My 1989 F250 7.3 rear main is weeping just a bit as indicated by the old guy puddle under where he's parked. He just turned 200000, but runs with no issue minus the usual wear and tear maintenance fails of the alternator, belts, etc.....
On a 10000 mile trip recently, I noticed some odd behavior with the oil pressure gauge.
I have used 15W 40 Heavy Duty for diesel in the crankcase regularly.
In the northeast I changed the oil at 5000 on the trip. The pressure gauge was where it usually sets. I ran down to the southeast and it was warm and humid. The pressure gauge dropped a bit as the oil thinned in the heat of the day and with the weep of the rear main, I figured this is OK. The temp gauge ran hotter as expected due to the outside temps.
The odd thing is that the drop was not consistent. On an even hotter day in Texas, the oil pressure gauge actually showed higher pressure than the usual spot where the needle usually sits.
Now I started watching the gauges as I drove across the long runs of the west. The voltage, temperature, and the oil pressure gauge all seemed to be connected somehow in that their variability that did not make sense. When the temp gauge showed hot in the heat of the middle of the day the pressure gauge would show higher than in the normal running of the cool of the morning.
Is there some actual physical property correlation in the performance of the engine that I am missing where hotter oil is thicker than less hot oil (the oil is never cool or cold of course except in the start of the morning and the gauges all hit their normal marks at start up) ? Is there some sort of funky ground problem with the 1989 gauge set in the dash that has each of the gauges interacting with each other ?
Is there something else I am missing ?
Since there were long stretches of summer travel, I noticed similar behavior on more than one occasion.
Thanks for the help.

 

Your oil pressure gauge is not a gauge. It's hooked up to a 3 PSI /switch/.
It's just an idiot light.

You are seeing variation due to temperature affecting the resistance of various components.

There are topics on how to replace the sender and cut out the loading resistor Ford installed to make it work with the switch instead of a pressure sender.


That being said... None of these gauges are particularly accurate, and our Fords have a problem with grounding on top of that.
If you really want to know engine temps or oil pressure to the PSI, install an aftermarket gauge. The cheap digital ones off Ebay work just fine.
Also, when you go through the truck, ground the **** out of everything. Wires from batteries to fender, to alternator case. Wire to firewall/cab. Wire to frame. Try to make sure you've got good connections between everything.

 

welcome to FTE.
as said above, the "gauges" in these old trucks are really just glorified idiot lights.
a set of real gauges and new grounds to everything helps solve a lot of little issues.
i use the stock battery to block wire, then add car size battery cables from block to frame and block to cab

 

I'm guessing the answer is no, but does anyone make a replacement cluster with real gauges? Or are there any gauges that'll fit the existing with adaptation, or threads on the subject?

 

Basically.... no, not that I know of, don't know?

Many threads exist on add in gauges, but not sure that anyone has done a cluster adaptation thread.... You'd have to search and look, but most people haven't really cared that much and just dropped in a random gauge, or some gauge pods.

I do think it would be neat to adapt some better gauges into the existing cluster, not sure it would be worth the hassle though. One option is to take out the existing stuff and slap in a sheet of plastic or metal with whatever gauges you wanted. It wouldn't look as clean as stock, and the wiring would take a little bit of work, but it could have whatever accurate gauges you wanted.