Hi there, I have a 99 accord EX 5spd, when the car reaches operating temp and your driving it does not over heat. When the car is at idle like at a long stop light it will jump in temp quickly. If you give it a little gas it goes back down to normal temp. Every now and then you hear the fans turn on cause the cars idle lowers and you can hear them. I was reading that it could be the fan switch on the thermostat or it could be the fan itself. Is there a way to test the fan, ie: taking the positive and negative wires and putting them on the battery to test if they turn on? Also is there a way to test the fan switch on the thermostat? Any help would be greatly appreciated!

 

The shortcut is just let the car get up to temp, turn on the AC and watch the fans. If they run then everything in that circuit (with the possible exception of the fan switch going bad with the trigger temp being way off) should be good.

You can test the fan(s) by putting 12V to them. Are they BOTH turning on? One is for the A/C condenser, the other is for the radiator - make sure (visually check) that they are both turning on - don't just go by what you hear.

You can check the switch by making sure there's continuity between the terminals at 200 degree or above.

The weird part about your symptoms is that elevating the RPMs cools the engine. It's been my experience that this points to a problem with coolant flow - as in the water pump.

 

It could very well be the water pump, the car does have 103K on it and has not had the timing belt done yet. I think what im going to do is replace the belt and pump and see if that fixes it cause it needs to be done anyways. I was just hoping the until i get the money together for the fix it would be something smaller Thanx for the help

 

Normally, when the car is fine while driving that means that coolant is moving and the air from driving is cooling it through the radiator which causes the car to run fine. I would guess the radiator fan, the passenger side one, is not coming on. This normally is caused by the fan switch on the thermostat housing going out. You can verify by starting the car, waiting for it to get to operating temp and seeing if it wants to overheat before the fans come on. Also, you can follow the lower radiator hose and see if that lower hose is getting hot. If it is, that means the thermostat is opening which is what you want. That means the thermostat itself is fine. The problem is the fan switch if the passenger side fan is not coming on.

Go down to the parts store and pick one up and ask for it like this "I need a fan switch for the thermostat housing".

If you follow the lower radiator hose to the back of the engine, it will have a switch on that same housing. That's what you're buying and need to replace.

 

Today i started the car up and let it get to opereating temp w the AC on and BOTH fans turned on. While under the hood i noticed a small dropplet of coolant right under where the upper radiator hose connects to the motor. The hose probably could be replaced but it shows no signs of comming apart its also not soft. Basically it comes down to either the water pump needs to be replaced or the fan switch on the thermostatis going bad. the fan switch is $30 vs the $100 for new timing belt and water pump. I dont have a volt meter to test the circut on the fan switch, so is there another way to test it?

 

You shouldn't be concerned with if the fan comes on when the AC is turned on unless you don't really plan on isolating the problem and/or plan on having the AC constantly while driving the car.

The first thing anyone should check is whether there is coolant. If you don't have coolant then there is obviously a leak somewhere. Obviously if you find coolant anywhere outside the system then you do have a leak.

You haven't said if the passenger fan comes on when the car is warmed up and the AC is off. This is what you should be concerned with, given the fact that you know the fan motor does work.

 

I agree. If you see signs of coolant leaking, making sure you have enough in the system should be the first step.

 

Yes the passenger fan comes on when the car is warmed up. Tomorrow ill check the fluid level when the car is cool. I do have this strange feeling that it might need some.

 

Radiator should be free flowing and the coolant should be the correct density.

 

Im having the same problem here but i have a 1990 Accord 4dr. I know the thermal switch is bad, so i bypassed it in the mean time to get around.
So now with both the fans running the car overheats at idle. If i rev up to 2k rpm it cools back down! Any thoughts?

 

Your coolant is low and/or the cooling system needs to be bled.

 

Coolant is topped off and bled! All hoses are clear of any buildup too

 

Coolant is full, no trapped air in the coolant, BOTH fans run and it over heats....you have a flow issue some where. The flow issue is either the coolant thru the system or the air thru the rad....if the above is true.

