I've had the bus for a few years now. All valves are open and coolant level is good to go. I'd "heard" that if the thermostat in the DT466 fails "closed", than coolant won't circulate to the heater cores. I can't verify this but after taking her out for a spin, the engine is definitely up to temp but it seems that coolant isn't circulating back to the heater cores. This is why I thought the thermostat was failed shut.
Got it. That fine of a detail for a DT is too many years behind me to remember.
Someone will chime in, I just thought I'd answer while others pondered.
However, I would think if I thermostat was stuck closed, you'd have engine overheat issues.
I thought that as well so I haven't pushed it much. I figured the DT466 on short trips would at least get to temperature without overheating with a closed thermostat. I'm stumped. I tested the thermostat located in the t stat housing (top of engine, large diameter rad hose attached). It opens at around 180-185 degrees F. I'm wondering if there's another thermostat housing somewhere near the oil cooler?