98 expy overheating problem for a newbie

Im new to the site... and mostly ignorant about automobiles... but this is a little problem that seems weird to me...

While driving on the highway at 65 during the daytime... my temp gauge will shoot up from midway to as hot as possible... if I turn the vehicle off for about 20 seconds or so... the temp gauge goes back to normal. The first time it happened I pulled over and checked the temp of the coolant and seemed fine... no steam or smoke. When I turned it back on all was well. about 5 minutes later, it happened again... this time I turned it off and back on again within about 10 seconds... and it was normal again. The third time I let the light stay on... and after about a minute or so... the CE light came on and I started having problems maintaining my speed... it felt very rough driving it... kinda like there was a new vibration. When I turned it off and back on again... temp was back to normal but the CE light remained. On the way to AZ to get the code checked... it happened again... but this time the CE light went out. So I didnt bother to get the code... also... when driving at night... or in generally cooler temperatures.... the problem does not happen as often... I can drive for 20 to 30 minutes or so before it comes on... and again... all I have to do is turn the vehicle off for a lil bit and all is well.

I've driven the vehicle for over a hundred miles in one shot... just turning the vehicle on and off when the temp gauge goes up... and have had no issues with it otherwise. After asking some friends about it... they think it may be the thermostat sticking... but if that were the case... wouldnt the temp stay up there?

Any ideas on this... any advise would help... im poor and cant afford to have a mechanic "guess" over and over and charge me thousands to fix a small problem...

Find an auto parts store that will scan the codes for free. Autozone does it. This could be a real live overheat problem, in which case the engine control computer is cutting off fuel to the engine to prevent it from melting down. If it's a real problem, and you've checked the coolant level, I'd head right for the thermostat. It's the most likely candidate and also the least expensive to replace. You could test it out with an infra-red thermometer, but the tool would cost more than a new T-stat. Or, it could be a false temp reading caused by a bad coolant temp sensor. You would need a digital multi-meter to test that. Or, once again, you could replace it under the theory that the part costs less than the tool. I hate to advise that since I'm always against "throwing parts at the problem." But, since you're broke, it may be your only alternative. But FYI, you're playing with fire here by continuing to drive it like this. If it's a real overheat problem, you could really toast your engine to the tune of $3-4,000 bucks.

wanted to say thanks for your help... got the codes checked out... engine overheat and head overheat... went ahead and put in a new tstat... drove the hell out of it for an hour... no problems anymore :)