When idling with low RPM (like at a stop light, or just warming up in the driveway) the heat blows cold in my '04 FX35, but under normal driving conditions it is nice and hot. I'm wondering what the cause of this could be and what do I need to check.

Same problem!! 2006 M35. Did you get any answers yet? Quick google searches suggest air in the cooling system. My reservoir was low and I topped that off..... no difference.

low coolant can create an air pocket preventing hot coolant flow thru heater core- fill and bleed cooling system if needed.

What is the best way to solve the air pocket problem and bleed the cooling system?

Bleed it a the highest point of the cooling system. Let the car run while you add water/coolant to the radiator neck. Do that until it's full. Cap it off, run it a few minutes.

Elevate the front of the car and repeat the above process. Repeat until complete.

Thanks speedeast.

Your engine has a bleeder plug located in one of the heater hoses. I couldn't open that section of the '04 FSM, but the '04.5 FSM shows the process on page CO-12. You can view that at www.nicoclub.com/FSM/

Heath

Did everything recommended to bleed and get the air out, but the problem still exists. There doesn't seem to be any air in there. Now I'm wondering if something else is causing the problem. Any thoughts or ideas are appreciated.

Live in a cold climate? Is the engine warming up slowly in the morning? Did you go through a hard freeze and not have the correct coolant mix (too much water)? Did the car sit unused for any length of time (weeks, months) or did you have an engine overheat? Any codes? There is a Nissan code that senses problems with the thermostat when the engine warms too slwly.

Maybe the thermostat has failed (they fail open), or a water pump missing a couple of impeller blades that's not pushing coolant through the system unless the rpm is high.

I'm in the Northeast so yes it's cold, but not frigid. I have a remote start in the car so it does warm up slowly in the driveway and there hasn't been a hard freeze. I do drive the car pretty much every day so it hasn't been sitting. The engine hasn't overheated and the check engine light hasn't come on. I haven't read it for any codes because of that. I have heard a whining sound coming from somewhere under the dash or under the hood. It's hard to tell while driving. The noise goes away when I shut off the heat. Sometimes it will start again when I turn the heat back on and sometimes it doesn't. The noise is intermittent, but it seems to be becomming more frequent.

Like to hear what fixed the problem, my 2006 m35 is doing the same thing its like the air conditioning is on when you come to a stop.

Little research, and the answers all point back to our solutions. Here it is with a little more detail quoted from a master technician:

"You have an air pocket in the heater core. Remove the radiator cap, turn the heat temperature control to the hottest setting but keep the blower fan off. It helps to have the front of the car higher than the rear so park on an incline or jack the front of the car up. Run the motor for at least 15 minutes to reach operating temperature. Rev the motor to 2,500 rpm and watch the radiator coolant for air bubbles. It helps to squeeze the upper radiator hose while revving the motor to get the air out. When you think you have all the air pocket removed let the motor idle and check the heater temperature at idle. You can turn the blower fan on to the medium speed to check for output. If it feels better, shut the motor off and look into the radiator neck to observe the coolant. If the coolant pulsates up and down you still have a bit of air in the system. If the coolant stays level, put the cap back on and you should be OK. I always put more coolant in the reservoir, about 2" higher than the max line. When the car cools down it will still draw more coolant from the reservoir. Check the reservoir level the next day before driving and set the level to the max mark."

speedeast wrote: shut the motor off and look into the radiator neck to observe the coolant. If the coolant pulsates up and down you still have a bit of air in the system.

You look confused...

haha sorry my wireless keyboard in the basement died last night while I was browsing so I only had the mouse, and I needed to get a post in this thread so I could remember and come back to it lol, the wtf sign just made the most sence

Im having troubles with an air bubble in my system aswell so Im going to try this method, but it may take alot more idling time since its so cold out??

So the water never boils and gets to hot and wants to gush out when your idling with the cap off??

That part kinda scares me

It'll take a couple extra minutes to get to temperature, but not much. The ambient temperature won't make a huge difference if it's just sitting still.

