Block Heater Question

KootenayMax · Jan 7, 2025

Hey all,

I have a 2024 1500 3.0L Duramax and was curious about people experiences with the block heater.

I've read the manual and I know that it's thermostatically controlled and claims to not come on until -18C but I had read in a few places that they were working for people at much warmer temps so decided to check for myself.

It's about -6C right now so I plugged in a cord that I had made for checking my kids block heater and surprisingly found it was pulling 3.2 amps. I figure I'll mess around and try again at a few different time and see. I'm pretty knowledgeable about the whole electricity thing, especially on the AC end so I know what I'm doing lol. I live in the mountains in British Columbia and while the nights have been chilly we haven't had any stupid cold yet this year (-25 or more) but I have found she really seems to like being plugged in more than not because she's been a little cranky the couple cooler nights she wasn't.

Anyhow, I was more curious than anything, and was wondering if anyone else had any experiences or knowledge about this.

Thanks in advance and hope everyone is having a good start to 2025!

gemarsh · Jan 7, 2025

I think if'n you read the manual again, it will say it "might be or may exist" thermostatically controlled. It has been decided that the diesels are not controlled but the block heater option on a gas burner is.

I plug in whenever it's going to freeze and run in the morning. Yes, these LM2 and L5P's start really good. I personally know down to 5°F, on their own.

But it is easier on the diesels and more fuel efficient to "identify as an ev" when it's cold.

Johnv76 · Jan 7, 2025

You said a bad word. EV's....... ewwwwww

BlueBrute · Jan 7, 2025

gemarsh said:
I think if'n you read the manual again, it will say it "might be or may exist" thermostatically controlled. It has been decided that the diesels are not controlled but the block heater option on a gas burner is.

I plug in whenever it's going to freeze and run in the morning. Yes, these LM2 and L5P's start really good. I personally know down to 5°F, on their own.

But it is easier on the diesels and more fuel efficient to "identify as an ev" when it's cold.

"Identify as an EV..." Good one!

KootenayMax · Jan 8, 2025

Still laughing at the identify as an EV lol.
That makes sense, and I did see the "might be" plus read the Duramax supplement but it wasn't super clear.
I'm the same and always plug in when it's cold anyway. Problem is I have one of those brains that needs to figure stuff out so here we are

.
Thanks for the info, really appreciate it.

pinebaron · Jan 8, 2025

KootenayMax said:
Hey all,

I have a 2024 1500 3.0L Duramax and was curious about people experiences with the block heater.

I've read the manual and I know that it's thermostatically controlled and claims to not come on until -18C but I had read in a few places that they were working for people at much warmer temps so decided to check for myself.

It's about -6C right now so I plugged in a cord that I had made for checking my kids block heater and surprisingly found it was pulling 3.2 amps. I figure I'll mess around and try again at a few different time and see. I'm pretty knowledgeable about the whole electricity thing, especially on the AC end so I know what I'm doing lol. I live in the mountains in British Columbia and while the nights have been chilly we haven't had any stupid cold yet this year (-25 or more) but I have found she really seems to like being plugged in more than not because she's been a little cranky the couple cooler nights she wasn't.

Anyhow, I was more curious than anything, and was wondering if anyone else had any experiences or knowledge about this.

Thanks in advance and hope everyone is having a good start to 2025!

Interesting. I'm inclined to check if my Duramax 6.6 block heater pulls any current in warmer weather.

That also reminds me of my pending project for which I have all the parts; installing an external battery charging port on the front bumper (passenger side) which will use an inlet port and external cable, identical to the block heater port, except this one will internally connect to the passenger side battery (dual parallel wired batteries in my diesel truck) and the external cable will be fed from a 12V floor battery charger.

NMTXAT4 · Apr 17, 2025

I have experienced the "fans staying on" problem with running the block heater when it's not 0F degrees or colder. The ECM thinks the temps are higher and run the fans, non-stop until a complete cold cycle is run. I tested and repeated this when the temps were between 15-25F. My guess is that the block heater on my 2024 Sierra is not temp regulated.

NTXBall · Jan 25, 2026

Jumping on this engine block heater thread if I may. I've got a 2024 AT4X HD, diesel. I'm in N. Texas, and while it's cold, it's not the bitter cold that many of you deal with. We got down to about 17 for an overnight low, with lots of sleet. Just to try it out, I plugged in my block heater and let it sit for about 3 hours. The truck started like a normal cold start (I'm thinking 3 hours was not long enough), but after a few seconds she started shuddering and stalled. Tried to start again with no success. Waited about 15 minutes and she started right up, but after a few seconds stalled again. I'm thinking possibly the fuel has gelled a bit?

gemarsh · Jan 25, 2026

NTXBall said:
Jumping on this engine block heater thread if I may. I've got a 2024 AT4X HD, diesel. I'm in N. Texas, and while it's cold, it's not the bitter cold that many of you deal with. We got down to about 17 for an overnight low, with lots of sleet. Just to try it out, I plugged in my block heater and let it sit for about 3 hours. The truck started like a normal cold start (I'm thinking 3 hours was not long enough), but after a few seconds she started shuddering and stalled. Tried to start again with no success. Waited about 15 minutes and she started right up, but after a few seconds stalled again. I'm thinking possibly the fuel has gelled a bit?

Yeah, sounds like it's time to get it in a warm shop overnight and change the fuel filter in the morning and toss in some anti-gel. How long are you guys in the cold for? A couple of more days?

Filters don't usually come around after getting waxed up.

NTXBall · Jan 25, 2026

gemarsh said:
Yeah, sounds like it's time to get it in a warm shop overnight and change the fuel filter in the morning and toss in some anti-gel. How long are you guys in the cold for? A couple of more days?

Filters don't usually come around after getting waxed up.

2-3 more days. Lesson learned!

Cablebandit · Jan 26, 2026

So do they not use winter diesel down that way?

NTXBall · Jan 27, 2026

Not in my area (North Dallas). After running the block heater all night she started right up. A bit rough for a few seconds but running smoothly now. I've added anti-gel and will replace the fuel filter just to be safe.