[Diesel_Dave]

I've been plugging in the block heater on my diesel regardless of the weather. Now that's it's getting cold I can tell more of a difference on startups. I've got oil pan heaters ready, but need to get a little bit of time to slap them on.

Obviously there's more benefit when the weather is cold, but I can't really think of any significant reason why pre-heating would ever hurt your FE. IMO, one of the biggest benefits to pre-heating is related to the oil, because of 2 things. First, when the oil is cold your oil pump does a whole lot more work to push the oil through the oil filter (because it's thicker). Secondly, when you start up, your oil needs to find it's way through all the different passages and into all the bearings, etc. Until the warm oil gets there, your friction is going to be much higher. That also decreases your engine life as well.

Remember too, that operating temps for coolant is ~200 deg F and oil temps are up in that range or higher so even 90 deg F is "cold".