White smoke / steam from exhaust

So yesterday I decided to open up both 454XL's for a bit. WOT for Port engine was 4200, 3900 for Starboard.

After 5 minutes of WOT my starboard engine starting throwing a lot of white steam/smoke out of the exhaust. I think I noticed a faint burnt rubber smell at first. The engine didn't overheat (175), seemed to be running smoothly, has started fine since then, etc.

I opened up the engine compartment and the exhaust hoses on this engine were very hot (couldn't keep my hand on them) compared to the exhaust hoses on the port engine. I also noticed some white steam/smoke in the engine compartment but couldn't tell where it was coming from. Seemed to be wisps from the exhaust hose area.

The white steam/smoke slowly went away as I made it back to the dock on both engines at around 2000rpm. It was getting dark and I only had a chance to check the oil and it appeared to be fine, not frothy or creamy colored.

I suspect I have insufficient fresh water flow and the exhaust hose(s) were burning up? This doesn't seem to fit the scenario of a blown head gasket but I'm not an expert.

Your description fits the initial assessment....don't be surprised if you have removed a fair amount of the inside of the exhaust hoses.....it only takes 'seconds' at cruise, with insufficient water flow, to cause hose damage....at WOT, it will take less time.

When was the raw water pump last serviced?

makomark said:

Your description fits the initial assessment....don't be surprised if you have removed a fair amount of the inside of the exhaust hoses.....it only takes 'seconds' at cruise, with insufficient water flow, to cause hose damage....at WOT, it will take less time.

When was the raw water pump last serviced?

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I suspect it's been a while. I've only owned this one a little more than a year and it's such a monumental task to get to the starboard raw water pump (remove oil cooler, etc) that I'm sure it's been neglected.

Bummer....if routine maintenance is "monumental", I'd suggest start liqudating the IRAs now - the added price for deferring it will begin to grow exponentially....

makomark said:

Bummer....if routine maintenance is "monumental", I'd suggest start liqudating the IRAs now - the added price for deferring it will begin to grow exponentially....

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Not for me - I meant it probably was for the previous owner therefore I'm speculating it's never been done. I've had boats for 40 years, it doesn't phase me

8.1L HO's here, 2002 motors.

Last year, same situation started occurring on my port engine......engine guy said my raw water pump was leaking badly. Replaced the 16 year old OEM pump and the problem went away.

Wanted to provide an update - had the marina mechanic look over the engine and how to replace the impeller due to limited access. They estimated a total of 4.5 hours to remove and reinstall everything required to replace the impeller on that engine (total $500). I told them to go ahead and schedule me.

They haven't done it yet but I did replace the left exhaust hose which had a pinhole leak. While I had it off I checked the output of the riser and I suspect I will need to replace it as well since it looks like the raw water discharge ports are a bit corroded.

Took it out last weekend and everything is fine until I go past 2500 rpm, then the steam starts. Engine temp itself continues to be fine.

We'll see what happens after the impeller change.