Qx4 Blows COLD Air. Supposed To Be Hot?!

[W O T]

Hey guys,

my qx4 started acting up, I can set my temp to 85* on the knob and have the heat nicely on medium velocity and all of the sudden (seems like after about 20min) the air switches to COLD

All byitself, you can switch it to shoot out different places and everything but it stays cold. Is a sensor going or something?

[bmlawless]

Sounds like it might be going cold as soon as the thermostat opens. Does it blow warm air when you raise the rpm's? Check your coolant level.

[SnowSurfLax]

If your coolant level is fine, then check out the Diagnostic KoukiS14 put up in another thread on here and it'll tell you if you have a sensor on the fritz.

[W O T]

The heat DOES change with rpm! Didnt notice til today cause I havent driven the car, but it blows perfectly good HOT air when your driving or the rpm are passed 2000. But when you idle and crank it to high speed heat, it becomes cold within 10 seconds. Start driving and 10 seconds later you have heat.

Coolant level is absolutely perfect

[Domenico]

check when you are stop and the the car is just at a idle..if the heat comes out on idle or when you give very little gas and not when you are giving more gas it might just be a vacum line..

[bmlawless]

It would have been nice if your coolant level was low. That is the easiest and cheapest fix. Just to double check, make sure you were checking your coolant against the correct line on the overflow tank. There is one for cold and one for hot.

If we don't get lucky on that, there are a couple more diagnostic things that might give us some more info to work with.

1) Is it behaving the same on "Econ" and "Auto"? Econ will not turn on the A/C unit. 2) If you go into manual mode, does the air blow hot if you crank the temp setting up to a really high number?3) Try the diag routine mentioned above. This would help you identify if there is a vacuum leak or sensor acting funny.

There are two more common mechanical things that could cause the issue:1) You could have a failing water pump. When was it replaced? If you are around the 100k mark, it is reasonable that this may be on it's way out.2) You could have air in the system. If this is the case, flushing the system would get rid of it. Another cheap and easy thing to try.

[W O T]

Well I started driving the car again because its bitter cold out and its still doing it!

Only when the car idles, you give it gas and make it idle @ 1500 and it will blow perfectly good heat, come to a stop and within seconds your back to regular cold air. I also noticed you sometimes have to give it a little gas to get it going

You guys think its a vacuum line? Like one not connected to something or one just routed wrong?

Thanks

[AlabamaDan]

There's some kind of mix door that might be messed up.

Sure it isn't low on coolant? Check at the filler neck in front of the plenum and make sure it's full there.

You haven't changed the thermostat have you?

[W O T]

Yeah the overflow tank is FULL, pop the rad cap off, FULL

Havent touched the thermostat since I bought it 5-10k ago, dunno when it was replaced before then

Just kinda odd that it switches to cold air when the cars idling, then goes dead hot in 2 seconds as soon as you hit the gas

[AlabamaDan]

Just kinda odd that it switches to cold air when the cars idling, then goes dead hot in 2 seconds as soon as you hit the gas

That's why we asked you to double check the coolant level. I had that exact problem in my Q45 and it turned out to be low coolant. Now that you're sure it's not coolant, I'm stumped......how about the mix. Is it 50/50 water/anti-freeze?

[timmack]

water pump...its too cold out for the engine to overheat with it pumping a little bit. pump is too weak to flow enough coolant at idle but as soon as you hit the gas, it spins fast enough to do something. think of a fuel pump going out and imagine the total opposite. at idle the pump can flow enough to keep the car running but when you hit the gas, the pump is too weak to fulfill the demand.

[Buzzman]

I saw this problem once before on a Buick Regal a few years ago.Turned out to be the heater core was partially blocked.At idle, the water pump doesn't have enough oomph to push the coolant through the core, but as soon as you rev the engine, coolant starts to flow, and you get heat. The other thing to check would be the hoses to and from the heater core. One of them may be partially collapsed.

Another thing just popped to mind. I haven't checked my truck, so I don't know if this even applies to our vehicles, but on some cars, there is a valve on the heater core inlet hose that opens and closes and prevents coolant from running through the core. This is only supposed to operate when you have the air conditioning on. What it does is it prevents any unnecessary heat from entering the car, thus making the A/C more efficient. If our trucks have such a system, you may want to have it checked out.Good luck.

