The front cover relief is set at 140 pounds to protect the oil cooler. But
not the "O" ring junction. The pressure relief in the rear iron controls all oil
pressure.
However since this valve is at the very end of the oiling system, all
locations ahead of this valve get a higher oil pressure than the relief valve
setting. Where the relief valve is in the pump, all locations after the pump
receive a pressure that is lower than the pump relief pressure setting. So, the
Mazda has an advantage in that regard.
But the lowest pressure is furthest from the "O" ring junction. So when oil
is cold, or cool, the pressure may be quite a bit higher than the pop setting of
the valve. The relief valve has some hysterisis and may move slowly to
its pop pressure. This allows for a large over pressure between the valve and
the oil pump. So, you have the pop pressure of the front relief valve and the
"O" ring failing in order to save the oil cooler.
Reving the engine quickly from idle, or from one RPM to a higher RPM
may produce this effect. But once the engine is running and or the oil is
warm the valve is sitting in its popped position and leaking oil to
maintain its set pressure. So movement to control a surge in flow will be slight
and fast as the vent is a series of round holes.
A hat section device with a flange to fit the land area about .050" or more
thick with a thin walled tube to fit into the front cover gallery or even a
counter bore in the gallery to fit a slightly larger tube and maintain the
original gallery diameter. There will be no "O" ring to blow out. A flange of
.050" or even thicker would overcome the cover from being pushed forward from
shear preload. Some leakage might occur but would be minimal. Another approach
would be to trim down a thick "O"ring seal washer for this job. Washers (usually
aluminum) with an "O" ring molded around the hole.
The key will be to have a thick enough spacer (flange) to stop the cover
from moving off of the land area. After May I can work on this problem.
Perhaps a test rig to measure leakage at such a fix.
Lynn E. Hanover
In a message dated 5/12/2013 12:08:26 P.M. Eastern Daylight Time,
bartrim@gmail.com writes:
Hi Lynn;
My oil pump outlet is now in the front iron where there was previously a
brass plug. From there it flows through a remote mounted oil filter then on to
the oil cooler before returning to the engine through the original point in
the rear iron (although I did change that fitting).
The front cover still contains one of the oil relief/pressure control
valves while the main one is still located in the rear iron. My memory is
beginning to fail as I recall that one of these is a oil pressure control
valve and the other is a safety relief valve, but can't remember the
details at this point.