oil pressure relief valve test results

Here is the oil pressure relief valve and the tap used to pull the gunked up valve out of the engine. It is the 1/4" npt 18 tap. It is a little undersized but when you screw it into the valve, a little side pressure grabs the valve enough to pull it out.

This is the tap set that the tap came from. It is the harbor freight set. The 1/4" tap is the same size that you use to tap the oil galley plugs for insertion of threaded plugs.

I used vice grips to grab the tap and pull out the valve.

Here are all three parts; the valve, the spring and the slotted plug that holds the thing in the engine

The results of the test were positive but did not completely cure the low pressure problems. I still get the light but only at idel and only when the oil is up to about 140 temp. At operating temp of 200 at idle, I have about 4 lbs of pressure on the guage. This is about 4 lbs more than was reading before cleaning up the pressure relief valve. My idle is very low. With just a little throttle, bumping the idle up to a normal sounding idle (no tach) the low oil pressure light is now off. At temp and running, I now have about 4 more pounds of pressure. This is a great relief. Now I am up to over 30 lbs at the shift point, cruising at 60 in 4th gear at about 26 lbs.

So I do believe that the gunked and stuck pressure relief valve was a bit stuck open causing lower pressure. I still have a little loose bottom end. Next rebuild I am going with oversized bearings, machined crank shaft and/or all new. Hopefully, this engine will hold these pressure values for a couple more years.

oil pressure relief valve theory

When I rebuilt the engine, the pressure relief valve never dropped out as it was supposed to. I did undo the large slotted plug in the bottom driver's side of the engine that I am sure is regularly confused for the oil drain plug (that has a hex head and is in the center of the engine). I have had decent pressure at speed and temp but low at idle and at running temp. My theory is that the pressure relief valve was stuck slightly open. The valve is a small piston about the size of the last digit of your pinky that sits on top of a spring. It is common practice to shim the spring with a washer to increase the pressure on the piston. This had been done in my engine but I do not think the valvle was moving. I pulled the valve out of a junked engine and it came out easily with a magnet on a stick tool available at autoparts stores. A tap fits into the bottom of the valve. This is what I used to pull the stuck valve out with. It was stuck and it did have some junk on it. I do not think it was moving based on the amount of pull it took to get it out even after I tried to wiggle it around with a screwdriver. I cleaned up the valve out of te wrecked engine, used the longer of the two springs and kept the shim washer in place. This morning I will test drive to work to see if it makes any difference with the idle oil pressure.

So I have been using the van as my daily driver. Unbelievable. I am almost to the point where I am not completely paranoid that the van will die, self destruct, blow-up every second. I completely obsess over oil pressure and oil temp. It is no longer the heat of summer so the oil stays about 20 degrees cooler. I run at about 200 in the cooler weather compared to 215-220 with temps in the 90's. Temp makes a massive difference in pressure. At cruising highway speed i am at about 26 lbs in cool weather and about 21 at higher temp. I know these pressures are low and it means that the tolerances at the crank journals, bearings, end play are too loose, but it is better than the old engine was before it threw a rod. Hopefully it will keep going for at least a year.
I should have gone with oversized bearings and some machine work on the cam to make the bottom end tighter. I can start rebuilding the other engine I have and do it better.
I also might have a problem with the pressure relief valve. The valve, according to samba, should just fall right out when the screw/plug is removed. It never did. So at the next oil change, I might try to knock it out or push it further up in there. I will definitely shim the pressure relief spring with the 1/4" washer like tencent says.
I am only getting about 16 mpg but that is mostly city driving and short errands. The tank holds 16 gallons. That gives a range of not quite 250 before you are really pushing it. I did run out of gas tuesday-drifted into the gas station-living right.
priced deep cycle batteries today. The size that does not fit under the seat (group 24) $79 for 90Ah. The size that fits about $140 with less Ah. 90Ah is enough to run a truck fridge efficient refrigerator and a little microwave so long as you drive somewhere every day and enough to run CD players, etc. without worry.