Exhausting problem

[Hooked]

I have a Perkins Prima 50 and while replacing the unbelievably expensive water pump due to a previous owner mucking it up , I decided to have a look at the exhaust elbow and the rest of the cooling system. The pictures are of my aluminum exhaust elbow. This is where the raw water gets injected into the elbow. The rest of the elbow looks great. Better than I expected. My thought is the stainless steel bolts and the aluminum did their thing and the result is galvanic corrosion. The fitting that was on there was held by the gasket and corrosion.

My question is what should I put on the bolts (if anything) to stop the corrosion? TefGel? Duralac? The temps there can get warm to hot I reckon. Not that I have a ton of experience with engines but my Yanmar had a steel exhaust elbow. Didn't worry about galvanic corrosion. I worried about the whole damn thing corroding.
Thanks for reading
Marcus

[donradcliffe]

I had an aluminum exhaust elbow on the Perkins 4108, and it seemed to fail about every 10-12 years. That's a nasty environment for any material, and I don't think you can do much better with other materials. I suspect that tefgel and duralac would break down at those temperatures.

[Irish rambler]

Hooked, I'm suprised your water pump was so expensive, Perkins parts are normally very reasonably priced. The closed circuit(engine) water pump can be sourced from parts4engines.com (+ other Perkins parts) the seawater pump is a Jabsco.
Most Perkins engine parts, except marinisation parts, can be sourced from a local Massey Ferguson tractor dealer, they used the same engines. Marinisation parts can be obtained from Bowman.co.uk
I'd be inclined to manufacture a new exhaust elbow from mild steel, or (if you are going to keep the boat), stainless 316 grade only, with an extra 'wear' plate welded inside where the water hit the casing, assemble with bolts coated with copperslip.
In respect of the corrosion I would strongly suspect/test your Cathodic protection for a fault, either none fitted, wire connection broken, sacrificial anode eaten away.
I hope this helps.

[Hooked]

Thanks for the response!
From what I gather the Prima 50 is a rebadged Volva-Penta MD22 hence maybe the expense in procuring parts. I am getting a Jabsco pump that is similar to the stock Jabsco but much less expensive. $300 instead of $600.
The engine does not have zincs as it is not grounded unless the started is engaged. Theoretically anyway.
You might be right in suspecting Cathodic protection as a fault. I am still pondering.
We are planning on keeping the boat but I don't think I'll go the stainless steel elbow route however. Well I might once I look up the price of a new elbow. Luckily I have one in reserve but it came with the boat so I have no idea of the cost.
Thanks for the response and the links!!!

[Irish rambler]

Your welcome, forgive me saying but your back to front, Volvo engines below 60 hp are built by Perkins so shop around for spares as Volvo are known in the trade as reasonable to install, but very very expensive for spares.
Case, Rolls Royce and some Cat diesels up to 350 hp are all built at the Perkins factory.
Go for a mild steel with the extra wear plate inside, take the spare to a machine shop for an exact copy.
The leaders in Cathodic protection are M.G.Duff.co.uk if you google them and go on their website you can download loads of useful free info.

Good Luck