1973 F100, 2X4, 390, C6

Hi everybody, this is my first time posting in this forum and hope you can help me.

I just purchased this truck and noticed that the oil pressure seemed to be low on the factory guage. I bought a new sending unit and that wouldn't even register any oil pressure. To verify what the oil pressure really is I acquired a aftermarket mechanical guage and it showed 0 oil pressure at idle and about 20 lbs at a very fast idle.

The oil dipstick showed the oil to be about a quart over so I changed the oil and filter. When I pulled the old filter there was hardly any oil in it. I put in 4 quarts of oil and one quart of Lucas oil addative bringing the oil to the full mark on the dipstick. I started and ran the engine at a higher than normal idle for about ten minutes then checked the oil level expecting it to be a quart low. The oil level was still at the full mark. I ran the engine for another 15 min with the same results. The new oil filter was the purolator brand. The oil pressure after the change and at a idle slightly faster than normal gave me about 5lbs pressure and 25 lbs at a very high idle. Sorry, forgot to mention I used 20W50 oil.

I realize that the proper place to start checking for low oil pressure is the bearings but I question the lack of oil to the filter. I have never seen bearings prevent oil flow to the filter. I would appreciate any guidance you could give me.

Thanks in advance
Paul

 

One thing you could do first is pull the oil pan and inspect the screen on the oil pickup tube to see if it might be plugged from who knows what .

 

the 20w50 seems to be really thick unless your in a high temp climate .

 

Sounds liek a blockage to the pump or the pump is going bad.

Pump shaft must be OK if you get any pressure at all.

 

Thanks Rusty

The screen sounds like a good starting point. Would pulling the oil filter bracket(?) show me anything?

I am in Florida with the temps getting up into the 80's. The only reason I went to such a high viscosity was to see how it would affect my oil pressure.

Thanks
Paul

 

Thanks gtex

Would a stuck pressure valve give me this problem?

Paul

 

That was my next thought. If it is stuck open even slightly.......you'll loose all kinds of pressure.

The only way to check is pull pan and pump. Not a fun job, but it would explain alot.
How old is the motor? Rebuilt? 100,000 miles?? Could be nylon from the old cam gear sticking things.

 

Freightrain

Thanks for the reply. I have no idea on the engine. All I really know is that the previous owners seemed to jury rig everything that they did. To give You an idea see my posting in the 73 to 79 forum https://www.ford-trucks.com/forums/s...d.php?t=368468

Thank You
Paul

 

I'm with Freight on this. I'd at least pull the pan to have a look. Hopefully the screen is just clogged. You can pull the oil filter adapter to check it. There could be something blocking it and it's easy enough to check first. I've found old pieces of gasket and such before. I've also seen the oil pump bolts come loose and cause a loss of pressure. G.

 

FFR428

Thank you for your input. I think I will pull the "oil filter adapter" first tomorrow and if I don't find anything there will pull the pan.

Paul

 

All Pumps have a Check valve in the pump..amd the guys are right it could be a clogged screen??? Or a stuck pressure Valve??? Also As mentioned. the bad Oil pump? There are guys out the that rebuild engine's and dont replace them?But for all of us that know better..we know its cheap Insurance to but new!!


Good Luck,

Russ

 

What kind of oil filter did it have before you changed the oil?

 

Paul, A lot of great advice here. A well worn FE will get low on oil pressure. It is not uncommon for idle pressure to drop way low, and can pick up to 20-25 at operating speed. Normally I would suggest not to bother with it, just figure a rebuild or replacement in your future.

IMHO tis better to keep oil in the pan than to worry about pressure on a tired ol horse.

What ever you do, DO NOT replace the pump with a high volumn or high pressure pump.

Another; 10W30 is thick enough oil to run also.

John

 

Whoa there. I bet half the guys in this forum run the high volume melling HV57 pump. Why do you suggest not to run a high volume pump?

 

Well, if it runs, don't knock and does what it needs to.........then I would agree on not touching it. Yes, I would agree, if it has alot of miles, then it's just plain wore out. No sense beating a dead horse. If the motor was relatively new, then I would tear into it. That is why I questioned the condition.

As for HV pump, I guess Jo is following the usual advice on a HV or HP pump will suck a stock pan dry. Never really proven(as have ever seen for my own eyes), but possible I guess. I think in this instance it would actually help since it will help fill the void(clearance) that is now between crank and bearings. Kinda a bandaid or sort.

I think the use of this motor needs to be considered before any heavy teardown is done. No sense in making work for no reason.

Back 20yrs ago I ran my 302 with ZERO oil pressure for over a year. The only way to get pressure was to run it at 3500 rpm or so. The most it ever saw was 5-10 lbs! Never a noise from it. It never got worked hard, just daily transportation to school/work.