during the day, the car runs fine except that i’m getting a CEL, but at night, if the car has been sitting for a little while, when i start to drive, the temp gauge drops down to cold. if i let the car sit and idle, the temp gauge starts to rise but as soon as i start driving, the temp falls. it seems like the cold air coming into the engine makes the temp drop, but i have a stock air box so the hot air from the engine bay is what the intake’s sucking up. the only thing i can think of is that i don’t have a thermostat in my car. i had an overheating problem before and took it out but haven’t had the chance to put it back in.
you don’t have a thermostat!! thats your problem right there. I was gonna say that yours is just stuck open… but thats not the case since you don’t have one. Go do your car a favor and get a thermostat, its a VERY easy install, and cheap too.
Typically during the day and at idle the thermo is supposed to be open, so it will run normally at these times. but if its colder outside (like at night) and at higher speeds where the radiator works more efficiently the thermo should be closing to keep the engine temp constant.
i actually thought it was very hard to change since it’s sooo cramped in the engine bay…
no, i did mine a couple years back and it was a snap. Its really not that hard to reach. I think it might be on the vtec engines though.
i figured that’s what it was. the only reason i was doubtful is because i had the thermostat for a while now and the temp problem seems like it only started like a month or two ago.
also, i heard that having a faulty thermostat that stays open can cause the rpm’s to fluctuate because there’s too much coolant getting into the engine that isn’t needed. is this true because if so, maybe putting in the thermostat will help me with that problem too.
you shouldn’t have an idle problem because of the thermostat. During most driving conditions the thermo is all the way open, which would mean that our car’s would almost always have an idle problem.
however, coolant does have something to do w/ the idle. Low coolant can cause your idle to bounce up and down.
funny thing is that i had almost the exact same problem as you. It was fall/winter and one night on the highway i noticed my temp fall all the way down, I had to drop it into 4th and keep the revs up to keep the temp up. I had also had the bouncy idle problem for quite awhile.
the next day i put in a new thermo (the old one was stuck open), and topped off the coolant level. The car ran at the right temp, and the idle problem was solved.