Oil pressure drop when enigne warm
 

i got a 87 f250 with a 4.9. i recently changed the oil. cold engine has good oil pressure, and when the motor gets up to operating temp it drops below the N on normal... but not past the white line. i used 10w-30 conventional(valvoline?). right now my idle is high (1000) and i'm worried when i fix it the motor won't have the rpms at idle to keep decent pressure. when i changed the oil there was some bearing stuff in it. can i just switch to diesel oil or would that eat the pump up(i read the 4.9s do that)? any suggestions on what i can do?

you could run SAE 30 instead, but you are on borrowed time if bearing material in oil...

I'm concerned with the bearing material, but also you should really invest in a mechanical oil guage. The stock gauge is operated by a sender that only registers @ 7 psi. There is a a write-up on making the stock gauge work correctly and if you want, you can give that a try as well. This was just discussed several weeks ago with another member, but can't remember who all contributed to it. Just use the search function here on FTE in the 87-96 section. The install and cost of time, will be worth it, say if in fact you lose complete oil pressure, say from a Fram filter(Orange Can of Death) that collaspes inside for instance.

I also own a 4.9, and always noticed a copper in the oil when I would drain it. I had to install a new oil pan gasket last year and I removed the lower main caps and noticed that some of them were starting to show copper. I always had that notorious dry, start-up rattle( I hated that every time I started it) From what I have read, the 4.9' were notorious for going without oil and water, and still wouldn't blow up. There one of the most infamous motors built. Long story short...

I installed a oil-prelubing system in mine, so I could prime the remote oil filter and the galleries before starting. No more rattle on start-up and after draining the oil, 1st time in 3 months when I installed, I let the dain pan sit for a day and I couldn't see any copper showing. I hope to eventually pull the motor and/or completely overhaul it. even at best, I could roll in new main bearings, and that would easily get my by for another 50K miles.

Hope this helps.

thanks for the replies. i'm not really trying to throw any money into the truck, if i dont have to (pre lube system idea). i'm just using it until i get my other vehicle finished... hopefully by the end of the summer. i regretfully have to admit i have one of those orange cans of death. i usually use napa stuff, but it was a sunday and advance auto had a deal (and i wasnt aware it had such a great name haha). i'm going to be changing the filter tomorrow, and the oil to some 10w-40. when an oil pump gets old (and 125,000), does it have that problem at all or does it just fail? and can i drop the pan enough to get at the pump without lifting the motor?

changed filter... its not as bad as fast, but it still does it.

Put a real oil pressure gauge on that beast. The factory sender/gauge is not very accurate. More like an On/Off switch.

Ford still installed a variable resistance sender in '87, so the gauge is an actual gauge. However, the position of the needle still can't really be correlated to a pressure in PSI. If it's not knocking, I wouldn't worry too much. If you change oil, you'll need to go to something like a 15W40 - SAE 30 won't be any different at operating temperature than 10W30.

Was this an overnight change in pressure, or a gradual one? You can also double check engine grounds to make sure the sender has a good ground path, and that the wire has a good connection on top. Higher resistance will show as lower pressure and a short to ground should make the gauge sweep all the way to the high side.

i think we have a real oil pressure gauge laying around our shop that is brand new. i will be putting that on this sat. what i think started the problem was when i got the truck the 2 grounds to the batt for fuel and ecu relays were disconnected and i was trying to figure out why the fuel pumps weren't turning on and trying to start it for a couple weeks. i i kept reading about these grounds that were supposed to be on there and werent... tucked under the batt tray. fixed em and my 1st ride around the block the pressure started dropping once motor and oil had time to warm up. before that, it was a work truck that sat for a couple years and was good when it was parked. i probably wiped the crank bearings out, but i wanna try everything else before i have to pull the motor. and no the motor doesnt knock. it also takes a few seconds more than i'm used to (compared to cars in general) build up oil pressure, if that means anything.

Just did this mod a few weeks ago on my 91' 351w. I don't know about the 300 as i haven't looked to closely at the one in the garage. But i highly recommend the factory sender extension over say brass tube. It will make your life much easier. You can get one a jeff's bronco's graveyard and im sure many other places. My truck is right at the middle with the mod cold startup which i've heard is around 30psi. http://broncograveyard.com/bronco/i-...extension.html

the 300 is on the left side towards the back of the block, clear of everything. its pretty easy to get to. since the sender turns on at 7, i think i'm looking at like 8-10 warm. it hovers the white line, but doesnt cross it.

i just found out the truck has over 300,000 instead of 100,000. ugh whats an exceptable low oil pressure reading?

Does the pressure go up with RPM? Your truck has a variable resistance sender that doesn't have a "turn on" pressure like a pressure switch would. If you put an actual gauge on it, I would look for 10 psi minimum at idle, and others say that there should be approximately 10psi per 1000 rpm.

once it has warmed up, it pretty much stays near the low white line... idle or normal driving. i shift around 2500 (4speed), and usually try not to go to far past that. sometimes i can let off the throttle annd it will rise a little but once i accelerate again it drops back down. it never dropped below that line, so i dont know if it has the sender type your talking about- i'll take your word for it. my 93 mustang had the turn on kind (ford racing sender) where if it hit the white line, it shut off and dropped completely.

as for the pressure thing, for now, i'm just gonna wait till i put the gauge on it and see what happens. i'll chime back it with numbers and see what you guys think.

Look forward to your results!

so i hooked the gauge up... cold start 45-60psi, its slowly drops as the engine warms and hovers around 20, idle or not. i didnt take a long drive in it... maybe 10 mins. and let it idle and warm up in the driveway stayed at 20#s. it started dropping below towards the end of my drive... like 18-19psi. it wont rise when rpms are increased... and as stated before, pressure will increase a little when i let off the throttle only to drop back down when i accelerate again.

Just throwing this out there...

Oil pump may be on the weak side. You should notice a increase when giving it throttle. Could be pickup screen clogged with gunk, could be just time for a general overhaul. It depends on how many $$$ your path for freshening the engine up.