oil pressure regulator? (on f150 w/ 302)

[BerniniCaCO3]

Hey--
Buddy of mine has a 1991 f150, same vintage as my grand marq, and same engine block, the 302. Probably the same transmission.

He has an oil gauge proper, not the idiot switch, and it's reading low. Not naught, which is very good of course, but once the engine comes to life the needle swings just a little ways, too low to even enter the "normal" range. 180,000 miles btw.

Now, when I sit in the car and give it some gas, the oil pressure does not move, does not increase.

I have some options:

a) sending unit itself, although it is registering something, just not enough.

b) wire to the sending unit, dirtied or high-res fault eating voltage

c) how does the pressure regulator work? There is one, right? That is to say, when you're at 500rpm pressure might be 20psi, when you're at 1000rpm pressure might double to 40psi, but when you're at 4000rpm pressure stays at 40psi. Fictional but plausible numbers there. There's a valve that regulates and releases pressure so it never rises above what's sufficient? So... I'm wondering where this regulator is, and how it works, and ultimately wondering if a bad regulator could end up keeping pressure down too low? This comes to mind just because revving the engine does not result in proportionally higher pressure. If straight up worn main bearings were the cause, pressure should rise correct?

d) despite the musings of c), which is my real question here since I just don't know about how pressure is regulated, perhaps it is just worn rods and mains, a worn-out pump that's not holding pressure, or even a popped galley plug.

[85crownHPP]

There is one, right?

Never heard of it... sounds like something a modular motor might have, if anything.

[1990LTD]

I'm not aware of an oil pressure regulator, but I'm not aware of many things. It doesn't exist on any 302 I've seen.


*worn bearings = low oil pressure.




* - too much clearance between the bearing and the crank/rods, whatever the cause. a poorly assembled new motor could have problems

[86VickyLX]

The only pressure regulator I can think of is in the pump. And that is supposed to bleed off excess pressure. There is no external regulator. Is the engine knocking?

[BerniniCaCO3]

oh, ok-- so the pump itself has a built-in check valve?
I figured something of the sort must logically exist.

Nope, sounds like a truck engine should. Friend was just worried about it.
I'll tell him to change out the sending unit and see if that's all it was.
If a new $10 unit --and cleaning the electrical lead, too, of course-- still reads low, and/or if an external gauge to check it with reads low, then the only thing left is a worn-out engine or worn-out pump. Maybe just drive it 'till it dies, make preparations for a new truck or a donor engine.

[1990LTD]

lucas and drive it till it blows up

[86VickyLX]

Don't put no additives in the oil. Drive it till it dies. If it starts to knock, go up to a higher viscosity oil.

[85crownHPP]

If the pressure is low, it would be worth trying a new oil pump, if the pan isn't a huge pita to drop.
I'd verify with a tester gauge, the gauges in the clusters can act up too.

[86VickyLX]

Before I lost 4.5/5 quarts on I95, my Lopo with a new oil pump was a steady 50psi @ hot idle in drive.

[1990LTD]

Don't put no additives in the oil. Drive it till it dies. If it starts to knock, go up to a higher viscosity oil.

I was just kidding, hence the blowing up part. Sorry!

[gadget73]

are you sure that isn't one of the idiot gauges thats either 0 or normal, and not actually a pressure gauge? Hook a real tester to it to verify what its got. Sometime in the 90s, the pressure gauge stopped being a gauge and started being a fancy looking idiot light.

[91waggin]

are you sure that isn't one of the idiot gauges thats either 0 or normal, and not actually a pressure gauge? Hook a real tester to it to verify what its got. Sometime in the 90s, the pressure gauge stopped being a gauge and started being a fancy looking idiot light.

I'm pretty sure it was earlier than the 90s. I thought they were doing it in their 80s trucks. Anyway, the story is that most Ford oil pressure gauges are actually not a gauge at all. It is a gauge that is wired to an oil pressure switch like would normally be hooked to an idiot light. If the switch is closed, the oil pressure gauge reads right in the middle. If the switch is open, the gauge drops into the warning area. The switch closes above 6 or so psi. In the OP's case, I would be thinking about bad switch grounding.

[gadget73]

well, if its the idiot gauge thing, the resistor could have drifted in value. THats a common thing with electronics. Either way, I'd be using a real gauge to see what is going on with the motor and not relying on the stock instrumentation. I had a Dodge that the pressure gauge suddenly dropped to 0 while driving. Testing with a real gauge gave me 60 psi, so the actual problem was the gauge sender. Scared the hell out of me when it suddenly dropped like a rock tho.

[mrltd]

Yeah, those gauges are as accurate as the idiot light. Put a real gauge on it.

My old ho converted lopo with 250K had 0 psi at idle and was fairly quiet. Ran like a raped ape. And that was with an Autolite mechanical gauge.