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Old 05-20-2021, 07:36 AM   #1
Broncopower
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Member#: 334133
Join Date: Oct 2012
Default Green Slime in Coolant Overflow Tank

I recently bought a 2011 outback on Craigslist with 175k miles and limited maintenance history. Why did I buy this!?

I haven't driven the car too much, but never overheated on me. I changed the oil, looked good. I sent a sample to Blackstone about a month ago and haven't heard back. I hope they follow through with the test results.

I am in the process of installing an Aisin timing belt kit, and noticed green slime in the overflow tank. This terrified me, as I have read horror stories about head gasket issues.

Please see pictures attached, and let me know if this is common/normal, or an indicator of a bigger problem such as a head gasket leak.

I plan to drain the coolant shortly, and will let you know what I find. Do you recommend that I perform a compression check?

I am also in the process of replacing the front cv axle, hub, and struts, so I want to rule out a head gasket or other serious issue before sinking more time/money into this car.





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Old 05-20-2021, 12:57 PM   #2
Elbert Bass
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Member#: 283429
Join Date: May 2011
Chapter/Region: South East
Location: Down yonder.
Vehicle:
2016 Fuji Sunfire 03
Silver

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That car should have had blue coolant originally, does it now have green coolant? Green coolant could indicate a previous repair to the cooling system or refilled with the wrong coolant. That won't hurt anything, the blue is just a longer life coolant.
The slime could just be green coolant that all the water has evaporated out of or it could be some sort of stop leak additive. Evaporation would more likely be the case if the overflow tank was dry except for this goop in the bottom. it is not uncommon to find a non-oil slime if the overflow level has not been maintained in the bottle and allowed to to get very low.

I will say as far as head gaskets that particular year EJ25 OB engine would have had the MLS gasket from the factory. My experience with those is they do not leak externally near as much as the old composite gaskets. When I have seen those gaskets in that year OB failed it is between the cooling jacket and combustion chamber and 9 times out of ten only presents an overheat symptom when under heavy load as in driving up steep grades or prolonged heavy highway driving under continuous load.
Compression test will only indicate catastrophic head gasket issues - a cylinder leakage test will give you more information. Unfortunately if it is that intermittent leak as I described above you may be unable to see any definitive test data.
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Old 05-20-2021, 02:28 PM   #3
Broncopower
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Default

Wow, this is great information, thank you! Yes, the car has green coolant currently. I plan to switch to oem blue when I replace the timing belt. It also has an aftermarket radiator....

The overflow tank had a little bit of liquid coolant, with the sludge at the bottom of the tank.

Do you have any advice for determining if stop leak was added? Will I see it in the coolant when I drain the radiator?

Good to know about the possibility of an intermittent head gasket issue. If that were the case, is there an area in the engine that I can look for an external leak?
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Old 05-28-2021, 08:40 PM   #4
Elbert Bass
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Join Date: May 2011
Chapter/Region: South East
Location: Down yonder.
Vehicle:
2016 Fuji Sunfire 03
Silver

Default

Quote:
Originally Posted by Broncopower View Post
Wow, this is great information, thank you! Yes, the car has green coolant currently. I plan to switch to oem blue when I replace the timing belt. It also has an aftermarket radiator....

The overflow tank had a little bit of liquid coolant, with the sludge at the bottom of the tank.

Do you have any advice for determining if stop leak was added? Will I see it in the coolant when I drain the radiator?

Good to know about the possibility of an intermittent head gasket issue. If that were the case, is there an area in the engine that I can look for an external leak?
As I mentioned that block with an MLS gaskets generally does not exhibit an external leak. If it is an intermittent leak those are ALWAY internal and can only be diagnosed by creating the overheat condition that accompanies the leak and then perform a CO2 test on the cooling system once it is safe to remove the radiator cap.

As far as stop leak - unless way too much is used it's hard to tell.
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