1. #1
    gwt's Avatar
    gwt
    gwt is offline Junior Member
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    Coolant reservoir bubbling

    We own a 2009 Jeep Grand Cherokee, with the 5.7 Liter V8 Hemi engine.

    A couple months back, we were on a driving adventure, when we started hearing a "squeaking" sound ... figured it might be a loose belt, so we hightailed it back to town to the nearest repair shop; turned out that the water pump was failing, so we ended up replacing the water pump, hoses and a few other things.

    About a week later, we noticed that the radiator had a tiny leak ... somewhere. We also noticed something we had never seen before: if we were out on a hot day driving slowly, we could sometimes hear a bubbling sound! Upon opening the hood, we could see the coolant was literally boiling back into the coolant reservoir ... and the reservoir looked like it was about to explode from the pressure!

    Upon returning home, we had it checked out, and ended up having a new radiator installed. But the next time we were out adventuring, we experienced the same problem with the coolant boiling back into the reservoir. So we visited a nearby Jeep dealer, who determined that there was an air bubble in the cooling system ... unfortunately, after taking care of the that problem, the same thing happened the next day ... so we had to return to the dealer. This time, it was determined that the thermostat was faulty, so we had that replaced.

    Unfortunately, a week later, we experienced the same problem again!

    The interesting thing is that the engine temperature gauge never goes above the halfway mark. And I can't tell if the fans are running, but I know that the dealer we visited during our travels said they were.

    So I have yet another appointment with my local dealer, as we try to figure out what is happening.

    Has anyone else ever experienced this problem? If so, how was it fixed? If not, any suggestions on what I need to suggest to the service folks?

    I also have what may seem to be a stupid question ... but I'm not a mechanic, so I'll ask it anyways: a friend mentioned to me that while the engine was running, if I tried to squeeze the top radiator hose, it should not be easy to squeeze it because of the pressure ... but when I try to squeeze it, the hose is hot (expected), but relatively easy to squeeze ... that surprised me ... is that indicative of a pressurization problem?

    Thanks!!

  2. #2
    JPNinPA's Avatar
    JPNinPA is offline Senior Member
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    Coolant reservoir bubbling

    Coolant expands when heated and will push out the radiator cap into the expansion tank every time the engine comes up to temp. Slowly is normal.
    It shouldn’t be boiling out into the tank.
    When at or above 30 mph there should be sufficient pressure forced through the radiator to cool it. The fan should take care if it when it gets hot and bellow 30 mph.
    Do you have grill guards or anything blocking the radiator? Is the fan kicking on? Is it a e-fan or clutch fan?
    The radiator cap should be 18 lbs if it is less more fluid gets pushed out and it will boil over.
    Air in the system allows it to boil at a lower temp and pressure.
    A sticking thermo will cause it to overheat.
    Is the water pump the correct direction? Belt run properly to spin the pump the correct direction.
    A leak, cracked head or blown head gasket allows air in. Check the oil color. Should not look like milkshake. The temp should spike when it boils over. Normal temp is 210 deg. It once above 215 the engine will go into limp mode.


    Water only boils at 212 but with coolant raises it up. Be sure you have a proper mix.



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    Last edited by JPNinPA; 07-04-2019 at 05:35 PM.
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  3. #3
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    Re: Coolant reservoir bubbling

    Thanks for the response! Typically when the problem occurs, we are geocaching along a power trail ... so we drive 0.1 miles ... stop to quickly to grab a cache ... drive 0.1 miles ... etc! This is repeated for hours at a time. I have never been able to tell if the fan runs ... it is a clutch fan, I was told (by the people who serviced it in Idaho). I don't believe that there is anything blocking the air flow.

    I can't answer your question about whether the water pump is in the correct direction ... I wouldn't even know how to determine that.

    When I bring it in for service in 2 days, they plan on checking for a cracked head or a blown head gasket.

    I've never had the jeep go into limp mode ... nor does the temperature go much over half ... even when the coolant is bubbling like crazy!

    I wish that I had taken a movie of the coolant bubbling into the reservoir ... I was really afraid that the reservoir was going to explode ... it was so bloated!

    The coolant is the correct Mopar mix, as provided by the dealer.

  4. #4
    JPNinPA's Avatar
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    Coolant reservoir bubbling

    Where do you live? Desert area high altitudes?

    The Thermo is 195 deg and the PCM will keep the temp at 210. You mention mid scale but That may be higher than210. As noted above 215 it will go into limp mode.

    If it is boiling into the expansion tank but the temp is 195 -210 change the radiator cap. It's $3-5


    Regards,
    JPNinPA

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    Last edited by JPNinPA; 07-09-2019 at 11:16 PM.
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  5. #5
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    Re: Coolant reservoir bubbling

    What did you find?


    Regards,
    JPNinPA

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    "Never look down on anybody unless you're helping him up" - Jesse Jackson

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