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I have a 2006 fronty with the v6. Its been a little cool in the mornings here in boston so I've been putting the heat on. The trucks heater only works if it is being driven. Once i stop it will blow cold air. In the winter if I tried to warm it up by idling it would just blow cold air. Does this sound like a bad thermostat. I tried topping off the radiator fluid but it didn't solve the problem. Thanks, Chris
 

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Usually, if the thermostat is stuck open, you get LESS heat while driving than while stationary, due to more cold air being forced through the radiator while driving.

If the thermostat is stuck closed, the engine overheats.

Your problem sounds more like low coolant level - i.e., the water pump is moving a lot of air mixed with the coolant.
 
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x2 on checking the coolant level.
 

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Im with the last two, low coolant. Top up the rad AND the coolant reservoir is at the proper level. When you remove the caps make sure the rad cap goes back on the rad.
 

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Exact same thing was happening to me over the winter. Make sure the radiator is full and recap it. Then remove the coolant reservoir cap (next to the windshield washer fluid fill cap). Overfill the reservoir and leave it overnight. Check the level in the morning and go from there.

There are some threads on this.
 

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There are threads, but sometimes hard to find.

One thing to make sure you understand is the coolant level is checked on the reservoir with the engine cold and running. With the engine off, the level looks correct, but it is actually low.

Fill the coolant to the proper level with the engine running and either put the truck up on ramps or go park on a steep hill and run the engine with the heat on. You might need to repeat this process a second time.
 

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I have been thru this "no heat at idle" on two different Gen 2 Frontiers.
The first time I think it was my fault I opened the cap on the radiator to check the fluid level , which I am guessing created air pockets in the cooling system.
Second time I am assuming the dealer I purchased the "used" truck from (Not a Nissan Dealer) did the same as above.
Here is a thread on thenewx.org
How-to: Correct and More Problems if Heater Blows Cold at Idle or No Heat - Second Generation Nissan Xterra Forums (2005+)
I also recall squeezing the lower radiator hose with the radiator cap off to help burp the air as well as parking on a hill.
On both trucks it took at least two attempts to get all the air out.
I also recall reading that just over filling the reservoir and driving your truck around may fix it as well.
 
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Also agree with low coolant - but why is coolant low? Keep eye out for leaks/seepage.
 

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This seems to be common on a lot of the 2005 and later Nissan trucks. When coolant level isn't low, it is usually air in the system or a bad "heater pump." The heater pump attaches to a bracket off of the firewall and mounts inline of the heater hose. There are two wires going to it. It is essentially a small, electric water pump used to help circulate the coolant through the heater core. Many people see it and assume it's an electric heater ****, used to stop the flow through the heater core, but it is not. Before replacing one, though, try purging the system.
I've had to drain coolant from these engines a number of times and I've never had any heat issues (or lack of heat) develop afterwards. I start by removing the radiator cap and the reservoir cap and setting the heat to full hot (if it's an R51 with rear heat, I'll set the rear heater to full heat, as well). I fill the radiator with coolant and install the radiator cap. I add coolant to the reservoir to the "MAX" line. I jack up the front of the vehicle as high as safely possible (if you work outside, you could park on a hill with the nose pointed uphill). I start the engine and use an adjustable hood prop rod between the seat cushion and the gas pedal and fix it to run at approximately 3000 RPM. I let the engine run about 10-15 minutes or until hot air is coming out of the vents. Then, I remove the rod, shut off the engine, lower the front end if jacked up and after it cools for awhile, top off the system. If the heater starts blowing cold air again, repeat the process (I've never had to repeat). It there still is lack of heat issues and the mode doors are working properly and the coolant is reaching proper temperature, then I would replace the heater pump.
 

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I just bought my 2012 a couple weeks ago and am encountering the same issue of the truck blowing cold air when not moving. I will top off the coolant with Prestone 50/50 and hopefully all will be well.
 

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I too have a 2006 (nismo) with this issue.

It happened once before and it was coolant level so I refilled it and started getting hot air again, but that was about 6 months ago.

Last week it just started blowing cold air again. I just added some more coolant this evening so I'll check it tomorrow after a drive, but any idea why this would keep happening aside from a coolant leak, which I expect I would notice.
 

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This seems to be common on a lot of the 2005 and later Nissan trucks. When coolant level isn't low, it is usually air in the system or a bad "heater pump." The heater pump attaches to a bracket off of the firewall and mounts inline of the heater hose. There are two wires going to it. It is essentially a small, electric water pump used to help circulate the coolant through the heater core. Many people see it and assume it's an electric heater ****, used to stop the flow through the heater core, but it is not. Before replacing one, though, try purging the system.
I've had to drain coolant from these engines a number of times and I've never had any heat issues (or lack of heat) develop afterwards. I start by removing the radiator cap and the reservoir cap and setting the heat to full hot (if it's an R51 with rear heat, I'll set the rear heater to full heat, as well). I fill the radiator with coolant and install the radiator cap. I add coolant to the reservoir to the "MAX" line. I jack up the front of the vehicle as high as safely possible (if you work outside, you could park on a hill with the nose pointed uphill). I start the engine and use an adjustable hood prop rod between the seat cushion and the gas pedal and fix it to run at approximately 3000 RPM. I let the engine run about 10-15 minutes or until hot air is coming out of the vents. Then, I remove the rod, shut off the engine, lower the front end if jacked up and after it cools for awhile, top off the system. If the heater starts blowing cold air again, repeat the process (I've never had to repeat). It there still is lack of heat issues and the mode doors are working properly and the coolant is reaching proper temperature, then I would replace the heater pump.
Just wanted to say thanks for the info.
I bought a 2019 Frontier brand new and have this problem. (4 liter V6)
In Colorado it's not too bad of a problem, in North Dakota, big problem.
Thought it had everything to do with the aluminum block engine.
I'm thinking 7 inch high car ramps should be high enough upward tilt.
Could go high with a few 2x4s. LOL
 

