Engine cooling fans

[King Peetis]

I was at the emissions station getting the accord tested and the radiator sprung a leak and the car got hot. Make a long story short, I replaced the radiator and the temp switch (the one on the bottom of the radiator). Everything seems OK (no leaks) but the fans aren't turning on. I also checked the plug connections and they look good. The temp. reads the same as it did just before the car got hot too; Could the thermostat be stuck? What should I do to troubleshoot the system before I shotgun anything else?

[Buzo]

Turn your key on, then disconnect the thermoswitch in the bottom of the radiator and short-circuit the two pins in the connector. The fans must come on immediatelly.

If not, leave the short in place and start debugging the fuses & relays under the hood, in that way you don't even need to fire the engine up while trouble shooting the failure.

[King Peetis]

Lets see if I got this right--Turn the key on, disconnect the switch, then simply connect a jumper between the female leads on the plug, that way the fans should trip on; If not follow step 2?

[King Peetis]

I jumped the plug and the fan came on. I haven't heard those fans come on triggered by the system yet, only when using the jumper. Maybe I'm paranoid.

[Demon1024]

Is it over heating and the fans aren't coming on?

start it up get her warm and feel the upper radiator hose. Lotsa hot means thermo is open. not so warm then thermo is probly the problem

[Hauntd ca3]

remove and test the fan relay.
if the temp switch is known to be good and the fans turn on by jumping the 2 terminals at the switch plug, the relay is quite likely the prob

[Dr_Snooz]

There's a good schematic of the cooling system circuit as well as some descriptions and tests on pp. 25-110 through 25-114 of this manual (http://honda.roadpwnage.com/manuals/pages/usdm-accord-1989-full.php).

Are you absolutely certain that the fans are not working? Sometimes you have to wait a very long time for the engine to heat up enough to get them running. A handheld infrared thermometer helps a lot in diagnosing these things.

[King Peetis]

Turn your key on, then disconnect the thermoswitch in the bottom of the radiator and short-circuit the two pins in the connector. The fans must come on immediatelly.

If not, leave the short in place and start debugging the fuses & relays under the hood, in that way you don't even need to fire the engine up while trouble shooting the failure.

Done-worked great, fans came on-Thanks


Is it over heating and the fans aren't coming on?

start it up get her warm and feel the upper radiator hose. Lotsa hot means thermo is open. not so warm then thermo is probly the problem

There is definitely lotsa hot. The fans didnt come on when it overheated at the emissions station. Since then I changed out the radiator, thermoswitch and the temp sensor. I took the car for a spin; drove it hard then let it sit for a minute but still NO fans.--Thanks for the advice


remove and test the fan relay.
if the temp switch is known to be good and the fans turn on by jumping the 2 terminals at the switch plug, the relay is quite likely the prob

I'll run a test next week--Thanks


There's a good schematic of the cooling system circuit as well as some descriptions and tests on pp. 25-110 through 25-114 of this manual (http://honda.roadpwnage.com/manuals/pages/usdm-accord-1989-full.php).

Are you absolutely certain that the fans are not working? Sometimes you have to wait a very long time for the engine to heat up enough to get them running. A handheld infrared thermometer helps a lot in diagnosing these things.

My dumbass didnt even think about the manual. I got one too. I read it and performed the tests described and everything checks good. Thanks for the references.

I have a couple of other checks to do yet. There was a time when those blasted fans would kick on while it ran for just a few minutes, I dont know why not now! Im fearful its going to overheat while the temp gauge is reading normal.

[Buzo]

I jumped the plug and the fan came on. I haven't heard those fans come on triggered by the system yet, only when using the jumper. Maybe I'm paranoid.

The problem is your thermoswitch then.

It may be new, but it was set at a higher temperature.
I reapired the one in my car using a 60W Iron and a Dremel. if you have one or somebody can lend you one, let me know and can tell you the repair process that worked for me.

