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2007 Forester X SatNav MT 5 MT
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Discussion Starter #1
Just having picked up my Foz i noticed after driving about 250km the coolant resevoir tank is completely dry and from looking in the rad cap i cant see any coolant (its supposed to be just below the cap from the owners manual illustration).

So i take it into the dealer as they supposedly serviced the car 2 weeks earlier. They said the radiator was fine, full and it didnt take much to fill up the resevoir tank. Anyway drive for 2 days and notice the coolant level is about 2cm below the low line. I cant see any leaks on hoses or around the engine and havent noticed any coolant smell. What would be the most likely cause of this disapearing coolant?? It is a N/A 2.5L engine.
 

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01 Forester
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50 Posts
Check your rad cap.

About a month ago I had the same, disappearing coolant problem. Crawled under the car, with it running to see if the head gaskets were leaking externally. I didn't even see minor seepage. There wasn't any sweet smell to the exhaust, I was baffled. I think I read on here that a leaky rad cap might be letting coolant evaporate from the coolant system. I put a rad cap on, with a bottle of coolant conditioner, and its been great since. I haven't lost any coolant at all.
 

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2001 Forester S
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106 Posts
Coolant leaks are common on many cars. Sometimes lost coolant just seems to disappear. The system is closed, so this shouldn't be happening, and it has to be going somewhere.

+1 for rickj - check the rad cap for gunk around the rubber seal, and make sure the springy part moves back and forth okay. If you have any doubts at all, pick up a new cap because they are cheap. (Change it only when the system is cool.)

Other possible causes, cheap to expensive:

1. There could be a leak at a connecting hose on the radiator or engine, or the thermostat housing or o-ring is leaking. A hose leak is more dangerous because it could suddenly become a big leak, while on the road or even when you are looking at the engine. Be careful looking around while the system is pressurized. Use safety goggles at least. If you have a face shield, use that. Wear gloves. If the system is hot, don't go poking hoses that might be brittle. And keep your hands and tools away from the fans if the engine is running - they could suddenly come on.

2. The radiator could have a leak out of the top or bottom plastic tank. These are the large black parts attached to the aluminum core - the top tank has the rad cap, connection to the reservoir and the top hose connection; the bottom has the bottom hose connection. There is a large gasket that seals each to the aluminum part of the tank and these can leak. More rarely the tanks could develop cracks, but you would lose coolant much more quickly and a pressure test should have picked this up. I've seen a leaky gasket three separate times in my '01 Forester S over its 150K miles - two leaks in the top tank, one in the bottom. If you have been driving for some time (e.g. several tankfuls) but not getting overheating, it is more likely to be the top tank. The system may only leak coolant when the engine is warmed up and the system is at pressure. A small leak would allow coolant to squirt out when the system is warm, and it might be visible for only a short while. It would be lost on the road and you may not smell it or see it. To see an active leak, you could top off the reservoir and radiator (when the system is cooled off), get the engine warm, then look under the hood while the engine is still running. Leaks at the top tank are easy to see; leaks at the bottom less so. (Same precautions as above note.) [As a side note, if you are mechanically inclined, removing the radiator is not that difficult nor time-consuming, and you could have a rad shop test/repair it for about $100 or less. A new rad is about $120-$300. If the coolant was just replaced you can save it and re-use it. A dealer could charge two hours' labor (i.e. $150 or more) on top of parts, and they would need your car for at least a day, so it is worth your while to pull the rad yourself. If you do this, change out the thermostat too with a Subaru one (about $20). Don't overtighten the connecting hoses: The tanks and thermostat housing are plastic.]

3. There could be a pinhole leak in the middle of the tank. If the shop had pressure-tested the system, they should have seen it. If you pull the rad yourself and get it to a rad shop, they will test it.

4. The engine could be losing coolant due to a blown head gasket. When the gaskets first start to go, the leaking occurs when the car is first warming up, then the leak seals and whatever coolant was lost largely disappears. You would need to look around the engine heads for any trace of lost coolant if it is an external leak. Use a flashlight and hand mirror if looking from the top. Alternatively, the coolant could be lost internally, into the combustion chamber. You should see billows of steam out of the tailpipe, and bubbles might also be visible in the coolant reservoir at times (the exhaust gases being forced into the cooling system by the leak). A compression test should pick up an internal leak. Check other threads on this site for detection of head gasket leaks.

5. An engine head or the block could be cracked. A compression test should pick this up if the crack affects a cylinder, or a cooling system pressure test should catch it.

If you are still losing coolant and can't find the leak, try removing the bottom plastic engine skirt (usually taken off for fluid changes). Put some clean white paper all around the area under the engine when it is cold (a garage is best). Start the car and let it idle. If you are losing coolant somewhere, some drops should occasionally escape and land on the paper.

