Exhaust Manifold / Elbow Gasket Replacement

[tpenfield]

The joint between the exhaust manifold and elbows on my Mercruisers have been showing some rust over the past couple of years. So, I had a gasket replacement on my pre-season maintenance list for this year. Today was the day to start into it.




I should mention that I have twin Mercruiser 7.4 MPI engines with aftermarket (San Juan Engineering) FULL closed cooling system. I run in salt water . . .

The SJE cooling system had the Mercruiser block-off gasket to separate the coolant in the manifold from the cooling water in the elbow. I was concerned about the longevity of the gasket, since it is pliable and could possibly wear through. My preference was to go with the stainless steel block-off plate sandwiched between two block off gaskets.

Here is a picture of the gaskets . . . The 'Quicksilver' is the standard gasket and the 'Barr' is the rigid stainless steel block-off plate. Mercruiser no longer has the plate, as they say the gasket alone is adequate (yea, right . . .)




When I disassembled the elbow, the single gaskets looked OK, better than I was expecting.




Since I had the exhaust system opened up, I used my inspection camera to take a couple pictures of the exhaust valves. Overall, I think they look OK.





I prepped the joint and re-painted the elbow. First with a rust reforming primer, then with gloss black topcoat.





Here is the Starboard side of the starboard engine all done.




I got 3 more elbows to go. The port side of the engines have the ECM electronics box and remote oil filter attached to the elbows . . . much more difficult to do those.

Since there are more gaskets between the manifold and elbow, I did have to make a quick run to the hardware store to get slightly longer bolts. Probably going to take the better part of another day to finish the other elbows off.

 

[achris]

I have a couple of clients with closed cooling, and never had a problem with the Merc 'soft' gaskets...

I also see you have what looks like SS elbows... Lucky you!

Chris............

 

[tpenfield]

I have a couple of clients with closed cooling, and never had a problem with the Merc 'soft' gaskets...

I also see you have what looks like SS elbows... Lucky you!

Chris............

Yup, stainless steel elbows :thumb: Which seems to do well with closed cooling, since the coolant goes through the manifold and the sea water goes through the elbow. The boat originally had open cooling and the stainless steel depleted the iron in the manifolds. The PO put new manifolds on as part of the sales agreement when I bought the boat.

My only concern about the soft Merc gaskets is that the cooling system, being under about 14 psi (96 kPa) pressure would continually want to deform the gasket and potentially cause a breach. You can see the deformation in one of the photos of my first post. What I did notice about those gaskets is that there is an inner 'foil' layer of stainless steel that is sandwiched between the softer gasket material. The softer gasket material seems to have deteriorated somewhat over the past 4 years causing the seepage at the joint.