Thread: Intermittent oil pressure problems with my SBC

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Thanks. I am currently running 10w 30. Why would a change to 0-40 do the trick? Is there anyway short of a teardown to chekc hte relief valve?

The viscosity isn't what did it, it's the synthetic oil. My oil supplier told me he'd give me my money back if it didn't work, so I figured I'd show him! I put the 0-40 in and drove it 2 miles and the pressure went to normal, 25# idling, 40 revved up. Before, the pressure wouldn't even wiggle the gauge at idle, and there was only 25 or so at speed. Go figure!

Here is a simple question...you have hydraulic lifters in the motor. When you had to "limp" back to the dock, didnt the lifters rattle and clack quite a bit during that trip? If the oil pressure went to zip, the lifters bleed down fairly quickly and it starts to make noise....did it?

Out of the several times that the oil pressure has bottomed out only one of those times as the engine got noisy, lifter noise and valve tapping. I think that when I lose pressure I have about 2-4 pounds of pressure.

So the clacking is a good indication that it is really loosing pressure...not just a gauge or sender fitting stopped up temporarily.

In the SBC, there is the pickup tube with a screen...have seen shop towels in the oil pan that randomly covered the pickup. The pickup tube connects to the oil pump, if the tube to pump fit is loose, the pump can suck air and lose pressure. Inside the pump are the two gears and the relief valve. The two gears get worn but the symptom of grossly worn gears is not intermittent pressure loss. The relief valve has a plunger and the spring. Sometimes the plunger can stick open if debris gets in the system...it doesnt take much of a spec of debris to make the plunger hang open (or closed). The spring sets the force (oil pressure) that makes the plunger open and bleed off the pressure...it is kind of like a regulator. If the bypass is the problem, the solution is a new oil pump....dropping the pan in a boat is a chore unless you sazall out the bottom of the boat first (after lifting it out of the water, of course).

After the pump, the oil travels to the oil passage in the block which takes the oil to the filter. There is the interface between the pump and the block...if the pump bolts are loose, there will be a major oil leak with oil squirting back into the pan.

At the filter, there is the filter adapter which is a small aluminum die casting that has the close nipple to screw the filter onto. Not much there affects the oil pressure except IF the adapter is loose or the gasket missing...there is a bypass in the filter but that only allows the oil to bypass the filter if the filter is plugged.

Hope this helps.

mike in tucson