ok, so i have a 92 Civic with a B18c swap, Runs beautifully no issues what so ever until i travel at highway speed for about 20 minutes nonstop, then the temp gradually rises until i slow down to a stop, and at this point once it has heated up and even after I've let it cool down to normal temp vtec ceases to work, as soon as vtec engages it starts to misfire extremely bad and looses all power in vtec, if i shut the car off and let it sit for 5-10 minutes everything returns to normal, vtec works again until the car heats up past normal operating temps, i can also to around town driving all day and the car never heats up past normal temp and vtec will work all day.

Ive replaced the tps, distributer, and vtec solenoid. I have no coolant leaks, dual core aluminum radiator, head gasket is NOT blown, I believe the IAC is bad( I do have high idle and idle surging sometimes) plugs and wires are pretty new. any insight to my issue would be greatly appreciated.

 

Anybody?

 

do you have a fan shround aftermarket radiator? if no that is why you are overheating on highway.

 

#1 i dont think you should be revving ur car out when its above operating temperature aka overheating, ur begging for a blown head gasket.

#2 how do u kno for sure ur HG is not blown? My old em1 had an ls-v in it, had no signs of a blown HG, no over heating, no anti-freeze in the oil, NOTHING, but when id drive it all day when its warm outside when id shut it off i heard the anti-freeze in the over flow bubbling. Sure enough i pulled the head after it got warmer than normal operating temp on a summer day n it was a hairline fracture on the HG.

Im in no way saying u dont kno if a HG is blown or not but ive dealt w TOO MANY coolant issues in hondas, leaky rads, blown HG's, a gazillion thermostat issues so im jus spit ballin here since im not actually there to c what its doing. N mayb the ecu doesnt let the motor hit vtec if its over heating im not sure bc ive never tried to cross over if the engines too hot lol. Would b a good safety feature tho

 

You need to do a compression test. Either your head gasket is blown, your fans don't work, or both.

 

Try changing the radiator cap...if it dont let off pressure it can make bubbles in over flow and over heat randomly. Shot a clogged cat will overheat the motor.
Just make a list and start checking it off.. .its a honda it could be anything!!