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Old 08-07-2014, 09:25   #1
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Mercury 4-Stroke OB Reliability

Hi all. I am toying with the idea of replacing my 2-stroke 15 hp OB with a newer 4-stroke of the same size. I have a line on a newer Mercury 15 hp, but want to know if they are reliable. Do any of you use Mercury 4-strokes? I would love to hear about your experience with these motors.

Cheers, Bill

M/V Harmony
'79 Marshall Californian 42 LRC
Lying La Paz, BCS
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Old 08-07-2014, 09:33   #2
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Re: Mercury 4-Stroke OB Reliability

We have a 2 year old 9.9 merc. It has been 100% reliable. No malfunctions of any kind.

The only thing that surprised me was that when I dropped the oil drain plug in the water, the dealer didn't have one in stock. He had to order one. Am I the only one who has ever lost the plug?

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Old 08-07-2014, 14:15   #3
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Re: Mercury 4-Stroke OB Reliability

I'd avoid these engines unless you are in fresh water.

We have a 4 or 5 year old 9.9 Mercury 4 stroke. It was a deal, but I've realized:

1) Mercury support sucks. It's just terrible.

2) Simple parts quite often have to be ordered. Even from a large online supplier.

3) There are too many parts that just aren't designed for saltwater use. Bolts and fittings everywhere, that are unprotected steel. Just stupid.

I'd go with a Yamaha for the next one.
Bill Streep
San Antonio/Port Aransas, TX
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Old 08-07-2014, 14:24   #4
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Re: Mercury 4-Stroke OB Reliability

I have had my 3.5hp for four years. It is stored winter's in the garage. I hang it vertical from its mounts. Starts on the 2nd pull. Likes to be run hard. Fuel tank is a little small. Serviceable motor overall.
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Old 09-07-2014, 05:54   #5
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Re: Mercury 4-Stroke OB Reliability

We swapped out for a 25hp 4stroke merc on the big boat back in 2007.

Around 1000hrs on her and we are very happy with the engine:
- Quiet: First time we stopped for a bridge, we thought it stalled because we couldn't hear it. It's very easy to converse in the cockpit while motoring without raising your voice.
- Efficent: It gets twice the MPG compared to the old 2 stroke.
- Starts Quickly: This is an EFI. Not sure if the smaller engines are carburated still.
- Negligible maintenance (oil changes, 1 spark plug change)

Issues so far:
- At around 500hrs, the plugs did get fouled out from too much idling. The local service rep, looked at it and told me the issue without any charge. He said most people assume it doesn't happen with 4strokes but if you are tooling along in no wake zones it can eventually happen. Now every few tanks we put in some of the cleaner and we also open her up for 5-10 minutes at the end of a days run to clean things out. The issue has not reappeared.
- This spring we had trouble starting her. I had disconnected the fuel line and ran her dry, thinking this was best. It took a while to get fuel thru the system but once we got her started there has been no issues since. In the future, I will run some stabilized non-ethonal gas in before putting her to bed.

Mercury parts and assistance: Abysmal.
- It's next to impossible to get past the advertisement part of the website.
- They have issues determining what engine I have when I tell them it's a 2007 25hp EFI. I give them the model number and they still had trouble and even argued with me (I included a picture of of the model number on the engine).
- Parts basically have to be ordered thru a local rep (I'm talking about the zincs not something complicated)

Still a good engine and happy with it ($5k for an entire brand new drivetrain beats the heck out of $10-20k to replace the drivetrain of an inboard diesel). If the service was even moderately better, it would be awesome.
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Old 09-07-2014, 06:21   #6
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Boat: Teak Yawl, 37'
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Re: Mercury 4-Stroke OB Reliability

You may want to look at the weight differential. It could be significant. Right now the 2 strokes are sought after by many because they are very light weight. The weight may be important for boat trim as well as handling.

The other issue to look at is hp to weight ratio. I bought a 25 hp Yamaha. That same 25 hp block is used for the hp model increments up to 40 hp. Consequently, I could have got 15 more hp for the same weight.

It has been my goal to get to 1000 posts on CF. This is post number 1000 for me.

If one sets their goals low enough they can always attain them.

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