oil pressure issue JD 650J

question for any of you out there with more mechanical know how than I. I operate a 2007 JD 650J LGP (see avatar) configured as a Fire Dozer (Tractor-Plow). Engine currently has 1939 hours on it. On the last couple of large fires I was working, starting having an oil pressure issue. OP normal runs on the high side of the dial (upper 2/3rds). On several occasions, and only after about an hour of "on the ground" time, plowing and then blading out fire lines, oil pressure drops to below the halfway mark on the dial, then suddenly bottoms out into the red, Stop light and alarms come on, I stop tractor activity (engine is still at full throttle), alarm stops, pressure comes back up (though not to the high position). If I continue working, this repeats itself several times. Once I report the problem, I'm usually called off the line and walk tractor back out to my transport, At walking speed, tractor does not display this behavior, and usually once shut down, and somewhat cooled, does not resume problem. Also, this has not happened every fire, only 3 of the dozen or so I've worked this year.
Any thoughts on what might be the problem?? I'm thinking possibly a bad/intermittent oil pressure sending unit, or possibly the wire to it has a short...

Thanks

There is a good chance the gauge or sending unit is bad. If you are able to, I recommend installing a mechanical gauge and see if you get the same results as the factory one.

I agree with moriboy. Slap a mechanical gauge in and go to stalling out functions and see if they react the same. There's an oil pressure regulating valve in those engines that I've seen the tang around the poppet break and cause oil pressure issues but it wasn't that intermittent. Does this machine have all the fire package on it? It's possible that a wire is rubbing...

Tractorguy said:

I agree with moriboy. Slap a mechanical gauge in and go to stalling out functions and see if they react the same. There's an oil pressure regulating valve in those engines that I've seen the tang around the poppet break and cause oil pressure issues but it wasn't that intermittent. Does this machine have all the fire package on it? It's possible that a wire is rubbing...

Click to expand...

yes, the full fire package, uprated engine hp, fire program for computer.

Thanks for the suggestions, I shall forward them yto the maintenance shop fo followup

Any chance you have a fuel pressure gauge? or fuel pressure sender that got hooked up to the wrong place?

I've never seen a fire dozer, but I can imagine a "customized" package having that kind of mistake. If nothing is obvious, then you have a heck of a time diagnosing something like this. I'd add a second line to the oil pressure sender and a multimeter in the cab, then you can see if the sender is reading the same while the gauge drops, AND have your mechanical gauge to compare. For all the time it takes to go out and work it an hour on the chance it might act up, I'd want all the checks I could do at once.

update for all of you interested (and thanks for the help and suggestions!) had the oil pressure sending unit replaced ~ month ago, no oil pressure warning lights, buzzer noticed during normal (fire) operations