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Discussion Starter #1 (Edited)
Last August - hot weather out, long mountain pass drive...get into town, engine bucks and stops. Looked down, at overheat line. Limp to mechanic. Radiator cracked. Replaces radiator and thermostat.

Drive home from mechanic, highway driving. At high rpms after a whileand/or under load (going up a hill) temperature climbs steadily from 40%-ish to the warning line. If I pop it into 2nd and rev above 3000rpm, temperature goes back to normal for a while. I figured maybe waterpump blades were warped, replaced it. Problem still present. If I stop and put in neutral and rev, temperature goes back to normal. Presumably due to timing chain driven water pump, it's circulating coolant faster so that makes sense. Driving around town does not exhibit the problem. I expect I just didn't notice this problem when it happened the first time which resulted in the original radiator burst as pressure built too high.

The guy at this link (How to replace the Thermostat) had EXACTLY my problem, and a few others also have posted about this, so much so that it seems like a relatively common problem yet I've seen nary a solution for it - but unfortunately no solution was ever posted. Also here - 2003 Murano Overheating.... HELP!

Coolant is staying solid in level, not leaking, so cracked head or gasket seems unlikely. No bubbles in reservoir, and no white smoke.

What can this be? It's driving me NUTS. I really want to keep this vehicle, but I can't when it's like this. I've replaced most of the cooling system yet still have a cooling isue.
  • The vehicle is in GREAT condition other than this, and I'm getting by by driving around in 2nd all the time but that's not a great solution.
  • CVT slipping creating heat? It DOES however overheat when sitting idle only once overheating has already started so it may not entirely be transmission related.....
  • Bubble in system? I think this unlikely as the system has been pulled apart and re-put back together twice now, did they both screw up?
  • It's not CONSISTENTLY doing this. I drove up to the local ski hill in February after changing oil on vehicle, like magic the temp stayed perfect the entire drive. a month later I drove up again and it was a nightmare of overheating and i had to sit in 2nd the entire drive. Oil level was still fine.
Dealer has NO idea, and won't even help unless I let them take it yet again, and i don't feel like that's worth my $.

When the vehicle is at idle, what should the temp of the incoming and outgoing radiator hoses be? How about when 'overheated'? I have a good infrared gun.

Ideas please? I'm at my wits end here! My next thing to do is a head pressure test to rule out a cracked head or cracked gasket.
 

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My guess would be electric fans not running at proper intervals, but I may be missing important clues.
 

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Discussion Starter #3
Main radiator fan is running pretty much constantly from what I can tell. Never seen it not running in fact, other than when it's really cold of course. Also, if it were a fan that wouldn't explain why upping the rpms would make the temperature plummet from 'over heated' to normal in 3 seconds flat......
 

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Main radiator fan is running pretty much constantly from what I can tell. Never seen it not running in fact, other than when it's really cold of course. Also, if it were a fan that wouldn't explain why upping the rpms would make the temperature plummet from 'over heated' to normal in 3 seconds flat......
True, that tends to point more in the direction of water pump. I'm curious about the thermostat, too. The earlier posts aren't clear about whether it has been replaced.
 

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Main radiator fan is running pretty much constantly from what I can tell. Never seen it not running in fact, other than when it's really cold of course. Also, if it were a fan that wouldn't explain why upping the rpms would make the temperature plummet from 'over heated' to normal in 3 seconds flat......
The cooling fans shouldn't run at all unless you have the A/C turned on or the engine coolant temperature reaches a specified level (203F/95C). If the fans are running outside of those conditions then there is a problem with the cooling fan circuit and/or possibly with the ECT sensor. Do you have a scan tool that can read live data so you can see the readout coming directly from the ECT sensor? Also, is the MIL illuminated?
 

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When changing radiator fluid in the Murano, you HAVE to use a radiator top-off device to get the air pockets out of the upper engine water cavities. Failure to do this procedure when replacing the radiator will cause overheating symptoms like you're describing.

Here is what you'll need to properly fill the Murano cooling system:


You can also face the car nose up on a 15 degree slope. After the engine is heated up and with a high idle, repeatedly squeeze the upper radiator hose. If you're lucky, you'll purge most of the air out of the system.

Good luck.

Have a good day.

PS. Your old water pump was probably alright.
 
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Discussion Starter #7
Pilgrim - water pump and thermostat were both replaced when the rad was.

I Need Coffee - Hm, interesting. The rad fan looks like it runs all the time (from 1 time looking, last night, cold start, fan was running).

PaulDay - Yeah I'm regretting replacing the water pump, that was a CAD$1500 mistake I think. Is it possible that two different mechanics would not have bled the system properly? It looks like a bleed attempt is probably the next thing to try. I assume the radiator cap is still on when doing that bleed? If so, where is the air escaping to?

Thanks for the replies everyone!
 

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Pilgrim - water pump and thermostat were both replaced when the rad was.

I Need Coffee - Hm, interesting. The rad fan looks like it runs all the time (from 1 time looking, last night, cold start, fan was running).

