Searching for a coolant leak and odor on my 2006 ranger 4ltr sohc engine, 68k miles. I found the crack in the black plastic thermostat housing. I bought a new after market kit (plastic). The new thermostat had no safety coolant bypass drilled in the thermostat flange.

I replaced only the top half of the kit which had the leak (over torque I assume), I decided to use the same original thermostat, since all indications showed a vertical needle all winter with no warning lights.

So my queswtion is, is the safety bypass hole in the flange of the original thermostat required for this engine? It's about 1/16" wide with a very small and loose flapper component in it.

The engine runs OK, and the coolant temps seem normal. Hoses are hot but not overly hot. Engine oil color is normal and trans case is topped up and 5R55 auto oil is new and pink. Rad is the original.


Thanks