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2006 Nissan Murano and 2004 Nissan Xterra
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My daughter's 2006 Murano has experienced the following: Driving down road - smelled antifreeze - temperature gauge went to hot and all of sudden dropped to cold. This happened a few times before she arrived home. Antifreeze spewed from somewhere but I don't see any cracked hoses. Could this be a thermostat issue? If not, any ideas where this Mom should start?
 

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There are many small cooling hoses/lines/elbows that are very hard to see, and some are hidden requiring an inspection mirror and proper lighting to view. If you're not seeing any leaking beneath the car, it's possible the heater core behind the dash is leaking and possibly dripping coolant beneath the front passenger carpeted area. You could feel around to see if it's damp/wet, or if it smells extra coolant-sweet in that area. If you don't have an inspection mirror, you can use a tiny mirror or a makeup compact to look at the underside of hoses, to see if anything is split. As best you can, when everything is cooled off, check that the main radiator hoses aren't loose on their fittings. Again, there are so many hoses that it really will be nearly impossible to see every line...you can only see so much.

That the temp gauge went from cold to hot to cold could indicate air in the system or a hose that is old and has become soft and ended up buckling/pinching at one or more of its bends, cutting off the flow of coolant and forcing coolant to blow from a weaker/loose connection/hose, or even out of the overflow tank cap, etc. Or a hose could have split/ruptured. Once the pressure was relieved, the temp gauge returned to normal. Or, once all the coolant was blown out of the system, there was nothing left for the temp sensor to get a reading from, so the gauge went back to cold.

I would suggest removing the radiator cap when everything has cooled down, then topping off the radiator, turning on the car and letting it idle, and looking around for signs of a leak. I'd squeeze the top and bottom radiator hoses to see how soft they are. If too soft, that could be the root of the problem (again...a hose is collapsing when heated coolant starts flowing through it, creating a blockage and back-pressure...) Naturally, be careful around things that are moving around and hot...the radiator fans, the pulley/serpentine belt, etc. If you're not mechanically capable and don't have tools, you may just have to have it brought to a garage for diagnosis. If not seeing any leaks, turn up the heat all the way when the car's running, to see if that makes things start to go haywire.

Yes, it could be a sticking thermostat, given the erradic behavior of the temp gauge. If it's stuck closed, you shouldn't be getting any heat from the system. And if your system is completely empty of coolant, you won't get any heat. Whatever you do, don't run your engine without coolant in the system. You can use water in a pinch to see if you can spot a leak, but then you'll need to drain the system once the problem is corrected, and refill with coolant.

Be sure to wear some safety goggles in case something spews/sprays hot coolant in your face. You can observe things from a safe distance if you have good lighting. Try not to stick your face into the engine compartment when the car is running. Be safe.
 

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Your Murano may still have the original radiator cap. If you don't see any obviously burst hoses or a leaking radiator, I would start by replacing the radiator cap. Be sure to top off the radiator and expansion tank coolant, then check if the problem is resolved.

Check the coolant level for a few days to see if it needs to be topped off again due to air pockets migrating out. Also be sure to use a 50/50 mix of coolant to prevent boil overs and freezing.

The cooling system needs to be under pressure to prevent the coolant from boiling over, a good radiator cap seal is an absolute requirement to accomplish this...
 

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Forgot to mention the obvious last night... Although any part can fail suddenly at any time, since the car was being driven when the problem happened, it's possible an object in the road bounced up and struck the radiator, causing damage to a tank or flowtube which allowed coolant to burst out of the bottom and not show telltale signs on the upper areas. While coolant is being lost, the temp gauge would likely go to extreme readings as coolant and air pass through the system sporadically.

It's also possible that one of your cooling fans' blades or a fan strut broke off and struck the radiator and damaged some flowtubes. Lots of possibilities. Leaks of any kind can often be tough to locate.
 
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