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Thread: 7AGE running cold (and hot)

  1. #1
    Forum Member 1st year Apprentice
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    Default 7AGE running cold (and hot)

    Sorry for the very long post but I am at my wits end over the cooling system on my AE86.

    I've got a fresh 7age that I'm in the process of running in, it has a bigport head with mild cams, individual throttles and an Adaptronic computer. It has a Koyorad race alloy radiator.

    The temperature readings are from the ECU which has the sender in the standard location in the back of the head, there is also an Autometer gauge with its temp sender in the same location. I also have the original 4AC temp sender on the top water oulet to the radiator. I have always had this temp gauge throughout my different engines so it is a good comparison between them.

    The heater core is plumbed in with a hose from the back of the head to the tap, then to the heater, and back to the thermostat housing, I have always had it this way.

    The water pump setup I originally had fitted was a RWD 4AC rear housing with a FWD 4age front pump. I had a fitting in the top of the housing with a 5/16” hose to a FWD 4age top water outlet as the bypass.

    The first thermostat I had installed was a Tridon rated at 82C, I found that the coolant temperature would get up to around 90ish in traffic but drop below 60 on open roads. I have tested this thermostat with a thermometer on the stove and it operates correctly.

    I then put in a genuine RWD 4AC Toyota thermostat rated at 82C. The car would run at 88-93ish on open roads and when travelling at low speeds or in traffic would get up to nearly 100. If I turned the heater on it would drop a few degrees. The thermofan kicks in at 89 and off at 83 so it was running most of the time, it never had any issues keeping my old 4age cool on the stock radiator.

    I then tried another Tridon thermostat rated at 77C hoping that that would make a difference, however the car ran even colder down into the 50s.

    After this I drilled two 3mm holes in the genuine Toyota thermostat and cut out the little brass bleed thing. This made the car run at around 65C.

    As I felt this was still too cold I reverted back to a FWD water pump rear housing with a remote thermostat. This was the setup that I used with my 4age which worked fine. I used the original 82C thermostat that I bought for the 7age as it was the same style as the thermostat I used to use with this setup.

    After idling the car up to 85 and then going for a drive the temperature slowly dropped to about 65 degrees, it then increased as I drove slowly down my street, so essentially behaved the same as it did originally with the RWD setup.

    Does anyone have any ideas as to what would cause such sensitivity in the cooling system? I thought that even with the larger radiator the thermostat should maintain the correct operating temperature.

    Does anyone know of any cooling issues with a bigport head 7age?

  2. #2
    Junior Member Grease Monkey
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    Default Re: 7AGE running cold (and hot)

    What pressure radiator cap? and does it seal properly (in good condition).

    I had similar issues with my 1JZ with a brand new cap, turned out the pressure was too low and it wasn't sealing properly (it was supplied by the radiator builder).

    I picked up a 1.2bar Stant cap (that actually fits properly) and has sat at rock solid temps ever since.

    YMMV

  3. #3
    Forum Member 1st year Apprentice
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    Default Re: 7AGE running cold (and hot)

    Its a new CPC 560-90 which is standard for the Sprinter (most Toyotas)
    Its 90kpa (13psi, 0.9bar), I'm hesitant to increase the pressure too much as it may cause other issues

  4. #4
    Junior Member Grease Monkey
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    Default Re: 7AGE running cold (and hot)

    Just make sure it is sealing well then, and see if things are going up/down with temp in the overflow bottle.

  5. #5
    Spirited Backyard Mechanic Casey-G's Avatar
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    Default Re: 7AGE running cold (and hot)

    How have you rigged up the coolant bypass? The hose/pipe that would normally come off the water outlet on the head and go back onto the thermostat housing.

  6. #6
    Forum Member 1st year Apprentice
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    Default Re: 7AGE running cold (and hot)

    The radiator cap isn't leaking and the overflow system seems to be working correctly.

    For the bypass:

    Initially I had a 5/16" barb brazed into the fitting that goes into the water outlet, I then ran a hose to another fitting in the top of the rwd thermostat housing.

    I've since replaced the 5/16" barb with a straight piece of 5/8" pipe with a hose going into the top of the remote thermostat housing. This is essentially the same setup I had on my old 4age

  7. #7
    Forum Member 1st year Apprentice
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    Default Re: 7AGE running cold (and hot)

    This is still confusing me, does anybody have any other theories?

    Thanks,
    Blake

  8. #8
    Spirited Backyard Mechanic Casey-G's Avatar
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    Default Re: 7AGE running cold (and hot)

    Sure the sensor aint stuffed?

  9. #9
    Forum Member 1st year Apprentice
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    Default Re: 7AGE running cold (and hot)

    There is 2 gauges as well as the ECU sensor. The factory gauge in the cluster and an Autometer Gauge. They both seem to be indicating the same thing that the ECU temp sender is reading.

  10. #10
    Spirited Backyard Mechanic Casey-G's Avatar
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    Default Re: 7AGE running cold (and hot)

    I really dunno man, my 4agte is similar but it'll never get to 100 degrees C, though it will sometimes drop back to 72ish after sitting in traffic it gets up to about 92ish but as soon as i either start moving or the thermo fan kicks in all works out.


    Do you know if your thermo fan settings are correct? there isnt much point having the fan turn on at 95 if its gonna run till its back to below the tstat opening temp.

    another thing to check is for vac leaks. If you have one it will get really hot on idle even if your afrs are spot on.. i had this problem exactly n the high temps didn't dissipate till i got rid of the vac leak.

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