I've installed Frost Heaters in our VW diesels. The Frost Heater is just a installation kit built around a ZeroStart engine heater. In the instructions it says not to use the heater while the engine is running – I get why there would be little point in this – but what I'm wondering is whether there would be any harm in it.

The heater is thermostatically controlled so it is likely to shut off when the engine reaches temperature anyway (which seems equivalent to unplugging it). So I'm trying to figure out if I need to worry about it or if I can start the car and then unplug it, or even leave it running for a few minutes to help warm up the car if I didn't start the heater soon enough.

  • 2
    Would it be sealed? Commented Dec 22, 2016 at 17:29
  • 2
    @DᴀʀᴛʜVᴀᴅᴇʀ, yes it should be, it's in the cooling system loop.
    – dlu
    Commented Dec 22, 2016 at 17:30

1 Answer 1


From the second link you posted, the manufacturers literature on the third page, second question reads as follows;

Do not run your engine while the engine heater is plugged in.

This will create an air bubble around the element which will then cause the element to burn out prematurely.

That seems to be a pretty conclusive answer.

  • 2
    I so don't remember seeing that when I read the literature – which, admittedly, was several years ago. I was thinking about this again because I was trying to get the engine hot so that I could see if replacing the thermostat had brought the temperature back into the normal range. Very sorry for asking you all to (re)read the manual for me. Now I suppose the question is "why does the bubble form?" Makes me wonder if it isn't really an air bubble, but a void caused by the coolant flow once the water pump starts.
    – dlu
    Commented Dec 22, 2016 at 16:12

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .