- Joined
- Sep 25, 2025
- Messages
- 5
Hello, I understand this has been talked about to death but I would just like to share my recent experience with this stop leak product.
I worked on a 2011 Subaru Outback. It had been to the garage several times for overheating and low coolant. They performed pressure tests and found nothing, changed a couple suspect parts: radiator cap and thermostat. Everything seemed fine, until a few months later, the engine overheated and bubbled coolant out of the reservoir. After refilling the car drove for another several months before reproducing the problem, with no visible leaks along the way.
I think the engine overheated due to low coolant caused by a seeping head gasket. I read that this was a common problem on older subarus as they had faulty head gasket, to the point where subaru was recommending "coolant conditioner" with every coolant fill procedure to save their asses. My research online pointed to this conditioner being a rebadged stop leak. I decided to try a stop leak product because the owner was not willing to put thousands into a head gasket job plus nothing was confirmed for sure.
For the next coolant refill, I added 100ml of Rislone Head Gasket Repair, the subaru dealerships do not stock the conditioner in my area any longer.
link: https://rislone.com/wp-content/uploads/2021/07/21110-PDS.pdf
I thought this product might be a good replacement, and also used an amount far below what was recommended on the container itself (1/6 of the recommended dose).
Car was running fine, and I was checking the coolant level every few days and it was stable. HOWEVER! I started to notice that the upper rad hose was always collapsed when I went to look at the coolant level in the morning. Opening the rad cap, I could actually see that the stop leak was plugging the passage to the overflow reservoir (there's a small hole in the radiator neck that relieves pressurized coolant into the reservoir), and causing a vacuum in the system as it cooled. So it is a huge problem using this kind of product with an overflow reservoir type system. Maybe on closed coolant systems like some Fords this would not happen. But the product states it does not plug any coolant system components and is compatible with all makes and models... this is simply false marketing. And no, I did not add the product to the reservoir, but into the radiator as per the instructions, into an already filled/purged system.
Anyway, I flushed the coolant as best I could in my driveway, doing 3 radiator empties and refills until I felt it was good to go. It's now 2 weeks later and the upper rad hose has burst, and I checked the rad cap and what do ya know? The overflow is plugged again. So it overpressurized and thankfully the upper rad hose failed first. I'll be doing another few flushes and will have to monitor the coolant continuously from now.
Hope this helps someone who's thinking they can save some time with this kind of product. To be fair I do believe it stopped whatever was causing the leak, since the system holds both pressure and vacuum with the reservoir blocked off
I worked on a 2011 Subaru Outback. It had been to the garage several times for overheating and low coolant. They performed pressure tests and found nothing, changed a couple suspect parts: radiator cap and thermostat. Everything seemed fine, until a few months later, the engine overheated and bubbled coolant out of the reservoir. After refilling the car drove for another several months before reproducing the problem, with no visible leaks along the way.
I think the engine overheated due to low coolant caused by a seeping head gasket. I read that this was a common problem on older subarus as they had faulty head gasket, to the point where subaru was recommending "coolant conditioner" with every coolant fill procedure to save their asses. My research online pointed to this conditioner being a rebadged stop leak. I decided to try a stop leak product because the owner was not willing to put thousands into a head gasket job plus nothing was confirmed for sure.
For the next coolant refill, I added 100ml of Rislone Head Gasket Repair, the subaru dealerships do not stock the conditioner in my area any longer.
link: https://rislone.com/wp-content/uploads/2021/07/21110-PDS.pdf
I thought this product might be a good replacement, and also used an amount far below what was recommended on the container itself (1/6 of the recommended dose).
Car was running fine, and I was checking the coolant level every few days and it was stable. HOWEVER! I started to notice that the upper rad hose was always collapsed when I went to look at the coolant level in the morning. Opening the rad cap, I could actually see that the stop leak was plugging the passage to the overflow reservoir (there's a small hole in the radiator neck that relieves pressurized coolant into the reservoir), and causing a vacuum in the system as it cooled. So it is a huge problem using this kind of product with an overflow reservoir type system. Maybe on closed coolant systems like some Fords this would not happen. But the product states it does not plug any coolant system components and is compatible with all makes and models... this is simply false marketing. And no, I did not add the product to the reservoir, but into the radiator as per the instructions, into an already filled/purged system.
Anyway, I flushed the coolant as best I could in my driveway, doing 3 radiator empties and refills until I felt it was good to go. It's now 2 weeks later and the upper rad hose has burst, and I checked the rad cap and what do ya know? The overflow is plugged again. So it overpressurized and thankfully the upper rad hose failed first. I'll be doing another few flushes and will have to monitor the coolant continuously from now.
Hope this helps someone who's thinking they can save some time with this kind of product. To be fair I do believe it stopped whatever was causing the leak, since the system holds both pressure and vacuum with the reservoir blocked off
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