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Bardstown, Ky | I have an 855 cummins engine. Manufactured in 1989. I believe it is a big cam IV. It suddenly lost part of its oil pressure. One day it is normal and the next day, once it warmed up it runs at about half the pressure it should. At idle the pressure is low enough to cause the warning light to come on and the engine to shut down. We suspected a broken piston cooling nozzle. It wasn't that. However by the time I got all the nozzles out I ended up with the oil pan off. Now I'm not sure how to proceed. I was thinking I would replace the seals on the oil pump suction line while I have oil pan off. Could the pump suck air enough to cause this? When I was at cummins picking up parts I asked about a port to check the pressure of the pump. All the techs were younger than this engine, haha, and they weren't certain but thought the port where the pressure gauge comes out of the block was the closest I could get to connecting directly to the pump. Is this correct? How would I check to see if the bearings in this engine are the culprit? Doesn't seem likely as this happened so quickly. Any thoughts or ideas would be appreciated! |
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haskell county, ks | oil cooler blow? check to see if have oil in water. not many places for oil to go away on 855 if no major blowup. could have possible oil pump gear problem. on the block where the oil pump bolts on is an allen wrench plug that you could take out and just see if pump is moving a lot of oil or not but the 855 has all internal oil passages so if something is stopping the passages up will need to dig deep. take off oil filter and turn over engine a bit and see how much oil is flowing. make a big mess but easiest way to start looking. |
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WC IL | Been a while since I've been around one, so my memory may be sketchy, but I think there is a pressure regulating valve on them. It's kind of like a relief valve. I'm thinking they were both flow and pressure regulated. Seems like there is a plug you remove and the valve is behind it, maybe on the left side of the engine. Sorry I'm so vague, but it's been 25 years since I was around one. I'm with you in doubting the bearings. Hopefully someone else will chime in. |
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haskell county, ks | that is on the oil cooler. is a very simple spring with kind of a piston in there. may have a little different oil cooler on it than the older small cams that are on irrigation wells that i run. |
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WC IL | Is it on the oil cooler or on the oil pump? I'm thinking there is like a 1/2 inch plug on the bottom of the pump that has an o-ring on it that holds the plunger in, sometimes they get a little dirt in it and it doesn't function right. Can take it out and clean it up and sometimes it fixes it. IIRC. |
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| Also check where the oil sender to the shut down is. We had an owner operator call in with no oil pressure. He had driven it 2 hours to the truck stop with no pressure showing so we were pretty sure he had oil pressure. Turned out it was a piece of dirt where the sender plugged in. |
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central mich |
I sure would have checked out the oil pump first before pulling the pan. There are two pressure regulators in the pump.
One is the high pressure limit valve which is prob not a problem. The other is the Main Rifle Pressure Regulator.
There could also be a temp regulated bypass in the oil cooler.
But I would have looked at the oil pump first on the lower left hand side of engine.. |
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s nd | Somebody help me here. We had this discussion a couple years ago about the plastic things that go behind soft plugs on side of engine. Getting old, can't remember. Have pic. They fall down into the oil pan and drops your oil pressure.
Edited by ndred 1/4/2016 18:31
 (cummins plug.jpg)
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 cummins plug.jpg (55KB - 386 downloads)
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SCWI | We have a 1987 with an 855 in it. One day it lost oil pressure, ended up being a bad relief valve. I can't remember which side it was on, but it was easy to change. |
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| Like ndred said, it could be one of the little plastic piston coolers(not sure if I named that correctly). It happened on my 86. Was real easy to check and change them. One broken caused a reduction of about 8psi if memory serves. Was easy to notice on gauge, and warm idle was scary low.
Apologies. I missed that you went through them already. Good luck.
Edited by Cole Sibley 1/4/2016 19:42
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Bardstown, Ky | I pulled the pressure regulating valve out of the oil pump. Nothing seemed obviously wrong I will check out the spring tomorrow. The oil cooler has a valve in it, could this be an issue? |
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| buddy had the key ,shear off, that runs the oil pump
I have had the oil bypass ,on the oil cooler ,right side have a piece of cam shaft stick it open |
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s nd | Sorry cole, I couldn't remember what we did and what they were called as it happened six or seven years ago. Mine was a cheap fix. |
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| I have seen the plunger in oil pump stick. this is more common first thing when u take off with cold oil usually if you shut it off it will sometimes fix. Sometimes there can be a grove in the housing that plunger hangs up on if it keeps acting up you can pull the pump off polish housing to fix it. Have see the spring brake on the plunger. Five minutes should pull the plug from under the truck and drop plunger. |
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Dearfield Co. | The pressure bypass on the pump can get a weak spring over time. I would probably take it off and take it part and insect the gears and make sure they aren't wore excessively while I was there and look at the end plate where the gears run as they can wear excessively losing pressure. If it looks ok put it back on a pressure the engine up thru one of the ports with clean engine oil and then get under it and look for excessive flow. Make sure you have a good face shield and prepare to get a little oily I always wear a big trash sack with a hole for my head and arms. Sometimes things will look ok but be destroyed to where it dumps excessive oil and pressure out. The suction lines as well as the pickup tube in the pan can also crack allowing it to draw air. Most of the ones I have seen cracked is in the middle of the tube on a seam in the tube----------Good luck |
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Manitoba | nt |
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nw MN | Happened to one of mine this fall, lost about half of oil pressure. I pulled the relieve valve on bottom of pump. It looked good, dressed a few small nicks off the plunger and slid back into housing making sure it could travel up and down easily. Reassembled and all was good again. No major issue visually but this regulator must be very sensitive to small pieces of debris. Doing research I also saw it was possible for pump gears to slip on the shaft. They are only pressed on. Also piston coolers can cause this but you already looked into that.
Edited by OlsonKrist 1/5/2016 12:15
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855 cummins oil pressure problems
