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Our 2005 Armada just turned over 72,000 miles. While on vacation the temperature gauge suddenly shot up while my wife was stopped with the engine running. It then did it again. We put in a new thermostat thinking that was the issue. Well once again the temperature gauge went up on me this time while stopped. It went almost to the mark before hot. As soon as I started moving it came back down.

We then took it to the local Nissan Dealership who found some air pockets when they bled it. We also had them replace both the overflow and radiator caps as the upper hose was getting sucked down when the engine cooled.

Since that we've driven it a few weeks and put over a thousand miles on it with no issues until this week. While in line at a drive through, the gauge once again went up to almost the line before the hot mark. This lasted 10-15 seconds according to my wife. As soon as she started moving in the drive through line it went right back down to the normal range. She said it did it again on the way home at a stop light for about ten seconds.

This morning I sprayed out the condenser and radiator from the front and back with a hose and it seemed clear. My code reader shows no faults. I tried the newspaper test on the fan clutch and also revved it and that seems fine. I am not losing any radiator fluid. I am not getting any bubbles in the overflow. The secondary fan comes on when it's supposed too. The oil looks fine too

After all these checks I drove it for twenty minutes and then let it idle in drive for another 10 minutes. The needle stayed below half the whole time. I put my heat gun on the upper radiater hose and the overflow. Both were right at 195 F. The lower hose was at 188F. The radiator cap at 164F. All seems normal.

Any ideas? Could it be the sending unit? I not sure if it's buffered or not but the gauge goes from normal to hot in a matter of ten seconds. As I mentioned before we've driven it well over a 100 miles with numerous stops with no gauge issues and I can't seem to duplicate it. Oh the dealership kept it for 2 days and that was all they found. Is there any way to test the sending unit if you think that might be it?
 

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I'd wonder if the Water Pump Impellor is intermittantly slipping if it is a plastic impellor on metal shaft type. I've seen that happen on other vehicles. I have a new water pump for my Titan, but it is all metal iirc.
 

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Anything is possible but usually the water pump will leak coolant or the shaft can be moved. Neither is occuring. I'm starting to think/hope it could be the coolant temperature sending unit on the drivers side front head . However, it's next to impossible to get an ohm meter hooked up to it unless I can get a open wrench on it and unscrew it to test it off the engine.
 

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Start saving up for a new radiator. I know you put your heat gun on it, but the problem will not be shown with the heat gun. You are experiencing the beginning stages of a flow problem within the radiator, it will continue to get worse especially with the AC on. I had the same issues as you stated, changed the radiator and problem went away.
 

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What brand/type did you replace it with? I've read some have used a Koyo brand. Did you have the same symptoms? Does the radiator plug up internally?
 

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How does it run? Does it lose power when the temperature gauge goes up? Normally when a car overheats it starts to pull timing and the engine will lose power. I would try changing the coolant temp sensor.
 

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No it doesn't lose power. In fact when you start moving the temperature gauge goes right back down as quickly as it went up. Just a few seconds.
 

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These trucks have no issues with the temp sensor. The fan clutch is working fine, when the radiator starts to fail which is happening here, the fan clutch will act like it is not pulling air, it is but very slightly, the reason being is that it engages when the temp on the radiator goes up, the problem is that the radiator is not flowing properly so there are different temps on the cores of the radiator which causes the fan clutch not to properly pickup the correct temp and not engage fully. The reason the temp goes down when the truck is moving, or you give it gas, is cause the flow is increased. Trust me, it is your radiator, look into a Stillen unit or the Koyo brand. If it were your water pump, you would see it leaking from the pump itself, if it were the thermostat it would be overheating all the time, if it were the fan clutch, it would be overheating all the time, whether you gave it gas or not.
 

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Good luck, if there is anything else you need feel free to ask. How much did the Koyo radiator run you?
 

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Off ebay it cost $188.00 including shipping. Not bad as Oreilly, Autozone and Advance Auto want $275.00 plus tax for their brands.
 

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Real good deal there. The removal and installation is pretty simple, the hardest part is removing the fan, 4 8mm nuts, using a ratchet wrench helps with that. When removing the old radiator, having a set of spare hands helps to hold the tranny cooler and condenser to pull out the radiator.
 

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Thanks, I hear you on the extra hands. Have had to change out a couple radiators on my kids cars in the past. Will see if they step up to help now!
 

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Our 2005 Armada just turned over 72,000 miles. While on vacation the temperature gauge suddenly shot up while my wife was stopped with the engine running. It then did it again. We put in a new thermostat thinking that was the issue. Well once again the temperature gauge went up on me this time while stopped. It went almost to the mark before hot. As soon as I started moving it came back down.

We then took it to the local Nissan Dealership who found some air pockets when they bled it. We also had them replace both the overflow and radiator caps as the upper hose was getting sucked down when the engine cooled.

Since that we've driven it a few weeks and put over a thousand miles on it with no issues until this week. While in line at a drive through, the gauge once again went up to almost the line before the hot mark. This lasted 10-15 seconds according to my wife. As soon as she started moving in the drive through line it went right back down to the normal range. She said it did it again on the way home at a stop light for about ten seconds.

This morning I sprayed out the condenser and radiator from the front and back with a hose and it seemed clear. My code reader shows no faults. I tried the newspaper test on the fan clutch and also revved it and that seems fine. I am not losing any radiator fluid. I am not getting any bubbles in the overflow. The secondary fan comes on when it's supposed too. The oil looks fine too

After all these checks I drove it for twenty minutes and then let it idle in drive for another 10 minutes. The needle stayed below half the whole time. I put my heat gun on the upper radiater hose and the overflow. Both were right at 195 F. The lower hose was at 188F. The radiator cap at 164F. All seems normal.

Any ideas? Could it be the sending unit? I not sure if it's buffered or not but the gauge goes from normal to hot in a matter of ten seconds. As I mentioned before we've driven it well over a 100 miles with numerous stops with no gauge issues and I can't seem to duplicate it. Oh the dealership kept it for 2 days and that was all they found. Is there any way to test the sending unit if you think that might be it?
Wow I'm having the same problem when it's like raining it wont do it but when the humidity rises the temperature gauge goes crazy but doesn't do it st night time I've changed thermostat, fan, clutch water pump. And I still have same problem. If I'm on the highway it will go up and down for a few min then stop.man this is crazy
 
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