Raw water cooled engine life expectancy?

[wipe_out]

What is the life expectancy of a raw water cooled petrol V8 engine in salt water?

Also what is the service life of the raw water cooled exhaust manifolds and risers is sea water?

And I guess following on from that if a fresh water cooling system was added how long does the heat exchanger last in salt water?

 

[[2068]]

There are plenty of 20 year old petrol engines still running just fine.
And some that died anywhere between 5 and 10 years for various reasons.

I'd be changing raw water manifolds and risers after 5 years or so to be on the safe side, unless you have the latest generation of dry joint manifold/risers which you might be able to push a bit longer (the new designs are more resistant to leaks until the whole thing dissolves - I'm not sure if you can retrofit? Might be worth looking into...)

 

[wipe_out]

There are plenty of 20 year old petrol engines still running just fine.

That's impressive..

Is that on boats that stay in the water all year round? or would those be the ones that died between 5 and 10 years?

 

[[2068]]

The ones that died between 5 and 10 years are the ones that didn't change their manifolds/risers

 

[wipe_out]

The ones that died between 5 and 10 years are the ones that didn't change their manifolds/risers

HAHA.. Ok, fair enough..

 

[alruss]

I don't know how much time my boat spent in salt water but she is in brackish water on the tidal Thames and is now 45 years old with one of the engines the original, the other was changed because it produced no power, complete rebuild of used engine used to replace it. Don't know how long they are going to last, probably not long now I have boasted about their age.

 

[carlton]

Mine are 21 years old and counting. 33.5 knots at WOT and 24 knots cruise - sound as a pound. Change the mans/risers every five years.

 

[dustywings]

When I bought my boat it had twin raw water cooled petrol engines that were 28 years old and were in fine condition, I have changed them for diesels but sold them to another Riva owner who has used them in his boat so still going strong!

 

[Heat Exchanger Guy]

I couldn't comment on the life of the engine its self other than I assume those who say they have 20+ years of life have very well maintained engines?

As for the heat exchanger, this will vary depending on the exchanger specified and the operating conditions. Two key factors in the design are flow rate (too low and tubes can block, too fast and tubes can erode) and area of operation, for example shallow harbour water will contain more sediments than deep ocean water.

If you go down the route of using a sea water heat exchanger to cool a fresh water circuit, make sure the data you have is as accurate as possible;

Fresh water inlet temp
Desired outlet temp
Flow rate

Sea water inlet temp (can usually estimate based on are of operation)
Sea water flow rate (can be recommended by a heat exchanger manufacturer if not yet known)

From this information, a heat exchanger can be selected which will not only provide optimum performance but also be the right size to handle the flow rate and maximise the potential life span.

 

[wipe_out]

I have no heat exchanger on the engine.. That's sort of where the thought process of this thread started.. Have bought the boat and installed a new engine a few months ago.. Was toying with the idea of fitting a heat exchanger and having it fresh water cooled.. So determining the expected life of a sea water cooled engine vs the cost of the fresh water cooling kit (which it's self would need replacing).. If the raw water cooled engine should last 10 years plus then I don't see a need for a fresh water cooling system to be added.. If it was less than 5 years then it would be a consideration..

 

[Scarron]

I reckon the consensus of about 5 year life for cast iron manifolds and risers is about right. So given you presumably have a new set on the new engine? and a replacement set is about £500 - http://www.trickettmarineproducts.co.uk/mercruiser-manifolds.html so £500 will get you to 10 years and £1,000 to 15.

It is important to understand that the vast majority of closed cooling systems still put raw salt water through the manifolds and risers so you still have that problem! A 'closed' fresh water cooling system is around £1000 - £1500 so I can't see that it is worth it, the main advantage being more consistent hight engine operating temperature, especially useful if you are running fuel injection.

Another way of extending life is a Neutra Salt system - http://www.marinepartsexpress.com/prodbull/NS_engine_flushing_kit.pdf could be well worth doing?

The main thing to remember it that a new set of manifolds and risers is cheap in comparison to the engine damage caused when they leak internally and fill the cylinders with salt water.. new engine time! so if in any doubt at all change them.

 

[wipe_out]

That's pretty much exactly my thinking.. I suspect the previous owner hadn't changed the manifolds and that's what trashed the engine.. She has new exhaust manifolds and risers now so by the sound of it good for a 4-5 years at least..

So it seems the consensus is that the engine blocks don't have too many issues with sea water cooling, just the manifolds which are easily replaced..

Like the Neutra Salt flushing idea.. Will need to look into that a bit more..

 

[Scarron]

Yep, makes sense - go on push the boat out and change them every 4th year just to be safe -it'll cost you another £500 to get to 15 years. Pretty cheap insurance at £33.33 per annum!

 

[wipe_out]

Yep, makes sense - go on push the boat out and change them every 4th year just to be safe -it'll cost you another £500 to get to 15 years. Pretty cheap insurance at £33.33 per annum!

Absolutely.. Probably won't be able to get petrol any more before the engine dies..

 

[julians]

http://www.ybw.com/forums/showthread.php?247601-mercruiser-manifolds-lifetime&highlight=julians

As someone else mentioned earlier, the old style wet joint manifolds had a very poor design that meant the joint between manifold and riser would corrode very quickly and then leak water into the cylinders. The new style of dry joint eliminates this mode of failure. You can still get corrosion between the water jacket,but this takes a lot longer to occur.

Mercruiser switched to dry joint manifolds around 2002-2003 in their small block v8s. Im not sure about volvo v8s,but i think they might still use the old style manifolds.

Fwiw i started a similar thread a few years ago, see above