Mep-803a oil pressure drop

[Justin8321]

Just purchased a 2006 Mep-803a with 2500 hours on the unit. I changed the oil right when I picked up the getset and changed the filter as well with rottela t5 synthetic blend 15w-40 and a wix filter 51374. When the unit is cold I get a great 50 psi and as soon as the unit warms up to temp it goes down to about 21-22 psi. I can’t figure out why this could be. Any suggestions?

 

[Guyfang]

I would start by looking in the -10 TM. The -10 TM is the operators manual. It tells you what should be normal ranges for such things. If you know what the normal range of oil pressure is supposed to be, then you can decide if your oil pressure is high, normal, or low.

 

[Hard Head]

Refer to the TM (9-2815-253-24) on testing oil pressure. When you use a gauge the oil pressure should be 36 psi @ 1800 rpm If that fails follow the TM.

 

[Justin8321]

thank you I will look into finding a oil pressure gauge. should I not trust go off of the main gauge on the control panel?

 

[Justin8321]

thank you I will look into finding a oil pressure gauge. should I not trust go off of the main gauge on the control panel?

 

[Zed254]

Maybe your oil sender is failing. Search the Bay for "QTY (1) Datcon Oil Pressure Sender 80 PSI, 02504-00, 1/8-27 thread, 10-32 stud". I had one go bad and replaced it with a Datcon 02504-00 (different seller) and all works as it should now.

 

[Hard Head]

The first thing you need to do is download the TM on the ONAN engine. It will walk you thru the procedure to test the engine for this issue. Not to be the bearer of bad news but the min spec for normal is 25 PSI. That is an engine with worn or damaged parts like bearings that cause oil pressure to drop as they wear out. Now you will need parts on hand for if it is not the sending unit that is bad. You remove the sending unit, install and external oil pressure gauge on a hose , crank and test. Here is a simple video about removing and testing oil pressure and installing another pressure switch. Done on a car but the same thing for any engine.

https://www.youtube.com/watch?v=bhVvv__NH1I

If that also fails you will have to look at several things before performing engine surgery. Is the oil level rising when you run the unit? Clear or is it turning into mayonnaise? Did oil getting into the coolant when the engine warmed up? There can be injection problems that cause fuel to be added to the oil which drops the oil pressure. So before you change the oil sending unit you need to perform the oil pressure test with an external dial oil pressure gauge. Check the oil and level again. Check the coolant for contamination. Then move onto testing the oil pressure at the engine. That way there is not guess work. You have to follow the steps to rule out the easy fixes before you determine if you are going to need an engine rebuild. You are still dodging the low pressure kill right now since that is 18 PSI. So you can still run the engine and do this testing. Here is the oil path (the oil pressure relief valve may be your issue).

The lubrication system consists of an oil sump, dipstick, pump, relief valve, and filter. The pump draws oil from the sump through a screen which removes large impurities. The oil then passes through a relief valve preset to limit oil pressure to 47 to 59 psi (324 to 407 kPa). The oil then passes through a spin-on type filter where small impurities are removed. Once we get thru this path you go to the next!

From the filter, oil enters the cylinder head oil gallery and flows to the crankshaft and bearings. The connecting rod bearings are pressure fed through internal drillings in the crankshaft from the supply to the main bearings. Splash oil lubricates the gears, and the underside of the pistons. The governor camshaft is lubricated by a drilled bolt/oil jet. An internal crankcase drilling provides an oil feed to the hydraulic tappets. After passing through the block, the oil returns to the oil sump.

 

[csheath]

TM specifies normal operating pressure as 25-60 psi. I would assume the variable is hot-cold.



My unit drops to just over 20 and remains for hours under a 40 amp load. I don't plan to look any further into it.

 

[Hard Head]

Parts like bearings wear out or get spun and lower oil pressure. Remember these close surfaces keep pressure up just like you do when you pinch a garden hose to increase pressure. The larger the openings the less pressure you have.

 

[justacitizen]

Parts like bearings wear out or get spun and lower oil pressure. Remember these close surfaces keep pressure up just like you do when you pinch a garden hose to increase pressure. The larger the openings the less pressure you have.

low pressure could also be caused by low volume. say the pickup screen is obstructed? i will bet that it isn't really a low pressure problem but a bad sender.

