i have a 97 teg converted to a type r i just rebuilt the engine due to high milage i did pretty much a freshen up..i built it within stock specs did a mild port and polish..i had the itr cams in the motor then got a phearable chipped ecu then sold the itr cams and got buddy clubs..now the problem im having is the car runs great but some times the temp starts climbing alil past half way.. its in between half way and hott...ok so i keep driving to see if it goes down and it dosent so i turn on heat full blast and the needle shoots back over to normal.. it does it maybe one or 2 more times in a ten mile span sometimes it goes back to normal by itsself sometimes not. and when i get home i check under the hood and the resovoir is almost full..which makes me think blown head gasket but ive pressure tested in and it holds true no drop in preussure..my buddy says its my rad because its a single core ls rad..never had problems till i chipped it and changed cams which im sure it runs alil hotter...any info or questions please feel free hit me up

 

it could be your radiator, thermostat, or a sensor

 

i replaced the thermostat today and i refilled the system and burbed it took it for a drive and seemed to be good temp gague stayed alil below halfway then when i went to go home after maybe 5 miles it started to creep up about a 1/4 inch away from hot then i flipped the heater on and it went right back to normal and never rose again...im stumpped ive noticed the resovir went from being half full to full but it seems like once it pushes coolant into there it dosent suck it back out...blown headgasket? i keep checking oil but maybe its blown in a water jacket...ive prussure tested the system and it holds fine...help me out gurus

 

i have it the other way around mine runs super cold

 

same with mine! its been happening.. not really recently because i juss changed my radiator couple ago.. maybe it was your coolant.. because i flushed mine n added 1 1/2 bottles of coolant and today i checked.. it was all gone.. added 2 quarts of oil too.. now its ok

 

oh yeah.. sorry for double posting.. make sure your fans are running.. mine werent for some reason.. so my thermostat kept telling me that it was way over the normal temp

 

chances are your thermostat has failed open.