RWC to FWC conversion

"As a fairly new member to the

"As a fairly new member to the boating community, my brain keeps coming up with new questions, the latest of which is: Is it worth (from an economic point of view) converting my boat from Raw water cooled to Fresh water cooled? If it is has anyone done it and what was the approximate cost?

My boat is a 1994 Silverton 34 Express with twin 454XL's (900hrs) it is running fine (or at least it was when I prepped it for winter) and I will probably keep it for a few years yet.
It is used in lake water well inland, so no salt to worry about."

"I did a couple stern-drives m

"I did a couple stern-drives many years ago. I don't think the economic aspects have changed so here's what we learned.

There are two cost effective ways to convert without repowering: 1) buy an OEM kit for your particular model - it will save you a bundle compared to trying to buy each piece part, it will be complete, and it will be a known, working configuration or 2) find a compatible model that just had major failure for a 'donor'.

We converted from crusader to merc when the crusader HX went south. that was over a decade ago. Kits were provided at dealer cost. Escalating them with a retail factor would put those kits well over $1200/engine, today.

If your "sporty" and willing to adapt or mod aftermarket stuff, if needed, SanJuan and PerfproTech.com make kits for about $1000 for big blocks."

"[b]"Is it worth (from

""Is it worth (from an economic point of view) converting my boat from Raw water cooled to Fresh water cooled?
It is used in lake water well inland, so no salt to worry about."

Nope,....

Boating in Sweetwater,...

There's No Reasons to use Freshwater Cooling...."

"Re: [b]"Is it worth"[

"Re: "Is it worth" The way I see it

Winterizing
Being a inland lake guy my self, & having a single engine (NO coolers) boat with a twin engine deck, I never saw "the worth" of FWCooling. To winterize my Slick w/ single 195 Chrysler , it's a 3 step process.
1) Wait till the weather man sezs "its going down to -2c tonight".
2) Go out, & open 4 petcocks, pull 2 drain plugs, & drop 1 hose, (EASY, takes LESS THAN 5 minutes).
3) Come back in and have another beverage.

Now that its twin Big Blocks, and the out sides are a bear to get to, not having to squeeze & crawl to the outsides, & just having 2 coolers & a heat exchanger is well worth $100 a winter to me.

Temperature
I'm skeptical that FWC provides any better control of engine temp (less engine wear) than a RWCooled engine. Isn't that what having a thermostat is all about?

Corrosion Factor
FWC (Captive cooling) is defiantly the way to go! That being said, I've been here a long time and don't know of anybody that has had to re power because of an over heating from the rust build up in their block of heads. (I hope this stirs the pot to get some more opinions). I'd love to hear otherwise.

So if your Handy, Have time, & Have donor engines, I'd say go for it.
but that's my opinion,"

"[b]Temperature
I'm skep

"Temperature
I'm skeptical that FWC provides any better control of engine temp (less engine wear) than a RWCooled engine. Isn't that what having a thermostat is all about?

Why does the FWC have a higher temp 'stat?

Thanks for the insight, I guess I'll be leaving it RWC and put the dough into a Gennie instead."

"The FWC systems have high t-s

"The FWC systems have high t-stats because they can get away with operating at higher temps then the RWC systems in SALT water. You'll notice the difference is about 20 deg. in salt water, at the higher temps, certain minerals will precipitate out and rapidly clog your cooling system.

I never asked which ones as I have never had the experiment to verify the statements. They came from a prominent manufacturer's field rep and i decided it was good enough for me.

The higher temps are also supposed to reduce internal friction a bit thus reduce wear and tear. My hunch is the difference isn't huge as long as the cooling systemm is working."

"Does that mean I could put 18

"Does that mean I could put 180deg 'stats in if I don't run in salt water?
I'm curious because I don't "drive' fast (wifey gets nervous) and we plan on exploring the Trent/Severn canal system this coming summer, most of which has a 10kph speed limit anyway."

"here's what they say.

"here's what they say.

Q: What benefits will I get from Fresh Water Cooling?
A: See the answer at
http://www.perfprotech.com/store/articles/fresh-water-cooling-benefits.aspx}

good site MakoMark

Fred 156-M"

"[b]"Does that mean I coul

""Does that mean I could put 180deg 'stats in if I don't run in salt water?"

