All Wheel Drive Auto: Independent Seattle Subaru Service


Will Stop Leak, Fix My Subaru Head Gasket Leak?

Stop Leak in A Subaru

One of the questions I get a lot is “can I add some stop leak”

I have never found anything in a bottle that will resolve what happens to a Subaru Head gasket.  I took some pictures from a Subaru Outback in the shop today that had some stop leak put in, only to over heat the next day.   The cooling system is just full of this stuff and it really did no good as seen in the pictures below.

I really have never found anything that will permanently resolve a head gasket leak on a Subaru.   While I truly understand the displeasure there can be at the though t of a repair like head gaskets, I do also want to  warn that adding stop leak can add to the cost of the repair.

Stop Leak in A Subaru
Stop Leak in A Subaru

8 Responses

  1. 99 Forsester with exhaust gas bubbling out cooling system into the overflow tank. Combustion chamber head gasket leak.

    I tried the non glass type head gasket stop leak and it did not work at all. I used Perma-Tech, Dura-Seal and no improvement whatsoever, this stuff was supposed to be formulated just for 4 Cylinder Subaru’s and it cost $150, which is a huge rip-off because it does not work. It’s money back guaranteed but I had to contest it with my credit card company to get my money back. So Subie owners beware. Then I tried some Bars Leaks stop leak Head Gasket Fix #1111 and it only worked for a day because I drained the system after using it. Then I tried it again leaving it in and it seems to be working, not 100% but it’s only been a week now and it does seem to improve the more you drive the car. I strongly recomend removing the thermostat when using these products and leave your heater valve open all the time once you put it in and leave it in. Gut an old thermostat and just use the disc shell so you can put the gasket back in, the gutted disc will hold the gasket in place. My 4 cylinder 99 Forester does not overheat without the thermostat, the water flowing thru the radiator too fast theory does not apply with this engine. Anyways, it appears any product you have to drain from the system after use will not hold, you need a quality product that is designed to leave in and that appears to be what’s working on my Forester. Unfortunately, this means your water pump has to endure the metal flakes in these products so the jury is still out on how long the water pump will last. As far as the heater core getting plugged up, as long as you flush your system well and already have good flow thru your heater core you should be fine because these products are designed to only harden in spots where there is high temperature, the engine block not the heater core but I recommend you drive around with the heat valve open all the time just to keep an open flow thru it. Follow the instructions and I recomend placing a small rag by the throttle to keep the engine idling at about 1500 RPMs for at least 20 minutes after you put the stop leak in. Let it cool then top it off and drive carefully, try to stay under 3000 RPMs for at least a week if you have a combustion chamber leak like mine. Make sure you try to get it up to normal operating temp when you drive it, which is a little tricky when just driving on the freeway without a thermostat, stop lights and city driving should let it get up to temp. This way the circulating stop leak keeps coming in contact with the head leak over and over again hardening more and more at the leak repeatedly. I will post again and let everyone know if it’s still holding and the status of my water pump and heater core. Anyone else have any luck with a stop leak for a combustion chamber head gasket leak ?


    1. I have 472 000 km on my 08 impreza. Minor external leak and exhaust bubbling from my rad. Added duratite and only used half the bottle. Still going 2 years later but I lost heat in one vent but 3 out of 4 still work. Cross my fingers another 100 000 km. I live in canada so it doesnt see anything over 20 celsius.

  2. Hello

    I had a new head gasket put in my Subaru Outback about a year ago. After driving on the highway it lost a lot of water and started overheating like crazy!

    I heard a new head gasket does not always take! What now? Should I add the real good stop leak?

    1. If the head gasket repair was done correctly with the proper parts it should hold up longer than a year.

      Could be a cheap gasket, could have been an incomplete repair.


  3. hi Justin,

    I appreciate the advice! Since your comment I have taken my Forester into a Subaru dealer for another diagnosis. They have quoted me for the head gasket repair. But they also mentioned that the stop leak effected my radiator, and they have prescribed replacing it. Does this seem like a good idea?

    They have quoted me $460 for the radiator. I called Autozone and got a price of $250 for the radiator. I’m thinking maybe I can replace it myself. Is there anything to be leary of?

    They also found that my alternator is going bad. I knew I was hearing a strange noise from my engine, so it seems this is that. Again this seems like something I could fix myself (replacing it with an alternator from Autozone) and save some money. Is there anything to be leary of in replacing an alternator?

  4. Hi Aaron,

    Most like the head gaskets have failed.

    I try to stay a way from the after market re-manufactured products.

    Most likely you don’t need an engine, but lets for argument sake say you do, you would be better off and spend less money buying a Factory Subaru “Hybrid” engine, Having your heads re worked and never looking back.

    Having said that, repaired correctly there is no reason you should be able to get many miles out of what you have. Replacing the engine may be a waste if its truly not needed.

    Hope that helps


  5. Hi Justin,

    About a month ago I bought a 2000 Subaru Forester S. It has 94,000 miles on it. It was sold to me “as is” from an Acura dealer–they got it in as a trade. For me it a hopeful deal & project. (all they told me was that a new clutch was needed)

    My ‘check engine’ light has come on and the codes I’ve gotten are misfire codes for all 4 cylinders, fuel trim, and O2 sensor.

    Sometimes the engine idles with a “cough” (revs up and down) and at other times it just doesn’t give me the power I expect when giving it gas.

    I flushed the coolant and installed new plugs and wires. I drove it for a week and coolant seemed to blow out. A weird yellow substance is dried all over the right side of my engine (near the coolant reservoir). I had the radiator tested for exhaust fumes and they were found. The local shop told me its a head gasket leak. They said they’d repair it for 16-1700 dollars. They guessed that someone used ‘stop-leak’ to hide the issue. Maybe the previous owner.

    At this point, my engine does not overheat. But I want to do something soon.

    Do you agree that this is a head gasket issue, based on what I’ve said?

    I’m considering having a Jasper remanufactured engine installed, so that I can do this all right up front. But is this too much? Should I just fix the head gasket instead?

    I suppose I just feel more confident about the remanufactured engine. If I fix the head gasket, I may find more trouble and then spend more money. All the while I get closer to the cost of a remanufactured engine. So why not just do that from the get go?

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