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2014 OBW 3.6R Limited, 1997 OBW 2.5L Auto (sold, but not forgotten), and 1991 Ford F150
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Discussion Starter #1
DRAINING AND REPLACING COOLANT AND THERMOSTAT

I like to do this maintenance every three years or so of normal driving to keep the cooling system in tiptop shape. If you haven't had any overheating problems, you may decide not to replace the thermostat and/or radiator cap at this interval and I'm certainly not going to tell you you're wrong. But, many problems on our cars can be avoided by not overheating the engine and there really is no downside to being aggressive on this maintenance except spending a little time and money.

The graphics and steps below apply specifically to my 1997 OBW, but most should be applicable to both older and newer cars, as well.

This job can be done with your car on a level garage floor, but there are advantages to raising the front of the car. Easiest way is to drive the front tires up on 2x boards or (better) 2 stacked 2x boards. Alternatively, place front of car on jack-stands. Raising the front will give easier access to the thermostat and make it less likely to trap air in the system when filling the system with coolant.

I'm located in the U.S. with a left-hand drive car, so consider all references to "passenger-side" or "driver's-side" accordingly.

Parts you will need:
-Thermostat (Genuine Subaru only ... aftermarket ones don't seem to work well with our cars)
-Thermostat Gasket (recommended)
-Radiator Cap (optional, but if the thermostat needs replacing ... a "tired" cap can cause overheating problems)
-Either:
1-gallon of full-strength coolant and 1-gallon of distilled water *OR*
2 gallons of 50/50 premix coolant
-Subaru cooling system additive (optional for Gen1 but recommended for newer cars to prevent external head gasket leaks)

Subaru recommends using an "ethylene-glycol basis coolant". For the last few years, I have been using Peak Long-life coolant (green color) successfully. Others on this forum have reported using a Prestone brand coolant just as successfully. Of course, your local dealer will recommend and be glad to sell you Subaru brand coolant. Your choice.

If you live in a area with "soft" water, i.e. not mineralized, you may decide to use tap water with the full-strength coolant. But a gallon of distilled water only costs a dollar or so at the grocery store, so why not? Use the leftover for your battery.

Due to shipping charges, it's usually not feasible to order these parts online unless they're part of a larger order, so plan to buy locally. Warning: local dealers reputedly love to "gouge" walk-in customers. If you just walk into the dealer to get these parts, they will probably charge you 10-20% over list price. Call ahead or contact them via email for a price quote and use your negotiating tactics to get the price down. The only items you HAVE to get at the dealer are the thermostat and the additive.

TOOLS NEEDED:
-safety glasses
-10mm wrench or socket to remove thermostat housing bolts and radiator overflow tank mounting bolts
-pliers to loosen radiator drain valve
-phillips head screwdriver to loosen hose clamp and remove air vent plug from radiator
-towels to clean-up the inevitable spills
-safety glasses

Let's get started:
-Let engine sit and cool ... overnight is good.
-Remove radiator cap and open drain valve on radiator and drain coolant into a bucket. The drain valve is located on the rear passenger side of the radiator near the bottom. TIP: pull the hose from the radiator overflow tank and slip it onto the drain valve (it fits perfectly) to better direct flow into the bucket and save making a mess.



-Close drain valve (remove overflow tank hose, if used).
-Under the car (driver's side), have a bucket ready to catch coolant and remove the two bolts on the thermostat housing to separate it from the water pump and pull it down. The Subaru manual recommends removing the lower radiator hose from the housing but I haven't found it necessary to do so.
-Remove thermostat by pulling it down ... you might need a screwdriver to gently pry it out. Note which end of thermostat goes up so new one can be inserted in the same direction. Retain rubber gasket around the thermostat flange if you don't buy a new one.





OPTIONAL STEPS:
-Place bucket under water pump, remove upper radiator hose at radiator end, run garden hose into hose to "flush" dirt and remaining old coolant from the engine.
-Run garden hose into upper radiator pipe to "flush" dirt and old coolant from the radiator.
-Reinstall radiator hose.

