Possible themostat?

[Gt489]

When I leave in the morning its between 50-60 degrees out. The temp gauge reads just above the blue mark on my 30 mile commute to work. Currently when I leave its 90ish out. About half way home it gets up to the N and O on the gauge. But it will drop as low as the M and A. Im highly suspect of the t-stat. The car in question is my 89 SHO with 99.5k miles. Is the t-stat on SHOsource the right way to go??

 

[rubydist]

that would be my first suspect as well. any thermostat with the jiggle valve should be fine.