Nope,... the 143°, or the 160° will work just Fine...

Even in Freshwater, there are salts,+ contaminants that can create Problems..."

"Salt has nothing to do with i

"Salt has nothing to do with it--that's a myth that keeps popping up. Here's the real reason:

RWC motors don't develop enough back pressure in their cooling system to keep the water from boiling after a long, hot run--and steam is a lousy coolant! A FWC system develops up to 8 psi of pressure that keeps the boiling from happening.

So...for RWC you need a 140 to 160 stat; for FWC you can use a 160 to nearly 200 stat.

Jeff"

"Jeff:

help me with the phy

"Jeff:

help me with the physics here.

I understand the relationship between operating pressure and boiling point just fine.

Last time i checked my FWC system the sea water side of it is open; ie it doesn't develop any significant operating pressure. as long as the pump delivers the sea water, the heat transfer occurs, and no boiling happens.

Are you referring to a prolonged hot soak, after an immediate shutdown, following the run?

tnx mark"

"I sure did a crappy job of ex

"I sure did a crappy job of explaining that. Time to try again:

The pressure I spoke (poorly) of was in the block and heads. Take a RWC motor: At idle, the back pressure (from the resistance of the water flowing through the motor) is about 1 psi. (I know this 'cause I tested it and developed a low water pressure alarm system for my boat, one I won't leave the slip without.)

Now, at cruising rpms (2,500 in my case) the pressure goes up to about 5 or 6 psi. This is because much more water is being forced through the block and heads. At THIS pressure, I could run a much higher t-stat and get away with it, until I have to slow down. The motors--that are loaded with heat after a long run--suddenly receive a reduced flow of water--we're back to 1 psi back pressure again--this is not enough to prevent water boiling inside the motor. And this is destructive.

In a FWC motor, the enclosed, pressurized cooling system remains at, say 6 psi, when the throttles are pulled back, so no boiling can occur.

I hope that clarifies things.

Jeff"

"jeff:

i've been chewin

"jeff:

i've been chewing on this a while and am still missing something.

Understand the phenomena you are talking about with the flow reduction...again, both FWC and RWC see the similar flow reduction (engine driven pump). I think what is baffling me is you keep mentioning boiling point but neither system ever comes close to this when operating (assuming all things are working). the engineer in me (not a mechanical or anything thermo-based) says same engine= same heat produced; same cooling water=same heat absorbing capacity...why operate at 20-25 degree difference???Something other than heat transfer factoring in...

As far as your pressure measurements, where were they taken? (trying to assess what they represent: a static pressure or a total pressure, i'm leaning static.)"

"jeff:

i've been chewin

"jeff:

i've been chewing on this a while and am still missing something.

Understand the phenomena you are talking about with the flow reduction...again, both FWC and RWC see the similar flow reduction (engine driven pump). I think what is baffling me is you keep mentioning boiling point but neither system ever comes close to this when operating (assuming all things are working); why different thermostats still not clear.

the engineer in me (not a mechanical or anything thermo-based) says same engine=same heat produced; same cooling water=same heat absorbing capacity...why operate at 20-25 degree difference???Something other than heat transfer factoring in...engine efficiency proportional to operating temp...

As far as your pressure measurements, where were they taken? (trying to assess what they represent: a static pressure or a total pressure, i'm leaning static.)"

"The coolant (or water&#41

"The coolant (or water) at the thermostat housing might measure 160 degrees or so, but there are metal pieces much higher temp than that. There are head areas in contact with the coolant that exceed 212 deg presumably. Thus, there will be boiling at atmospheric pressure, not good."

"on the raw water version, as

"on the raw water version, as the water flows thru the block, it absorbs the heat. A given sample of water experiences a temp rises as it flows thru the block. If the sytem is cooling properly, there is no place in the block where the water temp exceeds that at the t-stat outlet housing. The metal (block and head)will have a thermal gradient across it, from hot to cold, that will be consistent, after a couple minutes, for a fixed rpm and cooling water inlet temp. if there's a 143 degree t-stat installed and say 70 deg cooling water, at cruise - 3000 rpm - i doubt the water out of the t-stat housing exceeds 165 degrees. The water down in the block can't be any hotter - if it was, the heat would be flowing back into the block, not out of the block. If there's no 'pressure' in the cooling system, that's 47 degrees of margin before you get to the boiling point - with fresh water...