-NOTE: If you wish to do a chemical flush, reinstall the old thermostat and follow directions on the container you purchased. Afterwards, you will probably want to repeat all the steps above.

-NOTE: if you wish to test the new thermostat before installing, see instructions on graphic below.



-Install the new thermostat with gasket. The Subaru manual says to set the jiggle pin of the thermostat to the front side.
-Place thermostat housing on bottom of water pump and tighten bolts to specified torque.
-Remove radiator overflow tank and empty into bucket, clean, then reinstall tank.

-NOTE: Follow directions on container for adding the Subaru Coolant Additive, if used. I have not used this, so don't know what they are, but if you fill the radiator with coolant, there will be no room for the additive and you will have to drain some coolant to make room.

ADDING COOLANT:
-Remove air vent plug from top of radiator (passenger-side) using phillips screwdriver.
-Slowly add coolant to radiator. If using full-strength coolant, add 3/4 gallon then top off with distilled water. If using premix, add until full, about 1.5 gallons. If you add significantly less than 1.5 gallons total, there is air trapped in the system.
-Replace air vent plug
-Replace radiator cap
-Add coolant to full mark on overflow tank.

There are several methods for adding coolant and purging air trapped in the system. If you raised the front end on boards, this will help. The method Subaru has in the manual is:

-Remove air vent plug from radiator.
-Fill engine coolant into radiator up to filler neck position.
-Fill engine coolant into reservoir tank up to upper level.
-Attach radiator cap and reservoir tank cap properly.
-Install air vent plug.
-Warm-up engine completely for more than five minutes at 2,000 to 3,000 rpm.
-Stop engine and wait until temperature drops to a safe level.
-If engine coolant level drops in radiator, add engine coolant to filler neck position.
-If engine coolant level drops from upper level of reservoir tank, add engine coolant to upper level.
-Attach radiator cap and reservoir tank cap properly.

Remember:
Check for leaks.
Recycle old coolant at auto parts store.
 

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1999 Legacy Outback,2.5L, Auto
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thanks rob..this is great information especially when i am in this topic since Feb 2010. yesterday, the shop told me they are not worried about my car coolant in the reservoir tank between full and low line as the radiator has coolant up to the neck. i prefer the reservior tank up to full line at cool engine but shop keeps saying' not to worry'. i saw online subaru expert and he also mentioned the coolant [at cool engine' between full and low line is normal.

How to Check Engine Coolant Levels in a Car: Car Maintenance and Repair Tips | eHow.co.uk

for now...i'm keeping an eye on my coolant in the reservoir and radiator!
 

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2014 OBW 3.6R Limited, 1997 OBW 2.5L Auto (sold, but not forgotten), and 1991 Ford F150
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Discussion Starter #3
The coolant level in my reservoir tank goes up and down as much as 1 inch from one day to the next, though usually it's closer to a 1/2 inch ... I guess that's "normal". After doing my HGs in 2008, I monitored the coolant level like a hawk for quite a while ... Lately, I've learned not to worry so much ... still spend way too much time watching the temp gauge, though. LOL.
 

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2014 OBW 3.6R Limited, 1997 OBW 2.5L Auto (sold, but not forgotten), and 1991 Ford F150
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Discussion Starter #5
AFAIK, all the Gen1 OB OEM radiators have one ... it's black plastic with a square head and a slot for a Phillips screwdriver and is located on top of the radiator right where the large upper hose attaches.

If you really don't have one, I'd raise the driver's side front of the car so that the radiator cap is the high point in the system.
 

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Hi sir roblog, I am planning to replace my thermostat this weekend and I'll be using your guide. I just want to ask for the estimate cost of expense for this? I had it checked on car repair costs and it gave me an estimate of $50 dollars. Is this correct?

thank you.
 

