I flushed the system last week and it has been fine for a weekso far until yesterday when out of nowhere almost home at a stop sign, i looked down and the needle was pinned on the red. it wouldnt go down either i had to shut the car off and wait and then after about 5 minutes it was all set and i made it home. so i headed out today no problems this morning it was about 38 degrees and then on my way home today after 15 minutes of driving most of which was highway i exited the highway and after about 3 red light stops i noticed it creeing up from its normal 2/5 to about half. and as i accelerated and tried to keep the engine rpm low it would slowly settle. then at the second to last intersection until home the temp guage rose to about 4/5 and i was finally able to turn onto the road and accelerate and it slowly went down to about 3/8 and from that point i approached the last intersection, and attached is a video of my guages as i approached, stopped, and took off down the road to my house.

Accord temp problem - YouTube

-this video doesnt show the dramatic changes but its all i could get for thinking of taking a vid last minute. i dont know if it will help but its available.

checked the fuse and its good and the water pump is about 4 months old. the thermostat is about 5 months old. when i shut the car off i heard the fan click on. so im thinking that its probably the other fan switch that controls the fans while the car is running.

also, the car never ran oddly or any different than usual during all this.

 

For future reference, turn on the heat full blast with outside air coming in. This will help cool the engine coolant. The heater core is just a mini radiator.

I noticed that your check engine light is on. You can stop by a parts store and have them scan for codes. The connector is behind the ash tray. This likely has nothing to do with the overheating. Post any codes on here.

Make sure the engine is cold. Remove the radiator cap. Make sure there is coolant filled to the top to the radiator. If not, fill up radiator to the top. Also, let us know how much is coolant in the overflow tank.

Also, when the engine is cold, start up the car and turn on the a/c. Are both fans on the radiator running? If not, tell us which one (passenger or driver's side) is not working.

Is your car a 4-cylinder or V6?

 

i did have the heat on when the guage was getting high up.

yes i forgot to mention the check engine light. it is lit because of the O2 sensor. the reservoir was full.

I have a slow coolant leak because of the heater core, so i always had to fill the overflow about 2-3 times a week with using the heat during cold days and i noticed i wasnt going through much this week and i usually fill it to damn near the brim because it doesnt "overflow" it just leaks and takes from the bottle. both hoses were hot, but i removed the radiator cap and saw no coolant at all. and the reservoir bottle was full since i filled it 2 days ago and i squeezed the lines now and the upper hose is all air and the lower hose is mostly air and a little slosh of fluid in it. so now that should be pretty self explanatory that the empty coolant lines is my problem. so im going to fill it right now. but what do you think is causing it to not take the fluid from the overflow all of a sudden and running to low on fluid? possibly the rad. cap?

 

You will have to find the leak. It could be anywhere.

If you go to the parts stores, some have a radiator pressure tester. It is basically an air pump with an adapter to fit on the neck of the radiator. The radiator should hold around 16 psi. If you do this test, make sure the radiator is full. If the pressure drops quickly, then try to find where the coolant is leaking.

There is also an ericthecarguy video dealing with overheating. Just do a google search and you'll find it on YouTube.

 

Check the level in the radiator. Even when the overflow is full the radiator can be low. When it's low at low rpms the water pump doesn't have quite enough water to push around so the car overheats. At higher rpms the water froths a bit more and keeps it cooler. This happened to ours, check the radiator.

 

As the engine cools the cooling system generates a vacuum to suck coolant back from the overflow into the radiator. But if your heater core has a leak the system can't generate a vacuum so the coolant just stays in the overflow and the radiator coolant level gets low.

X2 on finding and fixing the leak(s). And since the cap has double duty for both pressure and vacuum - and it's cheap - it wouldn't hurt to replace it.

 

leaking heater hose is where I would look if not a leaking radiator.

 

Im having sorta the same problem.
I drive a 96 accord, recently seen the check engine light come on so i went and had a new oil change and had radiator flushed and all brand new fluids for that and such. But check engine light still on...
But then noticed when i leave work at 5 am and get on the highway the temp gauge will rise above halfway then go down cuz i turn the defroster on blast.
it will do this for the 30 minute drive i have and just keep going down and then back up. It doesnt do the drive to work, only on the drive home, its the weirdest thing.
Someone please help me?

 

Have the codes read at a local store, or at least give us the old OBD-1 codes (pretty sure the 96 did both).

Assume this is a 4cyl?

Then, check the coolant level in the rad- cold please-yes I know it was just flushed, and be sure there is not any trapped air in the system. From there, I'd say go ahead and replace the t-stat-they are cheap-unless that was part of the service?.....let us know from there. Might start your own thread