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Heater blows cold during idle

Heater blows cold while in idle but hot while running. I’ve read about air in the cooling system as a common cause for Nissan Frontiers (and Titans). It has a pressurized coolant reserve tank and no bleeder valve. Is there a good way to bleed the system of air?

I’ve squeezed the upper coolant line and release one air bubble, but it did not fully fix the issue. Any directions would be helpful!

2012 Nissan Frontier SE. Coolant system drained and filled 6 months ago.

drive the front end up on ramps,open the radiator cap, fill the radiator and let it sit and the air will migrate up to the radiator and escape from the open cap. you might need to run the engine to circulate the water if it takes too long for the air to escape.

I had a '98 with a bleeder screw next to the thermostat housing. If yours doesn’t have one and parker’s method doesn’t work, you could loosen the thermostat housing until antifreeze runs out.

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The 2.5L QR25DE engine requires a special tool to refill the cooling system to effect an air bleed from what I can see. Tool number KV-991J0070. Involves using a compressed air powered venturi gadget attached to the top of the radiator. It’s not a simple procedure.

Based on that, its doubtful you’ll be able to solve this problem using typical diy’er methods. Probably best to have a shop with that tool do the job for you. You could try the method suggested above, get the front end of the vehicle high up in the air and run the engine until the thermostat opens with the radiator cap off, making sure the heater control is on max coolant flow to the heat exchanger. Might work.

Start the engine and let it idle until it comes up to operating temperature.

Loosen the upper radiator hose clamp and slip a small flat bladed screwdriver in between the radiator hose and the hose neck on the radiator.

Allow the engine to idle until all the air is purged from the cooling system, and nothing but coolant comes out.

Remove the screwdriver, and reinstall the hose clamp.


Heater blows cold while in idle but hot while running.

How cold? In my experience most vehicles blow much warmer air while under load. While trying to keep warm while parked and idling, I’ve many times resorted to applying the parking brake and putting the gear selector in Drive. If it’s a manual trans then beats me.

Interesting. I’ve never noticed that effect on any of my vehicles. The heater on my cars seems to blow the same amount of heat irrespective of vehicle speed, once the engine is warmed up of course. It seems like that has to be the case b/c from glancing at the dash gauge the thermostat keeps the coolant temperature in a quite narrow range.

Interesting. I’ve never noticed that effect on any of my vehicles.

I probably wouldn’t have either if not for my former job involving sometimes warming myself up in idling vehicles in frigid temps. On really cold days/nights, they all tended to lose coolant temp idling under zero load with the fan blowing on the heater core.

Thanks. I bled the coolant system as much as possible, was able to get some air out and top off the system. It warms up quick and stays at a steady temp, but heat still blows cool (maybe a little better…). It blows at about 70 degrees at idle (an can melt your face off while driving). I hunt and use the truck to warm up on cold winter mornings without driving. This happened with my 2008 frontier also, but I never sought to fix it.

Any other ideas? If not, I’ll plan on taking it in to my repair guy to test the heater core.

As I explained above, it’s probably normal.

It could be the case that the heater core is partially plugged up. My dad had a 1960 Rambler years ago with exactly the same problem–hardly any heat at idle. Flushing the heater core solved the problem.

Just left the dealer. Air in the coolant system. SanJose was right, diyer wasn’t enough. Dealer treated me well and heater works well. Thanks guys

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Glad to hear you got it solved. Good for you for not giving up!

Some of you think it’s normal? It seems new to me. Chev Uplander. 180,000 kms.
I filled the overflow bottle, just to be sure. Gauge says temperature is normal.
It cools down to luke-warm while idling. When I press the gas or motor under strain, the temperature is full hot.
I don’t want to lose this vehicle. I don’t want to spend any more than I have to. Garages get greedy changing parts and never solving issues.
Water pump? Thermostat? Flush the heater core? One thread discussed head gaskets.
Could get expensive. But if I ignore it?

Sideshot, had an ac that only blew cool at highway speed, turned out the fan resistor was blown out. Check to make sure the fan is running. $18 diy fix.