must have been air locked, the water needs to be in direct contact to make the stat react, air temp doesn't work - happens when you put it all together with little or no water in the engine and then fill it after it's all closed up - don't drain the rad below the level of the top of the engine, just enough so removing the housing doesn't flow tooo much out, having run it now there should be no air in the engine, so if you don't introduce any it should work fine - if you don't wanna drill the hole, make sure the engine is right full of water when you put the stat in, enough so putting it in causes some to overflow and there shouldn't be an airlock problem
Bill
