By on February 20, 2012


TTAC commentator kericf writes:


I have been a previous emailer with some questions about my Rodeo.  Now I turn to you in need of help with my wife’s 2005 Nissan Pathfinder (115k miles).  The HVAC system doesn’t emit heat properly.  A google search of the problem reveals I am certainly NOT the only person dealing with this problem.

We bought the car used about 4 years ago with 40k on the clock.  It is the SE model with the rear ventilation and Auto Climate control.  Since the beginning we have had small issues here and there.  At first the passenger side blend motor went out.  I located a service bulletin related to it online and made the repair myself.  Then the blower motor stopped working.  The blower motor resistor pack went bad (aparently a running problem of Pathfinders past and present).  Easy fix, almost like Nissan expected it to go bad as it was right there in the open under the dash.  In fact, most everything I have had to fix on the car has a flap or panel that was right in front of the part that went bad.  Like they almost know what you will have to replace and make a convenient way for you to do it.  The most difficult maintenance I’ve had to do involved changing spark plugs, which you had to remove the intake manifold to do.

A month or so ago we noticed that the heater wasn’t working properly.  It would blow heat for a few seconds but then the air would get cool if the fan was set on anything other than low.  On low you could feel very hot air coming out, but as soon as you turn the fan up it dissipated.  Usually the heater is very powerful, but living in Houston we don’t use it that often so I’m not sure when the problem started exactly.  The car also began to run very cool.  It never had heated to normal, but now it was running about a quarter on the temp gage.

From online forums I have found fixes ranging from air in the cooling system, bad thermostats, to messed up radiators leaking coolant into the transmission cooling coils, to heater core failures or leaks.  Many of the forums recommend just trying to purge all the air out of the system.  Since the car was running so cool I went with bad thermostat and replaced it and flushed and changed the coolant.  I let the car run with the front end elevated about 30 minutes to purge air out of the system.  Some forums suggested you have to vary the throttle for about 30 mintues to really purge it though because there is a flow issue before the heater core where air tends to get trapped.  I just let it idle for 30 minutes.  The temp is now running closer to normal but the HVAC system still isn’t blowing hot air.  Before I spend a lot of time and money trying to figure out where the problem is I figured I would give the B&B a shot.  I don’t think I have a bad radiator because I’m not experiencing transmission problems that should be a result of gunked tranny fluid and I didn’t notice any discoloration on the flushed coolant to indicate transmission fluid was mixing.

Any help is greatly appreciated.  I hope you get more emails from readers because the Piston Slap columns are some of my favorites.

Sajeev answers:

Great question, well thought out and explained.  And even though you live in Houston and have a heating concern, this leaves very little room for TTAC-branded snark! I use my heater on a regular basis, as cool weather and 100% humidity is like taking a cold shower the moment you walk outside!

It’s hard to know for sure, but I see two potential problems.

Not very likely: bad heater core.  It could be clogged to the point where no coolant enters the core, and one way to know for sure is to feel the inlet hose temperature relative to the outlet hose temperature. With gloves or something else that keeps you from burning your skin, son!  That said, both hoses should have about the same temperature, if the outlet hose is significantly cooler, you found your problem.

More likely: you didn’t bleed the system properly. This is where I should snark!  I cruised the forums and I see several methods to bleed the system, and what you did won’t cut it.  Often there is another vent hole, hose to pinch, etc and only the factory service instructions will help here. I don’t see a conclusive answer, but no matter what, I see alternatives you haven’t performed. And sometimes all I need to do is cast enough doubt in your mind to make you reconsider your position.

Bonus! A Piston Slap Nugget of Wisdom:

Maybe this goes without saying, but always run your heater when bleeding the cooling system, otherwise the air will get caught in the heater core! And there it is.


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14 Comments on “Piston Slap: A Lack of H-Town Heating...”

  • avatar

    One thing to note if your thermostat is indeed bad is when the engine is in idle and its cold, it’ll fluctuate up and down, at least it has for my older Ranger truck and the Honda Accord when their thermostats went bad, now they WERE from the OBD I era so can’t say if modern OBD II vehicles will still do this, but something to keep in mind.

    As for Sajeev’s nuggets of wisdom, running the heat while bleeding the system makes total sense for any car.

  • avatar

    There should be a factory method for bleeding the system. Our Odyssey also has a rear heater and the procedure for bleeding the cooling system is about 1/2 hour of work and involved running the system on full heat and full cool.

  • avatar
    Educator(of teachers)Dan

    Sounds like you need the service manuals, you clearly work on your vehicles yourself so it sounds like a good investment to me.

  • avatar

    Looks like the thermostat fixed the cold running engine problem, but it also sounds like a better air bleeding procedure might just cure the HVAC heat problem. I think you’re close to victory.

  • avatar

    I strongly suspect that the thermostat is what caused your initial problem. When changing it you introduced air into the system, and accidentally created a similar, but not the same, heating problem. Many modern cars are a real PITA to get all the air out without a special procedure or equipment…but I think airlock is the present problem…gillipsy nailed it..

  • avatar

    Hmm, I have had two third generation (J30) Maximas, and they all have very poor heating. Takes a long time to get any heat of the system, sometimes I’d arrived in my destination before any heat comes out. Maybe this is a common Nissan malady?

  • avatar

    Vacuum-actuated blend door sticking, perhaps. That’s all I can think of that hasn’t been discussed thus far.

  • avatar

    Chill, Sajeev. Here’s your snark. There’s no need to run the heat on one’s Miata while bleeding, since there’s no valve to stop the hot stuff going through the heater core at all times, like in the Summer, when the sun’s out, and you’re stopped at a light, in the sun.

  • avatar

    I have no solutions to contribute but agree with Mr. Whoopee. As another resident of the Houston Area I don’t need much heat. I have owned a lot of Nissan products and the one thing they generally had in common was the sheet metal placed stratigically in front of the radiator as soon as the weather got cold.

    I’ve lived in Japan and know it can get pretty cold there. That makes this recurring problem hard for me to understand.

  • avatar

    My only experience with no heat was with the infamous GM Olds diesel. The very first sign of head gasket failure was no heat from the heater. One could keep driving for months before replacing head gaskets, but until you did, no heat. I assume compression past the gasket was putting air into the system.

  • avatar

    I seem to remember the earlier (97) Pathfinders had a bleed valve in the cooling system since the cap wasn’t the highest point in the system.

  • avatar

    Not uncommon in V6 or V8 OHC engines. The motor is usually mounted fairly low and often the entry to the heater core is higher than the entry points to the cylinder heads. As a result air is trapped above the core.

    Many manufacturers have a fairly complex multi stage procedure for fixing this, including raising the coolant reservoir temporarily to push the air out. VW/Audi has an extension funnel tool screwed onto the reservoir filler to raise the level, plus an extra bleed point on one of the heater core hoses.

  • avatar

    No relevant Nissan expertise here, but those laser temp guns have become totally affordable, and handy for easy diagnosis on issues like this.

  • avatar

    After mulling this over, perhaps it’s just time to take it either to your dealership’s service department (gasp! the horror!) or just a good shop where they know how to fix the problem. It may cost you a bit, but the problem will be fixed, saving you the aggravation and time. What’s your time worth, anyway?

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