 

Experiencing the same problem. Overheats at idle. Noticed no fans turning on when temp got too hot and when I turned A/C on both fans turned on for a couple minutes but then started cycling on and off together in about 30-45 second intervals.

Should both fans turn on when A/C is turned on? Thanks in advance for any advice.

 

Didn't have any responses so I went with the obvious problem of the t-stat. I replaced the t-stat and it still overheats. Fans come on with the A/C but not when the engine heats up.

When it gets hot I turn the car off for about 2 minutes and the gauge shows the engine temp drop dramtically which seems odd to me after only 2 minutes.

Looking for any and all opinions/knowledge on this matter.

 

I'm having the same issue with my '99 Honda Accord 4cyl. The engine overheats in slow traffic or at idle. Also, if I don't let it cool down completely, it takes 2 or 3 tries to get it started. When it does finally start it runs really rough and, if I take my foot off the accelerator, it dies. If I'm persistent, it will finally start and run normally (problem goes away) but it still overheats at idle.

The coolant level is correct but I haven't tested the fans yet. I haven't noticed any mention of the water temperature sensor or am I looking at two unrelated problems?

 

Ok... disregard the above. Neither cooling fan runs at operating temperature. It's going to the shop on Monday.

Thank you for this forum though. This has been a huge help.

 

Normally a new thermo A switch from Honda would be all that is needed

 

The gauge on these things is really not terrribly sensative. If you have access to an OBD2 reader which gives live data. Plug it in and moniter the ECT. I noticed mine went from 180 to 218, and the gauge never even budged. 218 is pretty warm for these cars. Like mentioned already, ensure there are not leaks(The coolant system needs to be up to the proper pressure to work right). If the radiator cap hasnt been replaced, might want to think about that at some point.

 

Thank you both for your quick reply.

The coolant was at the correct level in the overflow bottle next to the radiator and there were no signs of leaks at the cap or the upper and lower hoses.

What I did notice is that the sound the relay makes when it should turn on the fan(s) is different. It almost sounds like a high voltage arc across terminals would sound. It's really weird.

Since there are two relays, one for each fan, I'm guessing that the thermo switch is probably the culprit but I'm going to let someone with a little more knowledge than I have look at it. I can't imagine both relays giving up the fight at the same time.

Thank you again for your help and guidance.

 

I'm having what might be the same issue.

The car overheated in stop and go traffic the other day and belched out the fluid. (wife was driving) I noticed that the fans were not running and they would not come one with the A/C. So I applied 12v directly to the fan(s) both bad.

Refilled radiator, installed fans, they work now w/AC but not when car is at temp. Regardless I drove a good 10 miles in the car with no problem. (taking it easy) I then drove hard coming home and it everheated and the fans did not come one. It blows the coolant out of something that looks like a small bypass hose for the thermostat.

I also noted that the upper radiator hose is hot, and the lower is cool. Odd, does the coolant flow in reverse on this car? Whatever. While the car is cool I can definitely see the coolant moving in the radiator. Goosing the throttle will send a large torrent into the radiator so I believe that the pump is good.

What does not make sense to me is the fans. The thermo switch ought to be switching the fans on. My best guess is that the coolant does indeed flow "backwards" and that the coolant at the temp sensor (and the thermostat) is cool. Even without them I should not be getting hot on the highway.

I am inclined to think that the thermostat is bad but I am not familiar with Hondas. If not it must be the pump.

Suggestions please.

 

Change the thermostat with one directly from Honda since they have a built in failsafe and you should be good to go. When it sticks closed it wont allow the coolant to hit the fan switch.

Its actually hard to believe both fans went bad though.

 

change the hoses and the clamps.
I had this same problem when I was stopped at a red light. it was the thermostat sensor. Change it and also changed the hoses. car runs now without any overheating issues.

the whole turn on the AC is only a temporary ban aid.