A few weeks back I noticed that when idleing my van the oil pressure drops down to around the N in normal on the guage. Then when I get up to speed on the back roads it will stay between the R and the M, when it used to stay around the A or the L all the time.

I changed the oil and replaced it with part synthetic and a Fram Tough Guard filter. That didn't help hardly at all. the van is a "92 3.0 with 186,000 miles on it. what things could be causing the oil pressure to run so low at idle... is it just getting old or what?


Thanks

-Mike-

 

I also have a 1992 3.0L. It has always been my understanding that the OPG in many Ford trucks from the late 1980s on is actually a glorified warning light. When the engine is running the needle on my OPG stays between the R and M at all engine speeds, although very occasionally, during the many years I have owned the van, the needle does go to a different position, without regard to engine speed, temp etc. Here's an interesting quote about it: "In recent years, Ford Motor Company has been doing something I view as a bit sneaky. They have taken the oil pressure gauge and turned it into a glorified warning light. It says it's an oil pressure gauge, it looks like an oil pressure gauge, but in reality it is not.

A conventional magnetic oil pressure gauge on a Ford consists of a gauge and a variable resistive sending unit. As oil pressure changes, the resistance of the sending unit changes, which in turn causes the gauge needle to move.

This system worked well for years, but starting in 1986 a change was made on some models that altered the function of the oil pressure gauge as we knew it. The variable resistance sending unit was replaced with an open/closed switch and an in-line 20 ohm resistor was installed between the gauge and the switch. Anytime you have more than 4.5 psi of oil pressure, the switch closes, completing the circuit from the gauge (with the 20 ohm resistor in-line) to ground. This then results in a gauge that reads just above the middle. As you can see, there is no variation to the gauge needle in this circuit. It will either read no oil pressure or half-scale (normal oil pressure). On this style of gauge circuit, if the oil pressure gauge reads in the middle, it is telling you only one thing - you have more than 4.5 psi of oil pressure. How much more is anyone's guess at that point. When oil pressure drops below 4.5 psi, the gauge will return to 0 and alert the driver of a problem. Didn't warning lights tell us that much?". Jan Richter

 

Is there a way to put a 'sending unit' in that would actually give me a good indication of my oil pressure, without replacing the guage? My dad drives the van almost four hours a day at interstate speeds so he would really like to keep a closer eye on it, especially with 186,000 miles on it. We thought it was a 'real' guage and not just some 'dummy' guage. Why did they set the thing to work after 4.5 psi? that seems really low to me!


thanks.

-Mike-

 

4.5 psi is the pressure at which the warning light is extinguished so I suppose it is regarded as a minimum safe pressure at idling speed. I think the gauge itself is a "proper" gauge and will work as such if you can find a suitable sender unit. I remember reading that someone was able to get info from Ford about which sender unit to use but I have no further details. Jan Richter

 

I know it's been posted on some other boards...but quite a while back. If you're really interested, try the Ranger/Explorer board.

I couldn't find it in the tech articles section.

Mark

 

Mike, you may be concerned needlessly, and here's why: Today's motor oil, especially the current "SL" SAE oils, are so slippery, that the oil is actually flowing so efficiently in the bottom end of the motor, the oil guage and sending unit is actually calibrated for yesteryears' good, but less efficient oils, as when the van was new. In fact, I even read in a few different sources, that the major brand conventional oils, are actually part synthetic, right out of the bottle! You think there is a problem with oil pressure, but it's only the oil doing it's job better! The new Mobil 1 (with SuperSyn) Redline, and Royal Purple are excellent full synthetic products. With the mileage on the van, make sure the oil and filter are changed at regular intervills, the crankshaft, main bearings, etc. love fresh oil. As long as the oil pressure is not 0, then I think you will be fine ...Ed

 

We decided to put a real mechanical gauge on our 87 van the other night. Turned out the sending unit was bad. We plan on leaving the mechanical gauge on perminently. We just hooked it in line with the new sending unit and put it inside the van. Now we should know when there is small differances in the oil pressure and not have to rely on an idiot gauge. We purchased the sending unit from Autozone along with the proper fittings........ The sending unit was only about $6.00 and the mechanical oil pressure gauge was $14.99. Extra fittings didn't cost much. I just went ahead and replaced the sending unit when I added the mechanical gauge since it was so cheap anyway. I just hung the gauge on my ashtray. Don't look pretty but it doesn't lie about my oil pressure. Hope this helps.

 

thanks for all the replys guys. you all have given me a lot of helpful information.

-Mike-

 

I had an 89 Aerostar with the 3.0L. This was a real sender yet and I had the same symntons. The light would come on at idle sometimes. This turned out to be a bad sender unit. My 93 aerostar with the 4.0L had the glorified switch sender as refered to above. Your 92 with the 3.0L may have a real linear sender like my 89 did and you may fix your problem with a new sender.

 

I have had my gauge on my '94 3.0L always stay in the middle for years. No matter if idling or cruising. Then a month or so ago it had dropped to between the N and O. So I was thinking a bad sender, etc. As part of routine maintenance I put a new battery on recently and guess what...the oil pressure gauge is suddenly back in the middle where it always was. The battery was never really bad, or never dead. Just had never been replaced since new. Everything else was fine. Just got a good deal on new battery and decided to replace it before the old one just died on me one night!