2003 Freightliner Columbia No Heat

I’m out of ideas other than putting on new hoses in case one is blistered inside. But, that’s unlikely since they were hot when you had them looped.

Good luck with this, I will be following and hope you find a solution.

 

When you install heater core and connect lower hose, pour coolant into top opening to fill it and to get the air out, then connect the top one. Otherwise I am out of any thoughts, even though I can ask tomorrow my shop mechanics, my bro in law has a truck shop.

 

I have same truck and engine my heater supply hose comes off the back of the head. There is temp sensor then the hose. Just don't think you are getting flow like you should

 

Well been doing is years mine works your doesn't. The other reason is you have air trapped in oil cooler seen this a lot.

 

As you see cold water flows into oil cooler then the block up to head to the thermostat with this being said you keep trying.

 

I once got the heater hoses hooked up backwards on my bunk heater core. Heat wouldn’t work. Swapped them and it worked. I know you said there’s no valve. The supply should be the one from oil cooler, the return should go to the Waterpump. If it’s showing 180 all the hoses should be hot. If the bottom hose isn’t as hot, including the small hose from Waterpump to oil cooler. I’d guess a thermostat is stuck open, still showing 180 because your idling. If it’s not cold where you are, it could stay at 180, but more likely drop if your fan came on, or if you drove the Truck. Just my theory. Maybe wrong. 2 new thermostats $70-$80. Should call for 180’s. Money well spent regardless. As long as you weren’t losing any coolant, and just lost heat, not any coolant. Thermostats would be the first thing to check. You can take them out, and boil them on the stove, with a thermometer to test them.