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Thread: Coolant Boiling Normal?

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    Coolant Boiling Normal?

    Hello Everyone,

    Tried searching but couldn't really find anything on 2019 Signature CX-5 model. I recently went on a roadtrip up to Mammoth Lakes. During the trip I drove to several national parks and climbed a lot of hills. Average speed, no stop and go, but car had 5 adults. After about 2 hours of driving up a mountain and pulling over for some site seeing, I heard some major boiling under the hood. I popped open the hood and saw that the coolant was boiling enough to cook some noodles. I left the hood open to cool it off while looking around and when I got back the boiling stopped so we continued on our trip. I did some google searching and believe it may be due to higher elevation but wanted to check with the group here. Never experienced this in my previous turbo SUV and I'm planning another roadtrip next month. TIA!

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    Quote Originally Posted by hawaiian_bread View Post
    Hello Everyone,

    Tried searching but couldn't really find anything on 2019 Signature CX-5 model. I recently went on a roadtrip up to Mammoth Lakes. During the trip I drove to several national parks and climbed a lot of hills. Average speed, no stop and go, but car had 5 adults. After about 2 hours of driving up a mountain and pulling over for some site seeing, I heard some major boiling under the hood. I popped open the hood and saw that the coolant was boiling enough to cook some noodles. I left the hood open to cool it off while looking around and when I got back the boiling stopped so we continued on our trip. I did some google searching and believe it may be due to higher elevation but wanted to check with the group here. Never experienced this in my previous turbo SUV and I'm planning another roadtrip next month. TIA!
    Did you temp gauge tell you anything?

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    2008.5 MGM MS3 rsvinylgraphics's Avatar
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    Was the boiling in the coolant reservoir tank? I don't think that is normal I would visit the dealer and get it checked out since this is a brand new vehicle and under warranty.

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    Water does boil at a lower temperature at higher elevations [lower pressure].

    But boiling in the reservoir doesn't sound good at all. Dealer for sure.

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    Registered Member Anchorman's Avatar

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    And he*s gone.

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    Temp gauge showed normal operating temps which is why I continued to drive the vehicle. The boiling was happening inside the coolant reservoir. Doesn't sound like that should be happening so I'll schedule a visit before my road trip.

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    Structural Member shadonoz's Avatar
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    You might find this interesting: What Does It Mean if Car Coolant is Bubbling? I did!

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    check if the cap on the coolan reservoir is tight. Dont see what else could be on a brand new car.

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    OP should check coolant level while engine is cold. To ensure there's enough coolant to keep temps in check.

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    Registered Member concept's Avatar

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    Quote Originally Posted by cz5gt View Post
    check if the cap on the coolan reservoir is tight. Dont see what else could be on a brand new car.
    Yes, a loose cap would do it.
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    Arrow Coolant Boiling Normal?

    Quote Originally Posted by concept View Post
    Quote Originally Posted by cz5gt View Post
    check if the cap on the coolan reservoir is tight. Dont see what else could be on a brand new car.
    Yes, a loose cap would do it.
    No, the coolant overflow reservoir is not a sealed container. The cap is not sealed tight like radiator cap. It doesnít matter if the cap of coolant overflow reservoir is loose or not.

    OPís coolant boiling problem is almost like those overheating problem happened on some Mazda SkyActiv-D diesels in some countries. No warnings, but the coolant is boiling from reservoir. And eventually cylinder head gasket is gone or the head is wrapped.

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    Quote Originally Posted by yrwei52 View Post
    No, the coolant overflow reservoir is not a sealed container. The cap is not sealed tight like radiator cap. It doesnít matter if the cap of coolant overflow reservoir is loose or not.
    How's that possible? I mean, how do you connect the overflow tank that is not sealed to the rest of the coolant system that is supposed to be quite sealed indeed?
    It is sealed for sure...

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    Structural Member shadonoz's Avatar
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    Quote Originally Posted by yugrus View Post
    How's that possible? I mean, how do you connect the overflow tank that is not sealed to the rest of the coolant system that is supposed to be quite sealed indeed?
    It is sealed for sure...
    The pressure cap on the radiator can release excess pressure to the reservoir. When it's not doing that, it is sealed. The reservoir isn't sealed; you just flip the little lid. But the rest of the system is sealed.

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    Quote Originally Posted by shadonoz View Post
    You might find this interesting: What Does It Mean if Car Coolant is Bubbling? I did!
    That was a good read.

    But kinda like going on WebMD. None of those things seemed like good news.

    Sure is odd for a brand new car to do this. especially with no overheating symptoms.

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    Quote Originally Posted by yugrus View Post
    How's that possible? I mean, how do you connect the overflow tank that is not sealed to the rest of the coolant system that is supposed to be quite sealed indeed?
    It is sealed for sure...
    The outlet for overflow tank is in the radiator neck above where the cap seats.

    See it stick out to the right in this pic:


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