When to replace exhaust manifolds

[cschauej]

The general consensus that I've heard for a mercruiser 454 in saltwater is for the manifolds and risers to be replaced every 5 years. How accurate is this. I did notice some leaking on mine between the manifolds and risers. I figured if they are leaking on the outside, good chance they are leaking on the inside. So... I ordered the parts and pulled the manifolds today. I did find corrosion but nothing I thought that would warrant replacing everything. Can't one just clean the gasket surfaces and reseal everything? I find it hard to believe that so much iron could rust away within the manifold as to cause a leak. Did I just waste alot of $?<br /><br />Also has anyone heard that the stock mercruiser risers are made of stainless steel? Is this just something the mechanic I spoke with dreamed up?

 

[Bondo]

Re: When to replace exhaust manifolds

That's an awful Expencive Engine to be Betting on!!!!<br />I'd say you did the right thing.....<br />I've heard 3 to 5 years in the salt.....<br /><br />There Are Stock Looking risers that Are SS, from Mercruiser out there, But the Stock Risers are Not SS, But Cast Iron.......

 

[cschauej]

Re: When to replace exhaust manifolds

Thanks Bondo. I guess I just needed some re-assurance.

 

[elpaso]

Re: When to replace exhaust manifolds

There are after market stainless risers.<br />They are a problem - cast manifolds and <br />stainless expand and contract different.<br />Hard to keep riser gasket from leaking.<br /><br />5 years in salt is time to change manifolds.

 

[magster65]

Re: When to replace exhaust manifolds

I have a 7.4 too, I just did my risers but the manifolds looked good inside (they have anti-freeze cool them). The risers lasted 8 years. You can get 10 years no problem if you install 'zinc plugs' in the risers instead of just standard drain plugs. They really help.

 

[cschauej]

Re: When to replace exhaust manifolds

Yeah I've heard that mixing different metals cause problems. Better off with the iron all around I suppose. Anyways, I got my new manifolds on today. That was an experience... Can any body tell me why mercruiser couldn't splurge on stainless steel manifold bolts. There wasn't much left of them by the time I got to them. I almost gave up. Four hours of hammering, drilling and cursing later they both came off. So no more worries for the time being. Is there any use for the old manifolds. Like I said, although they are rusted I find it hard to believe that much metal could rust away inside as to create a leak internally. Or should I just pitch them? If didn't know they sold zinc plugs for the manifolds. If I understand this right they act as a sacrificial metal and will corode bofore the iron... same priniciple as on the drive. I'll look for them.

 

[Yepblaze]

Re: When to replace exhaust manifolds

If you use zinc plugs will they be removable to winterize if required?