46 ford 239 one or two thermostats?

does the engine take one or two stats, my shop book shows two, just cking....

 

Yes, the motor is totally isolated between R & L water jackets and the coolant only mixes in the radiator tanks. That's why it's a good idea to use dual temp gauges.

 

what happens if only one is used? only one was in my flathead after sitting 38 yrs

 

The side that doesn't have a thermostat will mostlikley overheat and crack the block.
The Flathead needs a lower rate of water circulation than the water pumps produce to insure proper cooling, the thermostat provides the correct rate.

 

so two it is,what temp.is best?

 

I use nothing but 180's and Ive had no problems in mid 90's summer beach traffic and parades.
Be sure the block & head water passages are clean, radiator core is good and timing is on the mark. Use NGK B6L plugs.

 

where can i get new tstats....