My fuel heater is leaking and I'm wondering if anyone is running without it in cold weather; like a few weeks ago it was -20F and with the wind chill was -40F. 

I would say yes. Subzero needs heaters.

I got rid of mine and have no problems other than our local fuel is not treated to our weather. So I leave a glass jar with fuel that's in the tank outside so I know how it acts. Add more additives if needed. If your fuel is gelling in the tank heater on the engine is not going to help. The only time I could see it beneficial if you don't shut the truck off all day, but even then fuel return from the engine is going to be warm enough to keep rest of it from gelling.

And yeah you're going to get mixed reviews on this.

If you see temps colder than -15 then a heater is bennificial in the fuel canister. If fuel is going to gell it’s going to gell in the filter and plug it. You mostly need the fuel heater at initial start up and until you build engine and fuel heat other than that, unless it’s -20 or colder with extreme wind chills the heater is not doing to much driving around in moderate cold temps

 

I don’t know how the 12v heater is set up but the 24v is a two part system with a thermostat that triggers the heating element, mine is do for replacement but not do to leaking but either the thermostat or the heating element quit. sometimes in the really cold mornings I’ve had to heat the canister with a propane torch to maintain fuel pressure until I got engine heat going, I’m just going to replace both pieces and be done with it, they are reasonably priced. 

On the 12v there is a prefilter and the heater in a canister thing that is right before the lift pump which is before the fuel filter.

33 minutes ago, 01cummins4ever said:

If fuel is going to gell it’s going to gell in the filter and plug it

Good point