1997 Subaru Legacy Outback – Head Gasket Problem?

Reader Question: Hi Austin,

This is a follow-up question to your advice regarding K & W Block sealer. You recommended we leave the sealer in and drive for 500 miles before flushing it out again.

I have a 1997 Subaru Legacy Outback with 117000 miles. After replacing the blown radiator, hoses, radiator cap, and thermostat, we have learned the head gasket (or head itself) is bad.

Once the car reaches normal operating temperature, it overheats & spits coolant within minutes of driving. There is no water in the oil, and no oil in the water. I do have bubbles in the water, and a lovely plume out the tailpipe.

First, I tried the new K & W Nanotechnology Block Sealer according to the manufacturer instructions, which had no effect. After talking to them, they believe that since it is a pure exchange between the exhaust system and cooling system, the patch was not able to take hold due to the pressure coming through the breach.

They had me identify the bad cylinder (based on spark plug appearance), and try the same patch again, only without that plug firing (left plug in, removed the cable). I did so, but once I reconnected the fourth cylinder, I went right back to the bubbles and exhaust plume.

I would LOVE to try one more fix using your 500-mile suggestion, but as I said above, I cannot drive more than a few minutes before it starts blowing coolant.

Do you have any suggestions that could help me out? At the rate I am able to travel, it would take me 50 trips just to reach 500 lol. I just cannot afford to put any more significant money into this car. If nothing else, I am just hoping to get it running well enough to use as a trade in, but I cannot even drive it to the dealer.

Thanks for reading,


Howdy Dave,

Thanks for checking your auto insurance, hope you got a lower rate than you currently are paying.

I am not sure the additive is going to be of much help for you if you have that internal pressure building up that fast. I am assuming it starts “blowing coolant” because of compression gases in the radiator and not because the coolant is boiling over.

On a side note though, the additive is cheap compared to a valve job or head repair job, so you really do not have much to lose here. I would remove the thermostat, drain the coolant from the engine and radiator best you can anyway, add a can of the block sealer and top off the radiator halfway with plain water and let it idle for awhile until you can get the radiator 3/4 full of water then drive as far as you can.

I would also run the heater on full blast for a while to make sure there are no air bubbles in your heater core. Recheck your coolant level in the radiator after you run your heater.

If you can put a few miles on the engine without it overheating or puking coolant, I would replace the thermostat with a new one, do not use the one you took out. Thermostats can act strangely after they have been overheated.

This engine can be tough to bleed out the air bubbles in the cooling system. I do not remember, but there might be a coolant bleeder screw on or near the thermostat housing, which you can use to bleed out the air.

You want to get as much of this copper flake in the additive circulating around the cooling system to find and plug up the hole as long as possible.

I have yet to have luck using the product the way the instructions tell you to do.

I have my fingers and toes crossed for you, friend. Keep me posted, will ya?

Click to read my article about the K&W Engine Block Sealer Additive and how to use it.

Austin Davis

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7 Comments on "1997 Subaru Legacy Outback – Head Gasket Problem?"

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  1. BILLY says:

    And one more thing. . What if I use this liquid glass stuff/ k&w cause im thinking about getting some- without actually driving an putting 500 miles on it. Just so I don’t get stranded. Can I let the car sit an just keep revving it to push the sealer through?

  2. BILLY says:

    Ok… so I got a new radiator cap, still overheats. Still building air pockets. I pulled the radiator and flushed it. It was clean as a whistle. Water flowed freely through every whole. Even the drain plug and bleeder. I’m pretty positive its not the heater core, as I have heat all the time when it runs. I’m going for a leak in the gasket between coolant port and exhaust chamber. Now the guy at oreileys is a good friend of mine and he’s pretty car saavy. He told me the k&w sealer made his car worst. Now you’re telling me to use it. Considering I don’t want to clog the radiator. I would presume as long as I follwed instructions an flushed the liquid glass stuff completely until I seen water flow clean then I shouldn’t have a problem. I don’t have a pressure tester to check the system but at this point I think its pretty obvious that I don’t need it. Link your instructions in your next comment please. So I can get an idea of why your intructions are better. Not that I’m trying to say you’re wrong. I’m just desperate to.fix my car.

    • By Austin Davis says:

      Well, I have personally not used the Liquid Glass stuff, but have seen a radiator that was completely plugged up with the stuff….can only imagine what the inside of the engine looked like. I have personally used the K&W Block Sealer at least 50 times in my shop and all but a handful were a total success.

