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  1. #1

    Default Post heater core replacement temp issues.

    Finally had the heater core on an AC 85 V8 replaced. through here I'd seen posts where everyone suggested that the restrictor go in the larger hose that went to the intake and the restrictor going in that end of the hose closest to the intake. It immediately ran way too warm checked with the guy who did the heater core and was told it needs to go in the hose that goes to the water pump and the restrictor goes to the core end of the hose. swap that out still having issues running way too warm and now when I turn on the heat inside the car the temperature shoots up even more. Temperature was good with the bypass on the hoses pre core install.
    Dont think thermostat magicly went out.
    Also replaced temp sending unit.
    .currently guage is at the M in normal. With heater blowing it jumps to between a & l. . with bypass, guage sat at o or r.
    Anyone have any ideas or suggestions?
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  2. #2
    FEP Power Member Broncojunkie's Avatar
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    If the heater core and heater hoses can cause overheating, I've never heard of it. Personally, I would be treating this like any other overheating issue. I would probably start with a good flush, new t-stat (or test old one), and possibly even change the water pump. It would make sense if the radiator was partially clogged. Maybe a partial clog inside the radiator is forcing coolant to the path of least resistance (heater). I wonder if maybe a weak pump could do the same thing.
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  3. #3
    FEP Super Member cb84capri's Avatar
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    The restrictor goes on the core inlet, which is the hose that runs to the core from the intake manifold. That needs to be changed, these cores will balloon out without any restriction at all, and having it on the wrong side only makes the situation worse. Your overheating issue is because there is air in the system, and a lot of it is in the upper radiator hose. Jack the nose of the car as high as you can into the air when it's cold and remove the radiator cap. Run the car up to operating temp with the radiator cap off and car still in air. When the thermostat opens it will suck a lot of coolant out of the radiator into the engine. Have a jug of premixed coolant there to fill the radiator up all the way, squeeze upper radiator hose, and cap the radiator with the engine still running and hot.

    Good luck,
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  4. #4
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    Maybe it’s not really hot. With the heater blowing on high, this make a larger current draw and can affect the IVR. This can cause an incorrect temp reading. Repeat the heater test using the head lights in high and see if it still gets hot.

    Every time I turned on my Recaro seat heaters my car would show higher temps.
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  5. #5

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    As long as the restrictor is placed in series with the heater core, it will reduce flow through the core and result in a lower pressure drop across the core. It doesn't matter which hose it is installed in. See Kirchhoff's law for a explanation. The sum of the voltage rises is equal to the sum of the pressure drops in a closed loop.

    https://en.wikipedia.org/wiki/Kirchhoff%27s_circuit_laws#Kirchhoff's_voltage_law _(KVL)

    There is some other problem with the cooling system. Most likely air in it.
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  6. #6

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    Well I tried to burp it. Nothing. Put the bypass back on and still running hot. And still will get hotter when interior heat is turned on while bypassing the core.
    Only difference between now and when it ran cool is the temp sending unit I put on after core replacement.
    Was brand new from LMR. Guessing that has to be the issue.
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  7. #7
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    Have you measured the actual temp? Still sounds like an IVR issue
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  8. #8

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    I agree. I had a picture where both my gas and temp guage were pegged. I knew this wasn't true because I only had a 1/2 tank of gas. Shut the car off for 30 seconds and the guages went back to normal.

    This can also be caused by a bad ignition switch. When the wires get burned up, they increase resistance and give you an inflated value.
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  9. #9

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    Last edited by MERCURY MOTORSPORT; 08-11-2019 at 03:59 PM. Reason: I'm on OP's ignore list

  10. #10

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    Last edited by MERCURY MOTORSPORT; 08-11-2019 at 03:59 PM. Reason: I'm on OP's ignore list!

  11. #11

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    Last edited by MERCURY MOTORSPORT; 08-11-2019 at 03:59 PM. Reason: I'm on OP's ignore list

  12. #12

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    I still don't see how everyone has issues with trapped air. I bought a car that kept blowing coolant lines and a radiator. After a while I decided that I would just top it off with water until it got worse and I figured out what was really wrong instead of throwing money at it.

    It started out as just topping off the overflow every tank of gas and then countinusly got worse until the head gasket completely failed. Took 2 years and about 80k miles driving it daily, but I finally found my issue, a broken off head bolt that only leaked under load when hot, and squirted straight into the exhaust manifold which left no puddle.

    In that two years I never once had a problem with trapped coolant or randomly overheating unless I was out of water. I usually just topped off the overflow whenever I knew I was going to be driving over 20 miles or so.
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  13. #13
    FEP Power Member Broncojunkie's Avatar
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    Quote Originally Posted by Haystack View Post
    I still don't see how everyone has issues with trapped air. I bought a car that kept blowing coolant lines and a radiator. After a while I decided that I would just top it off with water until it got worse and I figured out what was really wrong instead of throwing money at it.

    It started out as just topping off the overflow every tank of gas and then countinusly got worse until the head gasket completely failed. Took 2 years and about 80k miles driving it daily, but I finally found my issue, a broken off head bolt that only leaked under load when hot, and squirted straight into the exhaust manifold which left no puddle.

    In that two years I never once had a problem with trapped coolant or randomly overheating unless I was out of water. I usually just topped off the overflow whenever I knew I was going to be driving over 20 miles or so.
    Exactly. If you have a working overflow tank with proper tube and radiator cap, the system will purge air after a few heat cycles. Just top it off a few times and you're gtg.
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  14. #14

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    Problem solved.
    It was a defective temp sending unit i purchased new from LMR. Tried another unit.
    Besides the bad temp sending unit, i also bought the heater core hose kit from LMR. That kit had a unusable water pump hose. Its just a straight hose rather than the correct molded hose with the curves in it. Wont work on an 85 as it get pinched and blocks any flow.
    On top of that, they over charged me 5 bucks.
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