overheating??

Hoping someone can help out with their wisdom---i recently bought an 86.5 Supra 3.0 l non turbo, beautiful shape, perfect body in and out, a miracle because i live in the salt capital of north america----anyway, promptly had tor ebuild motor bottom end plus new clutch, etc--had been overheating due to HG, which i see is a pretty prevalent problem, plus new crank etc. Anyway, working good now, can idle without overheating, can run around town without overheating, but as soon as i put load on it (acclereate onto highway for example), the temp guage will start up, and will go to about 85/90% max, than it'll come back down to where it should be and stay there---first time it did that, i kept driving on hghway for 2 hours, it worked perfectly thereafter. (till the next day, did it again) no coolant loss, has new thermostat. right now its more an annoyance, but this should not happan and i am concerned that it will progress to something worse.
Any ideas? (Thks)

Try elevating the front end of the car and running the engine with the radiator cap off. This will allow any air bubbles to escape. Next option would be to check the temp sensor. You could also run some cooling system cleaner through the engine. There may be some build up in the water jacket.

will try, thks. i've also bought another thermostat, this one from toyota vs the last one that may be faulty---pretty sure this is something stupid---should not be any air in the system given the work that i have already had done, by a very reputable garage, but anything could happan! thks

When the engine's hot, check the radiator to see if it has any cool spots. You may have some areas of the radiator plugged up.

You may have a bad water pump. If the coolant hasn't been changed often enough, the pump blades can corrode and the pump gets too inefficient to circulate the coolant fast enough to cool the engine.

Check the lower (suction) radiator hose. They can collapse internally and block coolant flow under high rev conditions.

alright, i will try that as well---i have changed the thrmo again, and although it does not seem to be as bad a problem (ie does not heat up as much, gets to about 50/55% before coming back down), it is still happaning nonetheless--plusas well it is apparentnow that there is a leak (i'm half inclined to blame this on the garage that put in the new thermostat not doing it properly)

Question: i thought about the water pump, or even a hose being loose, or constricted, but the thing that gets me is that it appears to cool down--would a bad water pump or hose be able to "catch up"? i would think that if it was bad, than it would just overheat, not cool back down??

thks for your advice..

The needle should be around half way on the dial when the car is warmed up, so it sounds like your ok except for that leak. If the needle is falling all the way down to "0%" when your driving then your temp sensor connection may be loose.

yep, i,m going to zip it into garage tomorrow for a little work, including checking re:leak, etc----the guage usually sits around 1/3 of the way up, when its been heating up beyond that, it;ll get up to around 60 to 80% before dropping back to about 1/3, than staying there. don't think its the guage as much as there seems to be a lag in the system reacting--hope to find out tomorrow asthis mechanic is pretty good, need 2 weeksl ead time to get into see him,worse than a doctor....no problem getting to see sll the crappy mechanics.