Whereas, my little experiment made no difference whatsoever...other than getting my hot water bottles dirty!
It is most likely that all that is wrong is that any flexible insulated wire needs replacing, but the heater element itself is probably 100% good as its been protected by sitting in oil when it was hot, rather than rotting away in boiling tap water if it were used in a water heater application. Or you do the Russian light a fire under the truck to heat up the sump. The 1500HP diesel engines on the seismic air gun compressors on one oil survey boat I was on had massive sump heaters with instructions not to start the engine until the sump oil was at 60C or similar.. Which was about half an hour of warming up the oil.
