Mercruiser closed circuit cooling

[PADDLES]

g'day terry, i havn't worried too much about riser failures on these newer dry joint manifolds, i figure i should be able to see the leak before it get's into the motor, anyway you don't have to worry about that any more with your stainless ones.

mine used to do the same warm up thing on the muffs, don't chase too hard, it'll probably just be your water pressure at home, i flush mine with spear water and have an 18mm garden hose off the spear pump and it doesn't warm up when flushing any more.

[snatchy]

Hi Guys

i have a 4.3 merc too. FWC and MPI from factory. The FWC function saved my bacon one day when there wasn't any sea water coming through to cool it. engine got hot but we shut down before any damage. lucky.... just a new impeller and all fine.

anyway, a mate retrofitted a FWC kit to an older v8 mercruiser and had numerous problems;
- the kit didn't have some provisions for the power steering or something similar. a mate of his ended up having to do a fair bit of custom machining to have it all fit. The lesson learned was to make sure the kit was 100% suited to your exact application. preferably find a guinea pig who has done it before and knows the pitfalls
- increased internal pressure within the FWC system found some marginal sealing and cracks, and coolant ended up in the cylinders. this "shouldn't" be an issue in a newer motor like yours, but you never know until you try.

remember the golden rule "for every thing you modify, 3 other things will be affected that will need modification".

i also remember reading on iboats about some issues retrofitting FWC systems to ex rawwater (saltwater specifically) sterndrives. you should try and search to find those threads on there

my 2 cents would be to leave it stock, unless you wanted to reduce some weight, in which case the stainless manifolds would be worth considering.

another thought - FWC engines operate at different temp to raw cooled. if your engine is EFI it might get a bit cranky?? just thinking out loud and something else to find out!

[PADDLES]

good stuff snatchy, this is the sort of info i'm chasing. yeah, the kits i've seen are very specific on which motor and setup you're using so they fit just right and miss all the accessories. i'll track down those threads on iboats now. i don't know how the mercruiser ecu works but most ecu's work via a simple "lookup table" style system ie. they recieve all different inputs from the sensors and are programmed to vary the things they control to match that identical combination of inputs. so i'd be hoping that it'd handle an increase in temperature. i've been worried about increases in pressure and temperature on a 6 year old motor, not to mention the scale and krap already in there, so i'm now starting to swing back towards just leaving it as it is and whenever the day comes to repower the boat i'll look at fresh water cooling on a new block/heads.

[terryc]

Yeah paddles that was my conclusion as well, I read of guys with 20 yr Motors still going strong so I will get closed cooling upon renewal in future. If you do follow though would be interested in outcome. I would still be checking your riser manifolds by the 4 year mark just to be safe.