Oil Pressure Relief Valve Cap Leak

[bjoness]

Does anyone have any tricks to stop an oil leak from the O-300 oil pressure relief valve cap? No matter how many times I change the AN900-14 gasket, the new gasket always seems to leak. I've even tried applying Loctite 592 Teflon PST Pipe Sealant IAW TCM SIL 99-2B, but even that doesn't seem to help.

[Bruce Fenstermacher]

I would check the nut or cap for a crack as well as the accessory case. After thatI might also try two crush washers though doing so will slightly lower the relief blow off pressure. I wouldn't be worried about the lowered pressure but if you found it worked the pressure could be restored with a washer the thickness of second crush washer placed in the cap under the spring. Of course two crush washers and the washer under the spring are not specified anywhere.

[GAHorn]

It sounds as if there may be a crack that the plug is opening-up when torqued....or there is a rough seat where the AN900 gasket sits.
If neither is the case, you might try a neat bead of Permatex Oil-resistant RTV gasket-maker ("Ultra-Black" at NAPA.)