Rad Heaters

[tsm1@domain.elided (Tom Mandera)]

I'm not familiar with the heater Joel or Eldon are discussing, but every
engine heater *I* have had is a very simple heating element.  I have one
('76 Luv) in the radiator, and one in the lower rad hose ('72 Scout 304).  I
*think* there' s one on the '77, but as I recall the hose was chopped, and I
haven't had a need to investigate (VERY mild winter).

This type just heats the coolant, and lets convection do the rest.  On a
quiet evening (or any night at 3am when I would come home) I could walk
through the garage and hear the coolant "boling" on my Luv.. at least, I
heard a gurgle coming from the radiator.. 

FAIK, it doesn't impede coolant flow at all. 

The in-line lower rad hose heater on my '72 might impede flow, but not
substantially... it's just a short piece of pipe, with a heating element
inside that gets spliced into the lower rad hose.  So it impeded flow no
more than any old extra string of metal would.

-Tom