 

[Hard Head]

If very well could be and I hope that is all it is. The easiest fix. Hopefully we will know more soon. Not knowing any history except the unit is new to him with 2500 hours and he put in new fluids and filters. Any number of things could be going on. Wear and tear, a bad sensor, some gunk that was in the crankcase moved around and got into the sump screen or pressure relief valve, cracks, leaking gaskets. Unknown to us now. I would like to know if it does the exact same thing the next time it is cranked after it cooled off. Did oil mix with fuel or coolant. When I keep my truck moving I have far less issues that when it goes nowhere. I run my generators every month. So what if the hours go up. I have less issues with one running than sitting for months and months.

 

[justacitizen]

If very well could be and I hope that is all it is. The easiest fix. Hopefully we will know more soon. Not knowing any history except the unit is new to him with 2500 hours and he put in new fluids and filters. Any number of things could be going on. Wear and tear, a bad sensor, some gunk that was in the crankcase moved around and got into the sump screen or pressure relief valve, cracks, leaking gaskets. Unknown to us now. I would like to know if it does the exact same thing the next time it is cranked after it cooled off. Did oil mix with fuel or coolant. When I keep my truck moving I have far less issues that when it goes nowhere. I run my generators every month. So what if the hours go up. I have less issues with one running than sitting for months and months.

very well said. these surplus generators are "like a box of chocolates" you never know what your gonna get.

 

[Justin8321]

very well said. these surplus generators are "like a box of chocolates" you never know what your gonna get.

Every time the generator starts it always starts with the pressure being around 50 and after running for a while is when I notice the oil pressure dropping to the low 20’s.
I also flushed the rediator because the radiator cap was missing the second rubber gasket So the coolant wouldn’t go into the overflow bottle. It ended up just dripping from the underside of the cap leaking onto the pan inside the genset.
I’ve rechecked all the fluids many many times and it doesn’t seem to be getting contaminated at all.

 

[Guyfang]

TM specifies normal operating pressure as 25-60 psi. I would assume the variable is hot-cold.

View attachment 721492

My unit drops to just over 20 and remains for hours under a 40 amp load. I don't plan to look any further into it.

Thats the reason I suggested reading the -10 TM. If it ain't broke, don't fix it.

If it was mine, I would drain the oil, fill it back up with Dextron and run it 30-40 min. and then put oil back in it. Then recheck the pressure.

 

[jamawieb]

Every time the generator starts it always starts with the pressure being around 50 and after running for a while is when I notice the oil pressure dropping to the low 20’s.
I also flushed the rediator because the radiator cap was missing the second rubber gasket So the coolant wouldn’t go into the overflow bottle. It ended up just dripping from the underside of the cap leaking onto the pan inside the genset.
I’ve rechecked all the fluids many many times and it doesn’t seem to be getting contaminated at all.

Don't trust the gauges, I wouldn't worry until your low oil pressure fault light comes on. If you need a new radiator cap, they are R28. Any parts store should be able to cross reference. I get mine from Oreilly's auto parts.

 

[CapePrep]

Fill it with auto transmission fluid???? You can' leave us hanging with that direction!! Please explain.

Thats the reason I suggested reading the -10 TM. If it ain't broke, don't fix it.

If it was mine, I would drain the oil, fill it back up with Dextron and run it 30-40 min. and then put oil back in it. Then recheck the pressure.

 

[justacitizen]

Thats the reason I suggested reading the -10 TM. If it ain't broke, don't fix it.

If it was mine, I would drain the oil, fill it back up with Dextron and run it 30-40 min. and then put oil back in it. Then recheck the pressure.

That is a good idea. Thanks

 

[DieselAddict]

In case its not obvious don't put any load on it when you have ATF in the crankcase.

 

[Zed254]

Most of the guys on this forum seem to use one quart of ATF at oil change time for a 100 or so miles to clean things up.
http://www.hotrodders.com/forum/atf-oil-change-26434.html

 

[Guyfang]

It was standard procedure to drain oil, add Dextron to the set, and run it 30-40 min., after a set came back from down range. In today's world, every gen set that comes back, goes to reset. But it was not always so. 15 years ago, the unit took care of its equipment. So that's what we did, and it came down from CECOM. All the crap inside the engine came out after doing this. I took the used Dextron and let settle in big glass bottles. The crap that settled to the bottom was, "impressive", to say the least. And do not scrimp on oil filters. Put a cheapo in when you add the Dextron. A cheapo filter and cheap oil, when you get done. Then 100 hours later, a good filter and oil. We normally always had an improvement on oil press, and a better feeling for where the engine stood. After you drain the Dextron, cut the filter in half. That's where you see real trash, if the engine has any to give up!