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  1. #1

    Default Mustang SVO cooling fan won't work

    The cooling fan doesn't kick on. So far I've driven it this way with no issues but as the weather heats up, I'd like to address this issue. Is this a common problem? What are some likely culprits?

  2. #2
    FEP Power Member 8384GT's Avatar
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    Same thing happen to my 83GT Turbo, searched for the problem for months. Then just bypassed the factory switch and added my own.
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    There is a little box under the steering colum with TRW that controls the fan.
    Kendal

  4. #4

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    Be careful of that relay under the dash. Many Foxes have become crispy critters because of that thing.
    84 Capri RS Turbo
    Vinemont, AL (formerly El Mirage, AZ)
    USAF 1986-2007 (Ret)

  5. #5
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    Take a look at the fan control relay under the dash first. If it shows signs of overheating i.e.melted plastic conn, then replace it. I had to replace the connector leads also. Another thing to look at is the coolant temp sensor on the lower intake. It has a single lead on it. With the car running take the lead off the sensor and short it to gnd. If everything else is OK the fan should turn on.
    Dave

    84 SVO # 110 (SOLD)
    86 LX
    93 Cobra # 2100

  6. #6

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    It's a common problem. The stock fan control system is terrible. You can fix the stock system, and you might get away with it, or it might overheat, melt, and potentially cause a fire under the dash. Or you can replace the stock system with something better.

    At the very least I'd throw the TRW relay box in the trash and wire in a good aftermarket relay (2 if you have A/C). But really the stock turn on temp is a bit high, and the stock fan is bulky old tech.

    Do a search if you want, the diagrams and several workarounds have been discussed on this board in the past.
    1986 Mustang Notch, 2.3L Turbo Project

  7. #7

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    Quote Originally Posted by qturk94 View Post
    The cooling fan doesn't kick on. So far I've driven it this way with no issues but as the weather heats up, I'd like to address this issue. Is this a common problem? What are some likely culprits?
    First. Is your car a reasonably nice, clean, stock car? The stock setting for the fan to come on, does not kick in until the temperature guage is almost pegged, can't tell you why. It just is. Most folks here have not had their cars since new and are convinced that the car has a badly designed fan cooling system from the factory because a previous owner before them had butchered the car beyond repair. (in my opinion)

    Test it this way. If your fan kicks on when you turn on the A/C, and/or, if the fan kicks on when you take the wire to the temp sender (switch) and ground it, everything is probably fine. The stock temp sender (switch) is just set really high (guage wise) to activate the fan for some reason. My car is now 30 years old, has never had a melted connector or wire to the relay box, and the circuit board in the relay box looks perfect to this day. Just don't jump to conclusions about the problem. Their might not be a problem. It is an odd deal with these 83-86 Turbo cars, by looking at the guage, they seem to run "cold" all the time while driving, then on a hot day sitting for a while, the guage seems to almost peg before the fan will kick on. It's fine, Ford designed it that way for some reason, and it works. But if it makes you feel better, check the connector at the relay box for heat or burn evidence, and pop open the box and look at the circuit board. My guess is that you will find no problems.

    I think most of the problems people have with factory setup usually has involved some sort of outside influence that has negatively affected the quality of the stock parts, like corroded wires or connectors, or the demand on the relay is something other than stock original. Moisture, corrosion, modified wiring, etc. could cause arcing at the connector or a heavy draw on the circuit and create a lot of heat and maybe melt the plastic connector or cause a fire. If everything looks good when you check it, it would not hurt to add a little electrical grease to the connector contact points, buy it from Home Depot or Lowes, etc. Electricians put the stuff on bare wire in electrical panels to keep corrosion down and promotes good contact to the lugs in the box.


    Jim
    JK
    1983 Capri RS Turbo (since new)
    1970 Boss 302 (since 1980)
    1965 Mustang Coupe (since 1976)

  8. #8

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    The stock fan turn on temp is so high because a hotter engine produces lower emissions. Further, the fan is only there to cool the engine while the car isn't moving, when the car is moving the radiator gets it's airflow naturally and doesn't need the fan. Combine those details with a 4cyl engine, and Ford didn't feel the fan system needed to be very robust.

