Water hammer? Or what is it?

[65fastbackresto]

I dont have the lever cap.

And it still does it.

BTW, harbor freight has the laser temp gun on sale for under $40 this week, I`m getting me one before I hurt something on my motor.

 

[68conv4sp]

Just checked. It is not a lever cap. It is an octagonal 14 lb. cap. Thanks for the thought.

 

[yeloxr7]

Have you tried a different thermostat? Maybe the one you are using is defective.....

 

[68conv4sp]

Update - I began to suspect that the thermostat was only needing to open a little since I have a 3 core desert radiator with a 6 blade fan (lots of cold water). So I placed some cardboard in front of the radiator for a few minutes and the hammering at the thermostat went away within about 30 seconds. This is the third thermostat so I know its not defective. I am switching to a clutch fan so that it will pull less air until the water temp comes up. This should cause the thermostat to open further. This issue took me a year to solve. Hope this helps anyone else in the same predicament.