Coolant Leak - 98 B4000

[Stereodoc]

FYI - I finally found an intermittent coolant leak that has been driving me nuts since putting in my new engine. I thought it was the engine but eventually discovered it was the heater control valve. Depending on the position of the heater control (including AC position) I determined that the heater control valve whether open or closed was the culprit. In the closed position it would piss out coolant intermittently right were the vacuum relay connects to the valve shaft. So if you have a mysterious coolant consuming problem or smell it but can't nail it try that valve. All you have to do is actuate it manually when the engine is hot by simply pushing on the vacuum diaphragm actuator rod. I didn't realize when I put the control into the off position or AC max that it would piss out coolant and a lot of it. Also realize that when the engine cools, it will suck air into the system too rendering the recovery system not to work 100%. Air in the system on a 4.0L engine is not a good thing. Replacements valves are $25.00.