8.1 Horizons at trolling/idle speed all day....problems?

[nowakezone]

I hope to be closing on a 340 with 8.1 Horizons in a week or two. We spend a lot of time trolling and also enjoy idle speed boating. The 8.1's hit the mark.

Presuming clean fuel and well-cared for engines etc...are there other foreseeable problems?

 

[skolbe]

I have always felt it is good to be at 1600 plus rpms to give the engines a little workout and a little pressure on things to keep everything circulating. Should be fine good luck.

 

[Jimmy Buoy]

Of any of Mercs engines, this one seems to be quite up to date regarding technology - so I would think it would be able to idle for long periods without issues.

Here's some of it's features directly from Merc's information...
Mercury-exclusive PCM 555 high-speed microprocessor that optimizes fuel mixture, knock control and ignition timing independently for each cylinder,
Distributorless ignition system that improves timing accuracy and eliminates mechanical timing adjustments
Closed cooling with 5-year coolant. Sequential fuel and spark control maximizes performance from every engine cylinder

The are two issues that I've seen with this engine. One is the aluminum exhaust manifolds when used in salt water. It's a bad combination that can result in terminal water injestion due to the salt corroding the aluminum material (often inside where you can't detect it). The second issue involves a fuel cooling unit but only if it is a Generation 3 unit. Apparently those units were painted black inside and out, but the paint inside flakes off and is carried along with the fuel to the injectors and the fuel pressure regulator causing expensive repairs. not sure what years would have this unit, but you might consider doing a quick search on CSR - lots of posts on both of these issues.

 

[nowakezone]

Great stuff! Thanks for the advice guys.

 

[nowakezone]

Thanks Scott.

The 1500 rpm mark is another spot where I anticipate spending a lot of time. According to the Boattest performance chart that's about 8 knots or just over 9 mph, fast enough to feel like you're getting somewhere but still getting decent gas mileage.

We plan to cruise from Naples to the Keys several times a year, about 110 miles each way. I've never cruised that many hours at that speed, although I've spent the day fishing and trolling that many hours at slower speeds. We love being on the water so I'm hoping the beauty and ride of this boat helps relieve boredom. The straight shot to Key West gets into fairly deep water so I can pull some lures when we go there.

 

[eauty]

I have a 2006 340 SDA with 8.1l and I have to chime in on this blog. I have owned and babied my boat since new taking care of everything and not abusing the hull or motors. Last season, while on an extended trip on the Great Lakes, my motors started to use more oil than usual. These motors have a history of burning oil but not necessarily excessive. At the end of the season I was burning a quart every 8-10hrs. I never cruise for an extended time at more than 3500 RPM and usually cruisied between 3200 and 3400 RPM on the trip. Obviously I was concerned and I contacted Mercruiser and they agreed to do a leak test on the motors even though the warranty expired 6 months earlier. It was discovered that my starboard motor had a 50% leak on the intake valve on cylinder #5. I had to have the heads rebuilt in that motor and what they found was the problem was excessive carbon build up. It was so bad the valves couldn't seat and they attributed it to "poor fuel" and not running the boat hard enough. Needless to say I didn't buy the fact that the boat was not being run hard enough because the manual stated the cruise range to be 3200-3400 RPM. As far as fuel, what can I say other than I tried to exclusively use ethanol free fuel whenever possible. The motors only had 400 hours on them.
This season I have used Mercruiser Quikleen #2 fuel additive with every fill up and I take the motors up to 4000 RPM+ on occaison and so far I have only added 1 quart to the rebuilt motor in 50 hours. I just changed my oil and went to full synthetic in hopes of minimizing carbon build up and I continue to use Quikleen #2 with every fill up. I know people who troll all day with these motors with no problems and maybe I just had a freak problem but I would say that it would be good to take those motors up to a higher RPM every once and awhile to make sure you don't have any carbon build up issues. If you want any other info on my dealings with Mercruiser please feel free to PM me. Other than the problem I had at the end of last season, these motors have been extremely reliable.

Thanks Scott.

The 1500 rpm mark is another spot where I anticipate spending a lot of time. According to the Boattest performance chart that's about 8 knots or just over 9 mph, fast enough to feel like you're getting somewhere but still getting decent gas mileage.

We plan to cruise from Naples to the Keys several times a year, about 110 miles each way. I've never cruised that many hours at that speed, although I've spent the day fishing and trolling that many hours at slower speeds. We love being on the water so I'm hoping the beauty and ride of this boat helps relieve boredom. The straight shot to Key West gets into fairly deep water so I can pull some lures when we go there.

 

[carterchapman]

I'm with eauty on this. I add Chemtool B12 injector cleaner at the ratio of one can per 20 gallons of fuel added, and I check and log my WOT RPM once every 30 - 60 days. This gives me an indication of my bottom/running gear condition and engine health as well as carbon removal....

 

[nowakezone]

I've always had outboards so the inboard/V drive thing definitely will be new to me. And the big engines. I've also used Quickleen routinely, I think Merc recommends it. I'll definitely continue to use it. I've also routinely used Startron gasoline additive. Even in non-ethanol gas it seems to add a kick. I know it does in my car with ethanol gas.

The practice of running the boat at higher rpm's, even WOT, for decent periods seems sound for all the reasons stated. A capt friend of mine suggested the same. I've always done it with my outboards. Making sure all is well at max rpm is good maintenance in my opinion.

eauty there's a PM coming. Not about the Merc situation, rather about the ride in the choppy slop the Great Lakes can throw at you.

Thanks guys!