Cat Thermostat Housing Leak

I have a customer that has a C-15 Cat that I have replaced the Thermostat housing on twice and now it is bad again. He has also had it replaced once at another shop. When I do the job I always install new gaskets and Thermostats. It has fresh coolant 50/50. The hole is always in the same area. This is not his actual housing.(See picture) Any idea why this is happening?

 

I talked to the local CAT Shop and they told me it is possibly due to poor grounding issues. Going to check that out ASAP.

 

Nope. Nothing loose or rubbing. I did as Cat suggested and checked for voltage in coolant but there wasn't any voltage.

 

I think 10 PSI. Truck will be back Wednesday. Coolant is properly maintained (PH and Mix).

 

Old ones are gone. Will take pictures of this one if I have to take it off. He had it patched for the moment.