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98 Subaru Legacy/Outback Headgasket repair vs Thermagasket?

Does Thermagasket work? And for how long. My car has had 2 head gasket repairs and apparently now needs a third at 175000 mi.

I’m not a fan at all of crutch products (Thermagasket is one) and especially overpriced ones which involve a certain amount of BS behind their use.

If the head gasket is simply weeping coolant and the head gasket breech is not into the combustion chamber then a crutch product may work for a while. You can find a stop leak product for far less money than Thermagasket though.

If the car is suffering repeated failures of the same gasket then the competency of the person doing the repair is questionable. They’re skipping some procedures or something.

If you are having repeated head gasket failures, I can think of only two reasons:

The mechanic is not using the “new design” head gaskets that Subaru came up with for these engines.
The heads are warped, and were not machined or replaced as they should have been.

Both of these possibilities lead me to the same conclusion that ok4450 came to, namely that the mechanic has questionable competency to do this type of repair.

Like the previous replies, I never liked these crutch products.

Even if it did “work” (for all definitions of “work”), how will that help you? Since these are just bandaids, when will the leak break open again? In 5 minutes, 5 days, 5 weeks?

Would you trust the repair enough to let a loved one take it out on a rainy or cold night, or on a long trip? I wouldn’t.

For what it’s worth, I’ve done more head gasket repairs by far on Subarus than any other make of car. I can’t even start to count them.

One thing that always baffled me a bit on the Subarus is how prone to cylinder head warpage they are.
One would think a short in length cylinder head would be adverse to warping at all but I’ve found about 90% of the Subaru heads I’ve worked with exceeded the maximum .002 of an inch allowed.

I’m also of the opinion that use of TTY head bolts and cutting the number of head bolts down to 6 per head instead of 8 has something to do with it.

Another point could be (theorizing here) that many techs do not use a sealant on the head gaskets. I’ve always used spray Copper Coat and find that the epoxy/copper particle mix helps a lot in a repair like this. I don’t know if Subaru still recommends it or not but at one time they even had a Tech. Service Bulletin out about using a sealant on the gaskets. Their TSB involved a product called Fuji Bond but Copper Coat is much, much cheaper and works just as well.
That’s the way I’ve always done it and never had one fail on me yet.

Thanks to everybody for their replies. The first two head gasket repairs were done in Marysville WA by a Subaru dealer (this was a couple years ago)… One a couple of weeks before I bought it used and the second a couple of weeks after I bought it. And yes, they charged for both times… saying the guarantee on their work did not transfer across a change in ownership… even though I bought the thing from THEM.

This time I am dealing with “Independent Subaru Service” in Marysville WA. Things are starting to get messy with this shop too but the dance is not over yet. So far I’ve had my toes stepped on to the tune of $1,100.00 and I’ve gotten a radiator and thermostat on the first visit and a written statement on the receipt that they found hydrocarbons in the radiator but that they were not affecting engine performance at that time… then it overheated again… I got a water pump on the second visit… then it overheated again… On the third visit they said I needed a new head gasket for another $1950.00 and I declined at that time.

I had a fellow from Thermagasket out and I thought he did a real good job of checking out the entire coolant system as I watched and sometimes helped. He found that my new water pump was not moving any coolant through the system. He said get that fixed and he would come back to do the Thermagasket thing. He charged me $74.00.

Here is how he determined that the water pump was not moving coolant:

Remove the guts of the thermostat.

Disconnect the hose between the engine and the top of the radiator (at the radiator).

Attach a 90 degree stiff hose to the top of the radiator and hold a garden hose above it to keep the water fill level in sight and in the vertical portion of the 90 degree stiff fill hose. The garden hose is not allowed to pressurize anything, rather to just ?pour? water in.

Put an extender hose on the coolant hose from the engine and hold the far end above a 5 gallon bucket.

Start the engine and use the garden hose to keep the radiator full via the 90 degree stiff fill hose.

What we saw:

If the outlet of the extender hose from the engine was below the level of the water in the 90 degree fill hose (attached to the top of the radiator) then water would flow slowly but evenly out of the engine… apparently via only gravity flow.

