F135 Oil Pressure WAY High...A Puzzler

[FJnotCJ]

So I'm working out the bugs on the red 1960 and hook up a mechanical oil pressure gauge and am impressed by 100 plus psi readings when cold. When warm, idle is about 40 and goes up to 100 or so when reved a little...odd. This gauge has seen service on other rigs and is my high tech diagnostic tool and mostly hangs on a wall

1. I changed the oil and rebuilt the filter, made sure all the little parts are inside. Not that it should effect oil pressure, it just needed done.

2. Removed oil pressure relief valve and cleaned up the insides, plunger moves freely now. Bolted on with hose to the rear, adjusting nut/bolt just about all the way out. Oil psi still too high, try a different relief valve, still too high.

3. Remove valve cover to check oil flow through rockers. All is well, nice flow. Replace a bent push rod and adjust valves while I'm in there

4. Compress an extra relief valve spring in a vise to weaken/shorten it, no help.

5. Remove spring all together, pressure still too high.

6. Remove plunger, pressure remains around 40 at idle...I'm guessing at this point in a normal engine most oil would be going back into the sump and there should be little to no pressure.

7. Remove the adjusting nut/bolt while running, good flow all over the floor and pressure drops to, well, nothing of course.

Any ideas before I open this can o worms further? The only thing I can come up with is the passage between the oil relief valve and the sump has been blocked by a Prior Owner or Rebuilder, or maybe the oil pump is feeding into (the wrong) one of two identical threaded holes that feed the oil pressure relief valve.

It has been a long night...good morning

 

[Toy Teacher]

I sent you a PM

 

[IDave]

* partially spun bearing
* blocked or partially blocked oil passages
* using an oil with too high of a viscosity (unlikely in an old landcruiser).

Still, most likely a malfunction of the pressure relief valve. Is the passage the plunger rides in corroded? I know, it would have to be similarly corroded in both valves you tried....

 

[FJnotCJ]

With the oil relief valve plunger and spring removed, nothing in it, the pressure will still read 100 at rpm.

After looking at the stovebolt forums dealing with old Cheby 6s I see there are some creative ways to boost pressure and turn these things into fully filtered systems. Looks like I will have to drop the pan to satisfy my curiosity, bearings will be checked then...

 

[IDave]

I suppose you could run some motorflush through and change to a low viscosity oil just to see how it looks.

You know, before you drop the pan....

 

[FJnotCJ]

So I took the pan off and there the answer was, a little grub screw/plug in the block right next to that brass fitting where the oil pump pressure line goes. It prevented the oil bypassed by the oil relief valve from going back to the sump, rendering the relief valve useless.

While I was in there rolleyes I pulled the #2 main cap to see if I should slice my wrists, looked very nice so you're not rid of me yet. Closed it all up and oil pressure is good now, 25 or so at idle and 50 or so at rpm.

Sorry for the drama, nothing to see here, move along

 

[IDave]

!













But I'm wondering what that thing you're talking about actually was. Screw Grub? Why was it there?

 

[FJnotCJ]

This is a mockup of what I found, top of pic is the rear of the motor...you can see where the oil pressure regulator lives. The top (rear of engine) hole is the pressure side, fed by the oil pump through that brass fitting. The bottom (front) hole is where the over pressure bypass oil goes, and then to the sump through the hole below the brass fitting....except here. The PO must have wanted some high pressure so he blocked the return passage to the sump with a threaded plug which prevented any bypass of normal excess pressure

I guess you could do the same thing by replaceing the the regulator spring with a stick or a piece of rebar

 

[IDave]

That's just bizaare. I wonder what would have made him want to do that.

 

[65swb45]

I have seen this scenario ONCE before. IT cost the machine shop dearly. The un-bypassed pressure was sufficient to SHOOT the oil galley plug out the front of the block and into a freshly recored high efficency radiator that I had just put into a customer's truck.

The machine shop paid for all the repairs [including another radiator] and I now have a very nice high efficiency radiator with a few soldered tubes in it in my own personal rig.

Consider yourself VERY LUCKY you found this Phil.

Best

Mark A.