I have a 1990 F-150 with the 300/6 and when it first starts the oil pressure is at 50 psi, after it gets warmed up, it drops to 25 or even lower and sits with a low idle. Is this something to worry about of could someone tell what to do about this, should i use thicker oil, if it matters the stock guages don't work and thats why i put the o.p. and temp in. any responses would be great

 

could be a bad oil pump

 

Well is there anything i can do to help this, i know an oil pump is probably a project and costly, does anyone think its alright to keep driving? thanks for the reply jcc...

 

My first guess would be a bad oil pump, but we are missing a few pieces of information. What is the mileage on the truck and what weight oil do you currently use? When did you install the aftermarket guages? I have installed a set of aftermarket guages on a friends car that would show 0 oil pressure and that the engine was running at 290 degrees right from install. Took those out and got replacements and everything lined up. Sun guages too, I couldnt believe it. No, I would not drive a vehicle with its oil pump on its last leg as you dont know when the dang thing will kick completly. Is the truck making any kind of noise?

 

i would fix it soon if it is the pump.
your gona have to drop the oil pan to change it then you will have to prime the pump before you run it

 

my truck has almost 127,000 on it the guages were put in november of 04', they weren't anything fancy, just guages oil & temp.It doesn't make any weird noises except for sometimes after it was ran and you start it up an hour later, you hear some kind of clanking but stops seconds after the key is turned, someone on here said it was just normal wear and tear . The oil i use is 10w30, i was thinking next oil change( which is soon) that i would add some lucas into it. i just don't want any more serious problems with this thing, i just wanna be able to drive it for a long time, thats why i bought the 300. thanks for the responses jcc and bigdaddyII, this site is the best

 

What you are experiencing is most likely normal cam bearing wear. That 300 I-6 will go another 150K with 50 cold / 25 hot idling. You've got the BEST truck engine Ford EVER made sitting in front of you. Cherish it....they don't make 'em anymore.

Sidewinder

 

While oil pumps do wear; with 127k on the engine, the bearing clearence (wear) is more likley the reason for the low oil pressure at idle.
The oil flow by the bearings is greater than the pump volume can produce until the pump speed goes up with engine rpm.

While higher oil viscosity will show an increase in pressure it is only proving the bearing clearence is wider by the pump not being able to flow the thicker oil at the same rate as before. Oil pressure is the 'back pressure' built up between the pump and the points the oil flows through the bearing surfaces and any other locations. (cam bearings, lifters etc)
With an engine in this condition, putting a pump in and using heavier oil is only a means to get longer life in the short run.
The engine should be overhauled now to keep crank journal wear/ damge risk low if it has not already occurred

 

I guess the bigger question is whether or not the pressure increases when you raise the RPMs. If it does, at least you know the pump is doing it's job. Rule of thumb is about 10-15 psi of oil pressure per 1,000 RPM. Using that, you're right in the ballpark so I wouldn't be overly worried about it. As long as you get pressure when the RPMs increase and you do HAVE pressure, I wouldn't worry.

 

Thanks for all the relpies guys, your right on....im so glad i stumbled onto this site,when i give it gas the pressure goes up, almost to 50 at 2 grand...I'm just a straight up Ford Man, thats why i wanna keep my six and now i can go on trying to get a new 5-speed, and possibly a flowmaster 40 series single inlet, dual outlet, i'll keep you guys posted on what i do next, and im sure that there will be a few newbie questions along the way...thanks again to everyone who gave feedback.

 

Indeed, and well-said. Another way of putting it is that pressure is not an indication of flow. Pressure is a measure of the resistance to flow.

Example. (I'm making these numbers up here) Say at a given engine speed, the oil pump puts out a fixed volume of oil. Now, if the engine is nice and tight, narrow clearances, tight tolerances, not a lot of places for the oil to leak out, the pressure will be high. Now, if you un-cork that engine, the oil pump may still be putting out the same volume of oil at the same engine speed, but the pressure will be lower because there's less resistance for the oil to overcome (i.e. it can flow freely).

Make sense? Or did I just muddy the waters even more? LOL

-Joe