JerryG
Super Member
There are very very few problems with block heaters sealing. Whether it is the type that has the threads, the ones with the adapter and the threads or the more common ones that have a single bolt that seals with an o-ring. If you want a block heater as opposed to a tank heater and you do happen to have a choice between the one with the adapter and the o-ring sealed one, get the one with the o-ring. Personally, if there is room, I would take a tank heater over a block heater every time.