Low oil pressure

My 84 has had electric issues as long as I have owned it. So I have installed a set of gauges to monitor the voltage. Doing so I saw the voltage all over the place 9 to 15 volts. I replaced the alternator and voltage regulator. And the voltage is fairly steady at 14.5 volts.

But that’s not what I need to ask about. I’m also seeing low oil pressure when the motor is hot. Start up cold and the pressure is between 45 to 55 pounds. After the motor warms up the pressure at idle drops to less than 10 psi have seen it down to 5 psi, higher rpm’s and it goes up to maybe 20 psi. Normal highway driving, 55 mph or so, it’s around 10 to 15 psi, pull a small hill it goes up over the top it’s back to 10 to 15.

The dash gauge shows low side of normal.

Oil was changed last week with 10 w 30 high mileage oil and a motorcraft filter. Did not change a thing.

My thoughts, plugged oil pump pickup screen, trash in the line to the filter, I don’t know if that would cause it only at temperature. Bad oil pump?

Any ideas?

What's causing low pressure at operating temperatures is excessive bearing clearance.

Remember, everything in the engine swells as it gets hotter.

Bearing caps are no exception.

You could use thicker oil in summer, or more expensive wide range synthetic oil in winter.

If you only have 45 psi cold, a worn oil pump could be contributing to your lack of pressure.

I'm used to seeing 60-75 cold..

10-40 isn't going to hurt anything.
You could go with 20-50 in summer.

First, you did good changing out both the alternator and the regulator.  One or the other was bad and one can easily harm the other.  Best to replace in pairs.

On the oil pressure, that is low.  Not terribly low.  And not so low it'll hurt the bearings, in my opinion.

I would have said it is due to engine wear.  But when you said "pull a small hill it goes up over the top it’s back to 10 to 15" you got my attention.  With a manual transmission if you are not losing or gaining speed I would have thought it have stayed the same on a hill.  Are you maintaining speed?  Are you shifting gears?  I'm at a loss as to why it would do that if you are maintaining speed and not shifting gears.

David/1986F150Six had an issue a few years ago, as described here, but his experience was that the pressure dropped as the RPM went up.  And as it turned out the screen in the pickup was partially plugged and that was starving the oiling system as the RPM went up.

But yours isn't doing that.  I'm not sure why, but other than the symptoms on hills it is consistent with worn bearings.

Gary, im of a mind that 5psi at hot idle is not doing any favors to his engine.
(Do you think that's adequate?)

What I get from him saying that, is - 'oil pressure is 10-15, it goes up when I throttle up a hill, but drops right back off when I coast down the other side'-
But that's just my interpretation...

Maybe a pint of STP or similar would help?
That stuff has some ZDDP and lots of friction modifiers to raise the viscosity at operating temperature.

I'm not much for 'Snake Oil', but these products exist for a reason.
I use it for assembly lube (except for cam and lifters)

It won't help, that's for sure.  And heavier oil would raise the pressure.  As would STP or somesuch.

But I have a question - where is the aftermarket oil pressure gauge connected?  If it is down by the oil filter, as it probably is on a Windsor, then 5 psi is LOW.  That's 'cause the oil may not be making it to the last lifter at that pressure.

My thinking about 5 psi not being too bad was based on my 460 and M-Block experience where the oil pressure tap is on the back of the block behind the intake.  And that's after the lifters on the M-Block, although I don't know for sure on the 460.  Anyway, pressure is naturally lower there as it is after a number of things have been lubed.  But if at the oil filter, that is LOW.

You have echoed some of my thoughts, but did not want to say out loud, Worn bearing.

Gary the after market oil pressure pickup is at the tube above the filter, I added a T, one way to the pressure switch for the dash, and the other to the add on gauge.

Jim your interpretation of what I was trying to say was right on the money.

I will get some STP, and see what happens, then change the oil to a heavier viscosity. I was planning on pulling the motor this fall to replace the gaskets, just looks like it will be more in-depth than planned.

I need to find a machine shop around here.

I meant to add, I have good compression on all cylinders and it’s not burning oil, just throwing it out the rear seal, and some where up front, I see oil, but can’t find the source.

I thought that you'd probably put a tee in right there, which means that you are seeing pump pressure and not after the losses of several bearings, which would be the case at the top/back of the block.  So that pretty well says your bearings are worn.

