Hi,

My 84 F250 runs great but I've just noticed a little quirk, lately. At lower speeds, the oil pressure gauge (stock) shows normal pressure but at highway speeds, it drops to zero. It has plenty of oil and runs fine. What do you think that this indicates?

 

Bad sender... If it really is at 0 you'd head tapping / clanking sounds.

David

 

A faulty ICVR (instrument cluster Voltage regulator) or Sending unit or a particle of something plugging the orifice.

To replace either one isn't that expensive

just time consuming on the VR as it's behind the Instrument cluster.

My suggestion:

Purchase a mechanical oil pressure gauge and T-it into the same portal the SU is in.

when the pressure reads low on the cluster gauge go look at the real mechanical gauge for a reading.

 

OK, thanks for the invaluable advice! That's what makes this such a great forum.

 

Not likely the VR if the fuel and temperature gauges aren't acting the same way. May just be an intermittent connection at the oil pressure sending unit terminal since it's in a dirty/oily location. But, probably the sending unit. For peace of mind, put a good mechanical gauge on it but beware of the el-cheapos; some are very inaccurate, especially at the low end. The good ones usually come with copper tubing while the cheapies come with plastic.

 

The one I am thinking of doesn't require tubing.

It screws right into the brass Tee and sits right beside the Sending unit.

Yes,, get a good gauge.

 

But it'd be kinda hard to read at highway speeds where he said the problem occurs, LOL.

 

He can pop the hood and rev it up when he stops the truck

 

I have seen well worn/ gunked up motors pump all the oil out of the pan up to the top end at high rpm, then the pump starts to cavatate, the oil pressure drops out and the lifters get noisy.
Slow the motor (and pump) down, the oil returns, the pressure is restored and the motor quiets back down.
When a motor gets old, all the clearences between parts become excessive.
These clearences are lubricated by oil being pumped thru them.
When the clearences become excessive, it takes more oil to feed them resulting in a lower oil level in the pan.
Also motors get "crapped up" inside from infrequent oil changes, blow-by from worn piston rings, old broken gaskets etc. This "crap" blocks the oil return holes back to the pan resulting in sluggish "drain back"
Of course this is a 'worse case" scenario
Like the other guys suggested, install a mechanical gauge tubing in place of the factory sending unit and mount the gauge under the dash.
This will aid in isolating the problem.
To gauge how worn your motor is, listen for knocking when you first start it up after an oil and filter change. Those seconds when the oil pump is priming the filter and oil galleys. On a good motor (new or freshly rebuilt) there will be no knocking.
With a worn motor that has excessive clearences a thicker oil will buy some longevity.
Good luck!
Steve G.

 

Thanks, again, guys...great advice!

 

By chance, do you have a 460 with in-tank electric pumps? The trucks with 460's from 84 to 87 that were carbed had low pressure in-tank pumps in an option that Ford called the "Hot Fuel" option. The fuel pumps have 2 circuits, "start" and run". The oil pressure switch will shut off your pumps if your pressure drops below 5 psi. Ford did this so in case you got into an accident and the motor shut off, the fuel pump wouldn't spew fuel into your engine compartment and cause a fire.

If your oil pressure gauge reads zero and the truck keeps running, it's probably just the gauge and not the pump. Good Luck!



Dan.

 

My 460 has a mechanical fuel pump which seems better than the "hot fuel" option. However, it did go bad a while back and allowed fuel to leak into the crank case, filling the engine. What a mess...it was a good thing that it didn't explode!

 

make sure theres not to much oil in it that will cause it to airate oil from crank hitting it and to and drop pressure driving down highway my 460 will do it at only a 1/2 quart over full

 

*Please NOTE:
I do not recommend installing an oil pressure gauge with tubing inside the cab.

If that pressure line ever bursts you have really hot oil blowing around inside the cab.
*Not Fun*

You don't need really one inside the cab anyway.

The Ford gauge is adequate for regular use in monitoring the pressure.

While driving : If you notice the gauge drop, the first you have is the inclination is to pull over to the side of the road and check things out anyway.
Once pulled over, you pop the hood and read the usual correct reading mechanical gauge.


I wouldn't take the chance with an Oil line in the cab.

I would buy an electrical oil pressure gauge for the cab first.