White smoke from one motor.

[SaltH2OHokie]

Twin 350 inboards, port 7 months old, starboard 2yrs old.

Where should I start in investigating one motor producing more white smoke/steam? Noticed it on plane a few weeks ago, then yesterday warmed up both motors in the slip and while idling noticed one motor (starboard, 2yrs old) was still producing more steam/white exhaust than normal. Punched the throttle on that motor real quick and it fogged the bulkhead so thick you could hardly see the pilings. Also put a slight film on the water, but that could easily have been unburnt fuel from the brief WOT. Water was 45deg, air was actually in mid 60's, motors were 160. I understand that'll make some additional steam, but the port motor hardly produced any steam...no odor that I could get from it, but it seemed to linger a lot longer than steam usually does.

[seabob4]

Manifolds/Risers on the starboard motor?

[GoneFission]

Are the motors raw water cooled or fresh water cooled?  It makes a big difference in what the problem might be...  

[gman 82 aquasport]

I'd start by pulling the plugs on the starboard engine, see if they look"washed"not sooted up..if you need a comparison, pull a plug or two from the other engine and compare...I would pull all 8 on the starboard one and one from each bank on the other for comparison..if there's a leakage issue into the combustion chamber, the plugs will usually show you somethings amiss...if it shows leakage, start looking at the manifold/risers like seabob said..good luck

[SaltH2OHokie]

Are the motors raw water cooled or fresh water cooled?  It makes a big difference in what the problem might be...  

Freshwater with merc style fwc exhaust.

[gman 82 aquasport]

When was the last time the manifolds or risers were changed, unless they are stainless they don't last long in a salt enviroment.

[SaltH2OHokie]

Motor is 2yrs old (actually a fuzz less than 2yrs), manifolds nor risers have been replaced.  I certainly hope manifolds and risers won't become an 18mo maintenance item.

Edit to add: same brand/size/configuration motor was in my last boat, which was used in the same waters...and manifolds and risers were fine when I sold it 5 years after the repower.  Hope quality hasn't slipped that much in the 5-6 years between engine purchases.

[dburr]

Were both motors 160 or was the starboard one a bit warmer? I had a hole in an after market manifold  with less then 100 hrs on it on a Merc 160 that showed up only under load and the way it did was the engine temp shot up.. Everything was ok until I slowed it down and at idle it sucked water in through a closing #6 exhaust valve, the piston stopped, rod bent and cam spun.. That was the end of that motor..

More steam could be as easy as better water flow through the heat exchanger to a hole.. Does the hose from the engine to the HE get firm? How about the expansion tank, does it pressurize more then the port side? All good info to figure out what is happening..

Good luck!

[SaltH2OHokie]

Were both motors 160 or was the starboard one a bit warmer? I had a hole in an after market manifold  with less then 100 hrs on it on a Merc 160 that showed up only under load and the way it did was the engine temp shot up.. Everything was ok until I slowed it down and at idle it sucked water in through a closing #6 exhaust valve, the piston stopped, rod bent and cam spun.. That was the end of that motor..

More steam could be as easy as better water flow through the heat exchanger to a hole.. Does the hose from the engine to the HE get firm? How about the expansion tank, does it pressurize more then the port side? All good info to figure out what is happening..

Good luck!

Actually, that motor runs a little warmer than port, but it always has.  No real spike in temp, just normal operating temp on starboard motor is (and has been) consistently 7-10deg higher.  They have different size and age HE's and different t-stat housings, so I assume that is the explanation for the temp difference.  It's usually 165deg starboard, 157deg port...though that's giving a lot of credit toward the accuracy of my gauges, which might not be warranted.  Regardless of accuracy, I assume they're fairly precise, and as such I trust that the motor is not running any hotter than usual now that this steam is happening.  Doesn't appear to be losing coolant either.  I guess I'll hop down there and check on all of these good diagnostic suggestions and report back.

While on the subject of temperature, an aside: the new motor has the silliest design for mounting the HE that I can think of: A mounting plate is sandwhiched between the t-stat housing and the intake manifold to hold the HE off the front of the motor.  The mount becomes part of the sealing surface.  That HE is not light, and I imagine (though I've never ridden down there to watch   ) that it is inclined to bounce in heavy seas.  Just seems to be inviting a coolant leak.  I've had 5 small blocks with HE's and this is the first with that mounting setup.

[seabob4]

Merc does some half azzed chit sometimes on their I/Bs, Ryan...

When Merc first came out with the 6.2 Horizon, I was still at Stamas.  Had a number of failures in the field due to water injestion, determined to be from not enough downward angle of the exhaust (although our installs met Merc's specs of 1" drop for every 1' of exhaust).  They determined we had to go with 6" spacers on top of the risers...and that didn't work (thank God we had deck clearance).  So we switched over to Crusaders...

Cam lobes and valve overlap was basically the issue.  So why didn't Merc just change the cam profile?  Yeah, they would have lost some power, but....

The problem was there was no longer the 7.4L (454) to bridge the gap between the 5.7 and the 8.2 (which GM also discontinued).  So the 6.2 had to take both the 5.7s place and the 7.4s place.  The 5.7 in base config was 260 HP, the MAG being 300.  The 7.4 was 330 HP in base, 385 in MAG version. So there was quite a large spectrum that one motor had to deal with.  Not to mention the torque issues of a smaller motor...

So Merc tried to make it a "jack of all trades"...ended up being master of none...