Mercruiser closed circuit cooling

[PADDLES]

Hi guys, does anyone have an opinion on closed circuit cooling vs. raw water for mercruiser engines? What are the pros and cons for both systems? Is it worth getting a kit fitted to a 6 year old engine (that's always been pulled out of the water)?

Even though the boat is out of the water on a trailer, the block still has water remaining in it that doesn't drain out after flushing. I'm planning on hanging on to this boat for a while and I'll be up for new risers within the next 12 months so am seriously considering getting the closed off gaskets and a closed cooling kit fitted when i get the risers done if there's a benefit corrosion wise.

[Noelm]

I guess the answer is pretty simple, "closed circuit" as you call it is just like your car, but instead of a radiator, it has a heat exchanger, that is a kind of radiator running in sea (cool) water, the advantages are no rust, a pretty good advantage I would reckon, the disadvantage is cost, a raw water cooling system is cheap and simple, but not so good for your engine, especially what amounts to a car engine running in salt water, and salt water in a car motor is not condusive to long life.

[PADDLES]

thanks noel, i can already understand the concept and also the fact that your engine temperature can be increased making it more efficient, but i was really chasing some practical info from someone who has chucked one on after a number of years and a couple of hundred hours of raw water use. are there issues with scale or has most of the scale blown through with the raw water before fitting the heat exchanger? does it really make a massive difference to the life of the engine? is it worth the $1k?

[Noelm]

yep, would certainly be worth it, at any price (almost)

[PADDLES]

that's what i'm thinking noel, and when i get new risers is the ideal time, labour wise, i just was keen to see if anyone here has done this.

[bastard]

Both my mercruiser engines are fresh water cooled and i wouldnt have it any other way,last weekend we pulled the head of my mates 470 which is fresh water cooled and i couldnt beleive how spotless it was,this engine was 26 years old,without fresh water cooling i would say the lifespan of an engine is about 12 years,i have just repowered but before that my boat was never stored in the water,always flushed and the heads lasted 6 years and were coroded out,also the inlet manifold was just about buggered after 8 years.

[PADDLES]

rightyo, i'll start sussing it all out. i'll compare the mercury stuff against this new "salt free" brand they're advertising in modern boating

[PWCDad]

I have the latest model raw water cooled 5.0litre 270hp Volvo V8 (chev 305ci) with a DPS duoprop drive on my Whittley Cruiser.

Raw water cooling has been around for many years and works well if maintained.

One thing that must be done annually is replacing riser gasket and checking the mating surfaces of the riser where the gasket sits. Taken apart and checked for flatness and no corrosion. New gaskets with factory installed method and products.

This small item will stop an engine fail by water bleeding through into the engine.

As for the corrosion issue of raw water cooled good flushing should see the iron headed and iron blocked engine last many years and engine hours. This has been proven by mercruiser and volvo for years.

That said ... I have what is called Volvo NeutraSalt System fitted to my engine from new. This uses a tank filled with neutrasalt or saltaway and an injection pump T pieced in the cooling line just before the water pump. Pressing the neutrasalt buttton on the dash for 30 secs injects the solution and denatures the salt water and prevents scale buildup.

I do this as I pull up at the last spot for the night or at the ramp just before shutoff on the trailer. Boat sits overnight on trips with no saltwater in engine!

When home I flush with a flushbox I've made. Fresh water flush and neutrasalt for 30 secs to be sure.

In my opinion the "closed cooling" that the heat exchanger provides is the best way to go. Glycol is run in the engine and the thermostat would be potentially different to raw water cooled giving a more stable engine temp and I would think closer the the ideal 85-90 deg C verses 70-75 deg C i get with raw water cooling. Oil temps would be reached earlier and closer to ideal temps IMHO.

Salt water still passes through the exhaust system and the heat exchanger so normal factory maintenance (and time schedules) would apply to stop corrosion allowing water to enter the glycol side of the heat exchanger et cetera.

The ultimate would be " Heat exchanger and then neutrasalt system injected into the salt water side of the system and exhaust.

I'm very happy with the raw water cooling and the neutrasalt system. Downside is the cost of the solution. I estimate its about $4 every time I hit the button at $112 for 1 gallon of the solution. Once out of warranty (2 yrs) I'll most likely change to SaltAway.

Regards
Anthony

[Dodgemeister]

A closed-circuit cooling system is certainly more efficient but it won’t prevent sea water attacking your manifolds & risers. When you put on the new risers, you should have the manifold faces machined flat or you can draw-file them flat yourself (dirty, messy job) & you should do some maintenance on the heat exchanger. Ideally, it should be cleaned out annually (we use pool acid - 32% hydrochloric acid. Of course take extreme care using it) to remove any calcium or detergent to remove silt, which will lower the heat transfer efficiency if not removed.

