does black stain on vernatherm mean head gasket leak?

[s199810]

I have a 1990 V4 140hp 2 stroke Johnson ourboard. One thermostat was not working and I fixed it. When disassemble it, found black stain on the vernatherm, looks like burned carbon deposit. I guess the thermostat had overheating problem before but why the vernatherm has black stain? It's in the cooling system and there is only sea water. Could this mean the head gasket have some leak that the fuel/oil misture gets into the cooling system?

 

[dingbat]

I have a 1990 V4 140hp 2 stroke Johnson ourboard. One thermostat was not working and I fixed it. When disassemble it, found black stain on the vernatherm, looks like burned carbon deposit. I guess the thermostat had overheating problem before but why the vernatherm has black stain? It's in the cooling system and there is only sea water. Could this mean the head gasket have some leak that the fuel/oil misture gets into the cooling system?

Guessing you're calling the thermostat a vernatherm?

When exposed to certain substances like acids, alkalis, or salts, the copper will react and form compounds that are dark in color.

Similarly, if a copper is exposed to high temperatures for extended periods of time the surface may become blackened.

 

[racerone]

??----A head gasket is cheap.----Replace it if you are losing sleep.

 

[s199810]

Guessing you're calling the thermostat a vernatherm?

When exposed to certain substances like acids, alkalis, or salts, the copper will react and form compounds that are dark in color.

Similarly, if a copper is exposed to high temperatures for extended periods of time the surface may become blackened.

Thanks! Your explanation makes sense. The vernatherm is the core part of the thermostat and that's what is called in the parts diagram.

 

[s199810]

??----A head gasket is cheap.----Replace it if you are losing sleep.

Never done that. Looks simple as the cylinder cover is quite exposed, and no other parts need to be removed before removing the cylinder cover.