Do Work in the Fall or Spring?

[Hwillcockson]

Guys -

I have a pair of 454 inboards and its time to replace the exhaust manifolds & risers. There are no problems with them leaking but they are 7 years old and used in salt water and are due.

Would you wait until the Spring to change these out or do the work now in the Fall while the weather is still warm?

:huh:

 

[sbw1]

There is so much work to be done in the spring I would do them on a nice fall week end on the Cape. In fact, I'd do as much hard polishing and waxing too. That would leave the hull and bottom paint for spring and then you are setup to get into the water early.

 

[Walz]

I too plan to do risers and manifolds, along with new plug wires, cap and rotor. Was planning to do next month, but decided to wait till next spring. Main reason is financial. Spent all my boat money on gas so I'll have to wait for my tax return to cover the cost of the parts! :smt101

 

[Beer Thirty]

I also agree with doing it in the fall. If you wait till spring you'll more than likely procrastinate and miss a few good weekends on the water. it will seem like a huge chore especially after you throw in the spring cleaning/prep.

 

[Loneranger]

Maybe a bit off topic but is changing the risers and manifolds a typical maintenance item when boating on salt water? Sounds expensive. Wouldn't this make a closed cooling system more economical?

John

 

[Henry Boyd]

John,
Bit of explanation of raw vs fresh water cooling systems:

'Closed' or fresh water cooling systems still consume outside (raw) water. A closed system uses anti-freeze like a car engine to cool the internal engine parts. Instead of an air cooled radiator, the anti-freeze gets cooled in a raw water heat exchanger. Additionally the anti-freeze will be used to heat the water in the water heater. In a raw water cooling system the engine internals would be cooled by water drawn directly from the outside. Some engines can be built either way because water by itself is enough to keep them cool. Others like the 496 must be 'fresh' water (anti-freeze) cooled, as anti-freeze is the only thing that has the heat transfer capacity to keep the engine in temp range.

On both types of systems, raw water is used to cool the exhaust and intake manifolds. That is why you can stand in your ER and put your hand on the exhaust manifold of the engine while running and not hear the sound of sizzling meat. So to answer the question, yes replacing risers and manifolds is maintenance on all boats, just more frequent on salt water boats, regardless of engine cooling system.

The above applies to gas engines. I am not that familiar with small marine diesels (less than 50,000 hp), so I can't comment on how they are cooled.



Back to topic

I try to get as much done in the fall and during the winter lay up as possible. Waxing gets done in the fall and then again in the spring. Oil, drive grease and filters gets changed in the fall, as does flushing and replacing engine anti-freeze. I do wait for spring on things like spark-plug replacement because fogging fouls the plugs and at $20 each.... Bigger jobs like bellows and gimbal bearings, or manifolds I will leave to the yard to choose when they want to do it, just as long as we are ready to go in the water by May 1st. When I had trailer/outboard boats a lot of work got done in the winter because the yard could pull the boat in where it was warm. With the larger boat on stands the weather plays a big part on when stuff gets done in the off season.

Henry

 

[tginz]

Henry:

Have to disagree - I can't comment on the bigger motors like the 454, but anything under a 350 typically has the exhaust manifolds and risers on the freshwater cooling system. The elbows are the only element on the raw water side in FWC. If you check the Mercruiser cooling diagrams, the antifreeze/coolant in a FWC system flows from the water pump (on engine) into the engine block, out the top of the engine into the exhaust manifolds into the risers - returning to the heat exchanger for cooling and back to engine water pump. My engine works exactly this way. The "plugged" port on the front of the riser blocks in RWC system is the return of antifreeze in FWC set-ups. This is exactly how my 5.0 is set-up as is my buddy's 5.7/350 Mercuiser.

At 3,250 rpms, my 5.0 engine is right on 155 degrees, exhaust manifolds and risers about 190 and the exhaust elbows about 100-110. All of which is below Mercruiser spec. I installed a Monitor System, who builds heat exchangers for Mercruiser. They offer an identical FWC system to Mercruiser - using all Mercuiser parts except they use a much larger heat exchanger of higher quality. I did a lot of investigating, talking, and testing before converting. This company and product are OUTSTANDING: Don't tell Mercruiser, but one of their techs. sent my to Monitor. Link http://monitorpro.com/index.php. My experience has been nothing but positive and I will only have to replace my "elbows" due to saltwater exposure.

Sorry now back to topic.

tginz

 

[comsnark]

Interesting stuff here.

First. . .actually, glycol blends have less heat capacity than straight pure water. Not a big difference. . but definately less. I know this from work in chemical plants where I see cooling systems get "bigger" when glycol/water blends specified. Increased cooling is NOT the reason to get a closed loop system. My brain is too foggy right now to give exact stats.

Second. . the other big reason to use closed loop systems is that with RWC in salt water, you will get corrosion products that will build up in the cooling passages of the engine, and eventually not permit cooling. Fixing this requires a new block.

Third. . .My understanding is that FWC that do the block only are refered to as "half" systems and FWC systems that do manifolds and risers are "full" systems.

Finally. . .Manifolds and risers are 190F sound hot. My RWC risers and manifolds run the same temp as the as the elbows. . . about 120-140 at last check. The engine temp is determined by the thermostat: in the case of tginz's boat, it sounds like he has a 145F thermostat installed. My 5.7's have 165F thermostats installed, and run something like 170-175 when shot with an IR gun.