Last night steamy coolant began billowing out of the rear heater quickly followed by spewing coolant. Pulled over and shut down engine. Thinking to do enough to get home, I bought a union fitting and bypassed the rear heater; topped up system with coolant. In just a few minutes of driving, the union (plastic) failed - actually snapped in half - and again coolant spewing.

Has anyone else experienced this?

What could be likely causes of so much pressure in this part of the cooling system? Thermostat failure? Water pump failure?

Many Thanks
Ron Johnson
Portland, OR
Betsy �91 Weekender