Do head gasket sealers in a bottle work?
August 24, 2008 6:58 AM   Subscribe

Do head gasket "repair" liquids work at all?

I think I have a head gasket problem (related 1, 2) in my 1998 Subaru Outback. The only symptom is an overheating engine that hasn't been fixed by a new thermostat and 'checked' radiator.
I don't really want to spend $thousands on replacing head gaskets if it can be avoided. Do the fixes in a bottle work at all? I don't particularly want to link them here if they are a scam, but the brands I have found are Thermagasket, Steel Seal and K&W Permanent Metallic Block Seal.
This wiki article at says maybe, but is obviously vulnerable to bias.
A medium term fix would be a win for me.
I would rather hear about real world experience, rather than an apprentice mechanic saying they would never risk it.
posted by bystander to Travel & Transportation (7 answers total) 1 user marked this as a favorite
No, and here's why. (At least not in your case.)

You put the magic fluid into the radiator, right? During operation, that gets pressurized to 15 pounds, and the magic fluid flows into the hole and seals up, right? Except that the hole in your head gasket is between the coolant and the combustion chamber. So every time there is a combustion event in the affected cylinder, which causes a pressure of way more than 15 psi, the seal gets blown out.

In the mean time, that gunk is flowing through your cooling system causing trouble.


(Seal tabs and liquid radiator stuff *can* fix leaks, under certain circumstances.)

((Further advice- find one of those shade tree mechanic guys and get him to do the job for a couple hundred bucks. Maybe on a Subaru internet forum? It can be easily done in an afternoon with not-too-sophisticated tools. I had the same type of failure on a 1990 Dodge Shadow, and I did the job myself in an afternoon having never done anything like that before.))
posted by gjc at 7:34 AM on August 24, 2008

Obligatory Subaru 2.5 liter headgasket FAQ

Be aware that when your motor overheats, you run the risk of warping the block/head, which would require either a new(/junkyard) head, or possibly having it machined flat. I believe the additive that Subaru adds to the coolant system in the newer 2.5 motors is basically a "liquid head gasket", and if your car is already experiencing overheating issues -- such a fix might be too late.

Right now its a $1500 fix -- but if you overheat it again, it might become a new motor fix.

As for whither or not a $100 bottle of magic stuff is going to fix this problem -- I would ask your local Subaru mechanic. The 2.5 liter motor (before 2005) is a well known motor by mechanics -- and if there was a simple fix, they would sell it by the case.
posted by SirStan at 7:42 AM on August 24, 2008 [2 favorites]

If it's one of those external leaks, the combustion pressure won't be an issue. Still don't trust them and never met anyone who's had a good experience with those things. They only sell because people try to save a buck or get desperate.
posted by IronLizard at 7:43 AM on August 24, 2008

Subaru put their "coolant conditioner" (supposedly a gasket sealer) in my 99 Impreza (same engine) around 80k miles, according to the previous owner's maintenance records. They did that once they started realizing that their head gaskets were dropping like flies. Didn't help - I was stuck footing a $1200 repair bill for the head gaskets at 115k miles.

I'm not sure that you're going to find an intermediate solution. If your car is overheating then you really need to be careful you don't warp your heads or do any serious damage to your engine.

Are you leaking coolant? My Subaru was leaking coolant like crazy right before I got my HGs fixed but that was my only symptom.
posted by PFL at 8:18 AM on August 24, 2008

If your car is overheating then you really need to be careful you don't warp your heads or do any serious damage to your engine.

Yes...I had a leaking head gasket on a previous car and most of the expensive damage was a consequence of this. Fixing the gasket alone wouldn't have solved the problems at the point where it was detected, and I didn't even have any very obvious symptoms like overheating.
posted by advil at 10:27 AM on August 24, 2008

Before you throw a head gasket at this engine, you might want to make sure that the head gasket is actually the cause of the overheating. You've ruled out the thermostat and (maybe) the radiator, but there are other potential causes of overheating -- the water pump comes to mind.

One way you could check this yourself is with a combustion gas tester. If the HG is blown, it's venting combustion gases back into the coolant. In really egregious cases, if you start the engine with the radiator cap off (only take the cap off with the radiator cold!) you can see bubbles being blown back into the radiator. Most of the time you won't see that, but there are test kits available that will tell you whether there are combustion byproducts contaminating your coolant. Although not foolproof, they work pretty well and are certainly cheaper than the labor required to replace a head gasket if it's not necessary.

If you still suspect a head gasket problem, or can't find one of these testers, then any competent shop should be able to do a leakdown test of the engine for you, where they pump each cylinder up to ~15 psi with compressed air and make sure it can hold that pressure. That shouldn't cost too much and will give you a definitive answer as to whether your head is leaking or not.
posted by harkin banks at 11:16 AM on August 24, 2008

PFL's Impreza has a similar, but not identical engine. Yours is the 2.5L dual overhead cam (DOHC), which was well known for internal leaks between the coolant jacket and the cylinders themselves, allowing exhaust to enter the coolant and eventually create bubbles and hotspots, overheating and other pretty much terminal engine problems.

The 99 impreza either had subaru's bulletproof 2.2L engine, or an upgraded 2.5L single overhead cam (SOHC) that had an improved interface between head and block, thereby stopping the internal leak problem. But it did have a habit of developing an external leak -- coolant to the outside of the engine -- which Subaru attempted to fix with a conditioner.

While those Checker Auto head gasket repair liquids might work in a tractor, or temporarily in a far cruder engine than Subaru's aluminum boxer-style block, no conditioner or leak stopper will accomplish anything but gum up the water pump in your Outback, unfortunately.

Though aftermarket parts makers did make reinforced head gasket replacements, Subaru itself never attempted to directly address the problems with the DOHC, which was used from about 96 to 99, and 2000 on some models. They just dropped it in favor of the redesigned SOHC. I had the same problem with a 98 forester.

I hope you haven't already replaced all the other parts of your cooling system before diagnosing the head gasket -- but if you've been on that fool's errand, you're in good company.

You can get the head gasket replaced, and a properly rebuilt DOHC is not a particularly bad engine -- pilots use them, for instance, in homebuilt aircraft, though the bomber 2.2L is the preferred mill. But before you get it fixed, have the engine pulled and inspected carefully for signs that water has been in the oil. If it has, for a long time, and the bottom end bearings are washed out, you'll need a new engine...

...or you could craigslist it as a mechanic's special, and buy an old Honda.
posted by M.C. Lo-Carb! at 12:15 PM on August 24, 2008 [1 favorite]

« Older Should I kick her out?   |   Help me with clothes for my... Newer »
This thread is closed to new comments.