B180 2.0 CDi - alternator problem visit workshop

Hi all,
Im newbe to Mercedea, bought recently B180 CDi 1150k milage 2005. Today on the way back from work glow plug light came on when car was on neutral, once i increase rpm light went off and was off untill again rpm went below 1k (neutral). From what i gather on this forum this probbaly is signal that one or more glow plugs are getting weak and need replacing. But also I found info that this could be faulty temperature sensor.Few days ago MB was replacing my thermostat as it stucked on 60. After when they replaced it reaching 78-80. Today I noticed while driving stady 50mph on 5th gear that temp indycator moved suddenly slighlty over 80 (81 to be precice) and during few seconds went back to 78. Is that normal? Can this be linked to this thermostat replacment done by MB for rediculisly high price?
Also does someone can recomend independed mercedes garage near Boston? MB prices for labour are simply redicules. I heard that Forest Motors in Lincoln does MB are they good...?

In addtion new message showed after few hours something like "Alterantor problem visit workshop"

Any ideas? Please help

Thanks
M.