ok first off the motor has a lot of miles 220,000....it burns a little oil but not too much...no check engine light...motor feels like it has good power...the problem is the last month or so the temp starts to get hot after about 15 mins on the HWY goin 70-80 mph....it has increased all the way to the red a couple times before i put the heater on full and that helped it cool down...It doesnt leak coolant anywhere and it only does it on the hwy... i bought a new rad cap last month after my old one went to pieces...other than that the whole car is bone stock...any ideas what it could be??? maybe air bubbles in the cooling or a bad thermo?? any help is appreciated

 

I'm thinking bad thermo or small clog in system.

 

ok so i guess ill go ahead and get a new oem thermo and perform a coolant flush....if that doesnt work what should be the next thing i look for???.....the fan(s) turn on when they are supossed to so i know its not that... maybe the radiator is clogged like u said but it doesnt leak. could it be the water pumpmaybe?

 

Look at the radiator fins, is there a bunch of dirt and build up on them.
Feel the radiator hoses coming out of the radiator when it's hot, (don't burn yourself ) and see if there is a significant temperature difference in the hoses after the thermostat is open.

If there is then you probably have a clogged radiator.

 

will do...i am at work but when i get home ill check thoses 2 things....either way i just might get a new oem radiator anyway seeing as this one looks to be the original one from 93...and just out of curiosity because its never happened to me. If my water pump were to go out how would i know before any damage is done ??

 

my radiator had some problems when I first got it with my h22a swap. I flushed it and it helped but not incredibly. I ended up buying an aftermarket half size radiator and it runs perfectly now, also got a mugen thermostat

 

i had some overheating promblem what i did was wire the fan to stay on when i turn the key to the run position and replaced the thermostat...just to be safe i replace the water pump...it could be your water pump

 

I've seen where the headgasket has caused it. It cracked between cylinders so it was never even detected until someone got the idea to pull the head and look. Hopefully that's not it though and one of the above posts solves it.

 

i checked the radiator and it seems like it doesnt have much dirt or other debris on it. so im going to go ahead and change the thermo on saturday.. hopefully its not the HG...if it is i might consider just gettin a fresh jdm h22 and sell this one...i havent noticed any smoke during driving as that is a sign of a leaking HG so thats good...my old d15 in my crx used to smoke on start up before the hg finally blew lol.

 

Well, that certainly is a good sign...
Are you running 100% coolant or is it a good mixture with water? I'm not sure if that would make it run hot, but it's still something not recommended to do.

 

Usually you'll see a lot of white smoke if it's your headgasket. Do a compression
test on it and see how close the psi of each cylinder is. They also make a combustion
chamber leak tester that will tell you if there is combustion gasses in the coolant
which is another sign of a cylinder head/gasket problem.