As an attempt to stop a tiny leak, you could try adding stop-leak (Subaru Coolant Conditioner). If it works, be thankful and keep watching the coolant levels.

Good luck...
 

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2008 2008 2.5i-2018 XT
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Once the radiator level goes down, you will have some voids in the system when you refill it. It might have to be topped a couple times. I would replace the cap. If there are no other visible leaks, its probably the Head Gasket (rarer in post 02 models but still possible)
 

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2008 Forester X Premium 5MT
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8,073 Posts
'07 should be under warranty. If it were mine I wouldn't even be buying a cap for it. Mention it to the dealer, but let them spend the money to diagnose it.
 

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2007 Forester X SatNav MT 5 MT
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96 Posts
Discussion Starter #7
Cheers guys,

I am taking it into the dealer tomorrow to find the problem; hopefully.

I am thinking its just a void in the system or needs a new cap. But your right im not paying for anything, the dealer can top it up and replace the cap if need be.
I will let you know what the problem was.
 

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2007 Forester X SatNav MT 5 MT
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96 Posts
Discussion Starter #8
Check your rad cap.

About a month ago I had the same, disappearing coolant problem. Crawled under the car, with it running to see if the head gaskets were leaking externally. I didn't even see minor seepage. There wasn't any sweet smell to the exhaust, I was baffled. I think I read on here that a leaky rad cap might be letting coolant evaporate from the coolant system. I put a rad cap on, with a bottle of coolant conditioner, and its been great since. I haven't lost any coolant at all.
Has anyone know if evaporation can occur from the clear reservoir tank? The cap on it seems much more likely to me to be the cause of any evaporation.
 

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2008 2008 2.5i-2018 XT
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There will be some loss of coolant due to evaporation. But its a small amount its hard to evaluate that because the level depends on ambient conditions and length the car is sitting. You can bring it up to a given height and mark it after the car is sitting say 8 hours and note the outside temp. In say 2 weeks there would be very little difference.

You will get more evaporation in warmer weather. I am going to make a guess that the evaporation might be an ounce/month on the average.
 

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2007 Forester X SatNav MT 5 MT
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Discussion Starter #10
Update

Hey have taken the car to the dealer twice now. First time they pressure tested and found nothing retopped fluid after resevoir tank was empty and said bring back in 2 weeks. Took it back in last thursday and they found the top radiator hose was swollen and needs replacement.

Luckily its all under warranty. I will let you know how it all goes.
 

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2008 2008 2.5i-2018 XT
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13,234 Posts
they found the top radiator hose was swollen and needs replacement.

Luckily its all under warranty. I will let you know how it all goes.
I'm doubtful they are getting to the bottom of it. Sounds like they are just groping. I think you have a HG leak. Pressure testing doesn't show up leaks in many many cases. The leak at higher temps many times.
 

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04 Forester X, MT
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1,051 Posts
I'm doubtful they are getting to the bottom of it. Sounds like they are just groping. I think you have a HG leak. Pressure testing doesn't show up leaks in many many cases. The leak at higher temps many times.
OK, so it is warranty and the dealer should take care of it? How many miles on your car?

Leaking that much without visual external leaks sounds like HG. :icon_frown:

Air can be trapped and lead to coolant level dropping quickly but this is often accompanied by overheating. And, once coolant is added several times to overflow bottle, level should stabilize.

It would be somewhat unusual to have leaking hoses that soon.

Subarus are bad for the big top radiator hose leaking where it attaches to the aluminum casting on the motor because it is not very round or smooth. When I replaced the hoses on mine this time I used 2 hose clamps and some sticky gasket goop in hopes it will last longer before it leaks. I replace hoses every 4-5 years as a routine matter. I did have one once with the clamp a little loose that didn't visually leak but over 200 mi or so at interstate speeds lost a lot of coolant.

You just can't see small-ish leaks because the liquid evaporates too soon to be noticed due to the heat. You have to pressure test cold. If pressure drops there is a leak somewhere and you then look for antifreeze which can be seen if the leak is external.

I have a simple 20 psi gauge attached to a tee with a tire valve in one end and hose barb in the other. Disconnect coolant overflow hose from rad and connect to barb. Pressurize with bicycle pump and wait, go back and check in 1/2 hr to 1 hr. Look for any leaks. The radiator cap will let it leak down some to about 15 psi or so. Do not use an air compressor to pressurize the system!
 

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thanks wormguy for the cheap to expensive possible cause
my 2004 is loosing coolant as well so this thread gives me lots of info

keep us updated guys I'll be reading this thread..

thank you

mine is old an out of warranty though but still just interested to see what is the most common cause
2004 XS with 230,000 kms
 
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