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Discussion Starter · #1 ·
2003 Santa Fe 2.7L, 128K mi.

Just noticed very little heat when heater on full blast. I get more heat when going faster and at higher revs. Thermostat opening properly. Checked radiator for air. Topped off and then ran at 2500 rpm for one min. 3x to flush air bubbles. Noticed a few. Radiator full. Small leaks/fluid residue at top radiator hose at thermostat connection.

Heater core IN line hot. Heater core OUT line lukewarm. I am thinking partially plugged heater core. Will a radiator flush at the dealership flush the heater core as well?? Or is a heater core flush a separate procedure? And can I "DIY" this? The heater core OUT hose looks like it attaches at the thermostat. Is there a way to back flush this line while leaving the other line (which looks much more difficult to access) in place??

Recommended best course of action?
 

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2003 Santa Fe 2.7L, 128K mi.

Just noticed very little heat when heater on full blast. I get more heat when going faster and at higher revs. Thermostat opening properly. Checked radiator for air. Topped off and then ran at 2500 rpm for one min. 3x to flush air bubbles. Noticed a few. Radiator full. Small leaks/fluid residue at top radiator hose at thermostat connection.

Heater core IN line hot. Heater core OUT line lukewarm. I am thinking partially plugged heater core. Will a radiator flush at the dealership flush the heater core as well?? Or is a heater core flush a separate procedure? And can I "DIY" this? The heater core OUT hose looks like it attaches at the thermostat. Is there a way to back flush this line while leaving the other line (which looks much more difficult to access) in place??

Recommended best course of action?
I would remove the hoses and just run either a water hose or air compressor through it a few times, from each end. Should get most of it out. The. Test the heater again.

My 1999 Mercury Cougar had the same issue and this resolved it.
 

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Repair the leak so you not lose coolant and have air in system.. heater work off heat exchange with hot water.. air in cooing system wont carry heat from engine, thus engine overheat and major repair time.

Of course outlet be cooler, you drawing heat off hot water to heat cabin, so coolant coming out be cooler.. it just a small radiator, same as out front, hot water in, exhange heat from liquid to air, and cool water back to engine to pick up more heat and remove it to air.
 

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Would wait until the car is cold and start it up with heat/cooling seting to cold. Check outlet temperature from heater core, then turn temp to hot and give it another feel.

+1 sbr711 water that has been through the core should be cooler as the heat has been transferred to the cooler air passing through it.

I don't think compressed air is the way to go as the baffles will quickly minimize the air pressure, plus you'd need a high volume of air through the core to do any good. Water flushing the core would be my preference. Try it backwards (in through the oulet) too.

Side note: Altimas are notorious for insufficient heat at lower RPM's. Still no fix for this malady on my 2005, as far as I know.

Good luck
 

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I see a blown up heater core coming here. DON'T blow anything thru it! No air, no garden hose. You most likely have air trapped in the system. It doesn't take much air to create this problem And never, I mean never use a miracle flush in a can. It will cause damage to the system later on. What do you do? Drain and refill every year, no more problems.
 

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I'll take umbrage at that. You can effectively unclog a heater core with compressed air or a garden hose. The biggest thing is to be careful with it because you are going to make a mess out of it, and you really don't want to unnecessarily blow a bunch of coolant all over the place. Get an old windshield washer jug or a long hose you can connect to the heater core hoses to keep the coolant you are going to send out of the core out of the engine bay.

Generally speaking, a heater core that isn't giving you heat until you rev the motor means either air or a restricted core. A restricted core will give little heat, and revving the motor will cause more coolant to flow through, allowing more of an exchange of hot coolant through it to heat the cab. You may want to try running the engine in the driveway with the radiator cap off to allow air bubbles to escape first though.
 

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Well here's the deal. Heater cores and radiators aren't made as robust as they were years ago., for 2 reasons. One they transfer temperature better when there is less metal mass. Two, there is the ever increasing cheap thing. With that said, with the labor time to replace a heater core going 8 hours minumum on most cars, and many going beyond 10 and 12 hours to replace, at a cost of how much per hour? Shall we average it at say $80 in a dealership? And then don't forget to add the cost of a heater core in with that. Go ahead blow away at it if you want, the garages need to make a living too. And don't forget the real possibility of the carpeting full of antifreeze, requiring the interior to be removed and dried out, and if it was me, I would demand a new rug.
 

