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Terpodion

Leak at exhaust manifold / header / Y pipe

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The 03 2.5L Impreza is doing what all my other Subarus have done - leak between the cylinder head and the exhaust manifold (header, Y-pipe or whatever you want to call it). My other 5 cars were all the 2nd (?) generation type with the pushrod engine. They all did the same thing. The bolts going into the head would strip out and make it impossible to get the manifold tight enough to stop the leaking. I eventually discovered an after market manifold from J C Whitney and was able to drill out the holes, tap them and put in bigger bolts that held much better. I haven't tried to tackle this job on the Impreza yet and can't find much about it on the net. So, I'd like to find out as much as I can before I jack it up and crawl under there. If I attempt to tighten the bolts or remove them to put in a new gasket, will they just take the threads of the aluminum head with them? Are there aftermarket solutions like I found with my old cars? 

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OEM gasket, new hardware, clean mating surfaces and you're done. 

Install new Subaru OEM exhaust gasket with new OEM studs and/or exhaust nuts onto clean mating surfaces to achieve proper clamping force. 

if you just install new nuts, or don't install any new nuts/studs - chase all the reused studs/nuts with a tap/die set so they're all clean metal and you get good clamping force. 

address any studs that strip as needed.  often times the nut just pulls the stud out with it and thus the stud/nut combo functions like a bolt.  sometimes the studs strip the engine block.  sometimes the nut is so rusted it just rounds off and won't come off.  address each individual scenario as it occurs, there's no way to predict if it will or won't.  use good 6 point sockets, do NOT touch those with 12 point sockets. 

they're the same thread and pitch as older Subaru's so you can do the same thing as mentioned many times - tap to that commonly used 7/16" or whatever it is exhaust stud size. i forget, i've got all the parts to do it though.   tap to 7/16" (i think), bottom tap to the same, then install your new gear.

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I'd probably remove the header from the car and sand the flanges.  It's likely they're no longer flat, light sanding with a flat block will show.  I've used a belt sander to get terrible ones sealing again.

Yeah the aluminum strips easily on these cars.  I've had studs strip the threads from just removing them.  All that heat cycling and corrosion.  I've used mapp gas to preheat the area then blast the nut until dull red to get out the stubborn ones.  As mentioned above, end of the day it's either easy or terrible depending on how well the fasteners come off.

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1 hour ago, idosubaru said:

OEM gasket, new hardware, clean mating surfaces and you're done. 

 

Yep, can't stress this enough.

 

The old studs rust, and then thread out of the head. A 10x1.25 thread repair tap is a great idea (careful with a thread cutting tap, as it will take off more material...not really a good thing).

I just did this job on my '00, and while it turned out the problem was really a broken weld under the heat shield right by the head, but I replaced the gaskets and hardware while I was there. I was thinking it might be nice to use Toyota studs, which have a torx end on them, so they can be more easily tightened down into the head to ensure complete thread engagement before really putting any clamping force on them.

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The EAs were notorious for pulling exhaust studs. 

I’ve not had this issue on the EJ engines. Lucky? Either way I don’t have the same angst with EJ exhaust studs like I do with EA units! 

Make sure you’re not over tightening the exhaust nuts as that will pull studs for sure. Tighter is not always better. 

Cheers 

Bennie

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