If the outlet of the extender hose from the engine was held above the level of the water in the fill hose (attached to the radiator) then NO water flowed out of the engine. That?s right NO flow of coolant. And the engine is running, we even reved it up to 4000 RPM and still NO coolant flow if the outlet was above the water fill level. This was true even if the outlet was only an inch above the observable water level in the fill hose.

I removed the two bolts that allow access to the thermostat chamber drained the system and peered up into the water pump. I could see the impeller and I used a screwdriver to turn it. There was some resistance but the pulley on the outside of the water pump was not turning with rotation of the impeller.

There was communication with the shop mostly via their office person who on one occasion said that the pump was designed to pump antifreeze and it would not work in water (Ya that really is what I was told by the office person) however their mechanic, during previous conversations, seemed quite competent…

On the fourth visit to the shop they said the water pump was working? no problem found. The car is still there and I?m in the process of deciding what my next step should be? any suggestions???

I don’t know about you, but at this point, my reaction would be to give serious thought to trying the Thermagasket and when that doesn’t work, taking advantage of Cash for Clunkers to unload that thing. I don’t think I would buy another Subaru at this point since you’ll probably be really annoyed with yourself if the new one isn’t a paragon of reliability.

I don’t have the slightest idea what to do about the water pump. If you keep the car you’ll probably have to replace it. Once the old one is out of the car, it may be obvious whether it is broken/defective or not.

If the car qualifies for CfC, maybe you can save a few bucks by skipping the water pump/Thermagasket and just getting rid of it even though fixing it might make economic sense in other circumstances.

My condolences. You appear to be going through a major soap opera with this car and I’m not sure I even have an answer for you.
The impeller turning and the pulley not rotating would definitely tell me the impeller shaft has cracked, which would cause overheating of course.

Wading into a bunch of money on head gaskets again would be very hard for me to swallow. If a pump fixes it then fine. If the problem is not the pump and does involve head gaskets then I’m tempted to go along with the recommendation to trade it off.

Just a few comments.
Head gaskets are frequently misdiagnosed as many techs will blame overheating on head gaskets rather than spend the time to do a proper diagnosis.
Any chance this hydrocarbon in the radiator problem could be caused by residual traces of HCs from a prior head gasket problem and the fault is simply the water pump?

You can try this backyard test. Not 100% definitive, but helpful.
Loosen the radiator cap on a cold engine. Retighten it and start the engine. Allow it to idle for a minute and shut it off. Quickly loosen the cap. If you hear a faint pressure relief hiss then a head gasket could be faulty.

Other tests for a faulty head gasket is a compression test, cooling system pressure test, and even the very simple use of a vacuum gauge. The latter only takes seconds to hook up and if a fault exists with a head gasket in the combustion chamber area(s) then the vacuum gauge will show it immediately.
The bad part is that few mechanics seem to want to use a vacuum gauge.
Examination of the spark plug tips can also reveal a HG problem. Coolant entering the combustion chamber will often bleach or shine the spark plug tip.

The part about the office help telling you a pump will only circulate anti-freeze and not water is pretty comical though.

How hard is it to change the head gaskets? Is this something that I might be able to obtain detailed instruction for, follow them to the letter and get the job done?

Oh Lord! The pump will only pump antifreeze and not water! I’m laughing so hard my side hurts!

I’m truely sorry to hear your story. OK4450 has, as always. given you excellent advice.

The other thing you need to be aware of is that if the head is warped or there is a channel worn in the head from erosion from the combustion gassaes and coolant moving back and forth through the breech, it may be impossible to get a headgasket to stay sealed without milling out the surface. ($$$$$$$$$$$$$). After a number of headgaskets and recurrant overheating, chances of a successful new headgasket replacement are IMHO poor.

Change the pump. And hope. If that doesn’t work, then it’s time to consider other options.

This engine does have 175,000 miles on it. What about a new engine? Dealer quotes about $5,500. How aggressive are the worms under the lid of this can?