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2014 OBW 3.6R Limited, 1997 OBW 2.5L Auto (sold, but not forgotten), and 1991 Ford F150
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Discussion Starter #8
Genuine Subaru thermostat w/gasket = $20-25

2 gallons 50/50 premix coolant = $10-15
******** OR *********
1 gallon full strength coolant = $10-12
1 gallon distilled water = $1

So, about $40 + beer = $50 ... they were right!
 

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2002 Subaru Outback
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I'm doing a coolant flush on my 2002 Outback. I drained the coolant from the radiator and only got about 5 quarts out. What's the best way to get the rest out? I watched
where they recommend draining "the core." I assume this is the heater core. Where is this located? If I can't drain the core, how can I be sure that the coolant flush I dumped in there (with distilled water) will mix with that coolant so it gets drained? After filling it tonight with the flush and water, I drove around for about 20 minutes with the heater on high but I don't know if the fan ever turned on.

Edit: I just tried to insert a link but it turned it into an embedded video instead.
 

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2014 OBW 3.6R Limited, 1997 OBW 2.5L Auto (sold, but not forgotten), and 1991 Ford F150
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Discussion Starter #10
I think in this case, the "core" is the block, which will hold some coolant after draining the radiator. The usual way to drain the block is to remove the thermostat cover, but it appears in your other thread ("Engine undercover bolts rusted shut. Help!") that this may not be possible in your case.

What I'd do to remove the flush chemical is refill the radiator with water, drive around for 15 minutes, let it cool for awhile, then drain the radiator again. Repeat 1-2 times until you feel confident most of the flush chemical has been removed and what's left is highly diluted.

Finally, add the appropriate amount of new full-strength coolant (about 3/4-1 gallon), then top off with distilled water and purge the air.
 

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2002 Subaru Outback
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I think in this case, the "core" is the block, which will hold some coolant after draining the radiator. The usual way to drain the block is to remove the thermostat cover, but it appears in your other thread ("Engine undercover bolts rusted shut. Help!") that this may not be possible in your case.

What I'd do to remove the flush chemical is refill the radiator with water, drive around for 15 minutes, let it cool for awhile, then drain the radiator again. Repeat 1-2 times until you feel confident most of the flush chemical has been removed and what's left is highly diluted.

Finally, add the appropriate amount of new full-strength coolant (about 3/4-1 gallon), then top off with distilled water and purge the air.
Thanks for your quick response (and for this helpful thread).

So if I drive it around for 15 minutes with the heater on high then that should open up the thermostat, correct? I drove it tonight for 10 minutes after it reached operating temp (so at least 15-20 minutes) and when I pulled up to my garage, the engine fan wasn't on. I read someone else's post elsewhere who said it took an hour of idling once to get the fan to come on. I just want to make sure I'm draining and flushing all of the old coolant. There was a LOT of rust and sludge in the bottom of the reservoir so I want to do this right. I'm going to drain this tomorrow and fill at least once more with distilled water.

What's the best way to purge air without an air vent? I was planning on filling up the system with a full gallon of coolant (capacity is 7.1 L, which would make the mixture 56% coolant, close enough) and then adding water until the system is full. Then, leaving the radiator cap off, turning on the engine and adding water as the level falls for 5 minutes or so. Then I would fill up the reservoir with coolant. Would this work?
 

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2002 Subaru Outback
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So an update. I flushed the coolant this weekend. I first put in a coolant flush solution from Prestone. I flushed that and it was light green. Then I put in distilled water and drove around for a while and then let it idle until the fan kicked on. Took about an hour. I drained that and it was dark green, almost black! Then I did another round of distilled water, and it was the same color! It was late and I really had to finish the job so I replaced it with coolant and moved on. But it was really bizarre. My only thought is that maybe the first time I didn't get the thermostat to open so all of the coolant in the water pump/heater core never mixed with what was getting flushed. The subsequent times I idled it for an hour to get the fan to come on so then it was probably mixing. But after three drains, I was tired of cleaning up coolant on the floor and pouring it into jugs. I wanted to be done. What could be causing this?
 