[W O T]

I REALLY love doing everything myself, but I dont think Id wanna tackle a waterpump on this car.... but how do I determine if its the water pump?

Could it really be a clogged heater core?

Im new to this whole maintenance thing, would love some advice (im broke)

[Buzzman]

Too bad it's not summer cause you could work on it outside. Having said that, what I've done (years ago, and not on my truck), was lower the coolant level, disconnect the two hoses going to and from the heater, and then shooting water through the core from my garden hose, flushing it out. I suggest you flush it out backwards as well. In other words, run the water from the garden hose in both directions. If it's blocked, it won't take you long to notice.

[bmlawless]

Hate to say it, but it sounds like a water pump. They usually leak when they are going bad. If you are not seeing a coolant leak, that makes it harder to diagnose.

[02pathy]

i would like to know what it says on the temp display when it goes cold, i am not too sure on what to think, i can picture the temp dropping if it is on auto but if u manually set to 85, does it go back on its own or does it stay at 85 and blow cold air. just wondering if its mechanical or electrical, but i can see how the water pump and heater core makes sense. look for any signs of deposits of sediment in the coolant with the cap of coolant should be a nice dark green, not no yellwish or whiteish or brownish business

[W O T]

Ya the coolant is absolutely perfect looking, perfect green right up to the top

What do you mean temp display (gauge cluster or heater display), because I just keep it on manual 85 degrees and the needle on the gauge cluster just stays right at 1/2 way

[bmlawless]

How many miles are on your rig?

In my opinion, it would be worth doing a flush and fill of the cooling system before going all out and replacing a water pump. A bubble in the system is unlikely, but still possible. Your owner's manual has detailed instructions about how to do it. Make sure you follow the guide since there are vent caps at the top of the engine that need to be opened to et the system fill without getting air in the system.

Around here, the tires shop that do oil changes and minor repairs (like Goodyear and Firestone) charge around $60 to do it.

[W O T]

I got 90,000 on the qx4

I could probably handle a flush on my own, Im rpetty good with cars, just these new ones (im used to older race cars) are so ****ing crammed in the engine bays and theres electronics for eveything! and Im in canada so -15 degrees aint fun.

What I dont get, is even if it was my water pump, which makes sence with the not pumping alot of coolant at idle. Is that WHY does it change to cold air within 2 seconds of me dropping the engines rpm, like it doesnt have any built up or anything, just runs instantly out of heat. And when you touch the gas, its hot right away

I also did a test on my way home from work, cruising @ 2000rpm with the heat coming out the front, I can floor it 3500+ rpm and it gets HOTTER, noticabley hotter

[bmlawless]

You bring up a good point. Just because warm coolant has stopped circulating through the heater core doesn't mean it should go ice cold instantly. May be we should go back to looking at possible vaccuum issues.

Did you ever run the diags procedure?

[SnowSurfLax]

I saw this problem once before on a Buick Regal a few years ago.Turned out to be the heater core was partially blocked.At idle, the water pump doesn't have enough oomph to push the coolant through the core, but as soon as you rev the engine, coolant starts to flow, and you get heat. The other thing to check would be the hoses to and from the heater core. One of them may be partially collapsed.

Another thing just popped to mind. I haven't checked my truck, so I don't know if this even applies to our vehicles, but on some cars, there is a valve on the heater core inlet hose that opens and closes and prevents coolant from running through the core. This is only supposed to operate when you have the air conditioning on. What it does is it prevents any unnecessary heat from entering the car, thus making the A/C more efficient. If our trucks have such a system, you may want to have it checked out.Good luck.

Y'know, after looking at the FSM, this is quite a curious problem for this guy. It might be as you said, that there is a valve that turns off the flow to the heater core. Looking at the flow diagram, you shouldn't lose any heat when at idle as it flows to the heater core before the thermostat opens. But, if there is a valve on the heater core and the water pump was going out out, it might not have enough oomph to push past the valve on the heater core. Or conversely, the water pump is fine and the heater core valve is malfunctioning and shuts off ot low pressure and then the water pump pushes it past the valve.

He could check this by running the AC at idel and seeing what he gets when he revs the engine up. If you get hor air when running the AC and revving the engine, then it's probablythe heater core.