Mercruiser exhaust replacement

[Harley558]

Confused here. I have a 2000 twin Mercruiser 5.7 EFI Horizons. OL397915 and 917 inboards. I was thinking about changing my exhaust before I begin to have problems. They were changed back in 2003 under warranty and nothing since.

My problem is do I have to change the whole system? Manifolds, spacers, and elbows? The frecken spacers are has much as the elbows? My book shows manifolds 860246A-15, Elbows, 807988A-03 and riser kit, 93320A-13. I was just going to do the manifolds and elbows, while having the risers sandblasted and ceramic coated/inside and out.

Any suggestions? Do I have to do all 3 pieces? Last year I noticed the port engine started running almost 10 degrees hotter than my starboard engine....180-185 to 170-172.

I was also considering just sending all three pieces out to sandblast and ceramic coated. I got a good price to get them completely done, inside and out by one of the best ceramic coaters in the US.

Suggestions?

 

[wingless]

Re: Mercruiser exhaust replacement

Confused here. I have a 2000 twin Mercruiser 5.7 EFI Horizons. OL397915 and 917 inboards. I was thinking about changing my exhaust before I begin to have problems. They were changed back in 2003 under warranty and nothing since.

My problem is do I have to change the whole system? Manifolds, spacers, and elbows? The frecken spacers are has much as the elbows? My book shows manifolds 860246A-15, Elbows, 807988A-03 and riser kit, 93320A-13. I was just going to do the manifolds and elbows, while having the risers sandblasted and ceramic coated/inside and out.

Any suggestions? Do I have to do all 3 pieces? Last year I noticed the port engine started running almost 10 degrees hotter than my starboard engine....180-185 to 170-172.

I was also considering just sending all three pieces out to sandblast and ceramic coated. I got a good price to get them completely done, inside and out by one of the best ceramic coaters in the US.

The side to side temperature difference appears to be a normal characteristic, because of the heat exchanger splitting the raw water flow with more water going to one side.

The issue I've seen on my exhaust is that the wall between raw water and exhaust gas deteriorates on the manifold, riser and knuckle.

The steps you've identified are fine, just ensure that the SOLID wall thickness between raw water and exhaust gas remains to keep raw water from dripping into the cylinder heads. There are lots of on-line stories about destroyed engines from the hot exhaust valve fracturing into the running engine from cold sea water dripping onto the hot valve.

On mine I've extended the life of those parts by also machining down the gasket surface to increase the solid wall thickness.

On salt water engines inspect the raw water passages and the solid wall thickness at-least annually.

 

[achris]

Re: Mercruiser exhaust replacement

... and knuckle.....

So what's a knuckle?

 

[tpenfield]

Re: Mercruiser exhaust replacement

Confused here. I have a 2000 twin Mercruiser 5.7 EFI Horizons. OL397915 and 917 inboards. I was thinking about changing my exhaust before I begin to have problems. They were changed back in 2003 under warranty and nothing since.

My problem is do I have to change the whole system? Manifolds, spacers, and elbows? The frecken spacers are has much as the elbows? My book shows manifolds 860246A-15, Elbows, 807988A-03 and riser kit, 93320A-13. I was just going to do the manifolds and elbows, while having the risers sandblasted and ceramic coated/inside and out.

Any suggestions? Do I have to do all 3 pieces? Last year I noticed the port engine started running almost 10 degrees hotter than my starboard engine....180-185 to 170-172.

I was also considering just sending all three pieces out to sandblast and ceramic coated. I got a good price to get them completely done, inside and out by one of the best ceramic coaters in the US.

Suggestions?

My suggestion is to disassemble and inspect and then do things accordingly. The key is to have enough surface area on the mating parts so that the gaskets can hold a good seal.

Salt water use will obviously deteriorate them faster than fresh water. Your set is coming up on 10 years, so an inspection is in order.

If you go to replace them, check out the 'dry joint' style as those have a better design to avoid water ingestion if/when the joints fail.