I've used these in many cars for 50 years with very good results, but in more recent times I've had these fail after 1-5 years of occasional winter use. Kats were first seen as seem iffy, but also the Tempro have had failures. Also OEM that I think some of Canadian manufacture. I had wondered if modern coolant was somehow a problem, but after pulling out the bad units, there were no visual signs. The circuit would opened up internally. These are typically 400 watts. Any ideas out there?