# Heater blows cold until the engine is revved up



## Kent in Victoria (Jan 21, 2016)

Hi, on a 2007 Frontier 4l. I have replaced the rad a year ago as I didn't want it to fail and cross contaminate. Since then ona frosty morning I can let the vehicle warm up , gauge at near half way and yet it is still blowing cold air on the defrost. If I get in and rev the engine , it blows very hot air, upon letting it return to idle the temperature drops again unless the engine is revved. Ant anwers suggestions, dealer said coolant is all up and at spec. Have wasted one trip in already and nothing has changed . This occurs from a cold start, Thanks


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## Z_Rated (Apr 29, 2006)

Sounds like maybe air in the system. 
In any case, my '05 Nismo does something similar. Idle = cold, driving = hot.
Z


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## jdg (Aug 27, 2009)

Air in the system, water pump impellers damaged/worn, collapsed/kinked heater core hoses


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## BRubble (Jun 22, 2014)

Kent in Victoria said:


> Hi, on a 2007 Frontier 4l. I have replaced the rad a year ago as I didn't want it to fail and cross contaminate. Since then ona frosty morning I can let the vehicle warm up , gauge at near half way and yet it is still blowing cold air on the defrost. If I get in and rev the engine , it blows very hot air, upon letting it return to idle the temperature drops again unless the engine is revved. Ant anwers suggestions, dealer said coolant is all up and at spec. Have wasted one trip in already and nothing has changed . This occurs from a cold start, Thanks


Well it stand's to reason,, that if this symptom of no heat started right after the Radiator Change, that maybe it has something to do with that install. Did the Nissan Dealer do it, and did you tell Nissan when this started happening?

Did you check the Coolant level in the Radiator; Not the Reservoir,, but the Radiator?


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## smj999smj (Jan 1, 2006)

This is actually a fairly common problem. Sometimes purging the cooling system works. Another problem that sometimes occurs is a weak or faulty heater pump. Attached to a bracket that bolts to the firewall, just on the driver's side of the engine, is a small pump that runs between two heater hoses and has two wires going to it. It is easily mistaken for an electric heater cock, but it is actually a small pump that helps push the coolant through the heater core.


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## smintents (Jan 24, 2016)

This also happens on my 2014 Frontier. Heater motor went at 8k miles, new one installed, and still happening. I agree with what smj is saying and hope that when I take it in, the tech's look at that, otherwise, the 2 bills I spent on the remote start is completely useless.


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## Kent in Victoria (Jan 21, 2016)

Thanks, I have had it into dealer twice and nice to know it may be something beyond an "airlock"


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## BRubble (Jun 22, 2014)

*SMJ Know's His Stuff..*



smj999smj said:


> This is actually a fairly common problem. Sometimes purging the cooling system works. Another problem that sometimes occurs is a weak or faulty heater pump. Attached to a bracket that bolts to the firewall, just on the driver's side of the engine, is a small pump that runs between two heater hoses and has two wires going to it. It is easily mistaken for an electric heater cock, but it is actually a small pump that helps push the coolant through the heater core.


Thanks SMJ,

I learn a lot of thing's by reading your post's. Haveing read through Ton's of Posting's where Owner's were haveing heating problem's,, this is the first time that I've seen anyone posting about the Heater Core Pump.

Never knew that we had one of those thing's. Lot's of change's since the '93 Hardbody that I had.

Found the Heater Core Pump in the Service Manual on Page 35 in the "CO"/Engine Coolant Section for the VQ40DE Engine.

I didn't see the Heater Core Pump in the QR25DE Engine Coolant System Schematic Description, so I guess the Heater Core Pump is only on the V6, is that right?

I bet that little bugger is the culprit in many of the Owner's Posting's haveing Trouble with getting Heat to the Cabin.

Can the Heater Core Pump,, be diagnosed useing a DC Multimeter? If so, do you know how to dianose it. Probably have to remove the Wire's from the Terminal's First?

Thank's SMJ


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## smj999smj (Jan 1, 2006)

The heater pump is used on the trucks/SUV's with the 4.0L-V6 and 5.6L-V8. I would think there's some kind of testing procedure in the service manual. My friend's Titan was having heating problems and after purging it several times without success, I mentioned to him about the heater pump. He went ahead a replaced it and re-purged and has had plenty of heat since. He said his was turning, but he thinks it wasn't spinning fast enough.


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## guivallo (Jan 17, 2015)

So, the heater pump is used on the trucks/SUV's with the 4.0L-V6 and 5.6L-V8.
But no used on the model Altima S 2.6 Correct?
I been trying to resolve this cold air at idle issue on mine, I just think that in deed I may need to replace the heater core.
Thanks in advance.


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