Thermostat styles

Here are two thermostats, the rusty one is 142 degree and the other is 140 degree. They are very different in design, both are marine. Has anyone else seen this?

Thermostats are something near and dear to me. I've actually dealt with both of the above thermostats in my job (designing diesel engine cooling systems).

The thermostat on the left is a standard elcheapo reverse poppet thermostat. The stat on the right is of a pressure balanced design, as GottaSki says probably produced by RobertShaw.

The opening of the thermostat on the left is effected by the pressure in the cooling system. Once the stat opens slightly and relieves some of the pressure the thermostat can close again (partially or completely). I've seen this cycle happen up to 10 times in my company's engines before the stat will stay open.

The thermostat on the right has a more balanced pressure on either side of the valve and is effected to a much lesser extent by cooling system pressure. The result is a much more steady and stable thermostat opening.

Both thermostats are actuated by a wax "pill" or motor. Basically there's a little chamber of wax and as it heats up and melts it expands which pushes a piston and opens the thermostat.

Personally I recommend the thermostat style on the right. We are no longer using the thermostat on the left in new designs due to the above mentioned problems.

64,

I just got my new tstat for the spring from skidim last week. It's a 143 and looks like the one on the right.

Alan