Oil pressure in low mileage 6.5

[Lokel Yokel]

Hello, I'm new here. Im real close to buying an RV with 35,000 miles that has a 6.5 TD in it. When I test drove the vehicle I saw 40 PSI in cruise. 10 psi when off the throttle...at idle....but then occasionally the oil pressure would smoothly drop to about zero. If I blipped the throttle it would come back up to 10. And possibly sit there. Not just drop right back down. A few minutes later at idle I would see it again.

I heard no valve noise. (Not sure though that these motors use hydraulic valves...maybe solid lifter in which case I would not here that noise.). Also the motor did not stumble for lack of fuel. I thought maybe the flow of fuel might be controlled by an oil pressure safety switch.

Any thoughts on this?

[More Power]

The 1997+ engines incorporated piston oil spray cooling, which lowers overall oil pressure somewhat. 10-12 psi at a hot idle is about right, and 40 at cruising speeds is also about right.

It's important that you use the correct motor oil. If conventional petroleum, a 15W-40 is appropriate for most folks. A 5W-40 synthetic or possibly the 15W-40 synthetic is best for a diesel that is worked hard in the hot summer heat. How an oil deals with heat will affect the engine's oil pressure. Jim

[Lokel Yokel]

Thanks for that.

Any opinion on how crank bearing, cam bearing or oil pump failures manifest themselves. Are they intermittent in the indication or does pressure just drop every time you let off the throttle?

I'd like to "TRY" to rule these out. And then considering the fact that the motor still gets fuel, (I THINK it's the PMD that closes under low oil pressure)....I could be reasonable sure it's the regular oil pressure sending unit that is the problem.

This motor is in an RV that I would like to buy. It is in Florida, I am in Vermont. I went down and test drove it then had to hustle home. Taking it to a shop was not an option. I was pretty sure it was reasonable to think it was the oil pressure sending unit, but began to question my thinking as I got to pondering it.

[JohnC]

Oil pressure plays a role in the operation of the fuel lift pump, but will not normally prevent the engine from running. I'd have the seller replace the oil pressure sender and see if it cures the problem. If it does, get it in writing. If it doesn't, I'd think about walking away.

[Lokel Yokel]

Okay.....I didn't buy it. The seller is going to put a scanner on it. I asked that he put a sending unit in. I won't buy it if I can't look at good oil pressure on the gauge. I don't think anybody will. Thanks for your input guys.

Justin

[Warren96]

Mine is a little different (it has no piston oiling as yours has ) I just use 30 w year round. Mine has a few more miles on it than yours, so see if you can use that as a bargining tool. Although "More Powers" response carries a lot more weight around here than mine! On his recomendation I would buy it.