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paulgato: I know you thought the coolant preheat wouldn't be as good as the oil pan preheat, but I think your oil preheated will run into the same problems.
As soon as it makes one pass through the engine, it will cool to ambient as the engine will be cold. I would be willing to wager you would see no change in the oil temp gauge by the time it cycles around.
The coolant preheater has the benefit of warming the entire engine; it will even warm that oil from the pan on its first pass after startup. And it also warms the oil that remains inside the engine/filter/distribution system.
Of course calculating the electricity heat used in comparison to mileage saved is still difficult.
The toyota prius uses a coolant preheat (actually a storage system) so it appears the engineers think it's relevant - they might be calculating emissions savings into the equation too. Other threads on ecomodder describe the system and attempts to mimic it. Toyota could do the same with the oil pan but they don't.
Even when the preheated coolant is dissipating it's heat, it is still a benefit in warming the engine whereas the oil pan will dissipate heat readily to the exterior of the car which doesn't do much. I would only be willing to try it if I used one of the interior direct contact elements that routes through a whole in the side of the oil pan as it's really efficient. Drilling and reliably sealing aluminum is not an easy at home task though.
You shouldn't have dry start issues on a properly developed car. Even my oil filter comes standard with a drain back valve.
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