Ford oil pressure gauge

I started my 1991 Ford F250, 5.8L and noticed no oil pressure on the gauge, so I shut it down immediately. I investigated on line and discovered the gauge on my truck and many other models are not a true gauge. The circuit employs a normally open pressure switch that closes on engine oil pressure. The gauge circuit is fixed with a 20 ohm resistor to make the gauge indicate a fake pressure, which never changes with engine rpm or temperature.

WHY WOULD FORD DO SUCH A THING?

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As long as you got enough oil pressure to lube the engine you are good. 30 or 80 lbs you are still just lubing the engine.

This allows for a cheap on and off gauge and sensor system.

(quoted from post at 02:57:02 12/08/14) I started my 1991 Ford F250, 5.8L and noticed no oil pressure on the gauge, so I shut it down immediately. I investigated on line and discovered the gauge on my truck and many other models are not a true gauge. The circuit employs a normally open pressure switch that closes on engine oil pressure. The gauge circuit is fixed with a 20 ohm resistor to make the gauge indicate a fake pressure, which never changes with engine rpm or temperature.

WHY WOULD FORD DO SUCH A THING?

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All of mine change with rpms and temperature. I have a 1978 F150, 1986 F250, and I just traded off a 1991 F150 and all of them the gauge would lower when warmed up and idling and then raise when the rpms came up.

I will not argue, but check if your trucks have a true sending unit or a pressure switch.

I read a long article about Ford and why they make gauges that don't fluctuate very much if at all. Has to do with people being concerned about what they are seeing. My 79 F250 ammeter barely moves to + or -.Temp is hard to get up to normal. Fuel gauge works fast on it way to empty. I can't remember where I read the article as it was years ago. Ford trucks forum info says yours is a bad connection and a common problem.

Almost all of their oil pressure gauges are what I call "idiot gauges". Just like an idiot light they only read no oil pressure under a certain PSI, just like when a light comes on, that pressure is 6-8 PSI. If the gauge actually fluctuates, either the sending unit or gauge is bad. It will read around the middle of the gauge if the pressure is above 6-8 PSI.

I don't know what models have real gauges but most of all gasoline cars/trucks used the idiot gauge for the last 20 or so years and older, diesels use real pressure gauges though, at least until the most current trucks. Its not just Ford that has uses those types of gauges, many other brands do and have for a long time.

Ford and others do this because of the whiny American consumer. We all know that two identical engines may not run the same oil pressure. Two neighbors buy identical trucks and inevitably compare the oil pressure readings. On Monday they will both be in the dealer whining, one saying his has too much pressure, the other too little. Neither truck is broken, but both want them "fixed". It is a customer relations nightmare. I saw this scenario many times when I worked at a dealer. Dodge and some GM models have gauges that show a theoretical pressure calculated on rpm and temp.

Same thing on my 1990 Bronco. Reads high when first started - the needle slides down the guage when it warms up.

Analog Idiot Gauge

Your post reminds me of when I got out of automotive school way back in the early 80s. An elderly man came into our shop and needed a new battery. I don't remember the exact make or model of this car, but it had to have been a 70-something Chrysler product. Anyway, his car had actual gauges in it, including a genuine ammeter gauge. He bought a new battery and the next day he came back because his amp meter was reading in the "+" side of the 0. He said it hadn't done that before. (Don't know if it did or not, we just took his word on it) So the boss gives him another brand new battery. The next day he was back because his amp meter was still on the "+" side of zero. My boss tells him to hit the road, being more polite about it than I just was. The elderly gentleman then hits a repair shop down the road and has them check out his car. They tell him it is fine. A third repair shop sees the guy the next day, but by then the word is out that this guy has a problem that doesn't actually exist and they tell him to hit the road. (It was a small town, the word got out)
All this could have been avoided if this guy had an idiot gauge on his car and the car manufacturers finally figured it out.
The same way with a genuine oil gauge. Most uninformed owners will freak if they see the oil gauge fluctuates from high to low as the oil heats up. But yet, they feel good having a car with a gauge, albeit a fake gauge, because they love to see the genuine reading on the gauge, even if it's a fake gauge. They just don't know it's fake.

Exactly right, Gambles. Think about all the money and time lost doing warranty repairs to "fix" the customer or simply ghost problems. All the batteries, oil pumps, bearings, engines etc. All the different fluctuations due to different types and brands of oil, temperature changes, other vehicles that are identical but different, lower or higher etc....