In most of my experience, it does want to gush out, but that's something that happens because of a little air in the system. Little pockets of air traveling through the water pump cause it to be unstable like that. If your coolant is no greater than 50 percent water, it shouldn't be a huge problem. Water is more affected by change of temperature than say, ethylene glycol. The perfect system has NO AIR. It draws from the bottom of the radiator constantly and dumps into the top without any aeration, etc.

I would definitely recommend gloves either way.

I do think I may have a poor micture, is the method you quoted above a sure shot way to get all of the air out of the system??

I figure theres air in there since when the engine is running the coolant is pulsing up and down, even though I just noticed the car should be off when you check that.

I just want to start the car thats already jacked up, pull the rad cap off, let it idle til it gets up to temp, rev and squeeeze hoses... top her up... hope its air free??

I also dont quite understand how the radiator draws from the resevoir. Why is the resevoir even needed if all the fluid just always stays in the rad?

Well, the block should stay full, the radiator should stay full, and the overflow reservoir is just that, an overflow reservoir. The thing is, the coolant system is pressurized and coolant slightly expands when it's hot. When it cools back off, it will draw coolant from the overflow reservoir. It's just there to provide somewhere for the fluid to go as it expands and contracts through it's cycle.

The methods above will work, but bleeding the coolant system can be annoying. My general rule of thumb for bleeding the coolant system is: when you think you're done, bleed it again.

Bleeding the air out didn't work extremely well. We changed the thermostat the other day and were able to get some air out after that. The thermostat got changed because we didn't think it was working very well. After that was done everything seemed to be working correctly, and the air temperature at idle it better but not 100%. It no longer is cold, but more lukewarm, not hot or cold. Right now I'm driving it while continuing to let everything cyle and I keep checking the coolant level. We're not sure if there's anything else that needs to be done or not.

It still sounds like air; but good luck.

I tried to get the air out by following the tutorial you posted about 5 posts up. Unsuccessful

I let the car cool down, started the car up, popped the cap off and let it idle. For the most pat it seemed as if the coolant was slowly rising, no bubbles at first, just kind of rose up and slowly dripped out of the top of the open rad.

Then after maybe 5 minutes of idling I started to notice some bubbly/foam come up and with some revving and squeezing of the hoses, the coolant level went down a bit, I topped it up a little since I squeezed out maybe 200ml. I kept letting id le, maybe 8-12 minutes into it the coolant inside the neck started going a little crazy, started coming out of the neck again, slowly at first, then it started geting a little "violent" bubbling up and spewing out, I could only bear to watch it do this for about a minute then it started to get progressively higher, tot he point where coolant was coming 2-3" above the rad cap splashing out, mahing a mess. So I stopped the test. Turned the car off.

The car took in maybe 1 liter after I turned it off. But still blew cold air when driving home, so I know it isnt done proper yet.

Im assuming the coolant wasnt supposed to "boil" out the top like it did. My aftermarket gauge said the coolant was only at 125-135 degrees when it started going crazy...

Suggestion? Thank you

There could also be a blown head gasket allowing air to stay in system. But the air in the cooling system can be a pain in the @@@ to get out the best way is to get a funnel and put it in knack of radiator and raise front of car up I have had them as high as the exhaust is touching floor and run engine for a minute at 2 grand with coolant in funnel and then let idle a squeeze hose and do this several times and then leave it raised and let it cool down with funnel in radator with coolant in it after cool down reinstall cap and top of fluid in radator and overflow tank is at max and retry

catperson wrote:When idling with low RPM (like at a stop light, or just warming up in the driveway) the heat blows cold in my '04 FX35, but under normal driving conditions it is nice and hot. I'm wondering what the cause of this could be and what do I need to check.

Question, do you have the setting on heat or defrost. On defrost, the AC kicks in to push dehumified warm air to your windshield. On my 2004 M it will feel cold if the temp is not totally hot as in normal running temp. With all the good advice you have been given so far, none of which seems to have worked, I'd question if the heater core is clogged and your not getting enough coolant circulation through it. Maybe a hose to the heater core is bad, collapsed and blocking circulation. Or, one last idea is your blend door is not completely closing to only allow warm air into the cabin.

