I have a 94 F150 with a 4.9L I6. I’m curious about the oil pressure.

When the engine is cold, it seems to hold 40 psi whether idling or driving at a higher RPM. The oil pressure seems to stay steady unless it is driven for 30 miles or so at which time it can drop to about 25 psi. Is this normal?

I’m currently running 20w 50 Castrol in it; changed about 1,000 miles ago.

The odometer has just over 350,000 miles on it. The guy I bought the truck from says he has never put another engine in it or had it rebuilt. He bought it from the original owner and was not told about a new engine or a rebuild either.

The engine doesn’t smoke and with the exception of a lifter tapping at cold startups, the engine runs smooth and runs strong.

Time for a rebuild? New oil pump maybe? Or is this just normal for this engine?

Thanks!

 

This is normal. 25 psi on an engine that has 350k on it is preaty damn good. As your driving the oil is heating up and thining out. The less viscous fluid offers less resistance and gives a lower pressure. If these are the pressures indicated at idle you have great oil pressure! Even while driving it is a serviceable pressure and should cause no concern.

My recently rebuilt engine gets 35 going down the road hot and 20 idling hot. This is a healthy oil pressure and so is yours.

 

Are you guys using electric or manual gauges?

 

I am using a mechanical gauge. I assume he is as well since a 94 ford has a gauge that reads "NORMAL".

 

Thanks for the reply flipklos! I am hoping it is normal since my 99 F150 (5.4L) is knocking.

 

I am using a mechanical gauge and the electric guage. The electric guage needs a new sending unit but when it's not sticking it reads from "N" to the middle of normal depending on RPM.

 

Try a K & N oil filter, they cost big bucks but they have less pressure drop across them. It would be an interesting experiment to see the change in oil pressure if you just spun on a new filter with the same old oil.

I would be very happy with the oil pressure you have and the total miles on the engine, bottom line I would just use the Motorcraft FL-1A oil filter. I think I paid $3-$4 at Walmart.

Jim

 

I have always been told that anything above the N on NORMAL is an acceptable reading.

My 96 was at O at idle and R on the road.

I am certain that you have a healthy oil pressure. If the engine runs good and dont burn oil keep using it. Just be prepared for an overhaul as it may bust somthing from age and use. Run her till she is done then do a good stock rebuild.

 

350,000 miles and still running strong. I'd venture to guess that the truck has been maintained fairly well during it's entire life, and could continue going well past 500,000.
I do have to wonder though, have the timing gears ever been changed? The stock gears are prone to failure after 200,000 or so, due to the cam gear having plastic teeth.....

Still, with that kind of miles on it, the oil pressure is still quite good.

 

Your stock gauge on that '94 is not a gauge at all, it is just a glorifed idiot light. The sender is the same sender as for a light, it shows good if oil pressure is 7 psi or more. The gauge has a resistor on it to swing it into the "normal" range when the sender is going to ground to indicate pressure.

 

What jas88 said...the stock gauge is an idiot gauge.

 

Isn’t the oil pressure sending unit a variable resistance type unit that sends a signal to the gauge that corresponds to the oil pressure being generated?

I haven’t actually tested one, but I am curious since I have seen some people state that it reads the same regardless of pressure (5-7 psi +) and then you see quite the opposite being said that the gauge shows lower/higher readings with engine RPM.

I know mine is bad because it sticks when cold and doesn’t correspond with the mechanical gauge I have installed until the oil warms up a bit. When I buy a new one I might run some test with compressed air prior to installing it and see how/if the resistance fluctuates.

Thanks everyone for the replies so far! I appreciate it!

 

1983, 4.9 just rebuilt, crank turned, new bearing, oil pump,etc....normal running temp,35/40 idle, 50/55 @ running 1000/1500rpm and above.
10w/30 havoline.. mechanical gauges on oil/temp/volts

 

my brother has a 93 and it's Guage went down a tiny bit so we did a lot of research. From what we found the stock "oil pressure Guage" is more of an idiot light and just goes up if there is like 15 psi. I may be wrong but I was under the impression that only the older and newer model trucks had actually guages

 

I have a 78 f150 with 4.9 and I haven't test the actually pressure yet but it has an actually membrane operated mechanical sending unit. I know this because I lost all oil pressure and searched over everything until I took off that thing. it had leaked a tiny bit of oil to the wrong side of the membrane and locked up. So I took it apart and cleaned it out. Also this little thing seems to send the engine temp as well somehow. It only has 1 wire, but my engine temp seems to have issues the same time my oil pressure does. Weird.