Has anyone else had problems with their radiator fan not switching on?

I changed my coolant a couple of days ago, following the service procedure to the "T"; but I ran into a hitch while doing so: my radiator fan wouldn't kick on.

After refilling with coolant - to purge whatever air may have been introduced to the system - I let the engine idle (with the heater at full blast) for at least 30 minutes, and the fan still wouldn't kick on. I stuck a meat thermometer into the radiator filler neck, and it instantly buried the needle (past 220 degrees fahrenheit), yet the overheat lamp never flickered either. As far as I can discern, the overheat indicator lamp is functional. Like all other indicator lamps, it comes on only for a second after twisting the key.

All other cooling and heating system components are properly operational. The t-stat is working, the water pump is working, the HVAC system is working, and so-on. By the way, both fans switch on with AC running. But why on Earth won't that radiator fan kick on when coolant reaches considerably high temps? 220+ degrees should be plenty (I assume) to cause the fan to start spinning. Anything above 250 is frightening territory, if you ask me.

Is all of this an indication that perhaps the temp sensor is faulty, thereby preventing the overheat lamp from illuminating and the radiator fan to kick on? Moreover, does anyone know the temp thresholds for the activation of the radiator fan and the overheat lamp? I searched tirelessly just to find that info, and it's nowhere to be found.

 

You might try raising the right front end up as high as you can and let it run to see if the coolant level might drop, then top it off again.. I have had to do that and repeat a couple of times to purge air from the system.. More than likely coolant isn't reaching the sensor. The thermostat begins to open between 176 and 183 F. It is fully open at 203F.

 

Thanks for the speedy response!

The thermostat isn't of concern. I know it's working. Upper hose builds plenty of pressure and gets hot to touch after several minutes of running. It's the fan that concerns me. Do you know what temp causes the fan to turn on? I'm a new owner, and I'm beginning to wonder if the fan ever turns on on these things I mean, why is it there if it doesn't do anything other than help cool the AC air?

 

With the heater going full blast, it's plausible that the coolant didn't quite get hot enough for the fan to kick in. The little engine doesn't produce a vast amount of heat at idle, and the heater core (I assume) is sized to be comparatively large because there's quite a bit of cabin to heat up.

The radiator fan should come on eventually if you're not using the heater (and possibly if you are). A bunch of searching suggests that it's perhaps around 200°F (at wherever the sensor is) for the fan to turn on, though perhaps that's changed from year to year.

I hope you cleaned off your meat thermometer very thoroughly before using it to cook a roast!

 

I did have a scan gauge hooked up where I could monitor the coolant temp. I have seen it over 240 degrees lots of times before the fan activated and that is with water wetter that dropped the average temperature 10 degrees.. I've never seen the temperature warning light come on even when stopped after a WOT run in 100+ weather. ... It has to idle for a real long time from a cold start on a cool day ,like 25 or 30 minutes before the fan will kick on.... My IAT sensor reading has been well over 180 a lot in the summer.. It still runs fine after over 7 years, 4 of them with a supercharger. The heater being on is cooling it down enough for the engine coolant fan to kick in.

 

Thank you, good insight!

Reason prompted me to shut it down after over a half hour (and some revving with the hope to bring it up to whatever astronomical [220+ fahrenheit] temp the fan requires), to let it cool. After allowing it to cool and topping off, I completely tightened the radiator cap, and started it up, hoping for some fan action. Still, after about 20 minutes of idling and intermittent revving, no fan. . . but also no overheat light or other physical indication of overheating (e.g. purging steam from cap).

Now, I'm here, and thinking the temp sensor is the most likely culprit. What the temp threshold is for the fan would verify or disprove my theory. Then again, I suppose the radiator fan relay is another possibility. Then again, the fan works with the AC switched on. ???

Furthermore, is it possible that both the overheat warning lamp and radiator fan are prompted by the same block temp sensor? If that's the case. . . what the hell were they thinking?! I mean, the radiator fan should be prompted by a temp sensor at the radiator, right?

Some verification on temp thresholds for the warning lamp and fan would be great!

 

As much as I'd love to run it for over a half hour without the heater on, I'm trying to purge air out of the cooling system. And the service manual explicitly instructs allowing the fan to cycle on and off at least twice. Maybe I shouldn't worry about the fans cycling while purging air?

