Repairing Coolant Leak Under Dash Thomas HDX

We recently had a phone call to our shop from one of our sports run bus operators. He was running a 2007 Thomas HDX Pusher. The operator stated that there was coolant on the floor and the inside windows were fogging up. It should be noted that this leak is very minor and the shutoff valves at the engine valves can be closed to isolate the leak and the bus can still be operated.

Since he was 4 hours away my hands were tied and I told him to take it into the nearest Thomas dealer to let them check it out. Shortly afterwards he said the leaking stopped and he limped the bus home without any further incident. Once we got a chance to inspect under the dash the coolant leak was no where to be found. The coolant temperature control valve is electrically controlled from a dash switch.

There is coolant running through the control valve where it is throttled on and off depending on the operators requirements. We decided to pull the front inspection door down and have a look, after a close look we found a leaking control valve where and o-ring seals the piping assembly. The operator must have adjusted the heat control to a position that stopped the valve from leaking temporarily. Thomas has a new valve available and replacement will remedy the problem. It's hard to detect where the leak is coming from until you physically pull out the front heater core and check the control valve itself.

Thomas heater cores are very durable and I have never seen one leak yet. The great thing about the HDX model buses is the accessibility to the front of the cab where you can drop down the front access door panel and work on the plumbing from the outside of the bus.