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'98-2.5L & '05-3.0L Subaru Outback Wagons
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Discussion Starter #1
2005 OBW Bean

When the HVAC is set to manual (not auto), 65 and either recirculate or outside, upper dash vent; the air from the vents is a lot warmer than the outside ambient temperature. The air from the vents gets warmer as the engine gets warmer. My 2001 Bean wasn't like that. The heater core blend door appears to move, vent air get's even hotter if I adjust the temperature higher than 65. I'd like the ambient air temperature but not heated. Anybody else have this issue? Solution?

Trig

p.s. If I switch to A/C the vent air is very cold.
 

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Master Caster
2005 XT, Mildly Modified...2006 XT Limited, Highly Modifed
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Yep....

I have the same issue with both my cars. I have to use my A/C at 62 or above to get the car comfortable. I don't think 65 (lowest manual setting) actually flows fresh air through the cabin...or the boxter is just hot and it's a byproduct...

I thought it was cause the turbos run hot. Bugs me tho...
 

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Outback 2.0XT, Audi TTq, Ducati M750
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The air gets pulled in from (in? around?) the engine bay, its always going to be warmer than just opening a window. Basically every car I've had is like this unless its cool enough outside where you don't really need the airflow in the first place. At least our A/C isn't a big drag on the engine like in my TT, the 1.8T is a great engine but bogs pretty bad, however having a manual and car OCD doesn't help.
 

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2006 Outback Sedan LLBean
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625 Posts
This is true of EVERY car, ever built! If ac ain't on, it'll never be colder than ambient temperature, just warmer. You're driving a vehicle that's BURNING fuel. What would one expect? #duh

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Master Caster
2005 XT, Mildly Modified...2006 XT Limited, Highly Modifed
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This is true of EVERY car, ever built! If ac ain't on, it'll never be colder than ambient temperature, just warmer. You're driving a vehicle that's BURNING fuel. What would one expect? #duh

Sent from my Nexus 6 using Tapatalk
This is significantly warmer than any other vehicle I have owned...except for my 1969 MGC GT...which was a hot box.

By comparison, my XJ will flow nearly the same temperature air. I am not joking. It literally feels to me like heat is being added by the HVAC system in the 2005 and 2006 I own.
 

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2006 Outback Sedan LLBean
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It all depends where the intake is.

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Master Caster
2005 XT, Mildly Modified...2006 XT Limited, Highly Modifed
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It all depends where the intake is.

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Agreed...

I just think Subaru expected everyone with the auto-climate to use it. My father has driven Audi for years and the d*mn A/C is on pretty much all the time due to the auto climate. I never use auto...I hate it.

I have been in base 2005s that don't due the same thing due to the base controls..
 

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2006 Outback Sedan LLBean
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Yeah me too. This time of year I have a routine. Hit auto, hit ac(off), hit fresh air intake. But otherwise I like the auto feature.

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Master Caster
2005 XT, Mildly Modified...2006 XT Limited, Highly Modifed
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I dislike the full-blast fan settings every time...until it normalizes.

I would rather 1/2 fan it and be able to think...unless it is going to be 100 or -20 all day in the car...then full-blast the weak fans *ss it is.
 

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In the 3rd gen, the HVAC air intake is cowl area under the black cover that's found below the windshield. The actual inlet to the HVAC is on the right side, but the path through the black cover is through a grill area on the left side. The grill is open to the outside, and for the most part, should not be drawing in air from the engine compartment. Nevertheless, the cowl area below the cover is part of the firewall, and it will be warmed by both the heat in the engine compartment and sun hitting the black cover.

In addition, the heater core is inside the HVAC duct. A vane is used to to direct the incoming air around the core when the temperature is set to the coldest position. However, because the hot engine coolant is always being circulated through the core, it could be as hot as the coolant. Some of that heat will radiate in the duct, and add to the temperature of the incoming air.

