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'03 Outback H6 VDC wagon - 117k
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Is it possible for a thermostat to intermittently work, leaving me with it blowing occasional cool air instead of the warm air temp I have it cranked up to?

I've only experienced thermostats that simply "die" but never this. After a few days of just using the seat heater for warmth, I tried the fan again and now it's blowing warm today. This switcharoo of cool one day, warm the next has happened a couple times over the last month.

- yes the fan works
- in mid-Aug, had the AC o-rings replaced and the system recharged. Its another failing repair, in that after 48 hours all freon was lost and the AC stopped working. I mention this only because one thing I've read is that "air in the cooling system may cause problems with the thermostat". Not sure if they are related ...

Any other things this behavior could be related to or is it simply safe to assume its a failing thermostat?
 

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03 H6 OBW & 06 WRX Sportwagon
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a/c unrelated - you may need to have an a/c expert 'sniff' for the leak location. If DIY, you could try charging with refrigerant that has UV dye in it. Trace the leak with a UV light source. Could be a rock dinged the condenser or a hose-end is leaking ????? On my 03 H6, I've had 2 discharge hoses changed for leaking. The one that bends 90* from the comp. going to the condenser. O-rings too of course.



are you getting coolant pushed into the overflow? On my car, I cut the bottom of the little overflow tube at a 45* angle. I also secured its other end to the rad neck's 'nipple' with a coupla small zip ties. Always check inside the radiator for coolant level, don't trust the overflow bottle - it's level - while somewhat important - can be unrelated to coolant in the rest of the system.

although we often suggest thermostats be checked/changed, they are reliable and long-lasting. But, sometimes they are swapped with poor aftermarket untis that WILL NOT work with our engines. A t'stat can be somewhat tested in a pot on the stove. Should be fully open at around 170*F.

has this behavior just started? any work or wrecks recently? is the car new to you?

 

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Lawn ornament XT
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Is it possible for a thermostat to intermittently work, leaving me with it blowing occasional cool air instead of the warm air temp I have it cranked up to?

I've only experienced thermostats that simply "die" but never this. After a few days of just using the seat heater for warmth, I tried the fan again and now it's blowing warm today. This switcharoo of cool one day, warm the next has happened a couple times over the last month.

- yes the fan works
- in mid-Aug, had the AC o-rings replaced and the system recharged. Its another failing repair, in that after 48 hours all freon was lost and the AC stopped working. I mention this only because one thing I've read is that "air in the cooling system may cause problems with the thermostat". Not sure if they are related ...

Any other things this behavior could be related to or is it simply safe to assume its a failing thermostat?
The thermostat only restricts flow through the radiator. Coolant is allowed to flow through the heater core at all times regardless of thermostat position or condition, as long as the pump works.

If you aren't getting heat, you aren't getting hot coolant out of the engine. Maybe an air bubble?

EDIT: added:

"air in the cooling system may cause problems with the thermostat"
Air bubbles in the system can make you think you're having thermostat problems, but the real problem is the air bubbles. That can be anything from simply low coolant, too long since last top-up, or it can be a blown head gasket.

It helps to understand the overall model. The water pump always pumps water when the engine runs. The water always flows from the engine to the heater core. The heater core removes X amount of heat into the cabin air, depending on control settings. The water then flows from the heater core back to the thermostat. Here we hit a branch:

IF the water is still hot after heating the cabin, the thermostat opens and allows flow to the radiator. Residual heat is dumped to the outside air and the cooled water is returned to the engine block to complete the cycle.
IF the water is too cold to open the thermostat, the water is diverted directly back into the engine block.
 

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'03 Outback H6 VDC wagon - 117k
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Discussion Starter #4
a/c unrelated - you may need to have an a/c expert 'sniff' for the leak location. If DIY, you could try charging with refrigerant that has UV dye in it. O-rings too of course.

are you getting coolant pushed into the overflow?

has this behavior just started? any work or wrecks recently? is the car new to you?
*****

sorry to edit down your comments Lucky Tex - my computer is acting wonky on this site today.

No, car not new to me, I've owned it since 18k and am planning to have the 120k major svc done a little early, as each major has been done a few thousand early.

Was planning to post separately about the AC problems because I had tried the O-ring trick provided by that kindly person in the DIY thread. And yet I see that oily leak appear at the kink in a hose, located directly right above the oil dipstick. Only mentioned it here due to what I read about air in the cooling system. I'm realizing now that I'm probably interchangably using cooling sys and AC ... whoops.

Never had a wreak tho' someone whacked the front fender requiring a repair / paint and left small, tiny superficial dink in front of radiator. Was worried about that aftermarket issue with any Subaru repair part so thank you for mentioning!
 

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that a/c hose failed early enough on our 03 that warranty covered the first swap. Then, many years later, I had it leak again. Got a part off ebay - it was over $100 IIRC.

I have also battled cheap/poor quality o-rings. They seem to be the right color - but don't last. Most recently, I've successfully used Interdynamics branded variety pack from Amazon.

on the heat issue - wonder if you could have a blend door that is sticking? any odd sounds or behavior from the vents/climate system?
 

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'03 Outback H6 VDC wagon - 117k
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that a/c hose failed early enough on our 03 that warranty covered the first swap. Then, many years later, I had it leak again. Got a part off ebay - it was over $100 IIRC.

I have also battled cheap/poor quality o-rings. They seem to be the right color - but don't last. Most recently, I've successfully used Interdynamics branded variety pack from Amazon.

on the heat issue - wonder if you could have a blend door that is sticking? any odd sounds or behavior from the vents/climate system?
No odd sounds other than that usual hissing sound when you know your AC is done for. I'm not using the AC right now, so no, no sounds of note when I turn on the heat.

Just drove the car roundtrip 15 miles this morning and heat working fine. I just don't see the value of having the shop swap out a thermostat that appears to be working right now. I am flummoxed by it's intermittent nature and the heat hasn't crapped out often enough yet for me to see a pattern. Hoping to narrow down some ideas because I've saved loads of $$ by researching here first and only then taking into the shop -
 

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don't trust the level in the overflow to accurately reflect coolant level in the radiator - certainly check the rad frequently until this problem is sorted out.

good luck
 

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'03 Outback H6 VDC wagon - 117k
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Discussion Starter #8
Thanks for your help Rasterman and 1 Lucky Texan -- I realize this isn't a terribly sexy repair quandary. The fix won't result in me posting a video of me ripping thru a snowbank ;-)

Checked rad this a.m. and it was full to neck.
 
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