Hey all,
I have been tossing the idea of converting from raw water to a closed cooling system on 502 mags in a fastech 312. Not sure if I should do half system since I have stainless marine exhaust or just do full closed. I boat in saltwater so, I see a lot of benefits from the conversion.Not sure of any disadvantages. However, I would like to know if any has closed cooling with on 502 or 454, and still have space to store the bimini top.

Thanks for any help you can provide.

Hey Phil! I was deliberating the same thing. What I think my course of action will ultimately be is to install a regular "T" before the sea water pump and run a hose up near each side of the engine compartment to be able to hook up a hose and just flush it out with a hose. The FW cooling would be great, but it will cost a small fortune to set up for two motors and then with a half system, the drive and exhaust still need to be flushed.

here's my post about this:
Fresh water flush options

I’m good with flushing, but was thinking of just running a closed system so I never have saltwater running through the engine. Also, this helps with in future if I ever want to run aluminum heads or water pump.

Also, I flush my motors roligously after every use but even still not sure it would be a good idea to run aluminum in salt with 2 dissimilar metals

That part I am not totally familiar with. However, there was a nice 311 I was considering buying (before I bought the 303 ) but it had aluminum heads and intake. I wasn't sure about that setup in salt either. So, I bailed on that deal, luckily...

Phil,

Is the boat you purchased a Fresh Water boat?

They do make kits for closed cooling of 502's (run north of $1500 ea), if it was in salt - likely the damage was done already and it's not worth the cost of closed cooling.
I had it on my 280ss, was awesome - as the boat was also a SW boat. Was cool, could remove the belt and run the engine w/o a hose if need - while diagnosing an issue. I wish mine had it, would have saved a lot of salt water damage - including the erosion of my intakes .

Anyone running 454/502 Big Blocks without closed cooling should have pulled their intakes and replaced the gaskets with the Fel-Pro design - blocking the rear water port opening. Mine were never pulled, the erosion of the intake led to not only a intake failure but allowed water into the cylinders - Thank you Mercury Marine. Just finishing the rebuild of the second motor - 300 hrs on each.

Thanks for the reply snowrunner. If may, I’m not sure I agree with your statement that the damage is done. If the motors have been flushed frequently after every use, and internals still look good, switching to closed system will prolong the motors. Corrosion from saltwater does not continue if properly treated. However, when switching to closed system if not properly installed with proper grounding and running pure water, I can see the corrosion process continuing , but will not be due to its previous saltwater use.

Again would love to hear others thoughts on this, as I know I can learn.

thanks

I’d agree they would likely be preserverved. But the scale and rust have already done a fair amount if damage mine were flushed and the boat hoist kept. My point is $3k is better spent on other things, or until you get aluminum heads - just my opinion.

i would recommend inspecting the intake before anything else, both of mine were destroyed. This is a common problem with any Big Block MPI ir EFI running the aluminum intake.