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2016 Base
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31 Posts
Discussion Starter #1
Hello all,

I have a 2016 2.5 non turbo. 15,000 miles. VERY POOR HEAT IN THE WINTER. I find myself putting the transmission into low gear to raise the revs just to get a little more heat out of the car. The heat warms up when I'm on the highway at constant 2,000 rpm, but for stop and go, it just doesn't cut it.

Now, of course, there's no engine temperature gauge so I can't really tell what temp the engine is running at.

So, what's my course of action? Is it possible the young factory thermostat is stuck open and I should replace it? Or is there an aftermarket high-termperature thermostat I should be using?

Really, the heat in my '01 Legacy sedan (which I replaced with this Forester) was much, much better. (The A/C was colder, too.)

Thanks in advance for any suggestions.

Jeff in Boston
 

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1999 "L" - 231,000 mi. AT
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715 Posts
Now, of course, there's no engine temperature gauge so I can't really tell what temp the engine is running at.

So, what's my course of action? Is it possible the young factory thermostat is stuck open?

Sounds like it, but also check that you have full load of coolant. As a temporary measure/test you can do what truck drivers do in extreme cold conditions, block off part of the radiator. In a car you could use a sheet of caardboard, duct-taped?, to block say 1/2 of radiator air flow. You'll be aware of what's going on so it should work out, and you can easily take it out. See if you get more heat.

I did something similar for an oil radiator on a motorcycle during cold weather and it helped/worked OK to bring the tranny oil up closer to normal temps for easier shifting.
 

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2012 Forester X 5 MT
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881 Posts
You may have a defective thermostat. Statistically, thermostats tend to fail open when they do fail - and so the engine runs very cool.

I think it's a bad idea to use a higher temperature thermostat.

The cardboard idea is good in very cold weather - zero and below. Just don't block the entire radiator.
 

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2018 Forester Manual
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418 Posts
I think it's the nature of aluminum 4 cylinders; they shed heat too quickly to be able to get the nuclear option heat. My Taurus, Cherokee, numerous Wranglers and pickup have cast iron blocks and make great heat. Past Accord, Focus and current Forester make adequate heat, but they just don't have the nuclear option like the iron block engines did.
 

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2014 Premium M6
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334 Posts
I think it's the nature of aluminum 4 cylinders; they shed heat too quickly to be able to get the nuclear option heat. My Taurus, Cherokee, numerous Wranglers and pickup have cast iron blocks and make great heat. Past Accord, Focus and current Forester make adequate heat, but they just don't have the nuclear option like the iron block engines did.
This, though my Toyota Tacoma (and my brothers Corolla) heat up quickly.

I'll say it again - after the head gasket problems of the prior generation I'd bet that Subaru modified how quickly the car heats up to mitigate sealing issues. Either that or it has something to do with startup emissions though most engines want to be as hot as fast as possible for efficient combustion.

Anyway, the FB is horribly slow at heating up. Nature of the beast.

BTW the thesis above isn't mine, I read it years ago in a "New" Dodge Ram tech bulletin that the engineers at Chrysler were modifying how quickly the engine warmed up and transferred heat to mitigate block deck/head warpage/head gasket sealing issues.
 

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2016 Forester
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898 Posts
I stuck a piece of aluminized bubble wrap in front of radiator on really cold days and it seems to help. A grill cover would be a better option but kinda hard to do with the three separate openings on Forester.
 

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2015 Forester 2.5 Touring CVT
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7 Posts
If you work on your own car, then I would just replace the thermostat with the one recommended for the car and see if it fixes the problem. As others have said, failed thermostats usually stick in an opened position resulting is overcooling of the engine. I know that this is a 'throwing parts at a problem' recommendation but thermostats are cheap and it is highly likely that its replacement will solve your heater problem.

If you need to pay someone else to do the work, then you might want to spend more time diagnosing the issue, although the diagnosis will most likely lead you to the conclusion that the thermostat is defective.

Your A/C not being cold enough is an unrelated issue. There are several threads addressing that issue on this forum.
 

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2018 Forester CVTI
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30 Posts
Hello all,

I have a 2016 2.5 non turbo. 15,000 miles. VERY POOR HEAT IN THE WINTER. I find myself putting the transmission into low gear to raise the revs just to get a little more heat out of the car. The heat warms up when I'm on the highway at constant 2,000 rpm, but for stop and go, it just doesn't cut it.

