Glad you've chimed in here.
I have replaced the fan clutch. Changed thermostat yet again. Engine still isn't getting up to temp. The coler it is outside or the faster I go, the cooler the gauge shows. Heat is barely warm. It's also taking the truck 15 or 20 minutes to get as warm as it going to.
This was an issue on the previous engine as well. It developed after a shop replaced the radiator if I am remembering correctly.
The cooling system had stop leak when I first got the truck. I flushed and flushed. Finally got it clean looking. The heater core though has not been changed. Also, in the mornings when I start out of the driveway I can hear a slight gurgle from thr heater core. It lasts about 5 seconds. Then doesn't do it again til the following morning. No foggy window or coolant in the floorboard. If I'm losing any at all, it is escaping as a gas and haven't noticed a level change.
I'm at a bit of a loss here. I thought about bypassing the heater core for temporary to give that a test of sorts. If it heats up right, I know where my issue is. Think that's worth trying?
Could an oxygen sensor play into this in theory? They're original as well.
I'm going to check codes tomorrow. It has to be throwing a P0125. Previously it was only throwing for EGR, which the new motor isn't equipped with. It was throwing egr codes on the previous motor with an entire new egr everything.
It has to be something that's on the truck. And not on or in the engine. I don't think we reused any of the 99 engine sensors, pretty sure the 2004 engine came with them all in place. So that'd leave the heater core, pcm, heater core/radiator...that's it. Water pump is new, Hoses are new, thermostat is new...
Id hate for this to prematurely kill the low mileage motor.
Apologies for the book.