Sullair 375 Compressor with John Deere Diesel

yes below the engine oil filter, right next to and below the lower radiator hose. tee'd off with the engine oil pressure switch on the same port. according to my mechanical oil pressure gauge that I set up the engine oil pressure drops slowly and steadily after about 5 minutes running time. yesterday when I ran it it dropped from about 58 lbs. down to about 41 lbs. in a period of 20 mins. is this for sure a bad oil pump? or could something else cause that? wondering if there are any other tests I can do before I pull the engine out because that's going to be a little bit of work. this thing is very compact and there's lots of stuff that has to come out in order to get the motor out...any ideas appreciated

60 to 40psi from cold to operating temp sounds about standard. Work on quite a few of those engines that have a LOP pre alarm at 20psi, and won't shut down for LOP until 15psi. Oil pump is built into the front cover, and is a process.

thank you for that I think will try running it again this time with the oil pressure switch wired to the harness and see at what pressure it is shutting down, and maybe after that run it grounded so it stays running and see if it continues to go down below forty after running it awhile at least if it is a bad oil pump I won't have to pull the whole engine out since its behind the front cover

Oh, you'd be pulling the whole engine out. Oil pan needs to be pulled to access the oil pickup tube before the front cover can come off. Usually the front covers start to leak coolant and has to be resealed, and like I said; It is a process. I know the rental company I previously worked for couldn't source the oil pump separate from the front cover, so it was big money if it needs to be replaced. Also way more work (and custom built tools) swapping the fuel controls over on the variable speed engines than the single speed, and getting the fan hub out can be near impossible. Just a warning to diagnose EVERYTHING before condemning the oil pump. There's a reason our Deere dealer wouldn't touch anything with a 4024 or 5030.

MarshallPowerGen said: There's a reason our Deere dealer wouldn't touch anything with a 4024 or 5030. Click to expand... Wow! No Deere dealer should be turning away Deere engine work. I agree, those engines have been a black eye to Deere, and can be a pain to work on, however, the dealer needs to support their product. The dealer I work for won't turn those away. We literally have worked on hundreds of those puppies (we have a large OEM market here), and that is just our branch.

I would like to be a fly on the wall when the Deere Territory Customer Support Manager hears about the dealer turning down engine work !

Going to keep my mouth shut and not get anyone thrown under a bus.

Dang that all doesn't sound good.. I guess I'm hoping its not a bad pump but if its normal for the oil pressure to go from 60 to 40 after warm up then I might be ok. I'm still waiting on an oil temp gauge so I can check the compressor air end oil temp. it hasn't arrived yet but when it does I'll run it again and see if that gives me any more clues like say if its getting hotter than it should...these things have a thermal valve that diverts the compressor fluid to the cooler once the fluid gets warm enough. I'm thinking the element inside that thermal valve might be bad and not sending the fluid to the cooler like it should causing the air end to run hot, although when I feel the hose going to the cooler it feels warm. so far I've gotten three error codes on shut down on different occasions. one was low engine oil pressure, the next was speed too low, and the last was compressor temp too high. so I've been thinking possibly the element in the thermal valve is not opening all the way causing excess heat, stress, and resistance, maybe, idk, which is why I want to take a temp reading on the compressor fluid in the sump. My unit doesn't have a temp gauge so I have to buy an aftermarket one to get an actual temp reading. I'll keep you guys posted

Just fixed a generator that had no dash display, was sold like that at auction for 10 cents on the dollar. Found bad ground connection and power feeding the display on the digital computer. Has run for over a month on a job. Since you had 3 codes go off at once , you could have an electrical problem such as bad ground, or power to your display. You may have tested all of this already, wouldn't want you to miss an easy fix. Read about your oil pressure testing, did the manual specify a specific weight of oil for the test? Just wondering as it will drop more with some than others. Good to leave gauge hooked up and put heavy load on unit and see if it drops oil pressure before shuttting down, with you supervising at gauge in case oil does start to drop off. If it doesn't go below minimum pressure in manual with correct oil, you have a wiring sensor problem, that simple. Simon C

well I took your advice about the ground and I realized I didn't't even know where the control panel harness ground was and went looking for it. it was sandwiched between a harness clamp and the block and both were painted. so I moved it to where the frame and battery are bonded to the block, and ran it for about fifty minutes or so and it didn't shut down at all. usually it shuts off after about 30 mins or so. Could that be it?? Seems too good to be true... gotta test it some more-didn't have enough time today just found out manual says to use only 10-30 for engine oil. I'm using 0-40 synthetic cause that was what had been recommended to me by somebody at Quinn when I changed the oil. had a pretty good load on it today but next time I run it I'll open the spare valve a little to increase the load and make things more interesting. and btw I was running it today with the oil pressure switch connected, not bypassed, and it never shut off. engine oil pressure was 58 at start up and dropped slowly to 44 lbs after about 15 minutes and stayed there till I shut it down 50 mins later

PanchoVilla said: I'm using 0-40 synthetic Click to expand... That oil is fine for that engine. That is the recommended oil for the electronic version of that engine, which is mechanically identical except for the injection system.

All control circuit problems should start at battery cables, Frame grounds , Panel grounds, ECU power and ground. Thats where I normally start along with the fuse panel for easy checks. Many a problem has been solved by checking these items first. Simon C

Seeing this thread and I'm having the same issue but a 375 with CAT engine.