Now, of course, there's no engine temperature gauge so I can't really tell what temp the engine is running at.

So, what's my course of action? Is it possible the young factory thermostat is stuck open and I should replace it? Or is there an aftermarket high-termperature thermostat I should be using?

Really, the heat in my '01 Legacy sedan (which I replaced with this Forester) was much, much better. (The A/C was colder, too.)

Thanks in advance for any suggestions.

Jeff in Boston
Our Forester is new with very low mileage but we have gone through this Vermont winter, which has been unusually cold.

My next car will be an EV. I hope Subaru manufactures a Forester EV!, with no problems whatsoever.

We have heated seats, wich helps because we do not turn the car heater on until after the CVT transmission gets to normal operating temperature.

Since you have a manual transmission, I guess you can just turn the heater on right away. But it seems to me that until the engine is at normal operating temperature, you won't get decent heating.

Now, if you still don't have enough heat at a stop light after driving around, you may have a clogged filter slowing air movement. I don't know but I can tell that your engine has PLENTY of heat to give you, no matter how far below zero it is out there.

The other thing I would check are those little doors that open and close in the HVAC system to either recirculate air or not. There might be a problem there. Hope this helps.:|
 

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2004 Forester
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2 Posts
I had a similar problem with my Chrysler van. Had me stumped. Then someone on the Chrysler forum suggested, as did UhOh, to check the coolant level, which somehow had not occurred to me. Bingo! Took about three quarts to top it off and the heat returned. Realized I couldn't even remember when the last time I checked the coolant level was. Felt pretty dumb.
 

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2016 Forester
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898 Posts
There's no need to look at things like coolant level or thermostat, it's just the way engine is designed. If you look at the oil temp in the MFD, you'll see it raise very slowly on very cold days, then sort of hit a wall at around 60°C, this is well below when thermostat is suppose to open.

As for why I don't know, some say it's because boxer has more surface area and lose more heat through the engine block, some say it's poorly designed thermostat placement that allow some coolant circulation through the radiator even when it's closed. Some say Subaru even unofficially admitted to poor heater design in this gen. But they are all hearsay with no way to verify them.
 

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2011 Forester 2.5X Automatic
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186 Posts
Hello all,

I have a 2016 2.5 non turbo. 15,000 miles. VERY POOR HEAT IN THE WINTER. I find myself putting the transmission into low gear to raise the revs just to get a little more heat out of the car. The heat warms up when I'm on the highway at constant 2,000 rpm, but for stop and go, it just doesn't cut it.

Now, of course, there's no engine temperature gauge so I can't really tell what temp the engine is running at.

So, what's my course of action? Is it possible the young factory thermostat is stuck open and I should replace it? Or is there an aftermarket high-termperature thermostat I should be using?

Really, the heat in my '01 Legacy sedan (which I replaced with this Forester) was much, much better. (The A/C was colder, too.)

Thanks in advance for any suggestions.

Jeff in Boston
Forget the hotter T-stat; I doubt you could find one if you tried. Besides, the T-stat is part of the emissions system in the car and determines how quickly it warms up so the only one you're going to find is the original opening temp. Better to use some cardboard to partially block the radiator ...more effective and easily removed. Had to do that with a little Ford Ranger I had when I lived in Chicago to get the coolant to rise into the normal range.

This being a relatively new car it is probably still on it's factory fill of Subaru coolant ...good out to about 100K-ish. Just for grins, check the expansion tank and make sure the coolant color is blue; OEM Subaru coolant is blue.

I tried a bit to look up how the heating system works but couldn't find it in the FSM. There may be a valve that allows or controls coolant flow into the heater core ...some cars have this but I have no idea if the Forester does. But, if the valve is out of adjustment or broken it could restrict the flow of hot coolant to the heater core.

In the same vein, the blend door in the HVAC plenum which controls how much hot or cold air is used in the cabin mix to determine temperature may not be working right. On my '11 Foz the HVAC controls are all manual ...at least they feel that way ...and directly move linkage or cables to make adjustments. Possibly the newer Fozzies use servo-motors or vacuum to move the blend door. In any event that is an area to investigate ...how is the blend door working and is it working properly.

My bet is you have something amiss under the dash in the HVAC plenum ...the blend door being the perpetrator of your chilly heating system. Possibly check out YouTube ...if you have this problem chances are someone else has had it and put up a video on it.
 
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