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Heater blows warm air, NOT hot

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1999 Boxster 2.5L with 98k miles.

Purchased the car in the middle of summer last year, so I didn't even think to test out the heater. Now that it's in the 30's - 40's (coooooold here in Texas!), the fact the heater only blows out warm air is starting to become a nuisance.

A little background story, last summer I purchased the car, and the temp gauge was usually at the beginning of the "0" in the 180 on the temp gauge when driving. When I would sit at a stop light, or ever get in some bumper to bumper traffic, the temp gauge would go up to the very far edge of the "0" on the 180, and maybe once or twice, actually went past the "0", but never hit that 3rd hash line. Not sure if this is normal or not, but it concerned me because my old cars have always had a temp gauge that just stayed dead center and never moved once it warmed up. Outside temp is about 85-95 degrees. Not sure about the antifreeze/water ratio.

Now that it's winter, and never above 60 degrees, the temp gauge has always been on the beginning of the "0" at the most, and usually around the "8" in 180. It takes about 10-13 minutes of idleing to warm up to the operating temp, and probably 8 minutes of driving to get it up to operating temp according to the gauge. Warm air starts to come out after about 10 minutes. Climate Control is always set on "HI", but it just blows warm air. The blower motor seems to be working fine, the fan speeds work, and it blows out a good amount of air.

What I've tried/looked at:

Coolant level is good

Opened cooling system burp valve in the trunk. Opened the valvue while engine was cold, then drove with valve open for approx 120 miles. Put in neutral, and revved up to 5000 rpms several times. Heat seems to get hotter after the engine is revved, and temp goes up on the temp gauge - but that may just be my imagination, and it still isn't "hot"

What should I try/do next?

Possibly related information - I was cleaning the front radiators last summer, cleaning the debris. When I was pulling off the front R AC condensor, I bent a tab, and the freon leaked out. I was cheap, and had the AC condensor tab repair (welded) back on a professional shop. I re installed it, and had a vacuum pulled on the AC system for 1 hr, and refilled with freon - AC tech said no leaks. But maybe once every 3 weeks, after my car has sat for about 2-3 hours, ill hear a high high pitched hissing sound for about 4 seconds that sounds like pressure leaking out. It may happen more often, but it's just hit and miss when i am there to hear it.

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It sounds like your engine is certainly getting hot enough, but perhaps your heater core is due to be replaced, maybe the heater flap could be the problem?

I'm not sure if the procedure to access the heater core on the 986 is the same as the 996.


Edited by logray
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No you don't have to flush the coolant, in the instructions you clamp the hoses going to the core before removal. When finsished you do need to bleed the coolant system.

Thermostats run around $100-200, h20 pumps about $300 and I don't have the latest prices on heater cores sorry, but you are probably looking at about 2-3 hours of labor including vacuum refill of the coolant system.

I would spend more time with diagnosis before diving into removal of the heater core. This is just a guess, there could be many other reasons for this, like I mentioned above, such as the flaps.

Search is your friend here. Have a read through this entire post, it has a wealth of information about this problem:


Edited by logray
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One other thing to check is for foam coming off the blend door. My 99 spent most of its life in Houston and the foam has been coming out for a couple of years. I do need to fix it as the heat isn't working as well, I park the car during the salted road time so don't drive in extreme cold very often. Anyways a search for boxster foam fix should find the fix.

Do you have any foam coming out of the vents, or is there evidence of foam pieces in the vents?

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Oh and on the varying temp, it's normal mine dose this as well. I cleaned my radiators last year and cleaned out tons of trash that was clogging up the system, improved the temp control singnificantly although it still varies more than I'm used to with other vehicles.

Edited by Lumpy05
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