405 cooling fan probs
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  1. #1
    max
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    405 cooling fan probs

    Having probs with overheating in my srdt. only happens during gridlock or towing uphill. thermostat is ok. I think the fan or something related to it is stuffed.

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    Any suggestions??

  2. #2
    Moderator Alan S's Avatar
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    Hi Max,

    Probably more of an addition to your question than an answer but, My BX 16V occasionally suffers from the same problem although saying that it is hard for me to judge as I live in a flat country town hence no hills & no gridlocks, but in Town type traffic, the temp gauge goes up fairly much & sometimes when I stop the fans are going. My thoughts are that it is (a) the fan sensor switch either working intermittently or cutting in too late (when the engine is TOO hot) or (b) cooling fans not up to speed, although they sound OK (c) air in the cooling system as the bleeder on the thermostat housing has broken the plastic screw end off, making it impossible to loosen.

    Now c'mon experts; any of those make any sense? oR do we have a common ptoblem with a simple solution?

    Alan S
    If it ain't broke, use a 12" shifter.....that usually does the trick!!

  3. #3
    max
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    thanks for the suggestions.

    I actually can't recall my fan even working. Fuses are ok too.

    Perhaps your suggestion of the thermo switch is more likely in my case.

    Yours probably sound like blocked rad.

    Again..come on experts where's the definitive answer??

  4. #4
    Moderator Alan S's Avatar
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    Yeah Max,

    Had thought of the blocked radiator but the car has only done 90 odd thousand klms, has been religiously serviced all its life, has always had inhibitor in it & was flushed just after I bought it around 10K klms ago. On the open road it doesn't seem to matter what speed you drive it, the needle seems to keep reading low & the fans don't turn on until you've been idling for a few minutes after a fast run, which to me points to either the fans not doing their job at the right time or not shifting enough air through the core.

    Alan S
    If it ain't broke, use a 12" shifter.....that usually does the trick!!

  5. #5
    max
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    Hey Alan,

    I had a toyota that acted similar. I had it for 200,000 kms and it always used to take forever to heat up. In winter in south Isl it used to take 15 km city driving followed by 10 km open road before i could get decent temp into it. the only time it over heated was when it died. My wife who never drove it was unfortunate to be driving it when the head gasket blew. Seeing she was used to driving a v6 Ford, thought the temp gauge was the fuel gauge on full...whoops!!!

    At least i ended with the frog i had wanted for ages.

    Anyway maybe your BX is just a freak of manufacturing, and doesn't warm up well...but then again it could be a combo of that and a sneaky air bubble.

  6. #6
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    Hi there, I just recently had this problem,

    First I got the radiator completly flushed, still the porblem existed, then I worked out that it was the thermoswitch not cutting in all the time, so I replaced that, finally When i was replacing the thermoswitch I noticed that the wiring from the thermoswitch had shorted out, so I got the wiring replaced and all is now working fine.

    This was an expense exercise, but I think what should do is rig up the cooling fan so it is always running and see if the temperature still goes up. If the fan doesn't work at all then its probably a faulty fan, but if the fan does work it may be the thremoswith not working properly.

    However you should flush your cooling system every two years so its proberly worth flushing the cooling system as well.

    Hope this helps, Dan.


  7. #7
    Fellow Frogger!
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    I had this drama on a Fiat 124 CC a few years back. I just ran the wires up to a small switch on the dash that allowed me to simply turn the fan on before it got hot rather than waiting for the thermo to kick in. Band-aid solution, but may help.

    Chipper

  8. #8
    max
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    Ok, call me a new frog, but where might I start looking for the thermo switch on a 1996 SRDT??

  9. #9
    Fellow Frogger!
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    My old man is the electronics technician, so buggered if I know

    All he did was get a small switch (from an organ I think) and wire the earth and positive wires into the back of the switch from the thermo, so as to run an auxilury switch as it were rather than replace the original wiring. The fan still worked as per temp operation, but the switch was there so I could manually turn the fan on as well.

    This was a non fuel injected car, so I dont know if any ramifications will occur to a fuel injected system.

    Chipper

  10. #10
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    on the radiator tank. usually rhs bottom. usually has nut with head of about 22-24 mm, with 2 wires coming out of it. brass construction.

  11. #11
    1000+ Posts PeterT's Avatar
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    My 405 showed all the signs of overheating, but was infact a high resistance on the M981 thermistor connector under the thermostat housing. This sensor controls the fans, heater, AC etc. and not the engine ECU. If this sensor see a high resistance or open circuit, both fans will go to high speed (indicating 102 deg) and cause the red and blue lights on the coolant temp guage to glow. As yours happens under load I doubt it, but worth a look.

    '92 205 Mi16
    '90 Mi16x4

  12. #12
    1000+ Posts PeterT's Avatar
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    sorry it's the M891 sensor. Just to help you check your fans:
    1st spd engagement/disengagement 98/93 deg C
    2nd spd engagement/disengagement 102/97 deg C

    '92 205 Mi16
    '90 Mi16x4

  13. #13
    Fellow Frogger! Cubits's Avatar
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    My thermoswitch is buggered, but i can run the radiator fans by turning on the AC (ahah!). Is the AC fan speed the low fan speed from the thermoswitch? My car seems to be running at only a slightly high temp now, but of course a little less fuel efficiently.

    Hopefully i can install my new thermoswitch tomorrow and have that part of the car all sorted. Descaling the radiator, changing the thermostat, and changing to a higher grade coolant were all kind of necessary some time or another (why oh why didnt i just look for the fans first?!).

    Oh, i'm getting a "little" bit of shunt at the moment because one of the rubber wedges on the engine mount has disappeared. I was thinking about using a skateboard wheel cut in two as the new rubbers. I'm going to give it a go tomorrow and see if that works. It seems to be just the right size, and should work nicely if i use a semi soft compound like a red kryptonic.

    Any other idea for replacement rubbers?

  14. #14
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    Icon3

    Hi Max, see my reply to Cubits's post above (today).

    Suggest you try the bridging trick on the thermoswitch, as a temp fix.

    Also every two years change the coolant and thermostat. Use PUG recommended coolant with demineralised water. At the same time service the aircon and check or replace hoses and belts.

    On average around the 150,000K mark the radiator may need overhauling. If you tow regularly then a heavy duty core should be considered.

    A thermo switch can go any time. I have had an auto sparky install a lighted switch mounted on the dash. This means that you can switch on the cooling fans earlier in extreme traffic/running conditions, or switch the fans on if the thermo switch dies. Maybe you can rig up a warning light that comes on when the fans are working - maybe through the switch I have suggested.

    Cheers ,,,,,,,, Nick

  15. #15
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    Icon9 thermostat

    Quote Originally Posted by max
    Ok, call me a new frog, but where might I start looking for the thermo switch on a 1996 SRDT??
    There are no thermostat switches on this car but you will find the a thermistor (two pin connector)just behind the distributor.This senses the temp and sends the information to a ECU which is situated just under the left side headlamp which activates relays to cut in or cut out the cooling fans-- best of luck-- maxx

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