[Buzo]

remove and test the fan relay.
if the temp switch is known to be good and the fans turn on by jumping the 2 terminals at the switch plug, the relay is quite likely the prob

what does "quite likely" mean? I believe I misunderstood your sentence. So I'm going to edit my original esponse.

[King Peetis]

The problem is your thermoswitch then.

It may be new, but it was set at a higher temperature.
I reapired the one in my car using a 60W Iron and a Dremel. if you have one or somebody can lend you one, let me know and can tell you the repair process that worked for me.

I have all of the above. Im going to use infrared to check the temp. as SNOOZ suggested. If its within operating temp range I'll just leave it be. If its a little hot I will definitely follow your advice. I'm interested how to make the adjustment. What do I do??

[King Peetis]

Have any of you heard of 'Water Wetter'? says it lowers the engine temp by 20 degrees.

[Pico]

Have any of you heard of 'Water Wetter'? says it lowers the engine temp by 20 degrees.

I use it, but to be honest I really havent noticed a difference.

[King Peetis]

Did you notice a difference when you first poured it in? Maybe the heat breaks it down after a short while.

[Pico]

I kept looking at my temp gauge and saw no difference

[King Peetis]

I ran a jumper from the temp. sensor connector to the frame and its working properly. I replaced the temp sensor too. I filled the system per the spec. w/ coolant and drove it back down to get the emissions done and although it didnt overheat, (got really warm though) the fans failed to come on again. I still haven't seen those blasted fans power up on their own!:banghead:

I failed the carbon monoxide detect. I think its gotta be the O2 sensor huh? I guess a third time will be the charm...

[King Peetis]

I just found an old link for the TW sensor. Come to think of it my car has been operating below standard ie hard starting, idling, poor cooling; obviously... The main relay might be bad. Im gonna check the IACV and the fan relay while Im at it.

[Hauntd ca3]

what does "quite likely" mean? I believe I misunderstood your sentence. So I'm going to edit my original esponse.

by quite likely, i mean a fair chance, or even bet.

if you have replaced the rad,temp sender and switch, make sure the fan fuse is good and if so,you need to find the fan relay,pull it out, find the batt feed to the relay and jump it to the feed to the fans. if the fans work from there, stick a new relay in it and try that.

[King Peetis]

I stopped by Honda on my way home and picked up a new tw sensor. 38 and change it cost. I was doing cart wheels in the dealership cuz they had one! I got home, removed the old one which was covered in gunk and replaced it. I drove around to get the temp up and pulled in the driveway to let it idle. The heat started to climb. Any minnnnuute and...still no fuckin fans! What the hell? OK, next is the relay...Im now about $200 in it. 3 sensors, a radiator and a bottle of coolant. Sheesh!!!!

[King Peetis]

Can anyone identify the fan fuse and relay with a picture?

[Buzo]

I ran a jumper from the temp. sensor connector to the frame and its working properly ...

This explains everything. Connecting a jumper to the frame is not the same as making a short in the terminals.

Please make sure you test with a piece of wire and short circuit the terminals. If the fans don't come on, then the ground side of the connector is open. Highlighted in yellow in this pic.

http://img217.imageshack.us/img217/5982/heresk.jpg (http://img217.imageshack.us/i/heresk.jpg/)

[King Peetis]

This explains everything. Connecting a jumper to the frame is not the same as making a short in the terminals.

Please make sure you test with a piece of wire and short circuit the terminals. If the fans don't come on, then the ground side of the connector is open. Highlighted in yellow in this pic.

Thanks for sharing the schematic. I ran the jumper to the temp sensor not the thermoswitch. The manual suggests testing the temp switch in this way. Once youve connected the jumper to the terminal wire, turn the key on and the temp gauge should immediately spike to hot; which it did. the system gets a thumbs up for the switch connection.

What happens if I short the TW sensor? Can I expect to see any change in the gauges or will the car will become hard to start? Hmmmm, I think I just answered my own question.