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I had recurrent low coolant and air pockets on my '13 V6. I never found an external leak. I checked the motor oil for water, I checked the exhaust for water, i checked the water for exhaust gas and never found anything. Then like a few others I replaced both caps even though they "looked good", filled it and purged the air one last time and I have not seen the problem occur again since then. Even the guy at the parts counter at the Nissan dealership asked me to confirm that I was actually buying two radiator caps -- they look the same but they are not.
 

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The caps are not alike, the one on the radiator just has a rubber seal and the one on the plastic tank is spring loaded. Fill the plastic tank about two inches over the seam and take a drive, the coolant will get drawn into the engine.

Clint
 

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Just wanted to say thanks for the info.
I bought a 2019 Frontier brand new and have this problem. (4 liter V6)
In Colorado it's not too bad of a problem, in North Dakota, big problem.
Thought it had everything to do with the aluminum block engine.
I'm thinking 7 inch high car ramps should be high enough upward tilt.
Could go high with a few 2x4s. LOL
This works very well as another way to fill it up.
Lisle 24780 Spill Free Funnel with Standard/GM/VW/Ford Adapters https://www.amazon.com/dp/B089T73TGJ/ref=cm_sw_r_cp_api_glt_fabc_RPVDAA8ASTP06WN97YDZ

Clint[/QUOTE]
 

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Alright so I have a question an need some help with. My 2017.5 Nissan Frontier SV 4.0 anytime I turn on my AC an go from cold to hot air on cool mornings, heater does nothing but blow cold air. If I park front end up hill an let run for a bit it will finally kick back in an hot air will work perfect until thermostat setting is turned back to cold, the does it all over again. So guess I'm getting an air pocket every single time I go from cold to hot. Guy a dealership told me something about a design flaw, said radiator sits just a little to low an that is reason it constantly develops air pocket.. Not real sure what I can do but maybe look at maybe lifting radiator up a little higher. So question is anyone else ever heard of this, or got any idea what I might be able to do to fix? So get easy stuff out way no it does not over heat, no leaking fluid, blower works fine, blend door work fine, whole system works fine, except for the fact it literally acts like an air pocket every single time going from AC to heat. Crazy.. thanks for help
 

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Alright so I have a question an need some help with. My 2017.5 Nissan Frontier SV 4.0 anytime I turn on my AC an go from cold to hot air on cool mornings, heater does nothing but blow cold air. If I park front end up hill an let run for a bit it will finally kick back in an hot air will work perfect until thermostat setting is turned back to cold, the does it all over again. So guess I'm getting an air pocket every single time I go from cold to hot. Guy a dealership told me something about a design flaw, said radiator sits just a little to low an that is reason it constantly develops air pocket.. Not real sure what I can do but maybe look at maybe lifting radiator up a little higher. So question is anyone else ever heard of this, or got any idea what I might be able to do to fix? So get easy stuff out way no it does not over heat, no leaking fluid, blower works fine, blend door work fine, whole system works fine, except for the fact it literally acts like an air pocket every single time going from AC to heat. Crazy.. thanks for help
Parking on a hill only eliminates the air pocket if you’re adding coolant, adding nothing won’t give you heat. Maybe your blend door is getting stuck or the actuator isn’t moving in it’s full range. For me adding coolant always took care of lack of heat. I kept the bottle level at the seam in the plastic. Leave the radiator location alone, you just create more headaches.
Sadly most dealership employees make things up on the spot or repeat things they heard. Ask to see it in writing from a tech book before you believe it.

Clint
 

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Parking on a hill only eliminates the air pocket if you’re adding coolant, adding nothing won’t give you heat. Maybe your blend door is getting stuck or the actuator isn’t moving in it’s full range. For me adding coolant always took care of lack of heat. I kept the bottle level at the seam in the plastic. Leave the radiator location alone, you just create more headaches.
Sadly most dealership employees make things up on the spot or repeat things they heard. Ask to see it in writing from a tech book before you believe it.

Clint
Well my coolant level has always been full, anytime I lose heat I check to be sure an so far have not added any. An I thought about the blend door, but didn't really seem like it could just come unstuck after so long. Something I noticed this morning though my temp guage had a little fluctuations to it. Went up a little higher than normal the dropped right back down. Did it a couple of times. An here lately I have notice my cooling fan constantly running.. makes me wonder we if I have bigger problems I'm not aware of yet. Thank u for the input, an appreciate any other help or advise provided.
 

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With the truck off can you easily spin the fan or is there significant resistance? The constantly running fan can be a bad fan clutch but not part of this issue.
Fill the plastic bottle a couple of inches above the seam and see if that gets pulled into the system. If it doesn’t go down a turkey baster is cheap and can remove excess fluid.

Clint
 
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