I recently bought a '95 F-150 with a 300 inch six. The oil pressure runs about 2/3 up the normal range on the gauge. The other day after it sat for 7 hours, I started it up and the oil pressure was at the very bottom of the normal range. I shut it down and checked the oil, which was OK. I started up and began to drive. After going two blocks, the pressure gauge came back to its normal position of 2/3. What gives? Do I have a gauge that occasionally may stick? The truck has 58000 miles and I put a quart of Rizlone in it when I got it about 200 miles ago. I have run Rizlone in all my vehicles for the past 20 years with no ill effects (176000 miles on my '84 300 incher and still running strong), but wonder if, since the truck probably never had rizlone before, maybe I dislodged something that temporarily restricted oil pressure?

 

I have had the same problem w my 90 f150 for ages .Ive replaced the sending unit that screws in the block several times ... has no effect ? I have screwed in an actual number pressure gauge and ran the engine at idle for several mins and it reads about 55 to 60 psi as it should . Its had Mobil 1 in it from day one ...now has 157K miles . Ive only ever heard of one owner that actually had an oil pump die on the 4.9 . I reckon its a Ford ghost ?

 

You might want to check for a loose wire at the sender unit. As I understand it Ford for years has used an ON/OFF type pressure sending unit in conjunction with a guage. The guage is in place of an idiot light. Just like the light you should either have pressure or not. You should notice the guage never moves from idle to high RPM and never fluctuaits with oil temperture change. The sender may be on its way south. I guess it is possible to disslodge some sludge with the oil additive. If you remove the sender unit you should find the build-up there if thats the cause. Let us know what you find. Chris

 

Today I removed the oil pressure sending unit and installed a number gauge and drove the truck for several miles ....Pressure at 2000 rpm stayed a little over 50psi . I then took a look at the gauge itself in the instr cluster . What I found was a small circuit board in the lower left hand corner of the of the instr cluster . Im not sure what it controls although I suspect it controls the values for the gauge to read and turn the info into the readings we see ? Its held in place w 2 screws . It had metal contacts that touch the little copper roads that send the power to all the gauges .Mine seems to have accumulted some dirt over the last 10 yrs and didnt seem to make good contact . I cleaned them up , reinstalled the cluster and now my oil pressure gauge is back steady and true as it was in its younger days . Removing the cluster is easy except disconnecting the speedo cable ...What I did was release the cable where it clips onto the trans and another clip just before it goes up thru the floor . This will give you enough slack to get your hand behind the cluster to release the cable and snap it back on .I hope this solves the problem for others .

 

I found this on the Performance, Hot Rodding, and Custom forum of this website:

"Oil (Idiot) Gauge"
Posted by Tom Davis on Aug-01-99 at 07:49 AM (EST)

Did you know that Ford has been duping us for a long time. The oil pressure gauge in most Ford Truck and Cars manufactured since about 1986 has had a "Fake" oil pressure gauge. The gauge is drive by a switch which switches on at about 4.5lbs which ties to a resistor that causes the gauge to deflect to about 2/3 scale.. I was totally unaware about this when I bought my new truck F250 Powerstroke. I sent ford a complaint and they said basically "It's designed that way and we aint gonna fix it".... Below is a link to a site that details this scam...
<a href="http://www.asashop.org/autoinc/march98/techtips.htm">http://www.asashop.org/autoinc/march98/techtips.htm</a>

 

ok here's one for ya,,,,,my oil pressure guage went to zero too and also my temp. guage is messing up,,,it never seems to go to the cold range,,it just about always starts at the normal range and goes up from there,,sometimes when driving it will bounce back to normal and be ok untill next time i start up. all this seems like an eletrical problem but i have checked all the connections,,any suggestions???

 

Get some real gauges so you know what is going on. My '82 still has the original gauges that operate like real gauges on an linear scale, but I'm going to get a good set of real gauges so I can really know what my oil pressure and temperatures are.

Slik

 

I asked my mechanic to install a real oil pressure gauge in my '95 F150. He is aware of the idiot oil pressure "gauge" (he used to be a mechanic at a Ford dealership). He said that he wasn't going to waste my money on the gauge because the gauge already in it is a real oil pressure gauge. He also told me that the needle won't move around as much with EFI as it will with a carburator. I remember my '84 F150's oil gauge didn't move around that much, but usually was about 2/3 up the scale and occasionally would move to the top of the normal range. I would think that with the dummy oil gauge you would see the needle just zip into place, but on my '95 when I start it, the needle slowly moves up to its normal place.