PaulDay - Yeah I'm regretting replacing the water pump, that was a CAD$1500 mistake I think. Is it possible that two different mechanics would not have bled the system properly? It looks like a bleed attempt is probably the next thing to try. I assume the radiator cap is still on when doing that bleed? If so, where is the air escaping to?

Thanks for the replies everyone!
Unless it was a dealer, I'd buy the item and do the air purge myself.

You have to start with the car on a steep slope, nose up, cold with the radiator cap off, fluid topped off. As soon as the engine is started, place the palm of your hand over the fill neck and start to squeeze the upper radiator hose. As the engine heats up and you start to see the water flowing, (Thermostat opens.) squeeze the upper radiator hose repeatedly. As air escapes, fluid level will drop. Keep adding fluid as needed. Finish by topping off the radiator before replacing the radiator cap. Unfortunately, this method needs to be done several times to completely get fluid up into the engine where the air pockets are.

Fill the overflow close to the HOT line and let the engine cool down. Fluid will be sucked back into the engine as it cools. Check the overflow daily and add if needed, until fluid level stabiles near the cold line.

Using the funnel method is a one shot deal and will be able to remove 100 per cent of the air from the cooling system.

Have a good day.
 
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The only thing I'd add to what Paul Day said is when you bleed the cooling system of air turn the heat on (highest temperature) with blower fan set to low. This will ensure that no air bubbles are trapped in the heater core and if you can feel hot air blowing from the vents when the engine is at operating temperature then you know that coolant is circulating normally.
 

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Discussion Starter #10
Bled it on the driveway (15deg driveway) as described by PaulDay above, then re-filled coolant as it was below minimum (was before bleed!). 15 minute highway drive with some hills put it into overheat again.

Got home after keeping the heat under control by putting in 2nd often and revving it. Took temp of top and bottom rad hoses (with vehicle off, need to do with vehicle on next time), 200F and 100F respectively. What should normal be? I'll drive it again today and test while engine still running. I'd really like to know WHAT is overheating as I'm pretty sure the cooling system is working fine other than a potential air-lock. If it's the transmission or head problem, then I'm giving up. My gut tells me transmission due to how the problem manifests.

Next step is head pressure test....or, effectively put it to auction on a trade-in for almost nothing (that's ok, it owes me nothing really) towards either a new '19/'20 Honda Passport (LOVE but $$$), or a '17 Pathfinder (love the tech features, however ugly as sin... looks like a minivan, but SIGNIFICANTLY cheaper and will do the job.).
 

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Discussion Starter #11
FWIW, two reasons I'm not going with another Murano if I buy something else, despite loving my Murano.
  1. They dramatically lowered folded-seat cargo storage space as of 2012-ish
  2. They lowered tow rating from 3500# to 1500# in '15 or '16
    • WHY???? same engine/tranny/frame, Nissan service couldn't explain to me why other than some hand wavey 'engine tunin'g fluff that was clearly made up.
  3. I want the tech features in the '14+ on my next vehicle
Pathfinder lets me do this, at the expense of aesthetics. Passport lets me do this at the expense of money.

If the Murano still towed 3500# and had '04 storage, I'd be rolling in a new one right now.
 

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Bled it on the driveway (15deg driveway) as described by PaulDay above, then re-filled coolant as it was below minimum (was before bleed!). 15 minute highway drive with some hills put it into overheat again.

Got home after keeping the heat under control by putting in 2nd often and revving it. Took temp of top and bottom rad hoses (with vehicle off, need to do with vehicle on next time), 200F and 100F respectively. What should normal be? I'll drive it again today and test while engine still running. I'd really like to know WHAT is overheating as I'm pretty sure the cooling system is working fine other than a potential air-lock. If it's the transmission or head problem, then I'm giving up. My gut tells me transmission due to how the problem manifests.

Next step is head pressure test....or, effectively put it to auction on a trade-in for almost nothing (that's ok, it owes me nothing really) towards either a new '19/'20 Honda Passport (LOVE but $$$), or a '17 Pathfinder (love the tech features, however ugly as sin... looks like a minivan, but SIGNIFICANTLY cheaper and will do the job.).
Assuming the engine is at operating temperature and coolant is flowing normally, the lower hose temperature seems really low to me because it's cool enough where one could hold it in their bare hand without being uncomfortable. Was the new thermostat OEM or aftermarket?
 

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And - was the thermostat tested before installation? I know I get lazy and assume they will work correctly, but they're enough work to replace that I really should test them before installing....
 

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Discussion Starter #14
I assume it was OEM, and I assume they tested it first. I'm told new thermostats essentially never have issues, since they are so simple. But, let's say it's the thermostat...why would revving the engine on the highway take the temp from the first danger line to the 40% (normal) mark essentially instantly? It just doesn't feel like a thermostate problem. To be clear, the car had been turned off a few minutes by the time I did the measurement, I just remembered that maybe I should test. Next time it's overheated like that, I will leave it running and check.