Why spend over $100.00, $75.00, or even fifty dollars for a product that claims to stop head gasket leaks when you can go to a local pharmacy and pick up a bottle of sodium silicate (water glass) for $20.00-$25.00? This is what NASCAR crews put in the cooling systems of their cars when a head gasket blows during a race so it can finish the race.

I have people come in with blown head gaskets. And when they can’t afford to have the head gasket(s) replaced, I pour a bottle of this in the cooling system to stop the leaks. One vehicle has been running the road for almost a year without a problem.

I always have a bottle of sodium silicate on hand for this purpose.

Sodium Silicate is compatible with antifreeze, right? So if I start using it, like how often can I put in? I notice your bottle is half gone; do you use just half a bottle per application? This might just buy me the time I need to learn how to work on this car myself.

The bottle you see is half empty. It was applied to a four cylinder engine. On a V6-V8 engines the entire bootle goes in.

You add it once, and that’s it. The repair can last two years or longer. You can read about here.


There seems to be water coming out of the tail pipe now. The last overheating may have been the last straw.

I went to look at new cars. It?s like a minimum of $360/mo for 5 yrs.

I?m 67 and would like to retire without car payments.

Looked on Craigs list and ?where is as is? stuff seems to come in at 4 to 6 K for what we need.

Maybe I need to buck up and face the fact that I cannot afford transportation in retirement unless I can repair my own vehicle. I do have a nice shop and plenty of tools. I?ve been repairing machines for small manufacturing businesses for 20 years. I plucked a WWII South Bend metal lathe off a scrap heap and restored it to working condition. I?ve done the same with a 10hp 1942 Curtis air compressor. I set up a vacuum assisted lost wax bronze casting operation. So it?s not like I?d be starting totally from scratch

Would this 98 Subaru Outback be a likely candidate for me to begin climbing the learning curve on? I need something that can haul stuff without eating too much gas and this thing has served well for that purpose.

I?m thinking I could put a new engine in this thing myself. Are there just too many pitfalls to hope to get it right on the first try?


It says on the bottle that sodium silicate is NOT compatible with antifreeze. So, do you flush the radiator before you put it in? And come winter, do you flush it again before putting antifreeze in?


At that mileage and especially if coolant is mixing with the engine oil, I’d say replace the engine assembly rather than repair the one you have. Coolant diluted engine oil will wash out crankshaft bearings and this essentially means a complete overhaul.

From the sound of it, it appears that you have the aptitude to change the engine out yourself with no problem.
Subarus are comparatively easy to do engine swaps on anyway with only a few things to watch out for and a Haynes manual, not a Chiltons, would be a good 20 dollar investment.

If the car has an automatic transmission be sure to replace the front pump seal located behind the torque converter. When reinstalling that converter (it just sits on the splines) make absolutely SURE the converter is fully seated on all of the splines. Failure to do so can crack the flex plate at best and cause transmission damage at worst. The engine should easily seat against the transmission and use a screwdriver to probe the converter before reinstalling the converter bolts. The converter should rotate easily. If not, back out it has to come.

It also helps to jack the transmission up an inch or two at the front.

I’d do some digging around on an engine. It seems to me that you should be able to find a decent engine for far less money than 4-6k. Check out eBay for one in your area (maybe even consider a JDM engine on eBay) or a local salvage yard.

I found your post encouraging.

Yes, I do believe replacing the engine is the thing to do. In the process I might learn enough to maintain my own car until I?m too old to drive.

I guess it starts with learning the vocabulary.

The engine type is EJ25DAXDYL.

I don?t think I want a used engine but I?ve heard one rumor that Subaru only sells the block and not the assembled engine. I?m starting to look around via Google.

I want to avoid the problems I see hot rod blogs delving into. Just a standard swap using the existing wiring harness and accessories (computer, AC, alternator, power steering, etc) is what I want. And I don?t need problems associated with putting a Japanese right side drive engine in my US left hand drive vehicle.

That said, I am curious as to whether an engine of later design might be less likely to have head gasket problems and if so would it drop right in and wire right up? Or would the computer need to sense different things on later engines? If so I guess I?m just stuck with potential head gasket problems.