I'm thinking there's another reason for the lower temp t-stats in the rwc systems...that preciptation theory - not necessarily salt, but dissolved minerals in general - appears to have some merit. Time for more research."

"Temperature inside the block

"Temperature inside the block and heads can easily rise to 300 ' F and higher without sufficient water flow to remove it, and that's what happens when the motor suddenly idles after a long run--the heat is still there, but the water flow has suddenly decreased markedly.

You've got is 600 lbs. of iron, and it has a LOT of latent heat stored in it, heat that can't be ejected to the water fast enough.

Ever noticed a car motor doing this: Really hot day (which I could use right now!) with the A/C on full blast. You pull up to get gas and shut 'er off. Seconds later steam blasts out the radiatr cap. Why? All that heat in the motor, that was being removed while the engine was running, has hit the coolant so fast it boils--poof!

Jeff"

"I did some more digging and i

"I did some more digging and inquirying on this today and the simple answer is the t-stat is set by the engineer/designer based on the trades he/she has been asked to make.

Jeff's scenario, though reflecting reality, doesn't factor into the selection process, at least that what two designers told me. grabbing the CRC book, the specific heat of cast iron is about 9 times less than that of water (room temp). This will vary some with temp but the point is that 100# of water will absorb all the heat 900# of cast iron can hold. (It is residual heat vs latent heat and is due to the thermal mass of the cast iron.) That 100# of water is ~12.5 gallons. My cooling pumps will delivery that in a minute at 1500 rpm. It gets a bit complicated if the engine keeps running (generating heat) but the point is going right to idle after a long run isn't good for any engine and will induce a momentary temperature increase. a couple minutes at fast idle, in neutral, will dissipate any residual heat - this applies for either cooling system type.

Turns out that 'salt precipitation' is a fact and is well documented. It is also known as scale and is driven by temperature and the mineral composition of the cooling water. If anybody wants a link to a semi-technical paper on it, just email and ask. Also driven by the same two factors (and others) is the rate of corrosion of the metals. These drive the engineer to select a LOW temp t-stat.

On the other hand, engine efficiency and longevity desire higher operating temperature t-stats. Oil life prefers this side, too.

The current industry 'standards', 143 for RWC and 160 for FWC(for gasoline engines), for the most part, have been honed thru trial and error over the years.

Bondo's point about fresh water having "stuff" in it that will cause problems, including scale, is also something to remember. It is also a local variable so, if the others at the same marina start to have 'new' problems, expect them inside your hull soon.

So, the bottom line is this: if you want to maintain the manufacturer's design point, use what they recommend. If you have a special operating regime, sustained low speed cruise, and you are tired of seeing all the junk when you change the oil, you may want to consider a hotter t-stat. This may come with a reduction of the life of the exhaust system. If you do make any changes, ensure that whatever goes in performs the same functions as what comes out (some marine thermostats are a bit more complicated than the simple auto types).

Jeff - thanks for your thoughts and patience in this thread and good luck next week. Hopefully, you'll sharing more of your experience and wisdom before next month starts."

"What we have here is a paraly

"What we have here is a paralysis of analysis!

Here's an article from the well-respected DYI Boating magazine on the subject:

Modern inboard engines use 160F degree thermostats. This is because the pressure in a marine engines with raw-water cooling systems can vary from 0.5 psi at idle to 18 psi at WOT. Water boils at 215F degrees at 0.5 psi. This means with a 180 stat water in the block after a hard run then returning to idle could be at 240 degrees at 0.5 psi. The water would then boil in the block and turn to steam. Steam will produce an airlock and then an overheating condition, likely cracking the cylinder heads. With a 140 stat the temp after a hard run is about 200 degrees at 0.5 psi below the boiling point, therefore no overheating. If the cooling system is closed-cooled the pressure remains at (up to) 15 psi constant therefore one could up the temp to 180. If this was a good idea every marine engine company would be doing it as it would increase fuel economy.

Steve Auger (Editor of DIY Boating)"