It's possible that the air blend vane (or vanes -- isn't it dual zone?) is moving, but not all the way when the HVAC is set to cold.

How much hotter is the air from the ducts compared to the outside air (what's the outside temp and what's coming out of the vents?) and is this after the HVAC fan has been on for some time (thereby flushing out any air that was warmed up by the core when the fan was off or the car wasn't moving)? Perhaps use a couple of thermometers to get some objective readings. Then others might do the same for comparison.
 

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2006 Outback Sedan LLBean
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Doesn't the coolant flow stop to the heater core when not turned on? I know my old explorer has a valve in line of the hose that shuts off flow when not in use.

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Master Caster
2005 XT, Mildly Modified...2006 XT Limited, Highly Modifed
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In the 3rd gen, the HVAC air intake is cowl area under the black cover that's found below the windshield. The actual inlet to the HVAC is on the right side, but the path through the black cover is through a grill area on the left side. The grill is open to the outside, and for the most part, should not be drawing in air from the engine compartment. Nevertheless, the cowl area below the cover is part of the firewall, and it will be warmed by both the heat in the engine compartment and sun hitting the black cover.

Denver has crushing mile high sun. This is a good point. The downpipe and turbo are also right on the other-side of the firewall...heating that up. Perhaps some thermal break material there would help...


In addition, the heater core is inside the HVAC duct. A vane is used to to direct the incoming air around the core when the temperature is set to the coldest position. However, because the hot engine coolant is always being circulated through the core, it could be as hot as the coolant. Some of that heat will radiate in the duct, and add to the temperature of the incoming air.

Add this to the above

It's possible that the air blend vane (or vanes -- isn't it dual zone?) is moving, but not all the way when the HVAC is set to cold.

Yes...I have the classic noises behind the dash during warm weather. It goes away in the winter time...Both cars.

How much hotter is the air from the ducts compared to the outside air (what's the outside temp and what's coming out of the vents?) and is this after the HVAC fan has been on for some time (thereby flushing out any air that was warmed up by the core when the fan was off or the car wasn't moving)? Perhaps use a couple of thermometers to get some objective readings. Then others might do the same for comparison.
I can do that the next time it is 65-ish and sunny. Today Denver Looks and feels like Cleveland and its 58*...

Hmmm Ok, if i go out today I will temp gun it.
 

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Doesn't the coolant flow stop to the heater core when not turned on? I know my old explorer has a valve in line of the hose that shuts off flow when not in use.

Sent from my Nexus 6 using Tapatalk
No. There's no valves. It's a constant flow circuit from the water (crossover) pipe at the top of the engine (hottest) through the core, to the inlet of the water pump (cool return to engine). Also believed to be important to proper thermostat operation.
 

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I can do that the next time it is 65-ish and sunny. Today Denver Looks and feels like Cleveland and its 58*...

Hmmm Ok, if i go out today I will temp gun it.
The subject is an H6, so not quite the same heat generation sources under the hood.

I note on re-read that Trig indicates the higher temperature appears even when the system is set to recycle, which eliminates the outside air and the impact on it of the engine heat and the sun on the cowl.

This could make comparison somewhat easier. If we take measurements of the air temperature in the car in the front passenger foot well area, and at the output of the face-level vents in the center, with the fan on high speed, after some time for stabilization, that might provide comparable references.

I know that on my 07, if I stop for a while even after having used the AC, and then start it up and turn on the fan to bring in outside air (but not the AC), the vents will initially blow hot air. But it dissipates after a short while, and was probably just the heat that was radiated from the heater core to the surrounding, stationary air in the duct.
 

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'98-2.5L & '05-3.0L Subaru Outback Wagons
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Discussion Starter #15
Testing, Gen 3 draws in air from the engine compartment and heater core duct...