    All the confirmation I need to see that the stock fan system is inadequate, is that Ford themselves changed the system in 1987 on the Turbocoupe, and a few years later on the NA 2.3L Mustangs. There are so many reported cases of the TRW controller harness melting with no other problems in the fan system, it's really hard to just deny there's a problem.
    1986 Mustang Notch, 2.3L Turbo Project

  9. #9
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    I also have replaced the controller and added a repair connector kit on two completely stock and well maintained cars and know of many others. Can't say if its due to design or age or both but its seems to be a common issue. Never had a fan fail.
    Dave

    84 SVO # 110 (SOLD)
    86 LX
    93 Cobra # 2100

  10. #10

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    I'm glad I found this thread. I took my car to the car wash and after I left, it started sputtering and acting crazy at anything over 2000 rpm. Temp guage never pegged out but I can never remember my fan coming on. Usually the temp guage is right next to the cool indicator. However, once I nursed her home and popped the hood, I imeediately noticed that the top radiator hose was distended at the clamp/thermostat housing. I could hear the water gurgling in the water jackets. Car was very hot! I didn't know about the relay and I'm really considering setting up a manual switch. Anyone have a procedure on this?

  11. #11

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    Quote Originally Posted by dfiveuu View Post
    I didn't know about the relay and I'm really considering setting up a manual switch. Anyone have a procedure on this?
    http://vb.foureyedpride.com/showpost...4&postcount=10

    A manual switch controlling the stock relay doesn't really solve the problem of the poor wiring harness connection to the relay. In other words, it's still a fire hazard. The way you eliminate the fire hazard is to replace the relay (relays if you have A/C) with a relay and wiring capable of carrying the load of the fan.

    Done with a little care, you don't even have to cut any wires. On my car I changed the fan under the hood to gain more clearance, and wired the fan, new relay, and manual switch. It ties into the car with two quick splice taps for 12V switched power (so the fan only runs when the car is running) and the factory fan switch wire into the fan controller. It can run as the factory designed it (without the fire hazard) or I can manually override the thermostatic switch to keep it from getting to 220*.

    Other options would include changing to a fan switch with lower on/off temps, or using the fan control built into the LA3, but I haven't really had a need yet to do that.
    1986 Mustang Notch, 2.3L Turbo Project

  12. #12
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    dfiveuu wrote "top radiator hose was distended at the clamp/thermostat housing. I could hear the water gurgling in the water jackets. " Sounds like you have a stuck thermostat!
    Dave

    84 SVO # 110 (SOLD)
    86 LX
    93 Cobra # 2100

  13. #13
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    My SVO has all the stock fan control components and works fine, however in the past with two different 84 Turbo GTs I had issues with inop fans for whatever reasons, one of which was melted wiring at the controller under the dash. I don't like the idea of all the power right there under the dash, I think that design is introducing a risk of fire.

    My solution on the two cars with issues was a inexpensive fan control system that can be adjusted for whatever temp you want and works with the air conditioner. It also is contained entirely in the engine compartment and removes the power from under the dash.

    http://www.oreillyauto.com/site/c/de...1388&ppt=C0331

    This is just one example, I think every auto parts has these, and they all seem to be about the same.

    It's just one other option that is safe and inexpensive-and adjustable for whatever temp thermostat you happen to be running.
    Mark
    ______________________________________
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  14. #14

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    Hello, I have a 1984 SVO. My electric fan no longer comes on. The relay box looks good, but the connector at the fan is burnt. I'm curious, What did you do to fix your issue? Thanks

  15. #15
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    You need to be careful and inspect all parts of the circuit. Any bad connection will cause the wiring to fail. Fix the fan plug and check the relay. There are some a Ford connectors available. I don’t recall what was used on the fan. A fog light plug might be high current enough for the fan. Check the fan motor too.

    Ac cars have a double circuit as the ac or defrost provides an override to turn on the fan.
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  16. #16

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    This fan problem was sorta addressed In my 1983 Capr RS Turbo by a toggle switch and new dedicated wiring when I was 17 (back in 1995). Now that I’m restoring the car I found the wiring feeding the fan was bad all the way from the fan past the shock tower... litterly the insolation was falling off for 3+ feet of it. It was a fire waiting to happen.

  17. #17
    FEP Power Member SchoolBoy's Avatar
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    So yes the fan control relay/black box under the dash is the most common fail point in the system. But its not the cause. The problem is two fold, the factory fan can draw as much as 80amps to kick on. The factory wiring is just way to small to carry all that juice.

    When my system had total failure.... the fan went, the controller went and the temp sensor all pretty much went at once. I replced the stock fan with a Spal, the controller was replaced with another oem unit, and an aftermarket coolant sensor was sourced that kicks on at 195 and off at 185. The key to all of this was the addition of a second relay. This relay allows the fan to pull power straight off the battery when activated by the factory controller. This has the benefit of taking the load off the factory wiring.
    Last edited by SchoolBoy; 12-17-2020 at 10:01 PM.
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