I have noticed a dark brown stain coming from the #4 (from the front)exhaust port coming out where the block meets the manifold on my '90 300SE.

I have kept an eye on it and it seems to have gotten a little darker. Would this effect idle or fuel mileage? Is this anything to be concerned about?

Thanks,

If it's leaking, it will only get worse. If you can hear a leak, then replace the gasket for that pipe. I think you will have to get a set of six, but they're easy to do. Be advised, soak the nuts and studs with penetrating oil be fore trying to remove them. On my 300E, I removed the studs and replaced them with stainless steel metric cap screws. That way, if you ever have to do anything with the head, the exhaust studs will not be in the way, and they won't corrode..

jeff,

Did you use stainless capscrews or something? It's normally a poor practice to use bolts instead of studs in an aluminum head. The studs are stainless and the nuts are brass or something. I would be afraid that the bolts, unless stainless, would run the risk of a bi-metallic corrosion problem.

I have learned from the difference in my MB's and my Vette that the studs in aluminum seem to be far superior. The ignorant people in Bowling Green who are trying to save a tenth of a penny per fastener used bolts through the accessory brackets into the aluminum heads and it is sets up a real problem.

I'm anxious to hear your experience and what you've learned, my experience and ideas about this may not be representative of the truth.

Duh, I just noticed that you said right there in your post that you used stainless. Sorry 'bout that. I still would like to hear your experience.

Thanks,

[Edited by LarryBible on 12-07-2000 at 08:44 AM]

One more comment as a word of caution. One you can hear the leak, hot exhasut gases are blowing by. The combination of temperature and corrosive gases, and velocity can cause erosion. If you wait too long, it could casue the sealing surface to erode and the it would have to be machined to get a good seal. This is only a problem after continuing to operate (for weeks) once you hear the leak.

Best Regards,

Larry, The stainless capscrews still look new. No heat discoloration or corrosion that I can see. After I read your post, I tried backing one of them out. Came out easily and torqued back down slicker than snot. BTW, I always use anti-sieze compound on any fasteners that get get threaded into aluminum.

jeff,

Yes, anti=seize compound is definitely key. I have a '78 Ford four wheel drive pickup that I bought new and use around the place. Ford's use capscrews on the exhaust manifolds rather than studs. It's very common for them to twist off. I took the exhaust manifolds off about ten years ago when doing a valve job. I managed to twist off only one bolt. I put everything back together with an anti-sieze compound which contains copper particles. I built a motor for it in '99 and there was absolutely no problem when taking it apart. These were not even stainless bolts. Aluminum is a different situation of course.

Using stainless bolts with anti-sieze compound will work over the long haul, but my thoughts are that studs and nuts are the proper approach for the factory to take. It's also easier to get the gaskets in place as well.

Had my old truck had aluminum heads, I shudder to think what I would have been up against the first time I removed the exhaust manifold bolts.

Thanks for the discussion. This is how we learn more, by sharing our thoughts and experiences.

Have a great day,

Larry, I would rather struggle with a gasket flopping around than try to pull a manifold away from a head when it won't clear the studs. Usually if the studs are in for a while, the nuts will get rusty and come out with the stud anyway. So what the heck, I replace the factory material with better stock and in a way that for me (and sometimes maybe only for me) works better if I have to go back and do something else in the same area. BTW, they look prettier also..:D

I can certainly see where it would be easy to get the manifolds off with bolts. It is definitely a wrestling match with the studs. I had forgotten about that.

My comments were without that in mind, and only pertained to the consequences of threading steel into aluminum.

Great discussion, thanks,