      I have NOT had good success using the sealer as the can describes though, and we have had to come up with our own version which seems to work great. Driving the vehicle with the sealer in the system seems to be the key to a long term success.

      The heater core will not cause overheating, you can block off the heater hoses with vise grips to shut off coolant to the core and it will not effect the rest of the system. I would still get a cooling system pressure test, that is the first thing I do in any overheating situation. It should also tell you if there is an INTERNAL coolant leak as well as an external leak. If the pressure test cant hold pressure…then there is a leak somewhere. If it can hold pressure, I would assume the system is ok internally as well.

      If you want to try the K&W, here is my own personal instructions. Obviously I can NOT be held responsible for any damage that might occur in your situation but I can tell you I feel comfortable with the sealer and would use it in my own personal vehicles if needed. This IS a last resort option though to removing the cylinder heads and replacing the headgaskets and resurfacing the head.

      Here is the link http://www.myhonestmechanic.com/articles/engine-block-sealer-additive.shtml

      Keep us posted on what happens, it will help the next guy.

  3. Billy says:

    sorry i submitted too early. darn phone


    My radiator fans work. they kick it when it reaches a little above normal operating temp. At idle everything works fine and it cools down.
    Only when i start driving is for about ten minutes is when it cools. My friend is a mechanic and we went through everything we cant figure it out. We bleed air out of it for hours. Drove it, and more air pockets built up. Its consistent with this. Coolant does spew into the overflow tank, the engine is definitely overheating. I think the only thing i havent tried is the radiator cap. Although, considering i replaced the waterpump and thermostat already, I have ran the car hot a few times to and from work. So im afraid that i might have warped a head. Other then that my buddy told me it could be the head gasket. (EDIT) he explained it to me the same as the gentleman who posted first. “believe that since it is a pure exchange between the exhaust system and cooling system” I bought some stuff similat to the k&w. its the liquid glass kind. Do you think i should try replacing the radiator cap first and possibly try flushing the radiator first? These cars are extremely hard to bleed air from.

    • By Austin Davis says:

      Hi, I am assuming you meant to say the engine runs HOT when you have been driving for 10 minutes? Typically if the engine overheats at freeway speeds or after driving for awhile it is either due to:

      1. A restriction in the radiator not allowing coolant to circulate through the engine, and a new radiator is needed….flushing basically does nothing.
      2. A coolant leak in the system somewhere and a cooling system pressure test should be done FIRST to rule out a leak….it should also tell you if there is a leak internally in the head gaskets.

      If no leaks are found, and the engine seems to overheat or run hot after driving a while or on the freeway I would take a gamble and replace the radiator with an aftermarket radiator from your local auto parts store.

      I would not use the Liquid Glass stuff, seen a few clogged up radiators with that stuff. If you are still suspect of a head gasket issue then the K&W Block Sealer is the best on the market, but use it as I direct not as the can suggests. You can search my site for “K&W Block Sealer” for my instructions.

      Keep me posted

  4. BILLY says:

    I have the exact same problem in my 94 legacy. I replaced the thermostat, water pump, and timing chain. And it still overheating. I’m thinking head gaskets but I don’t have any real distinct signs if it. No plume, oil isn’t milky and its not spewing out of the block. I do notice the if I take off the oil cap there’s air blowing back. I’ve checked the other vehicles of ours and none of them do that. Any suggestions before I do the head gaskets? I’ve bled as much air out as possible and it seems to keep building pockets and overheard.

    • By Austin Davis says:

      Humm, When are you seeing the overheating issue and is the engine really overheating or just showing overheating on the dash gauge? Meaning, can you feel excess heat in the engine when you open the hood and does coolant boil over into the plastic overflow bottle?

      If you experience overheating at stops or slow speeds I would be suspect of a faulty electric cooling fan motor at the radiator.

      If you experience overheating when on the freeway I would suspect a clogged up radiator that needs to be replaced, flushing does nothing for removing rust built up at the bottom.

      Air coming from the oil cap area is normal, so nothing to be alarmed with there.

      I would also try to squeeze the upper radiator hose together with your hand and a rag when the engine is overheating. if you can easily squeeze it together you have a leak in the system somewhere or there is still air in the system that needs to be bled out.

      So far, from what you mentioned I would not suspect head gaskets, but would do a cooling system pressure test to see if you have a leak somewhere.

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