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Thread: how to read Cylinder head temp ? as a few modern car don't have water temp gauge.

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    Senior Member bellwilliam's Avatar
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    Default how to read Cylinder head temp ? as a few modern car don't have water temp gauge.

    so my first Ford (RV don't count, may be it does)... apparently Ford (not sure if all Ford) don't have coolant temp sensor. coolant temp gauge is just "simulated" from cylinder head temp sensor. apparently cylinder head temp is a more accurate measure of overheating

    I've learned how to read coolant temp, like 180-200F thermostat opens. anything under 220F is good. anything over 230F is bad.

    my question is how do you interpret cylinder head temp ? what is high, what is low, at what temp will head gasket fail ?
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    CHTs are usually 5-10* but looking at some of my old race car data, it can be 10-20*F higher than coolant.

    230*F CHT is getting warm and 240*F CHT is pretty hot and i'd try to cool things down. I've seen cars hit 250*F and not puke water out -which if it doesn't puke water, the gaskets are likely fine.

    Modern cars run higher cap pressures so they can run hotter without catastrophic issues.
    Last edited by Stuntman; 10-18-2017 at 07:30 PM.
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    Senior Member JulioG's Avatar
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    /deleted post, replied to wrong thread

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    Administrator ucfbrett's Avatar
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    Of course, then the conversation becomes, "Where do you measure cylinder head temp?" On the side, internally? Where does the sensor attach?

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    Quote Originally Posted by ucfbrett View Post
    Of course, then the conversation becomes, "Where do you measure cylinder head temp?" On the side, internally? Where does the sensor attach?
    to the cylinder head...

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    What about coolant temp sensors that read from a port on the cylinder head? IMO none of this gobbledygook means anything. You need to ask the engineers at ford gm etc. what the design envelope is and design your temp sensors to read accordingly if they have chosen to leave such sensors out. Anything you add is just a guess on your part as to what may or maynot be acceptable.

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    Like worrying about 280*F oil temps in a car designed for it

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    Senior Member robburgoon's Avatar
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    Solution:

    Install water temp gauge in old clunker
    Install head temp sensor in old clunker

    Cover radiator, drive up a hill and watch the temps, and write down the numbers when the head gasket goes.

    You're welcome!

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    Mazda MZR has head temperature sensor.
    When using the AEM calibration curve for Ford Coyote head temperature sensor:
    The reading match the water temperature sensor, which match non contact IR thermometer reading on water hose at head.
    +- 5 deg F across 75-212 F

    One benefit of head temp sensor is that if you loose water you still get a reading.

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    Administrator ucfbrett's Avatar
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    Quote Originally Posted by Stuntman View Post
    to the cylinder head...
    Anywhere? Exhaust side or intake side? Front or rear?

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    Under the spark plug is pretty standard. There are many aftermarket thermocouples available. The key is to get to the metal that has the combustion on the other side. This was much more normal in the aircooled engine days. I had one on my shifter kart years back. It was a watercooled Yamaha YZ125. The CHT almost matched the water temp exactly. CHT was only slightly quicker responding to power changes, but not enough to tune from. Water temp sensor was drilled in a flat section of the outer head, and the CHT was under the spark plug, replacing the plug gasket.

    Cylinder head temperature sensor - AIM Store
    I bet google has most of the answers.

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    Quote Originally Posted by ucfbrett View Post
    Anywhere? Exhaust side or intake side? Front or rear?
    Rear of the passenger cylinder head, close to combustion chamber. Above the crank sensor (red arrow):



    Quote Originally Posted by GraemeD View Post
    Under the spark plug is pretty standard. There are many aftermarket thermocouples available. The key is to get to the metal that has the combustion on the other side. This was much more normal in the aircooled engine days. I had one on my shifter kart years back. It was a watercooled Yamaha YZ125. The CHT almost matched the water temp exactly. CHT was only slightly quicker responding to power changes, but not enough to tune from. Water temp sensor was drilled in a flat section of the outer head, and the CHT was under the spark plug, replacing the plug gasket.

    Cylinder head temperature sensor - AIM Store
    I bet google has most of the answers.
    CHT for Karting is a bit different than cars. In cars, CHT can vary by quite a bit from water temps.

    I don't think I ever ran a CHT sensor on my shifter, just water temp in-line before the radiator. I'm surprised to hear they correlated in your application but then again, taking water temp from drilling into the head is basically a CHT reading so that makes sense... Who races YZ's in shifters anyhow?

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    Please validate that this is the CHT.

    CHT.jpg

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    I think more racers should run EGT CHT CTS TPMS and trans diff sensors. Less breakdowns and oiling the track will result in more tracktime in general and while the other racers are occupied looking at all this stuff I can pass them when they aren't looking.
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    Senior Member bellwilliam's Avatar
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    an issue I see is CHT sender location isn't "standardized". So one car's 250F might mean kaboom, while the other's 260F might be just fine.....
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    S1 Supermiata - 220whp
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    Quote Originally Posted by bellwilliam View Post
    an issue I see is CHT sender location isn't "standardized". So one car's 250F might mean kaboom, while the other's 260F might be just fine.....
    It's a good thing there are factory fail-safes that put the car in limp mode to prevent that kind of damage, unless there's a mechanical failure, at which point where the sensor is, is somewhat irrelevant.

    Your concern is also irrelevant when you consider that there is no standard or consistent temp where there is a "kaboom". Depending on the engine and cooking system, that failure temp will vary. Cup cars and even my Mustang race are run at 260-280* water without blowing a head gasket it failing. Every car is different.
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