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We had consistent problems with oil temperatures. On cold days (near freezing), the oil temps were 160-170F (71-76C). This could be fixed with a small baffle (we have a cockpit control for this). As outside air temps approached 50-60F (10-15C), full power cruise produced 200F (93C) oil temperatures. At those same conditions, slow flight or pattern work drove the oil temps up to 220-230F (105-110C). New Mexico regularly has 90F days in the summer and we expect to have significant problems with oil temperatures. Bart at Aero Sport suggested that we might be having a vernitherm problem. The vernitherm is a bypass valve that is open when the oil is cold (allowing oil returning from the filter to flow directly back into the engine - with some oil making the trip through the cooler), and closes as the oil heats up (forcing all of the oil to flow through the oil cooler). Bart sent us a new spin-on oil filter mount with a different style vernitherm (from Superior) and valve seat interface.
Installed and tested the unit this weekend. Installation required removing the cabin heater scat tubes, oil cooler scat tube, and left magneto. Test flight conditions were not well suited to stress the oil temps. At 1500 AGL, OAT was 36F (2C). I flew circles above the airport at max power with the engine leaned out (to generate maximum heat). The oil temp ramped quickly to 185F (85C) and stayed there. I tried different power settings and speeds (including some constant 60-70 degree bank, to keep power up and reduce airflow - due to higher angle of attack). I was able to increase the temps up to approx 195F (90C). Now I'll have to wait for a warmer day to see how it really performs.
Maybe I'll fly over to Las Vegas
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This is
the vernitherm.
The engine
side of the spin-on filter mount.
The plunger
is the spring loaded device. It extends from left to right as the
temperature heats up. The center hole is where the filter screws in.
The upper left hole has a spring loaded valve (see backside on picture above)
that appears to be a over-pressure relief.
In cold
water, the plunger is retracted.
As it heats up
to 200F (boiling temp at 5300Ft here in NM), the plunger extends and the route
back to the engine is blocked, forcing oil to return through the cooler.
for a
couple of days - just to test the oil temps of course.