Piston Slap: A Lack of H-Town Heating

TTAC commentator kericf writes:

Sajeev,

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.

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry.