Block heater question

BigKahuna · January 24, 2021

On my recent 1500’s and the wife’s Yukon/Tahoe the block heater didn’t do anything until ambient temp was down to around -20 C. Is it like this for the duramax too? Haven’t been plugging mine in this winter as it’s been a warm one and temps haven’t been anywhere near -20.

Another JR · January 26, 2021

Owners manual says the block heater on the hd trucks functions at 0F and below, which is approximately -18C.

Edited January 26, 2021 by Another JR

Tomato · January 26, 2021

Did they change these? They used to be a simple heating element that was inside a coolant passage. You plug it in, and it provides heat.

Do they now have a thermostat or something???

txab · January 26, 2021

Yes they have a thermostat

BigKahuna · February 11, 2021

Despite what I read here I decided to try it and mine appears to be effective at -12 to -15 the last couple of days.

Colossus · February 12, 2021

On my previous 2 LMMs and 1 LML, I could plug in my block heater at temps of 30-40 F and it would kick in most of the time. Starting was quick, and there was heat much quicker. Yes yes yes, the owners manual says don't plug in unless below 0 but phooey to that. Some of us appreciate having heat quicker. (and it helps to defrost/defog the windows quicker) And no check engine lights either.

nick112288 · February 12, 2021

I never understood why the L5P block heater doesn't work down until 0, but both Ford and Ram work at whatever temp.

redwngr · February 13, 2021

On 2/12/2021 at 2:30 PM, nick112288 said:

I never understood why the L5P block heater doesn't work down until 0, but both Ford and Ram work at whatever temp.

The manual actually says the thermostat "may" exist.

An internal thermostat in the plug-end of the cord may exist, which will prevent engine
heater operation at temperatures above −18 °C (0 °F).

20gmctruckguy · February 13, 2021

I tried mine today and it seems to be working and our outside temperature is only around -7 C. Maybe mine does not have the thermostat? It's a Duramax.

redwngr · February 14, 2021

4 hours ago, 20gmctruckguy said:

I tried mine today and it seems to be working and our outside temperature is only around -7 C. Maybe mine does not have the thermostat? It's a Duramax.

I think (but of course can't prove) that's common.

I also think there is a lot of 'recreational' block heater use.