[Demon1024]

What happens if I short the TW sensor? Can I expect to see any change in the gauges or will the car will become hard to start? Hmmmm, I think I just answered my own question.

.... if it'll start. Probably get it to throw a cel that way tho

[King Peetis]

.... if it'll start. Probably get it to throw a cel that way tho

A 'cel' ????

[ecogabriel]

I was at the emissions station getting the accord tested and the radiator sprung a leak and the car got hot. Make a long story short, I replaced the radiator and the temp switch (the one on the bottom of the radiator). Everything seems OK (no leaks) but the fans aren't turning on. I also checked the plug connections and they look good. The temp. reads the same as it did just before the car got hot too; Could the thermostat be stuck? What should I do to troubleshoot the system before I shotgun anything else?

I would suggest checking the fan switch you got. Chances are the salesperson might have confused them

I checked the old ones I replaced a while ago. The one at the rad. bottom is stamped "90M" whereas the other at the thermostat housing is stamped "108", which I bet those are Celsius temps (108C is above 212 F)
Anyway, it is possible to install the high temp switch where the low temp goes; I checked the connectors and both are the same.

Hope it helps.

[King Peetis]

I would suggest checking the fan switch you got. Chances are the salesperson might have confused them

I checked the old ones I replaced a while ago. The one at the rad. bottom is stamped "90M" whereas the other at the thermostat housing is stamped "108", which I bet those are Celsius temps (108C is above 212 F)
Anyway, it is possible to install the high temp switch where the low temp goes; I checked the connectors and both are the same.

Hope it helps.

Good looking out! I'll take a look. I stopped by pull a part and grabbed a handful of relays and fuses. I also picked up a new fuse box cover with a good diagram on top. I had no idea what was what in that box without the diagram. This coming weekend, Im gonna go through the motions and start trouble shooting all over again.

[ecogabriel]

Good looking out! I'll take a look. I stopped by pull a part and grabbed a handful of relays and fuses. I also picked up a new fuse box cover with a good diagram on top. I had no idea what was what in that box without the diagram. This coming weekend, Im gonna go through the motions and start trouble shooting all over again.

I now realized we live in the same area. I kept the old working switches so if you want to do some testing I may pass them on to you. I live about 3 mi. away from I-78 and I-285. PM me :welcome:

[King Peetis]

I now realized we live in the same area. I kept the old working switches so if you want to do some testing I may pass them on to you. I live about 3 mi. away from I-78 and I-285. PM me :welcome:


Thanks for the offer, but I think Im good on parts. We should hook up anyway just to shoot the bull and do a little trouble shooting-I'll PM you tonight.

[Dr_Snooz]

Let us know what you learn. It seems cooling fan problems are always a big easter egg hunt.

[King Peetis]

Let us know what you learn. It seems cooling fan problems are always a big easter egg hunt.

Most certainly! Once I put all the pieces together I will definitely share. It seems to be a common occurrence for us. If you google "3Geez site: over heating" or "engine cooling" or "cooling fans" the hits are 10 pages deep.

How many sensors, relays, fuses and components make up the engine cooling system?

**Of course the fan and radiator
1. thermostat
2. TW sensor
3. engine cooling sensor (the one next to the TW sensor)
4. engine temp sensor
5. cooling fan relay
6. cooling fan fuse
7. thermoswitch
8. heater core

I think there is another relay...Anything I'm forgetting???

[Dr_Snooz]

The 4g manual has a troubleshooting section for the cooling fans. Too bad it's not accurate. The 3g manual would benefit greatly from something similar. Something accurate, that is.

[King Peetis]

I removed the thermostat and tested it. No problems. I tested a new one that I had around the house and it tested good as well. I swapped it jus cuz. I replaced the O2 sensor cause of the failed carbon monoxide test during the emissions check. I topped off the coolant and then I drove it around to get the temp up. I pulled in the driveway...the heat started to climb...and still no fucking fans!!!! I popped the hood, ripped open the fuse box and stared at the relays. I pushed on all three to make sure they were in all the way and I noticed that one of the two black relays was warm and the other was cold. so I said what the hell and swapped them.

