I think it might have failed, thermostat was stuck shut I guess, antifreeze poured out of overflow with the truck plugged in.
Last couple days it hasn't worked, I'll check the plug wire but I bet it's the heater.
My 5.9 has 470,000 miles on it now

I've had a couple of them do that, they're not hard to swap out

Ya it isn't too hard I think, I suppose a lot of antifreeze will come out, I'll drain it out, how much do I need to drain out before taking heater out?

Just unscrew the heater out of the block. Have the other one Teflon taped up and try to stick it in fast. I've done it on my old Dodge and a couple of tractors. I'm not good working under pressure. I usually have to add a gallon.

Thanks, I've never done it before, I'm guessing with that many miles it probably failed, ordered one for 42$

When you get the new one throw an ohm meter on the prongs of the new plug. Then do the same on the old one. That will tell you whether it has failed or not. Might save you the trouble of removing it if it is still good.

I replaced one on 2001 cummins last year. I didn't drain the coolant, I don't think I lost more than a cup to a cup and a half. Just have everything ready to put back in. Loosen the old one till it just starts to seep and get everything in place for the new install. You tube has some good videos on it also I have had to replacement too mant thermostats in this truck too. It's super easy. The worst part for me is slipping the belt off the pulley and putting it back on.

I don't know if I have one

I have to take a belt off? I better look on YouTube I guess

I haven’t changed one on a 5.9 but, a good thing is the weather is supposed to get warmer, so working with antifreeze won’t be to terrible.

Thank goodness, for warm weather.
Last two winters I parked the truck, easier to put my carpet cleaning equipment in the car, and not getting any more salt on my truck.
I've only driven it a few times, when no salt is on the road.
I've got 6 pin holes, three on two fenders, not bad for 23 years old and 470,000 miles

I saw on YouTube how to do it, I think I have a tool like that, I'll test it

Did ya figure it out ?

Yup ten bruises and three ripped open spots on the back of my hands! Lol I have old man hands
I took air tube off, oil filter, then changed it, new one is working.
My electric meter tool had dead batteries, so I just went and changed the heater.
It was 40° today finally warm enough.

Blood thinners makes a mess out of hands and arms, glad you got it changed.

I had this problem for a few years now, way before the warfarin, sucks, if I just bump the back of my hand on a table or something cleaning carpet it bruises bad or rips my skin open