450c oil pressure falls to 5psi at hot idle

[nelstomlinson]

When the engine is started, idling oil pressure is about 20psi, at 2000rpm maybe 25psi. Once the engine is hot, the idling oil pressure will fall to around 4 or 5psi, around 15-20psi at 2000rpm when hot.

Am I correct that this is too low? What is likely to cause this?

Using fresh 15w-40 Rotella T4, probably about 10 hours on the engine since I plasti-gaged the main and con rod bearings and found them to be OK, clearance about middle of the range. This is the loader I did the in-frame rebuild on.

[B Town]

Hello Sir,

I was taught you needed 10 # of pressure to keep the oil gap. I would say yours is low. Probably too low.

Did you do any work on the oil pump? I assume the in-frame didn’t include cam bearings or balancing shaft bearings. These can be common site of oil pressure loss.

Best regards, Bruce

[nelstomlinson]

Thanks, Bruce. I had to pull the oil pump to get at some of the bits in there, but I didn't think to check the clearances while I had it out. I didn't check the cam bearings.

Does anyone know if there is supposed to be a gasket between the oil pump and the block? I don't remember putting a gasket on when I reinstalled the pump, but that could be my bad memory.

The local dealer wants about $400 including shipping for a new pump. That's an expensive part to throw at the problem, so when I change the oil soon, I'll drop the pan and check the clearance in the pump and maybe put in a gasket.

[Jim B]

No oil passage direct from pump to the block to seal. Metal to metal where the pump mounts to the engine front plate. Pump body sections are metal to metal. The oil pickup tube and the oil outlet tubes have O-rings on them where they go into the oil pump body.

Unless you only want genuine JD parts; you might want to talk with and price a new pump from Lavoy, it might be enough less to make shipping worthwhile. Doesn't hurt to ask. This appears to be the same pump as in a number of the JD 4 cylinders. They made a change so that the pickup tube is removable from the body. The original one (which yours maybe) had the pickup tube welded to the back body section of the oil pump. I moved a good back section, with the welded tube, to an aftermarket pump that was built for the O-ring pickup tube, fit up is ok and I expect it will work fine, still working on the engine around hay season and other things. You could also order the O-ring pickup tube to go with the new pump. The pump outlet tube doesn't change. I would expect you can get everything for less than you were quoted. I know the A&I pump shows for less than the JD one at my Ag dealer. (JD owns A&I). Not all dealers will tell people about the option and only quote JD. The on line parts catalog shows the new pump kit and parts being substituted for the old weld pickup tube.

[Rustymetal]

I have heard this is a common complaint on 450C models . I’m not sure but I think that is an electric gauge if so you may try a mechanical one to see if it is really that low just a thought and you may have already done that if not it may save you some work and $$$$ good luck

[Jim B]

450C should have a mechanical oil pressure gauge from the factory. Either way it won't hurt to see what a different gauge reads.

[nelstomlinson]

There are two gauges, the factory gauge on the dash and an aftermarket one mounted nearby, and they give similar readings. I would like to have a good, reliable test gauge, where would I look for one?

[nelstomlinson]

I got the oil pump out tonight, and found that the drive shaft diameter is 0.0006 under the minimum spec. From memory I measured 0.6302, acceptable range is 0.6308-0.6312. I am not sure how to measure gear width, because they are 7 tooth.

Sloppy clearances would keep pressure up when the oil was cold, and would let pressure fall when the oil gets hot and thin.

I shouldn't be surprised that the pump is worn: this is the engine that had coolant in the oil.

I sent a pm to Lavoy, asking for a price on a replacement pump.