Oil pressure up and down, bad sensor??
 

This morning while my truck was warming up, I noticed the oil pressure gauge was not reading and the light was on. I put it in gear, it went up to normal and dropped back down again about 30 seconds later, then went back to normal. Oil level was OK and the truck was parked on an slight incline. I am getting it checked out tomorrow, but am wondering what the problem might be.

Be very carefull with what you do from now on man. I personally wouldnt drive it untill i found out for sure. My experiance has told me that by the time you see the oil pressure gauge fluxuate like you did when driving the damage is already done and the engine is probably damaged. It is very possible that the sensor could be bad, but thats not a mistake that is worh 4 grand for a new motor ( im estimating). Seriously get it checked by a professional if you dont know how.

Yeah, the oil pressure was normal after it jumped a couple times. If there was any damage to be done it is probable already done, because I noticed it after it had been warming up for a couple of minutes.

By the way the truck is a 2000 5.4 4wd, 148K miles.

Replace the sender switch. They fail at an alarming rate.

Install a true guage if in doubt. Remember, your dash "guage" is nothing more than a mechanical idiot light that should show a mid-scale reading at any pressure (as sensed by the goofy pressure switch) above 4-6 psi.

Steve

It probably was a faulty light. Just words of caution though.

ProjectSHO089 is right, the gauges arent very accurate and sensitive. Thats why by the time you see them fluxuate from a faulty pump the pressure has dropped, and your getting metal on metal somwhere. Aftermarket gauges are much better and more reliable.

Where is the sender switch and is it easy to access?

Well, I ran my truck this afternoon and the oil gauge and light were reading OK. I am going to go with the sending unit after hearing what you all had to say and what my mechanic said. If I am looking around the filter for this thing what should I be looking for. I have never had to replace one of these.

To clarify what I said...

The "guage" is not a pressure measuring device AT ALL. It, quite, simply is NOT A GUAGE in any sense of the technical definition of "guage". It is ONLY a mechanical indicator that could just as easily be eliminated from the cluster and you'd have exactly the same information available to you via the OIL fault light.

Do not expect the needle to indicate anything other than a minimal pressure reading. Beyond that, it is completely worthless.

The sending switch is easiest to replace if the filter is removed on some engines. Keep that in mind while you're planning your activities.

Steve

mine's doing the same
 

Mine has been doing this for about two weeks on very cold mornings. The first time it happened I had just pulled out on the highway and went several miles before noticing. Since then, i have watched it each morning, as the needle bobs up and down, there is no variation in engine speed, noise, anything. I have chalked it up to the sensor, believing if I really had lost oil pressure, that very first time I would have cooked the engine immediately(literally seconds??)

Is my reasoning wrong, if an engine truly loses all oil pressure, it will detonate VERY fast, correct? I mean literally in less than 10 seconds.

Never thought I would find a relevant post this fast but all the replys help quite abit. Thanks

I have a friend that was driving an 80s Dodge with a 318 when his oil light came on so he stopped and checked the oil. It was fine so he started the engine, light stayed off and down the interstate he went. It came back on about 2 minutes later and he stopped again and listened to the motor as it idled.
He said it sounded fine so he took off and about 3 minutes later....the engine locked up.
Be careful and make sure it's JUST the sensor and not the oil pump....like in the Dodge.

It wont detonate. But you will get metal on metal very quickley and it will start to loose power after a minute or two. You will have some time before the engine dies, but yes seconds after oil loss damage begins. And then usually it will lock up.

My old man and his friends took a plymoth slant 6 that was in a belvidier or somthing like that and drained the oil and water and put a brick on the accelrator. They did a raffle and the person who guessed the time that was closest to the time the motor locked up got money. That car went 22 min!!!! at full throttle with no oil or water. Them old slant six's were a bit more rugged than our motors. Ours probably wouldnt last more than five minutes like that but you never know.

Alright, now I'm scared again!!

Wouldn't you hear something or feel a drop in idle, etc? I've never believed or trusted idiot lites/guages, but have never experienced true oil pump failure either..

I get my "in seconds" measurement, from a Yamaha FJ1200, after changing the oil on it, and not having a very tempermental o-ring positioned perfectly, it pumped the oil out almost immediately upon starting, it filled the shovel fairing on the bottom of the bike and by the time the first drops overflowed that, I heard a very distinct "bang" followed by one piston seizing, and another "bang", that piston's rod, and then something that sounded like a screech owl in heat!!
I won't bother you with the sound effects that I let loose.....

My 2000 5.4 F150 does the exact same thing all the time, usually when it's pretty cold out. Up and down until it warms up. At first, I listened for valves tapping, now I just ignore it.

Mike

Just wondering if a previous post I had found on here could help with the true oil pressure reading. The link shows how to set your digital dash display to test several systems, including true oil pressure. I haven't looked at the link for a while, but the oil pressure will be displayed with numbers you write down and then look at a different link which tells you what your oil pressure really is. Hope this helps you find out if you are running normal oil pressure.

http://www.mustangworld.com/ourpics/fcar/dtcodes.htm

I have been driving mine now for two days, it also only malfunctions when it is cold. I bought a new sensor for $10, am going to put it in today. If it really is an oiling problem, it's too late now the damage has been done.

[QUOTE=ls973800]Just wondering if a previous post I had found on here could help with the true oil pressure reading. The link shows how to set your digital dash display to test several systems, including true oil pressure. I haven't looked at the link for a while, but the oil pressure will be displayed with numbers you write down and then look at a different link which tells you what your oil pressure really is. Hope this helps you find out if you are running normal oil pressure.

http://www.mustangworld.com/ourpics/fcar/dtcodes.htm[/QUOTE]

There is no "true oil pressure" available through the HEC test mode. See my last post for the reason why.

Geez, just replace the POS crappy sender switch.

Steve

My truck is doing the same thing. I'm pretty sure it's the sending unit. The truck is a 01' and only has 38700K on it. I moved the wires around on the sending unit and it didn't do it for a couple of weeks.
I did notice that if the wire is on the other side of the oil filter it pulls the wire pretty tight. So maybe I did it during a oil change.

If the engine is truely not getting any oil pressure, shouldn't the engine be making a lot of noise if you catch it right away?

My 97 4.6 4x4 has been doin this for about a month, I have 205k miles and if its gonna go its gonna go out in style! My question is where is the oil sendin unit.... by the filter I have read that a billion times. But on my truck the filter is behind the front bumper behind the foglight. So where should I look to find my sendin unit?
Thanks guys.

It is located right behind the oil filter where it screws on, above the front diff. I just tried to get mine changed but could not get the wire harness off. It is really hard to get in there to get a hand on it. I'll probably have to spend the $30 to have my mechanic change it out unless anyone has a trick to getting it off.

I don't know this for sure, just guessing. Follow the oil lines from the remote oil filter to the engine block. The oil pressure switch should be near where these lines connect to the block. Good luck! :-wink

Will do! Do they have this remote oil filter on the new generation trucks? This has been such a huge convenience that I cannot imagine goin back to layin on my back and reaching up past the front diff and skid plates through all that garbage to get to the filter.