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2002 Subaru Outback
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So an update. I flushed the coolant this weekend. I first put in a coolant flush solution from Prestone. I flushed that and it was light green. Then I put in distilled water and drove around for a while and then let it idle until the fan kicked on. Took about an hour. I drained that and it was dark green, almost black! Then I did another round of distilled water, and it was the same color! It was late and I really had to finish the job so I replaced it with coolant and moved on. But it was really bizarre. My only thought is that maybe the first time I didn't get the thermostat to open so all of the coolant in the water pump/heater core never mixed with what was getting flushed. The subsequent times I idled it for an hour to get the fan to come on so then it was probably mixing. But after three drains, I was tired of cleaning up coolant on the floor and pouring it into jugs. I wanted to be done. What could be causing this?
Here is a photo of said coolant getting darker with each flush. One on the left is first drain. The one on the right is the last.



:confused:
 

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2014 OBW 3.6R Limited, 1997 OBW 2.5L Auto (sold, but not forgotten), and 1991 Ford F150
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Discussion Starter #15
This is a little outside of my experience, but an Internet search led to a few possible causes:

-oil or combustion gases leaking into the coolant
-old stop-leak disintegrating
-radiator or heater hoses disintegrating from the inside
-use of a coolant with no anti-corrosion inhibitor (on a sailing site, distilled water was specifically mentioned as causing corrosion.)

Since distilled water has no anti-corrosion inhibitor, that would be my guess as to cause. I'd do a hose flush to get everything possible out of the system, then fill with a 50/50 coolant mix and hope for the best.
 

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98 Outback Limited - CCR EJ22 installed 2006
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Hey guys, I just replaced the t-stat and upper and lower radiator hoses on my Outback yesterday. I did it with the car on jackstands and I have tried racing the engine up to 3,000 a few times and turning it off, and also just letting it run at idle and at 2,000 rpms and I can't get the thermostat to open. It seems like there is no coolant in the lower radiator hose. A mechanic buddy (certified Subaru guy, has worked for a couple of dealerships) says to keep feeling the lower radiator hose and make sure it's hot (full of coolant); this doesn't seem to be happening. I watch the needle during these attempts to burp the system and it has never gone over halfway up; it has never even gotten there, actually. It fluctuates a bit which I assume are bubbles in the system passing the sensor, but I can't seem to get them out. I've also seen the needle "pinned" at the low end of the temp range when I'm giving it gas; it comes back up when I let up on the gas. Again I assume this is bubble-related. Any suggestions?

EDIT:

OK, after letting the car idle for quite a while and racing the engine a bit I got all the big (relatively speaking) air bubbles out. The lower radiator hose did get hot eventually. About the pinned needle problem, it turned out a harness under the p/s intake runners (vacuum lines connect to it) had worked its way loose. I tightened it up and everything's hunky dory now. Maybe this will help someone else who experiences that problem.
 

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2014 OBW 3.6R Limited, 1997 OBW 2.5L Auto (sold, but not forgotten), and 1991 Ford F150
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Discussion Starter #18
If there is coolant in the radiator, there is coolant in the lower hose ... the law of gravity hasn't been revoked.

The lower radiator hose should always be cooler than the upper hose. Unlike a lot of engines, in a Subaru the hot coolant exits the engine at the top, enters the radiator to be cooled, and exits the radiator at the bottom.

As far as air in the system, have you tried raising just the front of the car? If the car is back on the ground, run the front wheels up on a 2-3 of stacked boards to raise them 3-4 inches. This makes the top of the radiator the highest point in the system and the air will flow there. Loosen the radiator cap and run the engine for a few minutes then check the coolant level.

RL
 

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2006 subaru Outback 2.5i
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Where online do I find the Subaru cooling system additive? I'm not very close to a Subaru dealer. Thanks.
 
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