No the defroster is not on. It is better, but I still think that we haven't completely gotten the air out of the system. It is blowing warmer at idle, but isn't what I would think is 100%. At least now it's more comfortable and not an urgent issue although I do still think I have to check into it further.

catperson wrote:No the defroster is not on. It is better, but I still think that we haven't completely gotten the air out of the system. It is blowing warmer at idle, but isn't what I would think is 100%. At least now it's more comfortable and not an urgent issue although I do still think I have to check into it further.

Mine is the first Infiniti I have owned so not sure about Infiniti's, but in the 40 some odd years I have owned various makes and models of cars air in the coolant system generally resolves itself. As the one poster said, with the radiator cap off, the air should purge out. Of course with the cap off and no pressure on the system as the car heats up it will throw some coolant out too. One thing you mentioned was the coolant came out frothy. I don't know with out seeing exactly what you mean. Have you looked at your dipstick recently to see if has slimy gunk on it. The reason I ask is one poster did mention head gasket. It is possible for combustion gas to get into the coolant if a head gasket or head is cracked. Often it will also allow coolant to be sucked into the combustion chamber and a white smoke comes out the exhaust. Are you losing coolant or oil. If none of that applies I'd have a compression check done just to be positive. I still question the heater core and/or the blend door. I'm very interested in knowing what you find as the underlying problem.

So coolant spewing out of the neck with the rad cap off and it running is normal if there is air in the system?

Im in the same boat as op, I thought I got all the water out, but I only have good heat when the car is driving, at idle I get cold air.

I will maybe try jacking it WAY up into the air and let it run withe the rad cap off for a while, I would LOOOOOOOOOOVE to get full heat back again

CanuckQx4 wrote:So coolant spewing out of the neck with the rad cap off and it running is normal if there is air in the system?

Im in the same boat as op, I thought I got all the water out, but I only have good heat when the car is driving, at idle I get cold air.

I will maybe try jacking it WAY up into the air and let it run withe the rad cap off for a while, I would LOOOOOOOOOOVE to get full heat back again

The short answer is yes. But it has nothing to do with air in the system. It just allows air to escape. The longer answer is Boyle's Law of tempature, pressure and the boiling point. Coolant not under pressure will expand and come out an open system as it gets close to its boiling point. Put it under pressure, as todays cars do, you decrease the boiling point so the cars can actually run hotter and leaner to meet emissions requirements. Thats why the say never take the cap off when the motor is hot and its what the overflow tank is for. I still think you guys have heater core problems, blend door not closing or circulation of the coolant is too slow for some reason. Good luck....I hope you get your heat back. Let us know.

I dont have a heater core problem, the car was perfect and made perfect heat before my dumb hands got ahold of it. I recently changed my radiator and thermostat, and Ive had this problem since then.

So Im quite sure its just air in the system, but I just cant get it out!! Ive ran the car with the rad cap off, but never to 170+ degrees as I thought to much coolant was coming out of the rad neck. But it did idle for a long time and I revved it and did the test on an incline etc...

Ive yet to jack to car way into the air and do the test. But I was unsure why 1+ liter would spew out of the neck while it was running

I need a way to get that damn air bubble outta there

I fixed it WOO!! maybe this will help the op so I'll say how I fixed it.

Basically I drove the car to the bar tonight, packed my jack and 4 liters of coolant, parked it where there was a curb infront of me, and drove up on it, engine was definitely the highest point, then I even took out my jack and lifted my front tires right off the curb, car was ridiculously high.

Then I left it like that while I went inside for 3 hours, in -10 degree weather. Came back out and started the car up, popped the rad cap off and let it idle for 40 minutes, took forever to get the coolant to 150, once it got to 150 (I have an aftermarket gauge so I watched exact temps) I turned the heat on full blast, and used the throttle body to HOLD the revs at 2000rpm or so, some coolant dumped out, bubbles, plops of coolant, but then all of the sudden, after about 40 seconds of holding it at 2k rpm, the coolant level dropped atleast an inch (I could now see the cooling fins inside). I topped up the coolant, did a few more revs with nothing significant happening anymore. So I threw the cap on.

Started driving home... HEAT!! yay!!!! came to a stoplight a few minutes down the road, heat on full blast... still had heat!! YAY!!!

Coolant problem solved.