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Thread: 7age running cold - changed thermostat and now its running hot

  1. #1
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    Default 7age running cold - changed thermostat and now its running hot


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    CAR - AE86
    MOTOR - 7age, bigport head, mild cams, itb's, running adaptronic, only run 350kms since rebuild
    USE - Street
    PROBLEM/QUESTION -

    I've got a fresh 7age that I'm running in, it has a Koyorad race alloy radiator. The water pump setup is a RWD 4AC rear housing with a FWD 4age front cover.There is a fitting in the top of the housing with a hose that goes to the FWD 4age top water outlet as a bypass. The engine is running on water only at the moment as it had a brand new head gasket.

    I was using a aftermarket thermostat (Stant I think) that was rated at 180F (~82C) and the car would get up to around 90ish in traffic but drop below 60 on open roads.

    I took the thermostat out and put in a genuine RWD 4AC Toyota thermostat rated at 82C. Now the car is running at 90-95ish on open roads and when travelling at low speeds (less than 25) will get up to nearly 100. When I turn the heater on it will drop a few degrees

    The thermofan kicks in at 88 so is running most of the time. It never had any issues keeping my old 4age cool on the stock radiator.


    I have since tested the first thermostat on the stove and it opens and closes around 82 as expected.


    Does anyone have any idea what could be happening? Why the first thermostat ran so cold and the new one so hot.



    Cheers

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    different flow rates?

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    you're actually better off having the motor running in the 90's than at 60 which is way below operating temp.
    I found that having my thermo fans turn on when the motor was too cool ended up restricting the natural airflow when driving, (they were on the front of the radiator) and the motor ran cooler when i set the turn on point up a few more degrees.
    Andy

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    it sounds like the thermostat isnt seating to the bypass correctly check to make sure it is working alternatively you can drill a couple of little holes around the thermostat to let a little flow through that's what i did with mine to bring the temps down to where i wanted them

    mind you i have a 7a with similar specs mine has itb's and a small cam but my water pump is underdriven hope that will help


    cheers
    mat
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    I bled the cooling system again and put some corrosion inhibitor in it the other day.

    It still runs at around 88ish most of the time, when stopped in traffic it goes up a few degrees.
    The weird things at the moment are that when the heater core is closed the temperature goes up by a few degrees and when I accelerate fairly hard the temperature drops down quite quickly (into the 70s) before coming back up again.

    I'm beginning to think that I'm being a bit paranoid about it and that those sorts of temperature are fine. I do find it weird about the heater though.
    I am tempted to replace the crappy 12" thermo I have with 2 better ones just to keep the traffic temps down.

    mat,

    What temp was yours running at before/after you drilled holes in the thermostat?
    how many holes and what size?

    Cheers
    Blake

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    doesn't sound normal to me and you should never have to put holes in a therostat with an original cooling system design.

    Is the new thermostat a dual stage design? did you bypass or link any heater/throttle lines?
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    Sorry for taking so long to reply, haven't had a chance to take the photos.

    The thermostat is a standard toyota one (90916-03046) , what do you mean by dual stage? It blocks off the bypass as it opens.

    Is there an issue with running a ae82 4age water pump front housing on a 4ac rear housing? would it flow less, they are slightly different but I didn't think it would be an issue.

    There aren't any throttle lines and the heater is hooked up, I have attached some photos of the setup if you can see anything wrong with it. The bypass hose is 5/16" and I think it is a little bit kinked, could this be the problem?

    Water pump with bypass hose:
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    The bottom radiator hose goes into a U under the engine mount and to the radiator:
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    Normal FWD 4age water top water outlet with a barbed fitting on the pipe:
    Click image for larger version. 

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    Heater hose setup:
    Click image for larger version. 

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    if it blocks off the bypass as it opens then your ok.

    Looking at your pics I can't fault anything.
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    Thats not what I wanted to hear, some ridculous obviously wrong would of been nicer.

    So tonight I threw in a Tridon 76degree thermostat, idled the car up to 90ish to bleed the system and went for a drive. The temperature plummeted, it got as low as 45 degrees and was around 50-55 for most of the drive.

    My first thermostat was a Tridon 82degree and behaved the same way, however I tested the first one and it seemed to work properly.

    I have attached a photo of the first thermostat and the second Toyota one. The Toyota is the bulkier looking one with the red silicon.

    I really can't understand why the two thermostats are behaving so differently. Any ideas?

    I think my next step is to drill some holes in the Toyota one or to go back to the FWD pump/remote thermostat setup I previously had on my 4age, which I'm not too excited about.


    Click image for larger version. 

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