The aux water pump (electric water pump) adds flow at idle. When you rev the engine there will be more than enought flow. If you're not getting any heat at all then there's another problem.

Try bypassing the aux water pump with a short piece of 1/2" copper water pipe and 2 feet of 5/8" water line from the your local auto parts store. If you then get a lot of heat it's your servo. If there's still not heat then you've got a plugged heater core.

Please note that both the feed and return lines to and from the heater core are connected to the bottom of the servo. You have to bypass both the feed and return lines at the servo for this test.

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Steve S
Support Tech
UnwiredTools, LLC
www.unwiredtools.com

1982 380SLC
1994 E320TE
1998 E300DT