You can get by for a while with that pressure, but if you pull the engine you should do a lot more than just do the gaskets and seals.  A full rebuild is in order.

Having said that, I'd be looking at crate motors.  My experience with machine shops of late hasn't been good, and from what I've read a crate motor is frequently less expensive than having your own engine done.  And you'll get a warranty, which won't be the case if you build it yourself.

I'm not one to take dramatic Gary steps.
How many miles do you have on the rebuild since it was installed in 2003?

If the engine runs strong except the oil pressure I'd be very tempted to throw a high volume oil pump in it and keep going.
You have no idea how sloppy some race engines are set up.
And in their case increased circulation helps take excessive heat away.

If you really feel you need to take it to a machine shop for??? (Inspection?)
If the crank isn't scored or smeared, why bother?

Look at the bores, use a fingernail to feel for a ridge at the top of the cylinders.
Fill the ports with kerosene and look for valve leaks.

Look on the back of one of the crank bearings for an etched undersize.
Before you pull the caps try to shift the crank forward and back against the thrust bearings.
But, I guess most importantly is to look at the RMS surface on the crank for a groove worn in it.
Speedisleeve's are definitely available for the front, but I don't know about the back of your 302.

Anyway, don't make rash decisions until you have proof.

Just a thought, My 5.0 Bronco had great compression, 155 to 160 psi and showed in the normal range on the gauge for oil pressure. Right up until it spun a main bearing. That ruined the block and I had to buy a ford reman block. Then I rebuilt it the way I wanted, mostly stock but with 10:1 flat top pistons.

I guess what i am saying is to shut it down until it can be rebuilt. That way you still have a usable engine block.

I dont know what you have for millage on that engine, mine had just a little over 200000 on it.

Really?
You can't deck caps and line bore a crank journal?

Or is it just more work than going back to a stock bore?

I would do what I had to to keep the pressure good.

If it throws a rod or something I'm only out the cost of an oil change, and I gained -however many- more months.... or years.

I know I intend to toss my $55  eBay Milodan HV oil pump in when I finally get a chance to pull this lump and replace the RMS, pan gasket, ring gear and clutch.

I don't like low pressure at -really- hot idle.
But I know the inside of my engine is clean, so it's not a drainback issue.

Jim, when mine spun the main bearing, it egg shaped the bore and cracked the main bolster in the block at the main cap bolt hole. Yep, put a fork in it cause it's done. My wife had drove it to work and said that it made a hard clunk when she got on the freeway. She said she checked the gauges and all was good and drove it 40 miles at 65 mph. When I got home she told me that it sounded good until she got home then it was knocking hard. I couldent get it to to turn over with a 3 foot braker bar and a 2 foot cheater pipe. I pulled it out and pulled the pan and found the rest.

Even if he shuts it down and puts a crank kit in and some new cam bearings in it, he would still be money ahead.

Just a thought

Well I imagine dragging that bearing around for well over half an hour at highway speeds is going to kill the bearing pocket.

If you do that, you deserve to buy a block.

Well over year now I should have 'done something' and yet I still show no mercy to this engine.

I'm not going to advise anyone to do that.

Yep, and according to her, it was only making a "little" noise. So she mashed the foot feed and turned up the jukebox and came home. By the time it was all said and done, the only thing I dident have to replace was the tin, the heads and the manifolds.

I've got nothing more to say.

I'm going to go out and pull some stumps, then thrash my truck some more. (after I put the spare back)

Good luck with the stumps Jim. I am going to go and drill out some rear engine mount bolts from a C15 Cat in a Peterbuilt. Not sure who is going to have a harder day.

Good morning all, picked up a bottle of STP oil treatment yesterday, this morning I drove to the transfer station. Cold Starting up oil pressure was 60 psi, 3 mile round trip, back home motor at idle, temperature at 190 oil pressure at 22 psi. Much better than the 5 or so I had before the STP. Higher RPM higher oil pressure.

I spoke with the owner of the local NAPA store, there is a machine shop local, I will be checking with them after the holiday weekend.

I looked on line and the different parts houses all list a rebuilt 302 motor around the same price Summit Racing shows a standard 3 year warranty or a 5 year no fault for a couple hundred more. Lots of more research.

Those numbers are MUCH better, and the extra ZDDP can't hurt either.