I have one. Haven't used it yet. With the thermostat closed, water circulation will be minimal but some heat should make it into the block.

See photo number 3 in this link for a picture of my heater.

http://www.peachparts.com/shopforum/showthread.php?t=160706&highlight=skid+plate

If you do a search of this forum for "block heater," you will get lots of information.

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970