Zerostart is a good product, from Minnesotbrrr...

"It looks like the bottom intake on the tank heater got teed into the output of the water pump, or whatever is a 5/8" hose right above the alternator." So you got a good heater with a very poor installation. Perhaps because there's too much stuff under the hood, perhaps by installer without a clue. My vote is for the second.

Put your hands out in front of you, with one hand slightly higher than the other. The higher hand is the engine block and the lower hand is the heater in a good installation. It's that simple. So you have to 1) lower the heater and 2) find another inlet. Deep pockets for labor or do it yourself, which isn't that hard. If you can bleed brakes then you can do this.

How about a picture of your engine bay. And find out where the heater outlet goes. Worst case is that you don't have room for a tank heater, but let's see what we're getting into before giving up. I prefer tank heaters over a frost plug heater.

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daBenz - 1970 220D