Not to mention, I'm worried about overheating, considering a fan that doesn't activate after 220+ (or 240+ as verified by yourself). I may be making a mountain out of a mole hill, but a fan that doesn't kick on at 240 is worrisome. So, at what temp is it programmed to kick on? Can anyone verify? Anybody?

 

Most probably an air bubble in the system preventing coolant from circulating and allowing the coolant to touch the sensor.

That hose will get hot even if coolant it NOT circulating.

When it's hot shut it off and be sure the coolant overflow is full to the upper level and let it sit for at least an hour until it cools.

Then check the coolant level and it should be almost to the top of the radiator and the coolant level should have gone gown in the overflow so top it off again.

The fan turns on: 91-95°C (196-203°F)

and off: Subtract 3-8°C (5-15°F) from actual ON temperature

 

Got it, thank you! Now, that's the information I was seeking. So, I'm obviously over the threshold for fan activation. I suppose the overheat lamp illuminates at a much, much higher temp, like 300+. Do you know? Also, might you know where the sensor is located for the overheat lamp?

I'm going to get that front end up on some 4 ton jack stands ASAP. These puppies are like two feet tall without extending them. That should do the purging trick. I'll report back when I'm finished.

EDIT:

Okay, after doing some digging, I've discovered that there are indeed two separate temp sensors. There is one located at the bottom of the radiator, near the exit, and another at the engine, near the thermostat. The one at the radiator controls the fan. The one at the engine controls the dash temp indicator lamps. Given that both fans function properly when activating air conditioning, it's not a fuse or relay issue. Given that loudbang has confirmed that fans activate at between 196 and 203-degrees fahrenheit - I've also dug up confirmation elsewhere where individuals have claimed the fan does not activate until as high as 217 F - I've either got an air bubble trapped at the radiator sensor, or the sensor is faulty, or the sensor is just plain disconnected (or wires damaged).

Additionally, the upper hose not only gets hot, but it also progressively builds plenty of pressure. Hence, my assumption that the t-stat is properly functional. Then again, maybe I'm wrong? At any rate, I still need to get this front end jacked up to whatever ridiculous height is required to properly burp the system.

 

I think there may be a third explanation: the radiator (and heater) have been getting rid of enough heat without the fan that the temperature at the radiator sensor, near the exit, isn't getting high enough for the fan to turn on. In other words, everything might be working just fine and as designed; and if that is the case, you'll have a pretty hard time tracking down some fault.

How would you get an air bubble at the bottom of the radiator?

 

Of course, I have yet to eliminate that as a possibility. I may just be overly paranoid, but a thermometer needle that screams past 220 as soon as it's inserted in the radiator filler neck combined with a fan that won't kick on is more than troubling. Why would the coolant bury the needle of a meat thermometer that reads a maximum of 220 if the cooling system is in proper order? Heater on or off, 220+ is still scary. Upper radiator reading, 220+ is still scary. How air would get trapped at the temp sensor is anyone's guess, but I will not discredit it as a probability until I do some further diagnosis and gather further evidence. I don't think it's likely, but I don't know for sure. Right now, I'm open to just about anything if it helps me to deduce what might be wrong. I have yet to dig into it, but you can rest assured that I'll post up as soon as I. . .

After checking the radiator temp sensor connection and wiring, I'm considering pulling the entire temp sensor assembly from the radiator, then sticking my soldering/heat gun/butane torch under it to see if it activates the fan. If it doesn't kick it on, then I'll get a fresh temp sensor. If it does, then I won't worry about my objectionable dilemma until a summer heat wave. I'm in the St. Louis, Missouri, USA area, so overheating shouldn't be of concern for the next 4 or 5 months

Nevertheless, all of this begs the question: Why warning lamps instead of thermometer gauges? A gauge in the dash with numeric specifications in the owner's manual would provide so much more peace of mind. Instead, we get nothing more than a light and the suggestion to shut down the engine ASAP.

 

Don't use a torch. Boil some water in a pan on your stove and dip it in there. Much safer and won't ruin your sensor.

 

I would, but I'm pretty sure that the sensor is of the thermoelectric variety (at least, from what I've seen in photos, it is); it's not mechanical like the engine thermostat is. Not worries, I didn't plan on applying direct fire to it anyway, just the heat gun, and at a considerable distance. This soldering iron I have is butane powered. It converts into a heat gun and a blow torch depending on what attachments are used. It also has variable output. So, I can even crank it down to the lowest setting, apply it to my trusty meat thermometer so I can see what temp it is exactly, then go from there Thanks for looking out, though.

