There are a couple of thermostats that will physically fit the SDxx engine. Installing the wrong part will not cause problems in cold weather. But in warm/hot climates especially when you are hammering along in 4th and 3rd gears at full throttle, then the wrong design thermostat (one that does not close off the "bypass port" when the thermostat has moved off the full closed position) will permit a significant amount of coolant to bypass the radiator. Not desireable.
When the thermostat is CLOSED, the bypass port is uncovered. This allows coolant to circulate around through the engine block, head, water pump, and the heater too (if the control valve is open). G.Guest)
As the thermostat opens to about mid travel, the bypass port is closed off completely which ... forces ALL coolant to route through the radiator to get back to the water pump inlet.
Last edited by philip20 years ago, edited 9 times in total.
-Philip Passed 08May2008
My friend, you are missed . . .
1982 Datsun 720KC SD-22
Notice the spring clip alongside the spring. There is one on each side. When the thermostat reaches WIDE OPEN travel, the clip pops inward around the valve edge thereby preventing from ever closing again automatically. You MAY be able to "reset" it manually or it may become a toss-away.
-Philip Passed 08May2008
My friend, you are missed . . .
1982 Datsun 720KC SD-22
New issue: my 1981 "Orting Truck" has an off-center counterbore for the thermostat to drop into, putting one bolt hole too close to the pressurized counterbore.
(click on image for larger)
There is only about .045" material there for the gasket to seal. Without sealant applied to the gasket, and using a Fel-Pro gasket (that is not exactly a perfect rendition of the original hole size/spacing), I was getting coolant up through that bolt bore and quite a bit of it.
The first time I replaced the thermostat, one of the bolts broke off . I chose to remove the entire housing and take it to a machinist who torched it out. Even a "Time-Cert" would have been very close to coolant and gasket.
G.Guest)
