I have the fresh water cooling option. I understand that raw water enters the system and cools the engine coolant in the heat exchanger. The engine coolant circulates in the engine block and also with the hot water heater. So, with this set-up no salt water enters the block. Now, what about the manifolds? Do I have raw water circulating through the manifolds or is there coolant in there?
Engine Cooling
- Thread starter JV II
- Start date
- Oct 6, 2006
- 12,155
- Boat Info
- 1996 450DA
- Engines
- 3116 Caterpillars
The sea water is injected into the exhaust to expell it from the boat at some point. Some engines it is at the riser but most have the injection point at the manifold. Just look for a hose that enters one or the other and you'll have your answer.
Corrosion is the obvious concern, however, the riser and manifold castings almost never last long enough to corrode thru from the cooling jacket. Ambient air from right off the water enters and is in the exhaust system all the way up to the engine heads. This means the riser and manifolds corrode first from the exhaust passage into the water jacket and not the other way around. Every time you crank up a salt water boat and heat up the exhaust system, you blow the surface rust out of the exhaust passage. Then when you park the boat at the end of the day new surface rust forms and the process begins all over again. Sooenr or later, the casting gets thin and, one night when the castings cool and contract, a crack will occur and you will have an engine full of salt water when you return to the boat. If it is the next day, you can usually get things dried out and save the engine. If it happens to be a week or so before you get back, the engine is usually done for, but you may get lucky and just do a valve job. A valve job plus new risers and manifolds is still a big financial hiccup.
So.......even on FWC boats in salt wateer, you have to be diligent about removing the risers and checking them and the manifolds. On a new Mercruiser, the first time should be at year 4 or 5, if everything is good, then check them every year until you have to replace them. Use Mercruiser replacement castings and, once the new ones are on, you are good for another 4-5 years. If you try to save money with aftermarket castings, you should check the risers every year beginning the first year after replacement.
Corrosion is the obvious concern, however, the riser and manifold castings almost never last long enough to corrode thru from the cooling jacket. Ambient air from right off the water enters and is in the exhaust system all the way up to the engine heads. This means the riser and manifolds corrode first from the exhaust passage into the water jacket and not the other way around. Every time you crank up a salt water boat and heat up the exhaust system, you blow the surface rust out of the exhaust passage. Then when you park the boat at the end of the day new surface rust forms and the process begins all over again. Sooenr or later, the casting gets thin and, one night when the castings cool and contract, a crack will occur and you will have an engine full of salt water when you return to the boat. If it is the next day, you can usually get things dried out and save the engine. If it happens to be a week or so before you get back, the engine is usually done for, but you may get lucky and just do a valve job. A valve job plus new risers and manifolds is still a big financial hiccup.
So.......even on FWC boats in salt wateer, you have to be diligent about removing the risers and checking them and the manifolds. On a new Mercruiser, the first time should be at year 4 or 5, if everything is good, then check them every year until you have to replace them. Use Mercruiser replacement castings and, once the new ones are on, you are good for another 4-5 years. If you try to save money with aftermarket castings, you should check the risers every year beginning the first year after replacement.
Thank you. That explains all of the manifold adds in the magazines. There has been discussion of ceramic coated manifolds in other threads. What kind of life do you get out of these. I asked my dealer about manifolds and he said the Sea Cores are corrosion proof manifolds. I hopefully will trade up before 5 years, when my manifolds need replacing.