The fans came on.


The sub fan relay is bad (they are both the same anyway) so I'll just replace it. But anyway, that was the issue for the overheating problem; the cooling fan relay.

Oh yea, I passed emissions too btw. Im legal--finally.

[2oodoor]

I removed the thermostat and tested it. No problems. I tested a new one that I had around the house and it tested good as well. I swapped it jus cuz. I replaced the O2 sensor cause of the failed carbon monoxide test during the emissions check. I topped off the coolant and then I drove it around to get the temp up. I pulled in the driveway...the heat started to climb...and still no fucking fans!!!! I popped the hood, ripped open the fuse box and stared at the relays. I pushed on all three to make sure they were in all the way and I noticed that one of the two black relays was warm and the other was cold. so I said what the hell and swapped them.

The fans came on.


The sub fan relay is bad (they are both the same anyway) so I'll just replace it. But anyway, that was the issue for the overheating problem; the cooling fan relay.

Oh yea, I passed emissions too btw. Im legal--finally.
congrats! on both.

I think there is a wiring diagram in the factory manual and in another area there is a component location diagram. I am not sure though if those diargrams cover all the areas associated with the engine fans. If you ever need a wiring diagram I can give you one.

[ecogabriel]

I removed the thermostat and tested it. No problems. I tested a new one that I had around the house and it tested good as well. I swapped it jus cuz. I replaced the O2 sensor cause of the failed carbon monoxide test during the emissions check. I topped off the coolant and then I drove it around to get the temp up. I pulled in the driveway...the heat started to climb...and still no fucking fans!!!! I popped the hood, ripped open the fuse box and stared at the relays. I pushed on all three to make sure they were in all the way and I noticed that one of the two black relays was warm and the other was cold. so I said what the hell and swapped them.

The fans came on.


The sub fan relay is bad (they are both the same anyway) so I'll just replace it. But anyway, that was the issue for the overheating problem; the cooling fan relay.

Oh yea, I passed emissions too btw. Im legal--finally.

Good you figured out what was going on with the fans :uh:, and that nothing got broken in the process. Oh, and that you passed emissions!

I do not have to test the car (it is 1986) and it feels kinda strange... but good!

[Dr_Snooz]

Nice work! Thanks for the follow up.

[King Peetis]

congrats! on both.

I think there is a wiring diagram in the factory manual and in another area there is a component location diagram. I am not sure though if those diargrams cover all the areas associated with the engine fans. If you ever need a wiring diagram I can give you one.

Brotha Doo, long time! Yea man thanks! I will take you up on the diagram if its different from the service manual. Can you zip and email it? If not, send me a PM and we can figure it out.


Good you figured out what was going on with the fans :uh:, and that nothing got broken in the process. Oh, and that you passed emissions!

I do not have to test the car (it is 1986) and it feels kinda strange... but good!

Lucky you! I have two years to go!


Nice work! Thanks for the follow up.

Theres nothing worse than a fella that spends time on the forum getting advice and says "Thanks guys, I figured it out" without providing the solution...

[Hauntd ca3]

so i was right?

[King Peetis]

remove and test the fan relay.
if the temp switch is known to be good and the fans turn on by jumping the 2 terminals at the switch plug, the relay is quite likely the prob



so i was right?

Is that a rhetorical question? :idea: Yes, you were absolutely correct. Shame on me for not listening long ago. :uh: Now that I look back I'm not sure why I did not. I'm a parts and pieces; hardware kinda mechanic. I hate electrical related issues so much that I most often don't believe they are to be considered until all parts have been change out. Quite the phsyco-babble coupled with ignorance but the truth nonetheless...oh yea, and thanks again for the advice.