Over heating issues in a stock twin car

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Thread: Over heating issues in a stock twin car

  1. #1
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    Over heating issues in a stock twin car

    I have a stock twin Supra automatic that is original with around 50k miles. It's originally JDM but has been coverted to LHD. I have noticed strange behavior with the temp and the car starts to over heat on these occasions:

    1. Driving on a freeway the temp is fine, but when coming off the freeway and I stop on the intersection, the temps start to rise and then drop back after a while. I think the stock secondary fan comes on every time it starts to over heat.
    2. When I park the car after a drive and shut the engine off and leave the key on so I can monitor the temp, the temp starts to rise and the fan kicks in.
    3. When I do a burnout, the temp starts to rise quite fast.

    So in normal driving the temps are fine, but on those three occasions, the temps rise, but it never goes so bad it boils the fluid.

    So far I've changed the thermostat (OEM) and put a stock TRD radiator cap. These did not help. I also tried to bleed the system with the front end lifted.

    Stock viscous fan, I'll make sure it's working but I'm pretty sure it is and I'm in the impression if these break, they go solid. I've had that happen once.

    Stock radiator with 50k miles.

    Any suggestions?

    Car in question:
    https://www.instagram.com/p/BwpJH4gFMDG/

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  3. #2
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    Have you removed the radiator and flushed the entire system? The first time I pulled my engine, I had the radiator out (stock as well) and backflushed it with a garden hose. I couldn't believe how much crap came out. Same with the engine block. My car has 44k miles, and had never been flushed out before to my knowledge. I didn't have any overheating issues, but if your system is even partially blocked, that might explain why you see temps rising during periods of low airflow.

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    No I havent done that but definately will if I will remove the radiator.

    I'm leaning torward air in the system. Wouldnt that explain the rising temp when I shut it down?

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  6. #4
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    I had similar behavior and the problem turned out to be my original radiator developed a crack along the top seam. You didn't mention it but have you done a radiator leak test?
    Nick 95 6sp
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    SupraForums Member supralover93's Avatar
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    I'd do pike the others said but if all of that checks out then I would look at the fan. It may not be pulling enough air at idle but when driving you have enough flow which is why it doesn't overheat in that situation.
    You could also have a clogged rad. What did the fluid look like coming out?
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  8. #6
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    Quote Originally Posted by Nick 95 6sp View Post
    I had similar behavior and the problem turned out to be my original radiator developed a crack along the top seam. You didn't mention it but have you done a radiator leak test?
    Havent done a leak test, but if the radiator would be cracked, wouldnt it leak some where. Mine isn't leaking.

    Quote Originally Posted by supralover93 View Post
    I'd do pike the others said but if all of that checks out then I would look at the fan. It may not be pulling enough air at idle but when driving you have enough flow which is why it doesn't overheat in that situation.
    You could also have a clogged rad. What did the fluid look like coming out?
    Fluid has been recently changed when the LHD swap was done. I'll try to check the viscous fan and see if it's working. But the viscous fan doesnt explain why the temp raises when the car is shut down.

  9. #7
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    Quote Originally Posted by Krister View Post
    Havent done a leak test, but if the radiator would be cracked, wouldnt it leak some where. Mine isn't leaking...
    My leak wasn't obvious enough to easily find it but as soon as we pressurized it we saw the seam leaking.

  10. #8

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    Sounds like your cooling system is working with full circulation, meaning thermostat is fully / near fully open, so when extra heat is generated, there is no "reserve" left.

    +1 for radiator/full system flush. When i did this, amount of dirt coming out was huge (70k miles unopened engine). Or new radiator.

    Since all usual symptoms are covered in previous post, just one more (marginal) to check, i had similiar broblem with old evo: radiator cap was good but the place where cap lower rubber seats in radiator, there was "smudge" in edge and system didnt pressurize properly --> caused temps to rise.
    Last edited by kaahari; 04-29-2019 at 02:08 PM.


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  11. #9

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    That is strange indeed. If your radiator was plugged it would still overheat on the freeway. That’s how to stress test a radiator. 3rd gear mid rpms and 60-70mph. Should be flowing good cuz of the Rpms and max airflow if cruising at those speeds. If it still runs hot then rad is restricted. That is not your case however. I would defiantly make sure your coolant level is good and burped well and also your mixture must be 50/50 or more water. Too much coolant concentration and it will run hot. Btw what are you using to monitor temps? Is it auto or manual? How is your fan switch on the bottom of the radiator? Have you tested it to make sure it comes on? Does it happen only when a/c is in? Do you have an aftermarket intercooler(front mount)?

  12. #10

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    T stats only keep your engine from running too cool. Once it is open it is open. Airflow and fans across the radiator are what keeps your coolant temps from running away.

  13. #11

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    Also how is your fan shroud? Good and sealed? Not broken? The fan clutch can be taken apart and new silicone can be installed so that it locks at whatever temp you want to set it to by using different viscosities. There used to be a good website that had a chart for what viscosity to run for different temps. Just FYI

  14. #12
    i recorded mark7m001.mp3 Mark 2JZ's Avatar
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    other than what has been already said do you have the oem undertray in place?
    1994 Supra PT71GTQ

  15. #13

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    another +1 on the clutch fan.
    1994 Auto TT Supra

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