Hey all well I may have run into another problem with my truck. Before I start with the story I will tell you about my truck. It is a 1992 Ford F-250 4x4 with the 351w V8 and the ZF 5 speed manual transmission. It currently has 189,000 miles on it. My truck was sitting for a few weeks as I was driving my other car to save gas. Well, I needed to take some stuff to the dump the other day so I fired up my truck and let it sit there and warm up as we loaded it. Everything looked, functioned, and sounded normal. Then we drove about 10 miles to the closest gas station so I could put fuel in it. I realized as it was filling that I never checked the oil after letting it sit for a while so I popped the hood and pulled the dipstick.... woops. The oil was barely on the dipstick, yet the oil pressure gauge said it was normal. I do know that the oil pressure gauges are fake and only act like an idiot light. I found out that they show normal as long as the oil pressure is about ~4.5psi! That is super low!

Anyway, I decided to go to the nearest auto parts store so I could buy 3 quarts and top it off. I fired up my truck and immediately noticed that the oil pressure gauge never got to the normal range. It was higher then the red, inside the "normal" bracket, but only a little. It wasn't half way in the range like it normally is. This is what it looked like:

I always watch the oil pressure gauge when I start the engine and this is the first time that it has never jumped right to "normal." So I backed back into the spot that I had just pulled out of and I shut the engine off as fast as I could. I then went inside and paid $5.50 a quart for 3 quarts of Vavoline 10w30 conventional oil. (That is what I put into it when I changed it last time.) I put the oil in and fired up the engine. The oil pressure gauge went just to the right of the red zone again just like it had a minute ago. I let the engine idle and I slowly gave it some gas. After about 30 seconds of running the gauge jumped to the middle. I thought, OK that was the issue, it was just low on oil and I drove to the dump. The rest of the day everything worked fine. Then the next day I went to drive the truck in the evening and I started it and the oil pressure gauge went to the middle and looked normal. I drove it about 75 miles and it was working OK. Well then after hanging out at a friends house I was gonna leave and go home. When I stated my truck the oil pressure gauge was showing really low again. I shut the engine down and pulled the dipstick. It was showing at just above the add a quart line. I didn't have any oil with me and it was 11 pm so I just drove home carefully. I didn't rev the engine past 1500 and I was constantly listening for any weird noises like knocking so I could shut the engine down if it really was low. I got about 3/4 the way home. (About 15 miles) and the gauge just suddenly went back to half where it is supposed to be. I parked the truck last night and fired it up this morning to take another load to the dump. Again, the gauge is showing low. I need to make one 40 mile trip to the county dump (today) but I am afraid that I really have no oil pressure. The weird thing is though, that everything I read said that if I had no oil pressure the gauge would be all the way over to the red like it is if I turn the key on without starting the engine.

But, the gauge is showing something. This is what it looks like:



I need my truck today, and right now I'm guessing it is just a gauge issue because everything else sounds and functions normal. This is the only symptom I have. Another thing I read is that bearing wear in the lower end would cause low oil pressure, but it is running normal and doesn't sound any different. Also, when I started it the other day for the first time in a few weeks it started the second I hit the key. It literally didn't even crank over twice before it was running. This engine runs very good, always starts right up, and I always change my oil every 3,000 miles.

 

You are wise to always observe you gauges on startup.
The stock gauges are mostly go-nogo.
What you need to do to verify the real oil pressure is to locate a MECHANICAL test gauge and attach it.

 

That guage just says you HAVE oil pres.......not how much. The sweep (range) in normal is really meaningless.
I would say nothing has been damaged and you are good to go, but you need to install a good mech oil pres. guage if you really want to know the pres. you are running.

I would be more concerned with finding out where your oil is going, sounds like you have a oil consumption issue.

 

I knew that the gauge only showed that you have pressure, but not how much. I just know that when the sender unit says there is enough pressure the gauge is supposed to show about half and mine isn't. Weird thing is right after I posted the first post I went out and fired up my truck and it went to the middle like it was supposed to. I just drove the truck about 50 miles and it was working fine. The oil is leaking, I knew about the oil leak. It really isn't too bad. I usually can go 2,000 miles before I have to add any, usually it is about a quart for 2,000 miles. I now have about 2,500 miles on this oil change so I am assuming it was so low because I didn't to check it and it sat for a while. I believe that it is leaking from the front crankshaft seal, at least that is where it looks like it is coming from.

I will change the oil soon, and see about getting a real oil pressure gauge and hooking it up. I'm not too worried about it now, I mean I just drove it 50 miles and it was fine.

Thanks for your help,

Derrick

 

Every '93-'96 I've ever owned (I've had many-something like 25+ at last count) regardless of the engine/trans combo has always, without fail, had issues with that *$#% oil pressure gauge. Its always smart to check the pressure mechanically, but really this is such a common thing with these trucks, I wouldn't worry...
Roger

 

My 1989 f150 with a 351w has always looked like that pic. you posted. I have not had any issues with it in 3 years, so it must not be a major problem. It wouldn't be a bad idea to hook up a mechanical guage though, so you know what pressure you are truly running. You can't believe everything you read, except on FTE! HAHA!

 

IF you are loosing oil and there are no leaks found on the engine, its probly that stupid oil sending unit leaking and causing the wierd readings. On my 89 the guage went low and set the check engine light off. Found the sending unit full of oil. I went ahead and put on a mechanical guage as I had one. Found out at fully warmed up at idle I get 15Psi, rev up engine it goes to 35 to 40Psi.

 

thank god lol my 93 says the same but raises a little if i change the oil i figured it wasn't a problem 210,000 is just breaking in a ford lol

 

I see that these trucks have dummy gauges .for some reason I forgot to check oil only for 6 days .when I checked it was 6 QTS low.cand find any drips or spots in driveway . bottom engine does have light coat oil though thats wet. But cannot seewwhereas coming from. 1991 f-250 7.3 ohv diesel 445 cid .... So I topped off oil . four days ago I drive 120-170 miles a day in last two weeks . truck seems to be running fine .did notice pressure gauge has always been in middle of normal.since topped off oil .it is in middle of normal on sweep on streets and idle. When I get on hwy between 55-85mph there are fluctuations from middle to the n on normal. Then back off highway goes back to middle of sweep.could the oil pump not be maintain enough flow at highway speed cause this???? Possible sending unit? Or pump ? Thus truck had oil change 1 month ago and I have put 2099 mikes in two weeks .after it sat a while only has 92,0000 miles and is a 1991 .so has sat a lot over 25 years. What should I check first .oil has stayed at full mark for 4 days 600+ miles. What could cause loss of 6 QTS in week. With no evidence of bad leak doesn't drip on driveway ? Please help .need advice worries about ruining engine as this is my only vehicle and I am currently commuting 120+ mikes day round Trip.

 

Welcome to FTE if you'd like a good response to your question I would start by making a new thread, there is a button on the top right of the page that allows you to do so and will grant you better answers to your problem than a post from 2010.