make sure it is all clean and no broken springs then check out the oil pressure relief if all else fails.

Thanks for the heads up on the thermostatic oil valve, had no idea it was present and the manual really has no check procedure for it other then a visual inspection...it may be the issue as it looks similar in design to a regular coolant thermostat and I have had those act strangely before.

Oil pump looks like it would be a real PITA to change out and my experience is a gear style pump works or not and really would not fluctuate like this.

 

[Keith_J]

Could be diesel in the oil since Ambac (Bosch) have no real seal between diesel and oil side on the plunger, leaking o rings on the static sides can also leak.

this is why you should take note if the engine is "making" oil. Or oil level rises.

 

[BadBrad1]

Well got to spend some time on the generator it is up and running solid with 38 lbs steady oil pressure. I did a oil and filter change on it and started it up and it shot right up to 40 lbs. pressure and once warmed up drops to about 37-38 lbs and sits there steady. It was about 2/3 quart low on oil but I don't think that was the issue. I did not do anything else to it so I suspect either the engine had the wrong grade oil in it or something was amiss in the installation or manufacture of the old filter. I ran it for 3 hrs. and it is rock solid on the oil pressure with no drops or fluctuations. I used Rotella 15-30 Diesel motor oil for the change and I am so happy it was not a oil pump needing replaced.

Thanks for all the ideas guys.