30 Psi

[FMSPEED49]

My oil gauge reads 25 psi at idle, and 32 or so at hwy speeds, cold or hot, new oil or old, didn't seem to matter.

230 l 6 in a 49 wayfarer btw

The oil pump had a fairly good leak so I wrote it off to that, Bought a NEW oil pump and put it in, and absolutly no change, so i pulled the relive valve and all seems well there.

had the pan off and the screen was clean, but to be sure , I blew compressed air into the p/u when I had the oil pump off.

I might buy into mains , but it makes no difference hot or cold, oil has been changed from 10-30 to straight 30, to straight 40. no difference. I belive the motor to have been rebuilt not that many miles ago, she's 40 over, and the tops of the pistons were shiney when i got it. yet it may have been 30 years ago, unknown.

The oil filter is a wicks. i changed to a sock style, no difference, so i went back to the wicks.

So the question is, am I chasing a ghost?

[Guest Dodge Joe]

I had my engine rebuilt. They said i should use 15-40 diesel oil. That is what I'm using and I have good oil Pressure. Not sure this will work,but you might try.

[FMSPEED49]

Nope havent changed the gauge, but i may try that. it seems to indicate well, but at this point its gotta be somthing stupid.

[Jerry Roberts]

Try putting a spacer about a quarter inch thick in back of the relief spring . Streaching the spring has the same effect but the spacer is reversable .

[Fireball]

To me that pressure doesn't sound that bad at all. Rule of thumb is that you need 10psi for every 1000rpm. So 25 psi at idle is good, 32 at cruising speed should be enough.

[randroid]

FM,

I'd put a dollar to a donut that it's your bearings, and here's why; bearing clearances vary depending upon the material used, but a good rule of thumb is that an oil film is .0005" thick and due to having two surfaces to adhere to (the bearing surface and the crank or cam or whatever) that amounts to .001" of the bearing clearance. The other .001" is taken into account by calculating how much swelling the metal does when it gets hot, with the best of all possible worlds being that there is nothing between any of the surfaces other than lubrication.

(Please don't take my specs of .002" clearance for bearings as written in stone because different applications require different specifications; it's just a starting point.)

You have a new oil pump and new relief valve and clean oil passages so there isn't much else left to look for other than oil leaks under the car that might indicate physical dammage.

Drop your pan and take a look at your bearings. They should not be shiny because shiny means polished (aka "Wiped" in metalurgical parlance) and that only occurs when metal touches metal without proper lubrication, but be more of a matte color of silver or whatever. Plasti-Gage them and at best you can rule them out as a problem and the worst is you've got a new project without barbequing the engine.

When I installed my new oil pump it didn't do squat with pressure so I slid a rubber "O" ring between the oil pickup tube and the suction line to the pump and never had to look back. You still need to drop the pan to do it but that ain't no hoot with the engine in the car.

Best to you,

-Randy

[FMSPEED49]

Thanks everybody, I think I will try the spacer, I don't think its the bearings, due to it doesn't change from start up to high speed freeway speed ( wow when did I start to consider 60 mph high speed?) every motor i had with bad bearings would be ok, then drop to nothing when hot. So I'll stick a spacer in and see if thatll get it up a little. Maybe i'll drop a viagra or two in the oil cap, that might help, lmao.

[1just4don]

That oil pressure in an engine is directly related to the condition of the 'cam' bearings,,,thats where oil pressure is made or lost.

How ever I dont think YOUR pressures are all that bad,,lots of motors dont run 'that' much, specially since its a golden oldie!!!

Putting one on the motor is a good idea,,,but,,,hard to read at 60 mph,,,I cant run that fast,,,and the hood shouldnt be up at that speed!!! Better IF you wanna read pressure to run a hose all the way inside,,,LOL!!!

BUT,I would drive it at those pressures,,,and save my fix it money for a better day!! When it drops to almost nothing when cruisin,then I would do 'something'

[Young Ed]

I've always heard that too. And I would still drive an engine at those pressures. When I started my coupe for the first time it showed about 20 at idle. After 1 trip around the block it was at 0 and knocking away. DONE. Went inside ate dinner and afterwards pulled the engine out.

[Plymouthy Adams]

Pressure is made by the pump....excess oil pressure is diverted by the pressure relief valve..loss is evidenceof leakage..leakage is at the bearings...and I quote the following...

LOW OIL PRESSURE

If the pump appears to be in good condition, that leaves the bearings. Check the clearances on the main bearing closest to the pump (since this has the greatest effect on pressure), and clearances on the furthest rod bearing (since this will show the greatest wear).

Main bearings and low oil pressure are like peas and carrots...

[Merle Coggins]

Actually, if you want to get technical, a pump only produces flow. It's the resistance to flow that creates the pressure. That's Basic Hydraulics 101.

So if there is too much clearance between the bearings and the journals, there is less resistance to the flow, hence the lower peressure. Higher RPM produces higher flow which will increase the pressure against the same resistance. Or it could be a weak pressure relief spring too. It's a heck of a lot easier to add a shim to the spring, than to pull the engine apart. Start with the easy things first.

Good luck,

Merle

[BobT-47P15]

Don't suppose that length of rubber hose in the oil line to the gauge would do like a brake hose that's old.....collapse on the inside. That might permanently slow down a pressure reading. Just my guesstimate. (Had a bad brake hose at one time)

[Lou Earle]

You can check your pressure by removing the intake to the oil filter and attaching an oil pressure Gage to it- I actually run my oil pressure gage off a ton the oil line to the filter on my 34 Plymouth. The other outlet is busted.

Works just fine so should be good to check

Lou

[grey beard]

Basic diagnosis calls for checking the easiest and cheapest things first. Before I pull a pan on one of these beasties, I'd hook up a master oil pressure gauge and get the engine up to full operating temperature. The pressure reading at hot idle is what I would most want to see. We all know pressures go up at road and engine speed, but hot idle is the acid test for flatties, IMHO

[james curl]

I once had a MG Midget that would not hold oil pressure even after rebuild. I worked with a fellow who was building a VW powered home built airplane and we both had the same problem. We both found our problems to be the oil pressure relief valve, which is a spring loaded piston with a tappered sealing surface. When I pulled mine it was black about half of its diameter. Took valve lapping compound, a drill, and a dowel that would fit tight inside the piston and lapped both surfaces. Took a lot of work to clean up most of the grit left from the lapping process but that solved the problem. Drove the car about two more years without an oil pressure issue.

[FMSPEED49]

Welp, pulled the relief spring, added a 1/16the spacer, put it back together and picked up a 3lb difference across the board.

Removed that, put in 1/8 spacer, she is now at 38 at idle and 43-45 at hwy speeds. so it apears that spring was a little worn.

Thanks for all the help guys......

[Normspeed]

Lots of good info in this thread. Shel, that handbook is great. I'll have to download and print it, but I may have to do it at (work, ugh) where there's a fast connection and a working printer.

[FMSPEED49]

I agree that was not a way to fix it, when it was newer, yet I don't think they had factored a 57 year old spring, at best they figured this car to be around for 10 years.