Interesting temp behaviour

[fruitcakesa]

Having replaced the rad, tstat, cap, all hoses but the bypass and new MB coolant in my 81, I figured the car would run at normal 80*-90* range.
And it does most of the time, but when I either put it in neutral and coast {I know, bad safety practice] or shut it off after a drive, the guage will rise towards 100*. Once I put it back in gear and the revs come up, the temp gauge drops quickly. Same if I restart after a shut down of say 10 minutes or less and begin to drive , the temp also goes back to normal.
Is this an unusual temp fluctuation?
Outside temp is in the 70* F range

[Squabble]

that happened to me a bit too until i unscrewed the expansion tank cap to the first tab (not all the way off but still loose) and drove it around a bit. got the last of the air out and it stopped doing that.

[fruitcakesa]

That will be easy to check. Thanks

[tbomachines]

Seems to make sense to me...the engine needs to be cooled and the water isn't flowing enough until you get the revs up. WHen I run my car for a while, park, then start again within 5-10 min, the gauge reads above 100 but quickly goes down as the coolant circulates.

[E150GT]

When the engine is turned off the engine goes into hot soak. It will rise in temp for a bit and this is normal.