FJCamper wrote: ↑Fri Oct 06, 2017 10:04 am
...The exception is the heavy-cased Fram HP-1....
I've had good results using standard filters from MANN, Bosch, etc. designed for Diesel-Rabbit applications too, without sacrificing filtration efficacy.
The flywheel-end relief valve in a dual-relief case is there to protect the cooler by dumping back to the sump at ~65psi. But the drilling which the relieved oil needs to pass through is too small to handle "thick" oil fast enough. Without enlarging that hole one must be cautious about revving a cool engine, especially if the stock cooler's still in the system. Even if the cooler doesn't rupture it can "balloon" under overpressure, closing off the air passageways - it'll still look normal to the casual eye.
I agree with Frank, only rarely should one ever need a pump any bigger than 26mm. Usually the concern is low pressure at hot idle, not at higher RPM, and a bigger pump is of no use there. In most cases (pun intended) a "blueprinted" 26mm pump with minimal gear endplay does the job just fine.
Since the stock pressure-control system reacts to pressure rather than temperature, excess pressure results in the cooler bypass passage remaining open (or partially open) even after the engine's warmed up so not all the oil has to go through the cooler. You end up wasting horsepower by putting heat into the oil at the pump as well as inhibiting the full use of the cooler...and wondering why your oil temp's so high even though the pressure looks ample. Changing the plumbing around to accommodate a thermostatically-controlled bypass valve only addresses the latter problem while introducing a potential point of failure; to ensure that the cooler's fully-utilized the pump-end relief valve spring pressure needs to be increased. IMO the stock system works well enough in most applications with the right combination of pump size and oil viscosity. "K.I.S.S."
