I have a 89 truck, and was told I have a lazy thermostat.  So I took the old
one out (the spring side was pointing into the engine), put the new one in
and started up.  I had the top of the rad open to add more coolant, and
noticed coolant running across the opening.  My first thought was that there
shouldn't be any movement of  coolant because the thermostat was shut.

My second thought was that the coolant was not only flowing, but flowing
AWAY from the thermostat. In other words the coolant was trying to push the
thermostat away from the engine block.  I thought the coolant should push
the thermostat into the engine block - the flange keeps it out of course,
but the pressure of coolant seats the thermostat against the block..

Test drive - engine stayed cool

Help please

John