Minivan heater blows cold air, HALP!!!

Here’s the situation- 

2004 Nissan Quest, runs and drives normally, no issues with overheating, but the heater blows cold air at idle, or anything below 2500 rpm. No noted coolant leaks, and the coolant level is not dropping, so it’s unlikely I’m losing coolant. The internet says these had a bad habit of trapping air in the heater core, which sounds like it may be the culprit. 

Question is this- do any of you fine individuals have any tips, tricks, or ideas on getting the air out of the heater core? I’m at a loss, and Mrs Recon is tired of freezing...

Not Nissan specific, but sometimes it helps to lift the front when trying to burp the air.  Do you have a coolant funnel?  They are very useful in getting the water level higher than the engine.  On tough air pockets I like to let them cool all the way back down with the funnel on.

that or clogged heater core. might be able to flush it 

No heat at all means there is a lot of air in the system.  Jack the front up, top off, tighten the rad cap the first click and hold the RPM at 2500 for a few minutes.  Remove cap, top off, repeat.

Feel the hoses going through the firewall to the heater core.  If they're both hot but no heat in the cabin then you have a blend door stuck closed.  

If one is hot and one is cold, you have insufficient (or no) flow through the heater core.

Sitting at idle, if I rev to 2500-3000 rpm, the heater will start blowing warm air instantly. Drop it back down to idle, and the air will stay warm for a bit, then cool back down. 

Is your temperature  blend door actuator vacuum controlled? I’d look there. Sounds like the actuator maybe bad, or the line going to it may have a leak. Maybe even a leaky check valve in that line. 

Doesn't sound like a cooling system related problem, especially if it just started happening randomly.

So how did that air suddenly get into a closed system ?

 Feel the heater coolant lines at the fire wall.   Both should be hot/warm.  If not the heater core is plugged.  Or if there is a water coolant control valve.

if both lines show heat then it is most likely a blend door problem.

 Agree with what Saron 81 said.

I have to say that I have never run into air in the coolant system problem. Not saying it doesn't happen.  

In reply to Recon1342 :

Now that could be a circulation problem.   Is the coolant 14 years old?    Maybe the system needs a flush.

You can disconnect the heater core at the firewall and back flush it into a clean bucket with a water hose, just to see if water flows freely and what comes out.

Recon1342 said:

Sitting at idle, if I rev to 2500-3000 rpm, the heater will start blowing warm air instantly. Drop it back down to idle, and the air will stay warm for a bit, then cool back down. 

I had this exact thing happen in my 2003 Sienna minivan. It was over a year ago so I'm guessing it happened when I needed to take the coolant cap off to check something (I don't remember what) when the system was hot. coolant spewed everywhere and I got the cap back on quickly. right after that the heater system started acting this way. It took me about a week to figure out that on this particular van I could take the cap off when the system was cold and add coolant then squeeze the hoses to move the air bubbles around and finally out of the coolant add hole where the cap goes. eveytime a bubble came out I added more coolant to where I could see it in the hole and squeezed hoses again. after about 15 minutes I had them out, put the cap back on and took it for a test drive, a warm comfy test drive.

Your symptom is exactly what happens when you have low coolant and a heater core as the highest point in the system. Air bubble. 

I looked at AllData and the factory fill procedure involves use of a tool you don't have and that cost $50-100. 

But there is this pic:

And it looks to me like hose #4 (the upper one) has a  T fitting looking thing that is probably a removable cap for purging air from the system, and if that doesn't work  you could disconnect hose #4 at the top and pour coolant into that with a small funnel until it's full. If you try to use the removable cap T fitting thing keep in mind it's old brittle plastic and somewhat likely to break in the process of you getting the cap out. Also, i would do this when the vehicle is cold and you have a helper revving the engine up to 1500-2500.

Vigo said:

Your symptom is exactly what happens when you have low coolant and a heater core as the highest point in the system. Air bubble. 

I looked at AllData and the factory fill procedure involves use of a tool you don't have and that cost $50-100. 

 

But there is this pic:

And it looks to me like hose #4 (the upper one) has a  T fitting looking thing that is probably a removable cap for purging air from the system, and if that doesn't work  you could disconnect hose #4 at the top and pour coolant into that with a small funnel until it's full. If you try to use the removable cap T fitting thing keep in mind it's old brittle plastic and somewhat likely to break in the process of you getting the cap out. Also, i would do this when the vehicle is cold and you have a helper revving the engine up to 1500-2500.

Just an FYI, the picture you linked to keeps changing.

As an aside, I know that on the older maximas it was common practice to raise the front end up quite a bit in order to get the radiator filler cap higher than the heater core in order to purge the air bubbles from the system.

If air in the system isn't found, then possibly the vanes on your water pump are worn off from debris and you need a new pump.

Is HALP another of those insider codes?

Just an FYI, the picture you linked to keeps changing. 

I knew there was a catch.. 

Anyway, it's the hose coming out of the heater core that goes up. Follow it to a point where you can purge air or introduce coolant.  

Same problem with my daughters Niaasan Altima.  Jacked it up in front and let it burp with the cap off, occasionally reving it to 1500 rpm, and holding it for a little bit.      Got some heat, but not the best at idle.  Nice and warm when moving though.  Told her not to worry, the AC is great, and warm weather is coming.  I guess my wife taught her that LOOK, that I caught.

I use an airlift system on difficult cars. It draws a vacuum on the system then that vacuum pulls the coolant in. You can check they system for leaks before you put a drop in. 

Similar to this one

https://www.amazon.com/OEMTOOLS-27066-Cooling-System-Refiller/dp/B01GSQA5BI/ref=sr_1_4?ie=UTF8&qid=1519683877&sr=8-4&keywords=airlift+coolant

It is the only way I can get the air out of old Fiat 124s or even my e28.

In reply to Jumper K Balls :

Link is broken. 

I like the the idea of drawing vacuum to pull coolant in...

But how would air get into the system? I’d buy that as the problem if you just did cooling system work, but not out of the blue. 

I still think you’ve got a blend door problem.

Have you checked the thermostat function yet?  Typically when these fail, the car will not heat up.

In reply to devina :

T-stat is fine, car will warm up and heat above idle. 

I had the alternator replaced about 4 months ago, which calls for the removal of the radiator...

link fixed

Saron81 said:

But how would air get into the system? I’d buy that as the problem if you just did cooling system work, but not out of the blue. 

I still think you’ve got a blend door problem.

old radiator cap, evaporation of old coolant.  Air could have gotten in over time and just recently was it noticed, but the radiator replacement mentioned after this post sounds like a likely culprit 

In reply to Brian :

Alternator was replaced, radiator gets removed for that job. 

Got the van back from the shop for control arms and alignment work, and it’s been heating just fine. I’m definitely puzzled...

Recon1342 said:

In reply to Brian :

Alternator was replaced, radiator gets removed for that job. 

 

Got the van back from the shop for control arms and alignment work, and it’s been heating just fine. I’m definitely puzzled...

maybe they left it running and had the front end up higher when doing some work?  :gotme:

BTW, if they removed the radiator to do the alternator, I hope they replaced it (put it back) :p