Overheating after 2mi

Hi,

I hope someone here can help me. My Explorer overheats after about 2 to 3 miles, on streets or highway. If I slow down the gauge immediately goes back to normal.

Also once it does this initial spike, it doesn't happen again unless stressed. (mountains) I have checked all fluids. I am stumped! and so is the mechanic.

HELP!

Muriel

P.S.No visible leaks

My thoughts go toward the thermostat.....sticking, late to open, once it's open all is OK.

i agree SRERCRCR it sounds like the thermostat but my sister has a blazer and it did the same thing replace thermostat no go, replaced water pump and has work ever since. so if it is not the thermostat i suggest trying the water pump