The thermo pellet located in the front of the eccentric shaft is prone to failure.  When it does fail, it fails in a mode where oil is bypassed and oil pressure drops - the only hint of this failure is maybe a 10-20psi drop in normal oil pressure.

The oil thermo pellet is designed to bypass oil until the oil heats up.  When it gets hot enough, the wax melts and a pin at the end of the thermowax pellet extends.  In this extended position, the thermowax plugs a bypass oil passage.  With the bypass oil passage plugged up, the oil then flows through the normal oil passages.

A cheap way to prevent this problem is to shim the oil thermo pellet with a bunch of M7 (7mm, metric) washers.  Use at least five M7 washers to shim the oil thermo pellet to a minimum spec of 6.5mm.
Click here for Oil Thermo Bypass Pellet shim procedure!

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