1965 d6 low engine oil pressure

1965 d6 engine rebuilt , new oil pump gears, shells etc. low oil pressure at low revs.
any known problems with this engine.

How low is low?
Most engine "lose" oil pressure as the rev's go down due to a lesser volume of oil flowing through the system.

Check your oil pressure gauge before getting too excited, if you have a good spare gauge try that first. I just rebuilt a 2 Ton Cat motor and fitted a brand new Stewart Warner "Wings" style gauge but couldn't understand why every time I started the motor it read different oil pressures, and would fluctuate, it has now jammed on 20 pounds pressure even with the motor off but with a good tap drops to zero, so it is obviously faulty, I can see the needle catching on the inside.
Good luck
Mike

Since you have looked into the oil pump, I doubt it is in a similar state, but the oil pump in the D333 in our grader was SHOT! Ended up getting a new one not to jepardize the overhaul we did. That was the second engine I had seen (both in graders!) which had sucked up small parts which had been left inside the suction bell of the oil pump. In this case it was a sheetmetal lock used on bols of the oil pump pickup assembly.

Do you have a turbocharger? Other than that, CAT generally designed their engines to survive on low pressure at low rpm as long as it increases with rpm. If a turbocharger, you must ensure plenty of flow for it to survive. Did you check bearing clearances and/or mic the crankshaft journals. What about the gauge, is it a CAT and the correct gauge for the machine? Have you checked with a calibrated gauge to determine the actual psi?

Older CAT engines used a suction throttling oil pressure control, but by the time your engine was made, a more traditional bypass pressure control was used. If the peak pressure is good, then unless the bypass is damaged, it is unlikely to be the source of the problem.

more info on low oil pressure, oil pressure checked with psi test gauge 4psi low revs - 30 psi high revs engine warm but not working temp.
oil pump gears fitted but not housing, crank ok std shells. added shim to spring in oil pump housing, new filters, should there be a bypass valve in filter housing.
new pistons/liners fitted not that this should affect oil pressure. no oil leak at turbo, low revs 500rpm is this correct. 15w-40 oil used.

Not sure how applicable this is to your engine. This article predates your engine by quite a few years!

Maximum oil pressure should reach 35-45 psi, limited by the pressure relief valve on the pump.
Lots of clearances to be checked on the oil pump besides just changing gears.

There is an oil cooler by-pass valve, a filter by-pass valve and if yours is a D6C, a turbo supply valve built into the filter base.

Low idle is 600 rpm.

ah ha, thanks for the post - that explains why the D4 30A guage goes off the scale as the guage is reflecting the fact that oil is being supplied at a pressure greater than 4psi, with no upper pressure being relevant to the position of the pointer, which will I guess max out on anything greater than 11psi!

That saves me from replacing the guage and makes me feel a whole lot happier that at least +4psi is present at idle!

Does the engine have any oil in it? just checking.. ROY

Change the gauge ,replace that 15w 30 with diesel grade 30 wt oil D333 engine was not designed for multi grage oil .
Raise low idle to 600 rpms if problem is not corrected ,remove oil pump ,and check housing to gear end clearance and housing to tip of gear clearance. Pull connecting rod ,and check bearing clearance using plastic gage to see if bearing to crank is in specs
Do the easy things frist .

I don't believe there is any "design" to make a diesel engine suitable or unsuitable for using multigrade oil!:behindsofa:

Unless there is a requirement for the oil to be extra stiff during startup in cold weather, the only possible advantage to single weight oils is if the viscosity ingredients of the multiweight oils were to break down before the oil change interval. So, unless you never change the oil in your machines, I would use a good grade of 15W40!

I've heard never to use multiweight oils in just about every old diesel here and used 15w40 (now DELO 400) in all of them from Detroit diesels to John Deeres to Cummins and several old CAT's (including two D333's) for years and years.

A few years ago, I had a recent rebuild on a Deere engine that had a rod bearing go out and was questioning the quality of the oil we were using at the time. Tore it back down and found dirt and debris still in the oil passage on the crankshaft which the machine shop had "checked, cleaned and polished". So much for the "cleaning". Now, if I have a crankshaft out, I clean it myself with rifle brushes, no matter what. Don't think anyone's oil could have prevented that failure!

I agree on the rest of the steps you mentioned. 👍

I cannot find a spec on minimum oil pressure.

Main bearing clearance depends on whether the bearings are early or late(with lead/tin overlay)
Early style max permissible clearance is 0.013" with new bearings should be 0.0053-0.0082"
Late style max permissible clearance is 0.010 with new bearings, should be 0.0030-0.0059

Connecting rod clearance new bearing .00032-0.0060 Max permissible 0.012"

Oil pump
total clearance on end of gears and cover 0.003-0.007" Cannot find a tip of tooth to housing spec in the books I have, however I believe the most likely place for the pump to be leaking is in the housing surface between the inlet and outlet ports. In other words, on the sides of the gears more than the tips of the teeth. The bypass/pressure control valve in the pump could dump a lot of flow if it's plunger and seat were not in good condition. The turbocharger oil valve sends unfiltered oil to the turbocharger during startup until pressure builds up, so I doubt it has any bearing on your problem. Same thing with the cooler bypass valve and oil filter bypass, neither one dumps oil flow to the sump, instead they bypass oil to the normal oil flow passage after each component if pressure builds too high because of cold oil or restriction from other causes.

The other grader engine I mentioned that had sucked up parts left in the oil suction bell screen was a D311 in a 212. We got it not running, pulled it off the trailer and started it, once, before clutch pressure plate stuck in the released position. As soon as the oil pressure gauge failed to come up, I shut it right back down. Pulled the engine to fix the clutch and diagnose the oil pressure. I soon noticed red silicone gasket maker on various engine covers and oil pan, oil gallery piping etc😞

In the end, I found that there were still 2 loose roll pins in the suction bell and one or more had been sucked into the intake of the pump and ground up in the gears. Not having another oil pump on hand and "just for grins", I took a file to the gears and the housing, removing any metal that was smeared up "proud" of the surrounding surfaces. Reassembled it all and it had good oil pressure always pegging the gauge when it was running. 😆