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Everything I know about engine gaskets and sealants


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#1 Snowman

Snowman

    Midnight Passenger

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Posted 01 April 2006 - 11:54 PM

It seems there have been a lot of threads recently asking about various gaskets, sealants, and the like, so here's my schpeel on that stuff, which I have figured out from my experience with EA81, EA82, and EJ22 engines. The newer DOHC motors are a different animal, and I haven't touched one of those yet, so this advice may or may not apply.

1. If you don't like re-doing gaskets and seals, use OEM ones for everything, especially the headgaskets and intake manifold gaskets. They are different from the ones NAPA sells, and yes, they are better. They are also not much more expensive if you get them from a discount place like 1stsubaruparts.

2. Headgaskets - ALL Subaru OEM headgaskets go on dry, with no sealant, adhesive, or anything. Adding sealant will not make them less likely to leak. It will probably get in the way of the gasket sealing as designed, and the headgasket will probably leak sooner or later. One exception I have considered but not experimented with is putting a tiny amount of anaerobic sealant (see section on anaerobic sealant) around the oil passage hole in EA82 headgaskets. I am going to try this at some point and report my findings.

3. Intake manifold gaskets - The OEM gaskets are designed to go on dry. Using RTV sealant in place of the gaskets or in addition to them WILL cause a water leak into the intake as well as externally. If you feel that you must put something on the intake gaskets, or if you are stuck using aftermarket ones, put on a light coating of copper spray-on sealant.

4. EA82 cam towers - Are you sick and tired of having this place keep leaking no matter how many times you reseal it with RTV? The solution is to not use RTV. Instead, spend the extra money for anaerobic sealant, which works much better for this application. Another good sealant to use here is Permatex Ultra Grey. I do not use it myself, but I have been told by others that it's good stuff. Be sure to put a dab of assembly lube on the O-ring so that it seats perfectly.

5. EJ-series oil pump - This metal to metal seal is critical, so it must be absolutely spotless. Like the EA82 cam towers, I don't like using regular RTV here. Others have reported good luck with Ultra Grey, but as usual, I prefer anaerobic sealant. Make sure you replace the O-ring with a new one from Subaru. On a related note, if you just need to replace the front crank seal, it's much easier and less risky to just take the oil pump off and drive the seal out from behind than trying to pull it out while the oil pump is still on the car.

6. EA82 oil pump - Use absolutely no sealant on the oil pump. Coat the mickey mouse gasket with assembly lube or engine oil so that it slips in and seats properly. If the oil pump shaft seal is leaking, it's easier to just replace the pump. The leak is caused by a worn shaft, so if you just replace the seal, the leak will come back in a few thousand miles.

7. EA81/EA71 oil pump - The paper gasket should be coated with the copper spray on gasket coating or something similar. Again, no RTV (you can probably tell that I really don't like RTV).

8. EA81/EA71 rocker cover gaskets - I like to use avaition form-a-gasket on the rocker cover gaskets. It seems to hold them in place well during assembly, and doesn't tend to leak. Put a little assembly lube or engine oil on the sealing washers.

9. EA82/EJ22 rocker cover gaskets - Absolutely no sealant should be used. Coat the rubber gaskets and sealing washers with assembly lube or engine oil.

10. Oil pan - I know it's often a huge pain to clean all the old gasket material off, but it's worth it in the long run. I've had the best luck coating the new gasket with anaerobic sealant, though aviation form-a-gasket works well too. This is one place that I would also use RTV, but only if I was desparate.

11. EA-series water pump inlet pipe - I like to provide a backup for the O-ring by putting a healthy ring of high-temp RTV on the pipe right behind the o-ring...don't let it actually touch the o-ring however.

12. EA-series water pump gasket - Use the spray on copper gasket sealant here for best results.

13. EJ-series water pump gasket - I've had good luck with anaerobic sealant on this gasket.

14. Why I like anaerobic sealant - You're probably wondering what's so good about this magic stuff. Well, here's why: Aside from the fact that it sets up better than RTV-type sealants and is less prone to leaking, I like anaerobic sealant because any excess that is not clamped in the mating surface does not set up (hence the name), and remains oil-soluble. This means that no little globs form on the inside of the engine, like when RTV-type sealants are used. Those little globs can catch in the oil pickup or the HVLA's, among other places. The other reason I use anaerobic sealant is that it's what all of the major heavy duty engine manufacturers recommend for use on metal to metal sealing surfaces. I figure, if it's good enough for Caterpillar, Detroit Diesel, Cummins, Volvo, etc, it's good enough for my Subaru.

15. It's not "the more the merrier" - Most people tend to put on too much sealant, thinking that if a little bit seals well, then more must seal better. This is a false assumption. In most cases, this extra sealant gets squished out, which accomplishes nothing, aside from putting a bunch of sealant inside the engine where it can harm things.

16. Exhaust gaskets - Use only OEM gaskets here. Everything else develops leaks in short order. You can often get away with reusing the OEM gaskets if they were not leaking already. Pay special attention to the mounting studs and how much you tighten the nuts, as this is critical. The studs really like to strip out, so too much torque is a no-no, but if you don't tighten them enough, it will leak.

17. Case halves - Another metal to metal seal, where anaerobic sealant is the preferred thing to use. Be very careful not to use too much, and to keep it away from the bearings. This mating surface must be absolutely spotless, as it is probably the most critical one in the whole engine.




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