Thanks for the tip. I have two mtc valves that have weak springs. It's fall season so I'm thinking about "the heater" again.

Just wondering...does the addition of the O-ring keep the valve from closing / sealing. Seems the result is water always reaching the heater core.

Also wondering if the "fix" holds at higher rpms i.e. highway speeds? That's when the valve seems to have a problem i.e. heater fine putting around town, then no heat on the freeway.

Thanks

P.S. I've also disconnected the pump. My understanding is that it is to help the heat at low rpms.

__________________

1986 300SDL 440,xxx