the temp gauge measures the water temp within the engine. The temp that would cause vapor lock is the ambient temp within the engine bay.
My vapor lock got much worse going up hills.
New Addition: 1982 Cherokee W/T
Engine: AMC 360 w/ Edel intake, 1.6 rockers, Class III cam, Comp pushrods, Holley truck avenger carb, headman headers, custom built exhaust
Suspension: 6" Lift 1" shackles up front
Axles: D44/AMC 20 w/4.88 and detroits
1985 Grand Wagoneer 360/727/229
TFI upgrade, 70k orginal miles will trade for the right j-truck.