BIZARRE Spark Plug Color?

[savatreatabvr]

Originally Posted by kalbert

That is bad. You have a problem here and the thermostat is not causing it.

You must run coolant/water mix. Coolant has anti corrosion components, wetting agents, lubricating qualities, and changes the boiling point of water.

A common misconception about the thermostat is that it controls how *hot* the engine gets. This is not true. The thermostat controls how *cool* the motor *could* be in ideal operating conditions. Mechanical problems will make it run hotter than the thermostat can control. Specifically a bad head or gasket will create an air pocket behind the thermostat that will not transfer heat from the coolant to the pellet so it opens to allow coolant to flow.

I would suggest a leakdown test on the cylinder in question. My expectation is you will see/hear air leaking into the cooling system. Bad head or gasket. This would explain the overtemp problem and the plug condition.

An interesting note is that not running a coolant/water mix can cause corrosion and fluctuating temps (excessive expansion and contraction) that can cause heads and gaskets to fail (among other things, burned valves). Not running a thermostat can also cause wild fluctuating temps resulting in the same. So which came first, the chicken or the egg?

How do I perform a leak down test on a budget?