Wet exhaust elbow explosion?

[Idle Hour]

Why is the elbow not cast in the same alloy as the heat exchanger? Aluminium.alloy elbows seem to be made for other engines, so why not Volvo?

Hi Vyv, How is the souloution holding up with the fix you did on the stainless steel elbow/ washers/sleves/gasket... Any more corrosion since ?

Kind Regards

Charlie

 

[vyv_cox]

Hi Vyv, How is the souloution holding up with the fix you did on the stainless steel elbow/ washers/sleves/gasket... Any more corrosion since ?

Kind Regards

Charlie

I think you may be confusing me with another poster. I have only ever replaced one elbow on my Yanmar with another standard item.

As I have explained previously, and on my website, these elbows fail principally by thermal fatigue, not corrosion.

 

[Idle Hour]

I replaced the cast elbow on my MD2040 with a parts4engines version in 2020, using the supplied gasket, and there was significantly more galvanic corrosion of the heat exchanger flange when I removed it last year. Having had the heat exchanger repaired I've isolated the elbow entirely using a mica gasket, high temperature fibreglass sleeves on the studs and Peek washers. I'm not knocking the elbow but the risk of galvanic corrosion is higher with stainless steel than cast iron and parts4engines have been looking at ways of isolating the elbow themselves, although my DIY solution works well and wasn't expensive as I located an offcut of the mica material. The sleeving is a few quid on Amazon and I ordered the Peek washers from a Chinese supplier on eBay, again for a few quid, although I had to wait three weeks for them to arrive.

Hi There,

How is the souloution holding up with the fix you did on the stainless steel elbow/ washers/sleves/gasket... Any more corrosion since ?

Kind Regards

Charlie

 

[Ammonite]

Hi There,

How is the souloution holding up with the fix you did on the stainless steel elbow/ washers/sleves/gasket... Any more corrosion since ?

Kind Regards

Charlie

It appears to be holding up well. I haven't removed the exhaust elbow as yet but its still electrically isolated from the heat exchanger and all looked well when I checked out the interior with an inspection camera. However, on this occasion I disagree with Vyv's assessment about thermal expansion being the main issue with the exhaust on these engines (MD20X0, D2-50/55 etc). I'm sure this plays a critical role with fabricated / welded stainless exhaust elbows, like those on Yanmars, but the cast iron Volvo versions largely fail due to corrosion/rust, particularly of the injection point. The cast stainless versions parts4engines supply don't have this problem but in common with the cast iron versions there is the potential for significant galvanic corrosion of the aluminium heat exchanger, which is what I'm assuming your question is about, and which my fix addresses.

 

[Idle Hour]

I think you may be confusing me with another poster. I have only ever replaced one elbow on my Yanmar with another standard item.

As I have explained previously, and on my website, these elbows fail principally by thermal fatigue, not corrosion.

Hi Vyv,

Yes I have, Thanks for getting back to me

Kind Regards

Charlie

It appears to be holding up well. I haven't removed the exhaust elbow as yet but its still electrically isolated from the heat exchanger and all looked well when I checked out the interior with an inspection camera. However, on this occasion I disagree with Vyv's assessment about thermal expansion being the main issue with the exhaust on these engines (MD20X0, D2-50/55 etc). I'm sure this plays a critical role with fabricated / welded stainless exhaust elbows, like those on Yanmars, but the cast iron Volvo versions largely fail due to corrosion/rust, particularly of the injection point. The cast stainless versions parts4engines supply don't have this problem but in common with the cast iron versions there is the potential for significant galvanic corrosion of the aluminium heat exchanger, which is what I'm assuming your question is about, and which my fix addresses.

Many thanks for the reply,

Did you also use an aisolating thread sealant on the studs ?


Kind Regards

Charlie

 

[Ammonite]

Hi Vyv,

Yes I have, Thanks for getting back to me

Kind Regards

Charlie

Many thanks for the reply,

Did you also use an aisolating thread sealant on the studs ?


Kind Regards

Charlie

I used fibreglass sleeving to isolate the studs, a 2mm mica gasket between the exhaust and the heat exchanger, using the original gasket as a template, and PEEK washers under the nuts on the studs.

https://amzn.eu/d/0j28umZE
Pardon our interruption...

PG-Therm is the mica gasket I used

 

[vyv_cox]

. However, on this occasion I disagree with Vyv's assessment about thermal expansion being the main issue with the exhaust on these engines (MD20X0, D2-50/55 etc). I'm sure this plays a critical role with fabricated / welded stainless exhaust elbows, like those on Yanmars, but the cast iron Volvo versions largely fail due to corrosion/rust, particularly of the injection point.

If you read my post again you will see that I state that this failure mode applies to welded Yanmar elbows.