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Leak at exhaust downpipe flange

Drew20

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Nothing turned up on a search, but hopefully this is a quick and easy query. I have a blow coming from where the cast iron exhaust manifolds meet the exhaust downpipe.
On a RHD car this is a single three bolt flange with a oval (ish) shape. It has a metal gasket. I had this apart recently as part of a bigger job and used a new gasket on rebuild, but no exhaust paste. Should I have used paste?
I think I have used paste on both sides of the gasket before, on other M30 engined cars
I've read that a smear of copper grease should suffice
Any thoughts?
 

Gransin

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I can only speak about my own coupe, and I haven't used any paste of any kind, only the gasket.
I've had the downpipes + exhaust removed from the car several times (at least 4 times) and I've reused the gasket every time, still no leaks.
The flanges have to be 100% straight, if they're not, you'll have a leak sooner or later no matter what paste you try to fix it with. At least this is my experience from dealing with old exhausts on different cars.
 

Honolulu

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The thin smear of grease is so that the gasket won't stick to the mating flange(s). It's not there to seal the joint.

As stated above, alignment needs to be correct. Granted, give the weight of the exhaust, that you're probably upside down with little clearance to wangle the thing into position, you have to trust (more than perhaps we should) that the hangers will hold things together.

I did a guibo replacement on a pal's E36 a little while ago... getting the exhaust off/on was a real PITA. I used Liquid Wrench, bald language and an 18" long cheater bar. Only broke one of the six studs. I 'fessed up, but the joint seems to be holding. There's a lot of anti-seize on those studs now, in case I have to go in again.
 

Drew20

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Thanks or the replies.
When I split that flange the nuts came off the studs like a dream. I had come prepared for a fight, but none was offered. And it went together easily too. It was so straight forward I didn't check anything, which may be the problem!
I'll take it apart, clean and check everything this time. Thanks for confirming, no exhaust sealant
 

Stevehose

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make sure the mating surfaces are flat, carbon build up etc can make them uneven and therfore difficult to seal. Filing and sanding (paper wrapped around a small flat piece of wood) worked for me.
 
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Ohmess

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Yeah, I'm with Steve on this. If you have had a leak around that area, you may well have deposits that are messing up your seal. The fact that the nuts came off very easily and you had a leak points to an improper install. If you can separate your exhaust, try separating the front section from the rest and installing it to the exhaust manifold first. I always do this when I drop my exhaust.
 

Drew20

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Dropping the exhaust is always an option. I've refitted the flange connection with a new gasket and a smear of copper grease. I ran my finger over the surfaces and couldn't detect any defect, or even any real roughness. I ran a damp cloth around the flange surfaces to clean it and used a different style gasket this time. Previously I'd used a composite gasket, with two circular holes. This time I used a single piece steel gasket with a single oval hole. I think this steel gasket is for later M30B34 engines, but I have a load of them and thought I might try one, done up v tight
It came apart and went together easily again, not that surprising since it was apart recently
The old gasket showed the blow, towards the rear of the join, ie the edge close to the scuttle /firewall

Will let you know if this got it
 

e9john

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Check that there is not a hairline crack on the cast iron manifold flange, I have 2 with cracks in them but not at the flange.
 
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