have a 90 integra with a fully built ls vtec. and everytime i get on the highway to do a run my temp gauge goes to cold? throgh town or just driving its perfectly fine. i really dont know whats going on with this. i loose vtec and car runs lean as [freak] on the big end. but as soon as i let off the gas it usally goes up but sometimes it jumps around for a little bit then goes back to normal. can anyone please help me out. thanks in advance.

 

Your thermostat is stuck open, replace it.

Why doesn't anyone replace the expendable parts on a rebuild?

 

its a brand new low temp one thanks. it only happens when i get on the freeway other than that its fine.

 

Why would you put a low temp thermostat in your engine? Do you know that when parts heat and cool at rapid rates, they warp/crack? Put a 195F thermostat in there, and go home with more power, and better fuel economy. You WILL NOT get that with a low temp thermostat.

I would also like an explanation as to how you think running the engine colder will help you produce power. There is a reason engines run at 200F ALL THE TIME. How can you tune an engine that has a wide temperature variation.