I have 1989 340, 454 Mercruisers. ...

[marklgunn]

I have 1989 340, 454 Mercruisers.  Time for manifolds and risers.  Is there an alternative that does not corrode so quickly?  Where can I get either a new light weight technology, or the old cast iron?

[wingless]

The OEM Mercruiser exhaust manifolds on my 2000 380DA w/ 454 MAG MPI Horizon engines would last 3-4 years in salt water before requiring discarding those obscenely expensive parts.

My boat was designed to retain salt water within the exhaust 24/7/365, with NO way to drain possible and NO way to flush possible.

At the last discard / replace cycle my totally disgusted level was maxed out, so I redesigned my exhaust system.

My new system now permits me to drain the manifolds, risers and exhausts after each usage. I then flush w/ fresh water, soapy water, then Salt Away. The exhaust is then drained bone dry until the next usage.

My exhaust was just disassembled for an internal raw water passage inspection, after three years of salt water usage. The exhaust parts still look brand spanking new.

My estimation is that my exhaust parts will now last the life of the boat.

[Big_mike1]

Call Mercruiser warehouse Kellogg Marine Supply in Connecticut google number stainless may be available 20 years life

[Flacoconut]

Wingless, you mentioned the redesigning of your exhaust system in a previous post in more detail. We are very interested in that for our 2008 330 sundancer. Can you repost that please? Thanks!

[cbruck]

I would also be interested in the design details as I just replaced the manifolds and risers on a 2010 with 496's.

[Smils]

Smils

[Smils]

Howdy - I would be wary of using S/S as, while manifold may last, I believe this risks setting up electrolytic action with the alum or CI in the motor acting as the sacrificial anode.

[Big_mike1]

Stainless risers Kellogg Marine Supply Connecticut

[Big_mike1]

Absolutely not true 15 years on stainless the only thing is welds crack after 10-15 years letting water into cylinders I’m a mechanic

[wingless]

What steps are required (including frequency) for inspection and for testing to ensure cracked stainless manifolds / risers / elbows do NOT go undetected, to prevent engine destruction?

[Big_mike1]

Code will spear on smart craft manifold temp high or spark plugs have water on them

[Topless]

You might consider a closed cooling system with a heat exchanger. I am repowering my Sundancer 300 (5.7 L Mercruisers) and installing heat exchangers. You will still have to replace the elbows periodically but that’s much easier. I will update on how well this works for me.