2000 freightliner FL112 heater core location

They probably just turned the valves off under the hood. Make sure they’re open. Everything’s on the passenger side of the engine. Follow the hoses.

 

Just flush the core through the hoses. Run it through both ways. If it doesn’t circulate, maybe the valve control cable is broke off or disconnected. The hoses should go up to the heater core through the floor. Right near the firewall, on passenger side. To access the heater core valve in the cab, take off the passenger inside left kick panel. Usually when bad they leak, heat stays on even when set to cool. That’s when you have to use shut offs on the engine side. The hoses are usually inline. The rear one is usually the input, the cab valve is just a few inches up, inside the cab. Best to get a look at it anyway. See if it’s leaking, make sure solid cable is attached and properly operating when dash temp (hot/cold slider) is moved. I doubt the core is suddenly clogged. Maybe the heater hoses are hooked up backwards. I did that once on my bunk heater core. Heat wouldn’t work because of it. Hoses should both be warm to the touch when operating correctly. If only one is warm, it probably needs to go to the input (valve) side. A picture of heater hose routing would help. Maybe since they changed the water pump, they got them hooked up backwards on the engine, No need to move them from the core side. Just a guess.

 

Maybe try shutting the valves on the engine side. Swap the lines at the cab. Might just solve the issue. If not just swap them back. I would try that first. New valve is convenient in spring fall. Eliminates having to turn them on and off on the engine. That’s assuming the old valve is leaking and still causing hot water through. I’ve seen them not work right on nearly brand new Trucks. When I changed mine, ( 2000 FLD) the new one was offset, also plastic instead of metal. Probably the same valve used on Cascadias/Coronados. It required a longer piece of hose running through the floor. In other words it’s no longer a straight shot, and a bit of a pita. Especially when you don’t realize till after you’ve wasted an hour trying to get the old shorter hose connected. Lol. Heads up. Good time to replace all hoses if needed.

 

I assumed they were the same as an FLD. My mistake. I’m not a Mechanic myself, just trying to help. Looks like it’s a big job. Steering wheel, dash needs to come apart. Hopefully you can get it to flush out if needed. Good luck.

 

Maybe @SmallPackage has some advice.