Swedish Steve
Do you have any reference to how the FOHE Oil bypass valve works? The AMM just says low temp.
The operating oil temps are 50-185 degC, and norm about 100-120. What is low?
The bypass valve is opened by differential pressure, basically similar to a relief valve. You were right that there is no thermostatic bypass, only the diff pressure one.
I haven't been able to find out the oil temperature at which the differential pressure would open the valve, but I agree with HarryMan it is likely to be around the bottom of the normal operating range.
vapilot2004
I had always envisioned a fin-on-tube arrangement for these FOHE's.
No finned tubes in the FOHE. It has a bundle of straight through small bore tubes for the fuel to flow through. The oil passes through a jacket around the tubes, with baffle plates to cause a zig-zag flow to maximise contact with the outside of the tubes.
As you said, finned tubes are normally used on air cooled arrangements, to maximise contact area for the air.
Sooty