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Exhaust replacement - Cat/resonator flange rotted out

Help, Advice, Owners' Discussion and DIY Tutorials on Volvo's stylish, distinctive P2 platform cars sold as model years 2001-2007 (North American market year designations).

2001 - 2007 V70
2001 - 2004 V70 XC (Cross Country)
2004 - 2007 XC70 (Cross Country)
2001 - 2009 S60
2003 - 2007 S60 R
2004 - 2007 V70 R

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JayPea44
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Re: Exhaust replacement - Cat/resonator flange rotted out

Post by JayPea44 »


vtl
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Post by vtl »

JayPea44 wrote: 27 Oct 2025, 10:52 This seems more expensive than just getting a new down pipe. My FIL is a welder, maybe I can ask him.
New OE DP costs exorbitant money. The affordable ones are made of thin cheap steel and cheap ceramic converter, which your rear oxygen sensor will dislike. I have a good quality 3" downpipe that has a cheaper converter, and the only reason I don't get a cat efficiency code is my ECM tune that ignores the downstream sensor altogether. But I can tell by smell that this aftermarket CAT is not anywhere near the expensive metal one that Volvo used.

Bring a 6-pack to your FIL, welding an old car with a relative is a good bonding experience :)

vtl
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Post by vtl »

JayPea44 wrote: 27 Oct 2025, 10:57 This seems too good to be true:
In any case: do not throw away your old CAT. You may reuse it in the next DP you build. This is not a rocket science, you can do it.

JayPea44
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Post by JayPea44 »

vtl wrote: 27 Oct 2025, 10:57
JayPea44 wrote: 27 Oct 2025, 10:52 This seems more expensive than just getting a new down pipe. My FIL is a welder, maybe I can ask him.
New OE DP costs exorbitant money. The affordable ones are made of thin cheap steel and cheap ceramic converter, which your rear oxygen sensor will dislike. I have a good quality 3" downpipe that has a cheaper converter, and the only reason I don't get a cat efficiency code is my ECM tune that ignores the downstream sensor altogether. But I can tell by smell that this aftermarket CAT is not anywhere near the expensive metal one that Volvo used.

Bring a 6-pack to your FIL, welding an old car with a relative is a good bonding experience :)
Yep the OE ones are thousands and the price of affordable one makes me think they're essentially junk. I'm going to go with some kind of bracket to hold it together for now then have the FIL weld it when he can. He's retired now so needs something to do :D

JayPea44
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Post by JayPea44 »

Looks like I don't have to make it myself - this is exactly what I was envisioning.

https://www.autozone.com/emission-contr ... 110783_0_0

cn90
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Post by cn90 »

Buy Chinese stuffs on eBay, you will regret in 1-2 yrs.

Buy Volvo stuffs (NOS), they last forever.
2004 V70 2.5T 100K+
2005 XC90 2.5T 110K+

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jonesg
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Post by jonesg »

JayPea44 wrote: 27 Oct 2025, 11:05 Looks like I don't have to make it myself - this is exactly what I was envisioning.

https://www.autozone.com/emission-contr ... 110783_0_0
those split couplers are rather flimsy, I bent several of them before finding something more solid, same idea. (link below).
You will very likely need longer bolts, stainless.
Clean the flange mating surfaces with a hand held belt sander (it can be done in place but use goggles)
hi-temp RTV , I doubled up the gasket, glued together with a thin smear of RTV overnite.
Support the joint when doing the final cinch up, I used a trolley jack sitting on a milk crate to lift it into alignment then final tighten the nuts.
Be aware the pipe might measure the typical 2.5 inch but theres a raised reinforced shoulder at the flange so get that measurement, not the pipe itself.

VTL is right about buying a mig, especially with a weldor in the family to teach you.
With all the horsing the system around I broke the flex pipe and had to weld a new one in.
I had to buy a tank of argon/C25 gas as flux wire burns hotter and I couldn't see the weld joint.

this link is for flat oval pipe, find the one for round exh pipes instead .
Can't recall if the pipes are flat oval or round, its been 2 years and it held up fine.

https://www.amazon.com/EVIL-ENERGY-Exha ... 9hdGY&th=1

vtl
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Post by vtl »

jonesg wrote: 27 Oct 2025, 19:29 I had to buy a tank of argon/C25 gas as flux wire burns hotter and I couldn't see the weld joint.
Need a better helmet? This one is freakin' awesome, I can see everything now: https://www.amazon.com/dp/B076H4MWDS

VanBoisvert
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Post by VanBoisvert »

Troubleshooting Volvo electrical issues can be tricky, especially with older models. Keeping track of wiring diagrams makes things much easier. Between research sessions, I like to unwind a bit on https://casinosanalyzer.com/free-slots- ... yal-Riches ; a short break like that helps me stay sharp while analyzing problem areas.
Last edited by VanBoisvert on 04 Nov 2025, 01:31, edited 3 times in total.
.

JayPea44
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Post by JayPea44 »

jonesg wrote: 27 Oct 2025, 19:29
JayPea44 wrote: 27 Oct 2025, 11:05 Looks like I don't have to make it myself - this is exactly what I was envisioning.

https://www.autozone.com/emission-contr ... 110783_0_0
those split couplers are rather flimsy, I bent several of them before finding something more solid, same idea. (link below).
You will very likely need longer bolts, stainless.
Clean the flange mating surfaces with a hand held belt sander (it can be done in place but use goggles)
hi-temp RTV , I doubled up the gasket, glued together with a thin smear of RTV overnite.
Support the joint when doing the final cinch up, I used a trolley jack sitting on a milk crate to lift it into alignment then final tighten the nuts.
Be aware the pipe might measure the typical 2.5 inch but theres a raised reinforced shoulder at the flange so get that measurement, not the pipe itself.

VTL is right about buying a mig, especially with a weldor in the family to teach you.
With all the horsing the system around I broke the flex pipe and had to weld a new one in.
I had to buy a tank of argon/C25 gas as flux wire burns hotter and I couldn't see the weld joint.

this link is for flat oval pipe, find the one for round exh pipes instead .
Can't recall if the pipes are flat oval or round, its been 2 years and it held up fine.

https://www.amazon.com/EVIL-ENERGY-Exha ... 9hdGY&th=1
Thanks - that's the exact ones I have in my amazon cart right now.

A welder is definitely in my future. I just want to get this on right now. I've done a little migraine welding in the past so hopefully I remember the most of it and my FIL can give me some better tips.

A trip to Harbor Fright for a welder might come sooner rather than later.

I did see something like this which would work a lot better if/when I can weld it on

https://www.amazon.com/FGJQEFG-Hardware ... F0aWM&th=1

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