I did some testing today. I put a smoke generator in front of the A/C condenser. Driving about 35 MPH and also stopped with one of the radiator fans running, some smoke enters the the passenger compartment (fan on 2 bars, visual and smell) through the cabin vents. It appears the inlet for the ventilation system "scoops" air from the engine bay past (over) the hood seal (rear of hood). There is probably a low pressure area there also that makes drawing engine bay air worse. The Gen 3 design seems to make that possible since the cabin air inlet grill is almost vertical and under the hood. Unlike my past cars, including my Gen 2 OBW Bean, those air inlet grills are nearly horizontal, not directly under the hood, limiting "scooping". The ventilation duct is also hot from the heater core constant flow. I used an IR sensor to see that.

I took the hood gasket/seal off and pulled some round 3/8 inch closed cell foam into the seal cavity to puff it up.
Seems to seal better now but not completely sealed. I will probably also put an inline ball valve in the heater (core) coolant line for summer use. That way the duct won't get hot.

BTW, the air temperature at dash vent outlet, before any modification was about 15 degF hotter than ambient. It was reduced by about 8 degF with the seal modification. Heater core is about half the heating. I've had some ambient air heating, perhaps 5 degF, in past cars but never 15 degrees.

Trig
 

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@Trig

The rubber weatherstrip is fastened to a lip on the black plastic cowl cover. The cover itself is held down against the firewall by a number of plastic push-pin rivets. Although it's not a tight seal, if the rivets are missing, or the cover is warped, there could be excessive engine compartment air getting into the cowl area. But even without that, as the sides of the hood are not sealed to the fenders, there's going to be some air coming out which can find its way to the intake grill area, although at 30 mph, I would think it would pass over/around the car far more than enter the grille.

I haven't had a chance to check my 07 but will then next time out.

Incidentally, was only one radiator fan operating? I'm not all that familiar with the H6 system, but on the 2.5s, both fans always operate together.

Also, if the H6 is similar to the 2.5, the heater coolant circuit could be important for the proper operation of the thermostat. Closing that loop with a ball valve might cause the engine to overheat.
 

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2001 VDC Wagon - White pearl - 302,000 km
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@Trig


Also, if the H6 is similar to the 2.5, the heater coolant circuit could be important for the proper operation of the thermostat. Closing that loop with a ball valve might cause the engine to overheat.
That's right. You will be better off to install an in-engine-compartment loop to bypass the heater core. Try to use street elbows rather that sharp 90's, so you don't impede flow too much. Be sure to cap off the open ports going into the cabin.
 

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Discussion Starter #18
OK, coolant needs to return back to the system. I will remember that.
As far as I can tell only one fan runs until the A/C is turned on.
It only reached about 65 degF here today though.

Smoke made it past the engine and into the ventilation inlet.
There must be a pressure difference at the lower part of the windshield.
Ventilation inlet seems to want to breath some from from the engine compartment.
I have my engine cover off (also called a sight shield), now that I think of it,
maybe that's making things worse. Sure don't like that thing, hides problems.

Trig
 

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Master Caster
2005 XT, Mildly Modified...2006 XT Limited, Highly Modifed
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OK, coolant needs to return back to the system. I will remember that.
As far as I can tell only one fan runs until the A/C is turned on.
It only reached about 65 degF here today though.

Smoke made it past the engine and into the ventilation inlet.
There must be a pressure difference at the lower part of the windshield.
Ventilation inlet seems to want to breath some from from the engine compartment.
I have my engine cover off (also called a sight shield), now that I think of it,
maybe that's making things worse. Sure don't like that thing, hides problems.

Trig
Well I like all the enthusiasm. I think the turbo has additional compounding problems...The solar gain here for six months plus a heat generator on the other side of it.

The H6 has headers that will surely heat up the firewall more than a NA 2.5.

I don't think the engine cover makes much difference. I dislike those as well. I can't get my hands on her if she has an overcoat on...
 

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2006 Outback Sedan LLBean
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Agreed about the engine cover. The worst is those plastic pins that hold it. If you need to remove it for any maintenance, they eventually break or get lost! Mines been off since I did the belt and pulley.

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