My dad rebuilt a D31P-18 with the 6D95DL. After first time he put it together the dozer had very low oil pressure. We researched and found out the wrong cam bearing was installed. Replaced the cam bearing and re-installed the engine. Now at first startup we have close to 100psi. Yes 100. After the engine warms completely (15 minutes of running) the oil pressure drops to around 10psi at full throttle and maybe 3-5 at idle. This seems way to low and we are not comfortable running it like this. My dad has already pulled the engine again in hopes of finding why the oil pressure drops so much after warmup. FYI, if the engine is stopped after warmup and restarted while still warm the oil pressure is STILL only 10psi at full throttle. After cool down if restarted the oil pressure is back to ~100psi.
I reckon I'd check that gauge against known values as a starting point. Cheers.
Scrub I'd hate to think it would be that simple but would sure like the cost of repair. We replaced the gauge the first time the oil pressure was low (before cam bearing change) but I know, we could have gotten a bad one. We will definitely check it.
Mechanical gauge or a sending unit? The sending units have diaphragm in them and if it gets a hole in it, the gauge reading will drop as the oil fills the space behind the diaphragm. The oil will go back in about the same time as it took to "drop" so you can start it back up, the oil will still be hot, but the gauge should reset mostly in that time. A tee and a mechanical gauge will show what's happening if that's the case. If the engine is out, test the gauge/sender teed with a mechanical gauge and hold the pressure the time it would take to warm up. The hundred PSI makes me wonder if the oil pressure regulating stuff is put together correctly?
Deimer It's a mechanical gauge but we'll still check it out. Can you elaborate on "oil pressure regulating stuff". I know there is a valve and spring in the oil pump and kind of suspected it was getting stuck or weak spring but my dad said it checked out good.
Yes, the valve and spring is what I meant. I'm not familiar with this engine specifically, but I've never seen an engine or spec that 100PSI would be normal. The valve is there so the oil filter doesn't blow on a cold startup with too thick oil. Plus, if the bearings were so tight that it was that high cold, why would it drop so much hot?
Yes something is definitely wrong here. cannot lose that much pressure cold to hot and not have something skewed.
Yes 100psi is a lot but I'd rather that than the indicated 10psi when hot. Hey, I'm here because we just can't figure it out. We will gladly take all suggestions and run them down. This is too good of a machine to burn up due to low oil pressure. I'm in Florida and my dad (and dozer) is in Louisiana so the relay time and answers might be slow. I appreciate all the responses and will report back with findings. Thanks for the ideas.
Also, I welcome any other ideas or questions.
xxxx
Come on scrub, chime in!! You are seeing something that is opening up when hot, could be the bypass regulator piston in the oil pump is basically locked in place, not opening cold and not closing down as viscosity leaves hot. I am thinking that as a possible not an absolute. What engine is in this?
There has to be a reason for this. Are you using the correct oil? Is there a diesel leak that is diluting the oil? Is anything else going on like low power, high or low tem? How about exhaust smoke? Anything else different from before the rebuild?
Dmiller It's the 6D95DL. That's kind of what I was thinking but like I said, my dad thought this "valve" was good. Not even positive how he checked it. Maybe just cycling it manually. Tempted to just change the oil pump because you can't buy the "valve assembly"
Did the dipstick get changed? or how much oil did it take to fill it vs how much is supposed to?
Former Wrench Engine runs like a champ otherwise. A little smoke on start up that clears within 30 sec or so. Now at first start up there was a lot of oil in the exhaust chamber that smoked like crazy but once engine was ran at temp for a while it burned off. Yes correct oil, no dilution that we can tell (oil level stays correct), temp stays normal as well as power.
Dipstick wasn't changed as far as I know. I'm not sure of the capacity or what it took but I will find out. If I can get my dad to create an account maybe he could chime in, he doesn't like computers very much.... He's probably going to read this though...
Former Wrench I noticed your last question was if anything was different from before the rebuild. Unfortunately the dozer came in a "box" so to speak. Still it runs great and has plenty of power, it's just the oil pressure we can't figure out.
Does it have the correct genuine Komatsu oil filter on it ? If it does is there any kind of bypass valve either in the filter or associated with it ? If all that is good then I would think that since the oil pump was dismantled it should be examined very closely again or preferably replace it with a new one.
Tinkerer I do not believe it's a Komatsu filter. The oil pump was replaced during the rebuild but we will definitely inspect it closely. Thanks Scott. .
I once did a rebuild on a old jeep. The person who "rebuilt it" before on worked on it, used so much silicone (RVT stuff) that it plugged up the strainer on the oil pickup, and trashed the bearings. I've also heard of rags getting left it a oil pan after a engine assembly. While this doesn't work with the high oil pressure side of things, is it possible you have something floating around in the oil pan?
A crack or gap in the oil pickup near the oil level?
Delmer My dad never liked the oil pickup configuration. He's going to check this also. Thanks for the info. Scott