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Discussion Starter · #8 ·
Went to the dealership and got the upper and lower radiator hoses replaced and the system "burped". New coolant also. The problem is still there. Little heat coming through. I get more heat the faster I go, such as hwy. speeds. Heat was fine awhile ago (last winter).

I've had 2 things done to the car in the interim (since last winter). Timing belt and water pump replaced and I replaced the stock "Monsoon" sound system with an aftermarket Pioneer unit. The car is not overheating so I have ruled out the water pump (low flow?) being to blame. I hear about a "blend valve" which blends hot air with cool depending on where the temp. dial is at. Is this vacuum operated on this vehicle? Did I potentially pinch a vacuum line behind the center dash when I took it out and replaced it when I installed the new stereo? And now the blend valve isn't working properly? I didn't see anything back in there when I pulled the center console but maybe I missed something.

I am looking for alternative causes here because I don't want to take it back to the dealership and they will go straight to the "you need a new heater core" ($$$$) thing. I am hoping that it is something else but I am out of answers.

any ideas?
 

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Okay, if you have a leaking heater core, it will smell inside the car first, then the windows will fog up. There should also be coolant seeping from the bottom of the case. A plugged heater core? My first guess would be no, as the heater is an active part of the cooling system, not an add on like years ago. I have not seen a plugged heater core in decades. It's just not hardly possible. A digital/remote temp gauge would be helpful, to actually check the temp in various spots. A thermostat? Again doubtful, but more possible than a plugged core. A temp check would reveal this. In the 3 miserable years I worked in a Hyundai dealership, I never saw a plugged core, or a bad thermostat, although it could be possible I suppose. I would pull apart the center console, and inspect the heater control itself, and check the operation while apart. Those controls are really cheapo, and need to be operated with little girly fingers, not Chevy gorilla hands. I replaced many of them. They break very easy. If you have a digital control (LX) good luck. However, you can still operate it while apart, and watch the doors open and close. If everything is not functioning axactly as intended, meaning door operation, the heater will not operate correctly. This is not rocket science, only a process of elimination, and don't just throw parts at it either, or worse yet listen to the "buddies"
 

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Discussion Starter · #10 ·
"...and watch the doors open and close."

Where exactly are these doors? And is the "blend valve" in the same area?

I'm assuming behind the center dash or the right side behind the glove box?
 

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You will have to remove the glove box, and the center control panel, and maybe the radio to watch the "doors open and close" The entire heat/cool system works on moveable doors within the heater case. There is no "blend valve" to speak of. There are doors in the case that direct the heat and cool air in different directions to satisfy the owner/operator. Nothing really "shuts off" the heater is always on, it is a part of the cooling system, coolant always flows thru it. When you want cold air (a/c operation) the heater is still "on" however the hot air is mixed with the cold air at the evaporator and "blended to achieve the right temperature, and to prevent the evaporator from actually freezing solid. Same goes for defrost mode, and floor and dash outlet air flow. Nothing "shuts off" the air is simply directed in a different direction, and mixed with the a/c part of the system, or blended outside air. A/C is on all the time also to dehumidify the cabin air and temperate the heater. The a/c compressor will not operate when the outside air is too cold to activate the compressor ambient air switch. The only time everthing is actually turned off is when the control is in "off" posistion. And even then in some cars, the fan still operates all the time on a low speed to pressurize the cabin to bring in outside air to force out possible exhaust or oil fumes etc. The air exits in the back of the car, remember seeing those little soft rubber "flaps" behind the bumper?
Is that clearer? You will actually be able to watch the doors move thru their cycle as you work the controls. They must move all the way in one direction, and the other to actually redirect the air flow. The blend doors will operate partially of course, hence the "blend" description. Some of the controlling can be done via a cable, some will be done with a vacuum valve, others can actually be electrically operated, tho these are rare cases. (too much money to make) The digital heater control is operated by vacuum that is controlled by the electric heater dash control. It's kind of hard to explain fully, but when you see it operate, it becomes simple. And again, make sure there is no air in the cooling system. If there is a coolant leak anywhere, there is air in the system. It can be very difficult at times to get it "burped" out.
 
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