Hey, I just went and looked at a 92 D350 that is for sale. It looked pretty good inside and out. I decided to take it down the road so I started it up. The oil level was good prior to starting and the oil pressure came up to normal. I drove it for about 10 minutes and then came to a stop at a light. I noticed that the oil pressure dropped down to the first mark off of L. When I pulled off, the pressure came back up. Is this common? My 91 W250 doesn't fluctuate like that.
Also, I noticed that the odometer did not work even though the cruise, OD, and speedometer did. What would cause this? This truck ran a lot cooler than mine. The temp gauge never came into the normal range. Mine usually runs about the middle at 60 mph.

Thanks,
Chris

 

If it's not making any bad noises I'd suspect the oil pressure sender. The temp could also be a sender or a stuck thermostat. Did the upper radiator hose get hot?

 

Both my 93s run at idle at the 1/4 up and at speed at the 3/4 up on the oil, neither ever run at 1/2 on the temp always just off the first 1/4 mark unless loaded on a 100 degree day pulling a grade. hope this helps

 

My '91 did the same thing and I was worried about it, so I looked at the manual. It clearly states that at idle it should be on the low end, and about 1/2 when at speed. It's right on.

 

I know mine runs on the high side. @ idle it runs at 60psi, I believe that is just over half on the factory gauge. It stays there unless you fuel hard then it will climb to 80 or so.
Heath

 

Yeah, the manual specifies that it shoud be at the low end at idle, which seems sorta scary, but I guess that if thats where they say it should be, then ok.

 

All right, thanks. I guess it is nothing then. Maybe this is how it should be and my 91 is the one that is not typical.

 

teh oil sender went bad in my truck shortly after buying it. It had always read lower than I thought it should, eventually got to where the light came on at idle. Put a mech. gauge on and the motor was just fine.
I have rarely been over the 1/4 mark on the temp gauge, even towing uphill in the summer.

 

I am not sure but I have heard that oil should be at least 10 psi per 1000 rpm. That is the minimal it should be and anything above should be ok. After a hot run down the track, mine has idled down to 40 - 50 psi (during summer) and have seen it climb to 75 - 80 during fast runs down the track. Upon startup (cold) I have seen it go right up to 85 - 100 psi on those cold mornings. Drive real easy and it settles back down to normal after a few miles. I have 215,000 miles on the truck. As for the stock gauge, usually around the 3rd line going down the road.

 

my 93 does, more or less, the same thing. i took it to a cummins shop for a look. they put one of their oil pressure gages on it and it read 25-30 lbs oil pressure at idle and it jumped up to 60 as soon as he hit the throttle. he said no worries.


jeremiah

 

ya, 10-12psi at idle is really enough. It'd be a sign that the motor is getting tired, but no damage is being done

 

On my 91.5 the red light would come on at stop lights,turned out to be the sending unit.The truck had 150,000 on it at the time.

 

I was told by a diesel mechanic these engines like a slight turn up of the idle RPM's. Helps things flow nicer, increasing longevity.