Reversion ?

[MOBILEMERCMAN]

Heres a pic of them in place

Not sure why your exhaust is plumbed that way but, this is how Merc does it.

http://www.mercruiserparts.com/Show_...NIFOLD%2FELBOW

It looks like this on a complete engine.

[ROGUE]

Worked with Gil closely on this in 1990. They prefered running all the water through the manifold instead of leaving the manifold without flow until the thermostat opened. My manifolds are 14 years old so I believe them. The y's were a way to modify these early Mark 4's to follow that thinking. Merc's idea to not run water to the manifold until the thermostat opened might not have been such a good idea on strong engines with aluminum exhaust manifolds. At least that was Gils take on it.

[ROGUE]

Heres a pic.

[MOBILEMERCMAN]

Thanks...

[Ratickle]

I just changed the Marlin over to a crossover. Which, warm or cold, system does that use?

[eightsecmopar]

So it looks like you have cold water flowing through the exhaust until the t-stat opens then you mixing the warm water into the system. Makes sense..... the water running through the exhaust would then be warm greatly reducing condensation.

[Ratickle]

I don't get what would keep the exhaust from overheating though????

[eightsecmopar]

My take on is you have the water flowing through the exhaust ( whatever the water temp is whever you are boating ) lets say Lake Mich is 70 degrees, after your engine warms up and the t-stat opens the 160 degree water is introduced into the 70 degree water which would make the water flowing through the exhaust around 100-110 degrees. If you look at the y fittings the way they are placed in the system that is where the warm water is introduced into the exhaust. You always have water flowing through the exhaust it is just cold water until the t-stat opens.

[ROGUE]

This is kinda veering off the original topic. Its been a long time since we made these plumbing changes and Im not sure I remember everything exactly. I think the gist of this way of plumbing it was to keep the aluminum manifolds close to the block temperature and not have them get hot due to not seeing water flow until the therms opened up. I think it was to keep the aluminum cooler and more stable. Not sure if there were problems with the way merc plumbed them but aluminum exhaust manifolds were pretty new in those days. Not sure when the first ones came out but it was mid to late 80's if I remember right. I dont remember if condensation was even discussed.

[MOBILEMERCMAN]

Merc started using Gils on 425's in '88 or '89. Mercs 420 cast iron exhaust had numerous issues and were finally abandoned. The problem changed at that point. The flood of water problems went away but exhaust valves and seats were having water related issues and failures. I don't recall how soon after the diffuser rings came out but, it wasn't long. In addition to the diffuser rings and wire reinforced gaskets a small rear water bleed was added as well.

All aluminum manifolds from Merc use diffuser rings. The 496 just call them tabulators.

...not have them get hot due to not seeing water flow until the therms opened up.

There is still water flowing thru them with the stat closed. The second hose is for high speed by pass. I think you guys are over thinking the cooling of manifolds.

[ICDEDPPL]

I pee on my manifolds till the stat open up, is this not right?

[Tony M]

I pee on my manifolds till the stat open up, is this not right?

What did you post ! I Was to "Bizzy" Looking at your Avatar .