On a side note I almost bought a Platinum Reserve Armada tonight...but held off due to finding out more about it's history. Was going to buy a '17 loaded Pathfinder earlier in the day but someone got it 5 minutes before me!

I can't buy a new Murano. Tow rating lowered to 1500#, and since 2014 they are SO much smaller, I need more room (Pathfinder or Armada/QX80). So, I'm shopping to pick up another one for in case the Murano kicks the bucket due this weird cooling problem...even weirder since it's seemed to happen to a number of people on the Internet over the last 15 years but not a single person has posted a solution to it.
 

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i'm assuming your "mechanic" was not a Nissan dealership. as such, my bet is that they put in a crap sub-standard non-oem radiator (because they got it CHEAP). often, non-oe parts are cheap for good reason. if they put in non-oe water pump and thermostat, those are suspect also. some aftermarket parts are good/high quality but they cost accordingly (i.e. close to factory part cost without the dealer jack-up). if "repairs" were made with el cheapo or Chinese counterfeit parts, then it'll never run right. money's rarely saved when you cheap out on parts.
 

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Discussion Starter #16
Surban1 - Water pump was not by the original mechanic, that was a followup when I discovered I still had a problem and figured only thing it could be was water pump. So, water pump is a Nissan one. Rad/thermo I have no idea, probably OEM, I'll find my invoice and see what it says. Could be anything really I guess. I was travelling with it in another city when it happened, and in a bit of an emergency situation and limped to the nearest mechanic and said 'fix it'. Thing is, this problem may have existed before then, as the original reason I went in was a busted radiator from overheating I didn't notice. And no, I don't think the head gasket was compromised (haven't tested, but no signs point to that from the 'tests I can do').

Question for you - If it's a sub-standard rad...why would revving the engine (e.g. pop into 2nd) immediately drop the temp from 'critical overheat' to 'everything good' in no time flat, and why would the problem not exhibit at stop, only highway speeds that involve hills? Those don't point to a crap rad, or thermo.
 

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Surban1 - Water pump was not by the original mechanic, that was a followup when I discovered I still had a problem and figured only thing it could be was water pump. So, water pump is a Nissan one. Rad/thermo I have no idea, probably OEM, I'll find my invoice and see what it says. Could be anything really I guess. I was travelling with it in another city when it happened, and in a bit of an emergency situation and limped to the nearest mechanic and said 'fix it'. Thing is, this problem may have existed before then, as the original reason I went in was a busted radiator from overheating I didn't notice. And no, I don't think the head gasket was compromised (haven't tested, but no signs point to that from the 'tests I can do').

Question for you - If it's a sub-standard rad...why would revving the engine (e.g. pop into 2nd) immediately drop the temp from 'critical overheat' to 'everything good' in no time flat, and why would the problem not exhibit at stop, only highway speeds that involve hills? Those don't point to a crap rad, or thermo.
The lower hose temperature is abnormal, even if you waited a short while before taking the temperature readings. That hose should be hot to the touch, but your measurement indicated it was barely above the normal temperature of the human body. This is suggestive of some kind of coolant flow problem. A faulty thermostat, water pump or obstruction in the system can do that, but so could an air pocket if it's large enough. An air pocket in the system could explain the phenomenon you describe of needing to increase engine speed to make the temperature drop because the water pump starts moving coolant more rapidly pushing the air bubble out of the spot where it's trapped. Did you use the spill-free funnel to bleed the system? If not, I'd suggest buying that kit and bleeding again. Even using that tool, it can take some time to get all the air out of the cooling system. Plus, those kits are universal so you can use them on any car you own to do cooling system maintenance.

Now, if there is definitely no air in the cooling system then you have to start looking at other things, even if you've had them "fixed" already. Pressure testing the cooling system and the radiator cap is also a good idea.

I'd also circle back to the cooling fans. If they run constantly, even with the A/C off right after a cold start, then they're not working properly. At the very least, do the Auto Active test for the IPDM (see page 23 of the service manual below) and make sure that the fans cycle on both low and high. If they only run at low speed (even all the time) the engine will get hot when it's under load. Do you have a scan tool that can read live data so you can check the readings the engine coolant temperature sensor is sending to the ECM?

https://www.nicoclub.com/service-manual?fsm_download=Murano/2004/pg.pdf

On a side note, have you checked the antifreeze/water ratio? Not sure an overly-concentrated ratio would be the issue here, but the test kits are inexpensive and stocked by most auto part stores. It might be worthwhile doing that to make sure that whoever did the work didn't accidentally dump undiluted antifreeze into the cooling system.
 

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Discussion Starter #19
Great thoughts everyone, thanks so much for the engagement. Funnel system ordered. Will also follow up on the hose temps once I can get another overheat situation.
 

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Even using that tool, it can take some time to get all the air out of the cooling system.
I agree, I experieced that. Use the funnel per the instuctions until you see the temperature gage stabilize. Make sure to turn on your heat to get water/air past that part of the cooling system as mentioned above.
 
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