 

So you think there is a difference in heat between a torch and hot water? You think the switch can tell the difference? You know it's put in the radiator so it can touch the hot water right?

 

I think you are making a mountain out of a molehill. Your temp monitoring components are probably fine. (Everything was OK before the coolant change?) Still, I recognize your concern, I had the same uneasy feelings when changing coolant, trying to follow the service manual procedure.

Next time, just run the engine for 10 minutes to warm it up. Maintain a 2500 - 3000 RPM speed to keep the coolant velocity high. Do not tighten the radiator cap, just have it loose.

Then, turn off the engine. Let it sit for 30 minutes. That way you will assure that the thermostat has opened and is not trapping air.

Top off the coolant, repeat. Then top off again and tighten the cap on the rad.

After that, keep an eye on the coolant level in the plastic reservoir. You will probably need to add coolant when the engine is cold. The level is easy to see by shining a flashlight beam through the reservoir.

Be sure to run the engine to redline a few times when you drive, this will purge air pockets.


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I had the same symptoms as you, the fans would never kick on despite a reading of 230F. on the Scanguage. Worrisome.

 

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I won't be able to see anything 'open up' like I would with a typical thermostat, if it's thermoelectric. Dumping it in water on the kitchen stove would be futile because it doesn't operate mechanically like the coolant t-stat in the engine. I'm going to try and pull it whilst leaving its wiring connected, then apply heat. If the heat gun doesn't turn on the fan, then the switch is bad.

If the switch can tell the difference between ambient heat and liquid heat, then I suppose I could try to stick it into a thermos of boiling water. It would probably be a cumbersome royal pain to get that boiling hot water under the car without spilling it everywhere; but if the switch is smart - although, I'm not sure how it would be - then it may be the only way to check it. I'll keep it in mind. I'm going to try and get out there today before my head explodes from too much research and counsel on the interwebz Thanks.

 

Thank you! I appreciate the advice. I can't be sure if it operated correctly before the change; I've only put about 1200 miles on the car, all easy going and cool weather. So, I never noticed the fan switch on before the change. Every car I've ever owned before had no problem kicking on the fan while circulating coolant after a change/flush. Only this one. It's scary. That you had a similar conundrum, though, doesn't really make me feel any better. That TexasCoyote was reading 240+ before fan operation doesn't make me feel any better either. It may be a sign of a common malfunction. I'll get back as soon as I'm finished checking that sensor. Oh, how wonderful it would be to know the temp thresholds for this sensor, so I don't feel compelled to test it.

 

I guess I should have mentioned that it was during an all time record Texas heat wave and I'd been driving very hard when my car got that hot while at idle.. As long as you have a 50/50 ratio water/antifreeze mix and the system is completely purged of air there isn't going to be a problem except for engine heat soak and power loss when in stop and go traffic.. Water is flowing through the heater whether it is on or not so there is no need to turn it on unless you're cold.. All cars are that way now, I had a hard time believing it but it's true.. You can always get a low temp fan sensor and thermostat but then you'll have a loss of power to the wheels when the fan is on.. Lucas water wetter will bring down coolant heat about 10 degrees.. 376 degrees F is the boiling point for a 50/50 antifreeze/water mixture so need to worry about pressure build up in the cooling system.

 

On my CR-V (which was the first of the fleet to get new coolant) the fans never cut on. The Scanguage read 232F until I turned the engine off and let it "rest". Then, with the air out of the system, the fans engaged at 205F.

I read somewhere that late model Hondas used a reverse flow with the coolant. That is, instead of flowing through the rad from top to bottom, the hot coolant enters the rad from the bottom.

 

VERY SIMPLE put a multimeter on the switch contacts then grab the switch with a pair of tongs, or hands if you are superman, then dip the TIP of the sensor, you know the part that touches water when it's screwed into the radiator, into the pan of boiling water and watch the multimeter and see if the resistance changes when put into the boiling water.


Or first thing check the fan relay in the fuse box under the hood

Relay number 5 look underside of lid for fuse box

Relay and Control Unit Locations - Engine Compartment

Then a jumper to the fan and see if it is working.

Or to make your head explode following this troubleshooting guide.

http://www.hondafitjazz.com/manual/A...101FAAT00.HTML