Toyota Repair: thermostat, blown head gasket, head gasket problems

Question
i replaced the thermostat on my 90 4runner the old one had a jiggle valve in it but the replaced ment that the parts store gave did not. i install it and 3 minutes later my head gasket goes. are they related. and what does the jiggle valve do?

Answer
Roger,

Chances are the head gasket was your original problem not related to the thermostat. These engines had a lot of head gasket problems hence the huge Toyota recall a few years ago.

The jiggle valve allows air pockets to escape when filling the coolant system. When I replace the thermostat if it does not have one I drill a small hole and place the hole at 12o clock to allow air to escape.  

You may not have a blown head gasket, but rather air trapped in the cooling system causing it to boil over. I would remove and drill out the thermostat. Make sure it is installed spring side towards the engine and try to burb all the air out.

Good Luck!!