Hey guys, finally back working on the truck. I had noticed when I cranked it oil pressure would show normal, driving hwy oil pressure would show normal, but when the engine was hot and driving on a slow road it would show low and at a stoplight it would drop tot he bottom of the gauge. I got an actually oil pressure gauge put on and now I have numbers to go with what I had noticed.

(All these numbers are at idle). At crank the oil pressure was 48psi, once it was warmed and ready to drive it was at 36. Drove across the yard and loaded the trash and it was at 12. Drive it around town and got home and it’s showing 6psi. Due to the gauge I currently have I could not get reading while I was driving it around (I’ll work on that).

But I need to ask, is this a problem? What numbers are expected? If the pressure is ok at high speeds does that mean the bearing are gone or pump?? Knowledge is power

1981 f150 4x4 302 v8 auto c6 (Her name is Rholanda)

 

You did not say how many miles are on Rholanda what weight oil you are running, if the inside of the motor is clean or dirty and the brand of filter you have on the motor.

I will tell you the rule is 10 PSI of oil for every 1000 of RPM so your 6 PSI at idle I would say is a little low in my book as I would like ot see it at 10 PSI or above.
Also not knowing the PSI at what RPM is hard to say but again I am guessing it is lower then the rule of 10 PSI for every 1000 RPM.

I have found the "orange can of death" (Fram) has giving me low oil PSI shown on a factory gauge.
If you are running 10w-30 oil you may want to step up to 10w-40 and come summer when warmer 20w-50
The only fix for low oil PSI is replace the rod & main bearings and to do that right it is a motor rebuild as the crank may also need turning.
I had a motor, not a Ford, that I never had running and found all the rod & main bearing showing copper, forgot to check cam, but the crank was within factory spec.
I replaced the rod & main bearings and the motor had great oil PSI, it was a fast cheap build for drag racing and it did vary good.
I also put a set of piston rigs in it as they were stuck in the grooves.

So you may get lucky and just throw a set of bearings in it and be OK but you will need to check the crank if with in spec and not need work.
Dave ----

 

Good points, truck is new to me so she just got a fresh dose of 10w-40 and a new filter (fram, didn’t know ppl hated em). Old oil was really old but I didn’t see anything unexpected about it. Miles on the motor is gonna be anyone’s guess, truck odometer shows 17,000 but looks like she’s lived a lot more life than that.

The truck does not have a tach so I’m all ears on the best ways to match psi with rpm once I get the pressure gauge in the cab.

 

Some like the Fram filters and up to about 10+ years ago I would use them till I had issues with low oil PSI.
Normally the dealer did free changes but they were far from the house so I hit the local oil quick change and they used Fram filters.
About a 1000 mile in I seen the gauge was lower than normal and the level was good?

Next change, 3000 +/- miles was at the dealer and no issues with gauge reading low.
3000 miles later back at quick change and Fram filter and sure enough about 1000 mile the gauge was reading low!
That was the last time I went to the quick change and will not use Fram filters.

You are already running 10-40 oil and if it is cold out it is not good to run 20-50, to thick when cold start up.
Also being new to you who knows how often the oil had been changed and dirty oil will hurt bearings.
In your case it could be the bearings are worn and why the low oil PSI?
Only way to know it to pull the motor apart and that is a rebuild in my book even if quick and dirty (not really dirty LOL) rebuild like I did on the drag motor.

What I would do is keep an eye open for a good running used 302 to drop in when you have time or when this one craps out all the way.
Being it is running hope it gives you some time to look.
Dave ----

 

I was a fan of Fram too, until the last Fram on the truck. My truck sits for many days, after the start up the lifters made noise, I figured the anti-drain back valve in the Fram was not working. I bought a Motorcraft filter from Walmart. When I pulled the Fram without draining the oil, no oil came out of the filter. I installed the Motorcraft, and since, the lifters are quiet on start up after sitting for days.

I would guess your truck has at least 117,000 miles if not 217,000. What does the wear on the brake pedal look like ? Lots of wear, shows more mileage.

Here's mine at 141,000 miles.

 

An empty oil filter? Wow. That's definitely an indictment of Fram. Fram does have two or three levels of quality, several filter lines. I don't use them, not for probably 40 years when it was the only filter most autoparts stores carried. I like Baldwin and Fleetguard filters. The only ones I trust for my diesel. I don't know what other engines they make filters for. Baldwin is large filter company right here in the heart of the USA. Fleetguard is made by Cummins. It's looking like Dave's name, orange can of death is a good nom de filtre.

 

I don't think it's the end of the world to have 6 psi on your guage at 600 rpm. The red idiot lights were set for 5 psi. We have all seen those flicker at low RPM. Engines with more miles will have lower pressure because the oil moves more easily through larger spaces. Lucas has oil conditioners that can raise oil pressure. But how are pressure and flow related? If there is more resistance, tight bearings, the oil pressure goes up but the flow goes down. The reverse is true if the pressure, a measure of resistance to flow, goes down the flow of oil increases. My thinking is that if you have good pressure with cold oil as you mentioned that indicates to me that your oil pump is working good.

 

If the rule is 10 psi per 1000 rpm, the 6 psi at 600 rpm would be a pass correct?

 

Yep. Extrapolates perfectly.

 

I had looked at the Lucas oil treatment just today. I am worried that trying to mask a problem could make it worse. But that’s why I’m here. I don’t really know what the consequences of the low oil pressure would be. I know the bearing must be worn and that a rebuild is in order but I guess I’m just wondering how much I can get out of her before I have to make the decision of how much $$ to sink into her.

And on the 6 psi at 600 rpm fitting the “rule” it does. Does that mean she’s in the clear?? Idk, interested in what you guys get with your motors.

 

In my opinion your oil pressure is good. You don't know the miles on the engine. Do you know how your compression is? What's your mpgs? How's the oil look at 3000 miles?

if you're getting 15 mpg +/_ and your oil is still clean after 3000 miles I'd say keep doing scheduled maintenance and drive on.

 

You can get many more years out of a engine like that. As long as it doesn't foul the plugs and you keep the oil changed and take care of it, I doubt you will ever need to do anything to it. If you start getting some heavy knocking after it warms up and under load, that's different.