[PADDLES]

thanx gents, good info, that's what i'm chasing. i got northside marine to lift off the risers last service and they said the manifolds were perfect but the risers were starting to corrode at the gasket face where the little upturn in the riser gasket catches the condensation dribbling down from the risers. i've got dry joint manifolds so i'm not too worried about water getting into the engine at all but i'll still replace the risers next year sometime. i'm mainly trying to figure out whether to get a fresh water cooling kit installed at the same time to save a bit on the parts and labour. i'm even more mindful of how strong the aussie dollar is at the moment (considering most mercruiser parts come from the land of apple pie) and am wondering whether to get parts ordered now to take advantage of this.

[cormorant]

If motor is in good nick you will extend it's life but it comes down to $. A new fully dressed crate motor with fresh water coolling is getting cheap wth a strong Aussie and you can just store it away until required?

Quite a few parallel importers here in Australia and also non genuine manufacturers including stainless manifolds , risers etc. Been a few posts on that lately

There was a US company which was doing a glycol cooled exhaust manifold with salt water cooling beyond that. I can't find them at the minute. They were bulky and expensive and required a larger or seperate heat exchanger and pumps

Newer Cupro nickle exchangers are expensive but scale up far less while being more effecient and smaller. Be very careful in knowing what parts you fit and put on appropriate annodes ( even when people say they are not needed). Cleaning, descaling s also done diferently.

Temps above 70-80 deg will lead to scale and the only benefit is slightly better emmisions which is negligible seriously. Engine wear dfference is bugger all as something will break or corrode long before you wear it out. That is why raw water motors are run cooler ad can still last a long time. Newer motors with small galleries don't have a chance compared to old style and wouldn't be allowed due to emmisions a start up temps etc. Raw water was perfect for USA lakes and freshwater rivers.


Check your dimensions of engine as some manufacturers have very tight engine bays and you may need to move batteries etc etc Newer injected manifolds may have a lower profile. Many retrofits screw up as there is no place to put a expansion tank high enough so it works properly . Try and search boatpoint etc for a sistership to see how they fitted it may be a simple way to see how tehy were done at teh factory.

[PADDLES]

thanx cormorant, the aftermarket ones i've seen pretty much copy the mercruiser one in size/location so i'm assuming that they'll be ok in that respect. agreed though with the engine space issue, it's for a whittley 660 with a 4.3l V6 so space is a little on the tight side and it looks like an alternative location for the recovery tank would be needed for sure (most installs have this straight on the front of the heat exchanger). i'm usually pretty good with getting anodes replaced too, they cost fark all so why not have em i reckon. a full kit that cools the block and the manifolds is less than US$1k plus i'd have to add the installation cost on top. with a new engine being over 10 times that cost, i figure that it only has to add 10% to engine life plus a bit of interest to have paid for itself.

it's just that all outboards are raw water cooled with way less cast iron than a mercruiser and seem to last a long time. also a lot of people say that the raw water cooled mercruisers last a long time anyway if you can flush them properly and keep them out of the water. i'm still interested in doing this though.

[terryc]

Hi there i've got a 03 whittley cruiser 660 same motor, only purchased earlier this year and i started off keen to add fresh water cooling, what put me off was reading a number of similar posts on the Iboats forum where the advice was that if the motor was older than 6 mths and used in salt water the build up of scale inside the motor would continually clog the heat exchanger. I ended up replacing the manifolds & risers with stainless steel. During the replacement i had the block empty of water for a week and at the moment i am chasing down a slight overheat at low revs which i think has been caused by some scale breaking off whilst empty of water. Worth pursuing further enquiries before parting with your cash.
regards terryc

[PADDLES]

aaaaaggggggggghhhhhh, terry, that's what i wondered. whether the motor was just too far gone and i'd be chasing scale out all the time. is your boat stored out of the water? is your slight overheat only when it's out of the water and you're flushing it? if this is the case then i'd be looking at your water pressure from the hose because mine did the same thing, it'd cooldown with a few revs but an 18mm garden hose did the trick just nicely.

[terryc]

Yes mine is on a trailer, no anti fouling so probably never sat in water long, only couple hundred hrs on motor. Yes overheat shows at idle on muffs lift to 1500 revs and temp falls back down. Already removed & replaced leg impellor before riser manifold change. Seems to be ok in water. My manifolds & risers looked ok on outside but when i took them off too much corrosion starting to block holes hence now stainless. i too would jump to the closed cooling but don't want to risk blockages. From what i've researched the biggest killers of these motors seems to be manifold riser failure causing water to leak into motor. When i switched to the stainless i opted for taller riser manifold to help protect against reversion.