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Radiator fan not turning on but will turn on when AC is on

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by ttou68, Apr 23, 2020.

  1. ttou68

    ttou68 Active Member

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    Hi all, having an issue/question about radiator fan and all help is greatly appreciated!

    Doing some maintenance on my son's 2010 Prius with 93K on it, the usual spark plugs, transaxle fluid change, both engine and inverter coolant change...

    After drain and refill coolant, I discovered that the radiator fan never kicked on. Even after running engine in maintenance mode for almost 30 minutes.

    I took it for a drive with an OBDII and phone app to monitor the temperature; temperature range 185~202 for 10 miles of mixed highway and city driving, so I'm thinking thermostat is working. but fan not once turning on, the only way for the fan(s) to kick on is when we are running AC!

    I plan on taking out coolant temperature sensor and test it, but is there's anything else I'm missing?

    Any suggestions is greatly appreciated!



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  2. tankyuong

    tankyuong Senior Member

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    Radiator only turns on when computer tells it to
     
  3. ttou68

    ttou68 Active Member

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    You mean radiator fan?
    Doesn't computer still need data from a sensor to activate radiator fan?

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  4. tvpierce

    tvpierce Senior Member

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    What did your OBD app say the coolant temperature was when the car was at idle for 30 minutes?

    EDIT: Except under extreme conditions, the fan shouldn't come on when you're driving. The movement of the car usually provides more than enough air flow over the radiator to sufficiently cool the engine.
    Same when you're at idle. If the radiator can keep up with the demand for cooling, then the fan doesn't come on. If the radiator can't keep up, the fan comes on to give some help. Once the cooling demand has been met, the fan shuts off again.
     
    #4 tvpierce, Apr 25, 2020
    Last edited: Apr 25, 2020
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  5. Mendel Leisk

    Mendel Leisk Senior Member

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    I've yet to do a coolant change on our 3rd gen (due this fall), but I have found with previous cars it can take some time for the fan to kick in. Having someone sit in the car keeping the engine rpms slightly raised can help. Also, if you can monitor coolant temp (ScanGuage, or one of various phone apps) you can get some feedback. I'm having a hard time finding spec'd coolant temp for fan to come on, but would guess somewhere around 190~200 Fahrenheit?
     

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    #5 Mendel Leisk, Apr 25, 2020
    Last edited: Apr 25, 2020
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  6. Grit

    Grit Senior Member

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    My radiator fan kicked in when we were taking the intake manifold apart at a meet up, I got poo poo'ed on here and was told you always pull the 12v battery lead off when working on cars. None of the credible videos on here said so :LOL:

    Now that I'm done venting, thought you can get the fans to come on when the heater is turned on high to bleed air bubbles in coolant?
     
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  7. Mendel Leisk

    Mendel Leisk Senior Member

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    It'll take longer to warm up if the heater's on high, since it's dissipating some heat. That said, you want the cabin heater set to high, to flow coolant through that circuit. I think the trick is to set the temp to high (so coolant's free to flow through the cabin heater core (aka little radiator in the dash), and the fan speed set to mininum, to reduce heat loss, help the coolant temp to climb faster.

    That's what @NutzAboutBolts does in his engine coolant change video: cabin temp set high, and fan speed low.
     
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  8. NutzAboutBolts

    NutzAboutBolts Senior Member

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    in that 30 minute while the engine is on, did you touch the upper and lower radiator to see if both are hot? if the top is cool, then the thermostat didn't open and the engine isn't hot enough for the radiator fan to kick on.
     
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  9. ttou68

    ttou68 Active Member

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    I was able to get radiator fan to kick on by turning on AC...
    We found engine temperature is between 185°~202° while taking Prius on a 40 mile drive with an OBD Bluetooth scanner...
    At this point I'll have to assume that there's nothing wrong with the radiator fan, as engine temperature fluctuate below 202°...

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  10. ttou68

    ttou68 Active Member

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    Both super and lower radiator hoses are hot...

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  11. ASRDogman

    ASRDogman Senior Member

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    Both fans will kick in when you turn the a/c on. It's to cool the hotter freon.
    I'm certain the fan IS coming on, or the engine would over heat.
    You won't notice it driving down the road because of road/tire, wind, and other noises.
    And if you sitting, the engine turns off, most of the time. The fan is not very loud.
    You could stick a Go-Pro or other camera in the engine compartment and drive. :)
    Then it would give you peace of mind. :)
     
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  12. ttou68

    ttou68 Active Member

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    I probably won't go that far to using a GoPro, but I do appreciate all the comments and ideas!

    So far all 3 of my Prius have been monitored while traveling the same route with an OBD and operating temperature seems to be identical, and all Prius are behaving similar..

    I maybe trying to find an issue that simply does not exist, perhaps that's what happens when I have too much time on my hands. Or perhaps I started a habit to looking for issues, when I replaced head gasket on the Pearl White Prius I just bought for fun and now looking for trouble.. LOL

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  13. ASRDogman

    ASRDogman Senior Member

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    Well, you could replace the face if you're looking for something to do! :):)
    I know the feeling... I've done a lot of house cleaning... I never wanted to stop, it was my clients... :(
    I'm hoping that will change this week or next...

     
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  14. ttou68

    ttou68 Active Member

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    Looks like I may have to replace both front wheel bearings in white prius, bought it with blown head gasket and did notice noise while driving it out from seller's home. I thought it's probably noise from rusty brakes and rotors from parking for few months....

    I took both front brakes and rotors out yesterday and clean off all the rust, lube all parts including sliding pins but noise still exist, will have to source a 30mm 12 point socket to loosen axle nut and check out the bearing today... My investment cost on this vehicle is on the rise!

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    #14 ttou68, Apr 28, 2020
    Last edited: Apr 28, 2020
  15. ASRDogman

    ASRDogman Senior Member

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    At least they are easy to do. Just wrap a rag around the boot so you don't tear it or pinch it.
    I replaced the rears 2 weeks ago, easier than the front.
    It's a good investment.
     
  16. ttou68

    ttou68 Active Member

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    Replaced rear bearing on my son's Prius little while ago, it was cake using long bolts and nuts through existing hole to pop them loose..
    However, I had a heck of time with my gen 2 front bearing.. not looking forward to replace this gen 3... Hopefully, I'll get lucky with this one.. lol



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  17. ASRDogman

    ASRDogman Senior Member

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    I couldn't get the bolts through the reverse side. That was my plan as it worked on my Van.
    But, I just used a big hammer and punch and rotated the bearing clockwise and counter clock wise a
    few time, then I was able to bang them out. Very little effort.
    With the fronts, I didn't disassemble the suspension, only took the caliper assembly off and the nut off
    the axel.
    I was able to rotate the hug, and install the bolts in the back. Simple!
     
  18. ttou68

    ttou68 Active Member

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    I'll try that when I have to replace them, this afternoon I swapped out a set of tires with my brother's Prius and most of the noise went away.. so wheels and tires could be the problem, but leaving me scratch my head because tires looked fine...

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  19. ASRDogman

    ASRDogman Senior Member

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    It's the tires, not the rims.
    I had Continental's True contact. Got 60,000 + out of them. But they were noisy.
    I replaced them with Cooper tires. Very quiet, but I lost 4-5mpg. I have over 20,000 miles on them,
    and they still look new. So MAYBE the mileage will make up for the lost mpg's...
     
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