I have the opposite problem. My 94 Accord never overheats while driving. I am in the Philippines where temperatures are always extremely hot and stop and go traffic for sometimes hours is normal. Cooling fans come on as they are supposed to while driving. My problem is when I turn the car off, I hear the radiator always pissing in to the overflow tank, so eventually lose coolant. The fans turn off when I turn the ignition off, even when left in the accessory position. If I turn the ignition switch back to on position after turning engine off fans will run until engine cools. Can anyone tell me for sure if this would be the sensor(B), and is (B) the sensor located on the thermostat housing? Or if it is timer relay behind glove box? Due to lack of tools here including volt/ohm meter and lack of language skills, I am willing to just buy part if I know it is a sure fix.

 

I made a new thread from your post, since you are dealing with a different problem.

This is for a US accord. Yours may be different. Temperature sensor B is not on the thermostat housing. Temp sensor B is where the upper radiator hose connects to the engine. It will have a green electrical connector with two wires going to it. To test this, unplug temp sensor B, use a piece of wire to short the two pins of the electrical connector. The fans should turn on immediately and run for about ten minutes.

If your car is overheating while the engine is running and both fans are turning on, then you have another problem that you need to diagnose. You do not want to run the engine when it is overheating.

If you turn on the heat full blast, does the engine cool down?

When the engine is cold, open the radiator cap and check that the radiator is filled to the top.

How often and how much coolant do you have to add?

 

my reply assumes cars in the hot Phillipines still use a coolant mix of ethylene glycol (antifreeze) and distilled water like we do in temperate climates.
50:50 is normal mix unless the car is arctic then antifreeze part goes up.

Almost sounds to me like your car may be running coolant w/o sufficient water in the mix. Water is what carries the heat away;
the antifreeze is for pump lubrication, anti-corrosion and heat extremes.

Check the freeze point of your coolant using cheap gauge from auto parts store. 50:50 (our normal) gives freeze point of -34F (you do the conversion to C, but about -37C).
If freeze point is lower, you need to get more distilled water into mix.

 

Thanks for the quick response. Tried your suggestion and jumped B at upper rad. hose inlet. Nothing happens. To be clear, car has never overheated. Temp. gauge seems to be functioning properly and never goes above half of normal range. Only problem is sometimes when I turn car off it will sometimes dump a lot of coolant on the ground through the overflow bottle, especially if I have just come up a large incline and then turn car off. Which here in Philippines is almost a normal being mostly volcanic mountain terrain. If car is not overworked, just normal stop and go traffic here for hours in 90 deg. heat, car will just **** out coolant into bottle for 2-5 min. As a result I am having to add coolant 2-3 times a week....gets expensive. I know fans are supposed to stay on after turning car off to prevent this, but they do not. At this point I am running straight water until I get problem resolved. I think issue is fans. But I have been wrong before.

 

Don't run plain water for too long, because antifreeze has anti-corrosive chemicals to prevent rust from forming in the cooling system.

Did you short the electrical connector? Just want to make sure you didn't short the actual sensor. After shorting, you may want to turn the car on, then off to see if the fans turn on.

When the car is running and you turn on the a/c, do both fans turn on?

 

Ahhhh ok. With connector jumped, main fan will turn on when ignition is turned off. You were right, ignition switch had to be turned on then off. From other posts here I believe that only the main fan(passenger side larger fan) should turn on. I understood to jump the connector not the sensor itself. As I said before, both fans run fine while running, and when A/C is turned on and car never overheats. Does this mean I need to replace sensor B? Also thank you, yes I understand the importance of coolant. But is expensive here and until I resolve this problem........So I think you have helped me to the conclusion of replacing sensor B? Thank you very much.

 

The radiator is building up pressure for some reason. When the engine shuts off, the coolant should cool down and coolant should be sucked back into the radiator.

If the engine is hot after you turn off the car, the passenger fan will turn on for about 10 minutes to help cool things down. If you keep that connector shorted and the coolant loss goes away, then I would replace the temperature sensor B.

I would also consider replacing the radiator cap, because it should be able to hold the pressure to 16 psi and not allow water or coolant to boil like that.

 

Thank you again. Will give it a shot for the next week or so and let you know what happens.

 

Take 2 - now recall that yrs ago I had similar problem with brand X car and it was operator solution. The A/C unit takes a lot of heat out of the air and in the summer if I ran A/C right up until I turned off car in driveway car would then overflow reservoir right onto ground.

solution was to (leave on fan blower but) turn off A/C compressor about a half to a mile before my destination. Apparently this gave time enough for the heat to be dissipated while moving.

 

The only thing I can think to add to what PA suggested, be sure to bleed the air out of the cooling system after the cap and switch replacement.

Slide the heat control to heat (this opens the heater control valve), open the bleeder and slowly refill the rad until a good stream is coming out of the bleeder, close the bleeder, top off rad, replace cap, fill overflow to proper level.