I have a problem with my engine coolant heater. It's in the lower radiator hose. It's similar to the one sold on Diesel Giant. First one worked great, but electrical contacts rusted. Second unit lasted until a couple weeks ago. Put in #3, a Kats. Worked a couple times. Yesterday put in yet another. While warming up engine and topping off coolant, I noticed the upper radiator hose didn't get hot, but the heater hose did.
Today, after being plugged in all night, the upper and lower hoses were cold. And yes the power was on, coolant full.
I still had unit 2 with hoses on in the basement. Put water in and it worked.
Could a bad thermostat be keeping coolant out of lower hose?
Thanks

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1984 MB 300SD Turbo

Does your car warm up normally when driving (i.e. does it read 80C or so and maintain that)?

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1992 300D 2.5T
1980 Euro 300D (sadly, sold)
1998 Jetta TDI, 132K "Rudy"
1974 Triumph TR6
1999 Saab 9-5 wagon (wife's)

The lower hose is always full of coolant. It's the lowest point of the system. If the lower hose is cold, the heater isn't working.

The upper hose may not get warm due to the distance from the heater (and the fact that the entire radiator is in the way.............).

Mine you can feel the heat from standing at the bumper . . . coming off the rad!

Heats the whole block, and even the front of the bellhousing on the trans . . . 1500w does a good job!

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82 240D Manual 277K and still rolling!
02 Volvo S60 AWD For Sale