I'm dealing with this same issue in my 99 Ex Sedan. I thought my thermostat was sticking so I ended up replacing the thermostat with a Honda OEM one from Ebay(probably faulty) my radiator, both upper and lower hosses since I already had it on hand cars at perfect temp then come to find out my heater hose that ran into my head had a hole almost the size of a BB where the clamp was on-top of the hose so i replaced that with that being said no more coolant leaks with the car running at perfect temp... oh I forgot to mention this was all within a week- to a week and a half ago. So with that being said I did all that and like 2 days ago we got a really humid day and I drove it probably 25-30miles and I'm cruising at like 35-40mph and all of a sudden I started running hot for like a minute but then went evened out. Shut the car off for 10mins checked for leaks, no leaks. Let the car sit for an hour to cool down and then drove home 20-25 miles didnt overheat. But what I did notice 10-15 minutes after I turned the car off to cool down the radiator cap was hot as **** like I couldent even touch it like it was going to burn me... most likely need to bleed the system or possibly change the thermostat out again? Is what I'm thinking my issue is.. but at the same time I drove the car today/tonight almost 25miles one way to and from work and it didnt overheat so it's not like it overheats when I get on it or anything. Its like it just did not agree with the humidity that particular day. If anyone has any info I would greatly appreciate it. Thank you.

 

I'm dealing with this same issue in my 99 Ex Sedan. I thought my thermostat was sticking so I ended up replacing the thermostat with a Honda OEM one from Ebay(probably faulty) my radiator, both upper and lower hosses since I already had it on hand cars at perfect temp then come to find out my heater hose that ran into my head had a hole almost the size of a BB where the clamp was on-top of the hose so i replaced that with that being said no more coolant leaks with the car running at perfect temp... oh I forgot to mention this was all within a week- to a week and a half ago. So with that being said I did all that and like 2 days ago we got a really humid day and I drove it probably 25-30miles and I'm cruising at like 35-40mph and all of a sudden I started running hot for like a minute but then went evened out. Shut the car off for 10mins checked for leaks, no leaks. Let the car sit for an hour to cool down and then drove home 20-25 miles didnt overheat. But what I did notice 10-15 minutes after I turned the car off to cool down the radiator cap was hot as **** like I couldent even touch it like it was going to burn me... most likely need to bleed the system or possibly change the thermostat out again? Is what I'm thinking my issue is.. but at the same time I drove the car today/tonight almost 25miles one way to and from work and it didnt overheat so it's not like it overheats when I get on it or anything. Its like it just did not agree with the humidity that particular day. If anyone has any info I would greatly appreciate it. Thank you.

 

Stop driving the car until you thoroughly bleed the cooling system with radiator cap loosened and the radiator and reservoir topped off with coolant.

 

I plan to bleed it tonight over at a friends which is roughly a 40 minute drive. it ran hot only once on that humid day it was like it didnt agree with the humidity at that particular time..which was like 3-4 days ago. Put atleast 100+ miles on it since and it hasent ran hot but it is definately something I just dont want to by-pass. Radiator full, reservoir has coolant in it, no leaks.

 

Soo.. I put the car on an inclinement and I took the radiator cap off and stuck a funnel in it, car idled at normal temperature for atleast 15minutes(Heat on high).. my fan did not kick on not once, I turned the car off put the radiator cap back on and let it idle for 5 minutes my fan still did not kick on, it was also on an inclinement at that time too, not sure if that would have anything to do with it or not. I know the fan does work, its brand new. I bought it not even 2 weeks ago, I've heard it kick on several times after my replacements of the radiator,thermo,lower&upper hosses. At this point I'm starting to believe my thermostat is not opening up and it is faulty.

 

The bleed process can take 20-30 minutes for the fan to come on twice when you start the procedure with a cold engine. Air trapped in the cooling system can prevent the ECT switch from triggering the fan to run.

Verify that the heater valve on the firewall is wide open during the bleed.

 

Conduct a coolant system pressure test, you can rent the tool from AutoZone

The U shaped heater hose can have a pin hole leak that will only show up when pressure is over 10psi

 

d16y8s only have 1 coolant temperature sensor right? Screws right into the side of the head? Overheating issue within every 200-300 miles replaced rad,fan,coolant temp sensor,therno,upper&lower hose and it's weird because I'll run it on hot humid days and it wont overheat itll only do it every couple hundred miles lol. Going to rip the thermo out tomorrow and bleed the system and see what I can find. D16y8s also dont have a bleeder valve correct?

 

The answer to all your questions is "I guess so".