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Old 08 December 2010, 20:59   #1
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Tohatsu/Mecury/Mariner 25/30 2 strokes

Just a word of warning if you own or are buying a new Tohatsu, Mercury or Mariner 25 or 30 two stroke which are all in fact Tohatsu only the label is changed.

In my opinion they have a design defect that makes them prone to corrosion if you are using them in salt water. I have raised this issue with Tohatsu Japan and they disagree, so you can be the judge of the situation.

These engines all have a large aperture about the size of your fist under the carburettor in the bottom of the engine shell. This aperture is not at all obvious. This will allow salt spray and water to enter the engine bay. To make things worse the engine cover is also vented at the top so the spray can blow straight through around the engine.

This may mean your engine gets coated with salt over the summer season and may sit corroding over the winter months unless you have a serious desalting routine as part of your corrosion prevention.

In Australia, New Zealand, and the Pacific Islands these engines are sold with no mention of this serious short coming to unsuspecting purchasers like myself. I donít know if this is the same elsewhere but I suspect so.

This problem has been recognised by Tohatsu Japan since 1985. I have their dealer maintenance bulletin (sent to me this month) of that year that states this. The bulletin shows that the engine cover was redesigned to incorporate a baffled air intake for the carburettor in the tilt hand grip at the top rear of the engine. A new grommet was designed and is available as an option ????? to close of the air intake under the carburettor and it notes that this helps stop corrosion.

The part number is Grommet D, Lower Cowl Part # 346-76161-0

In my opinion for salt water operation

1. All new Tohatsu/Mercury/Mariner 30 and 25 two stroke engines need to be fitted with the Grommet D, Lower Cowl Part # 346-76161-0 before they are sold in the Australia, New Zealand and the Pacific or anywhere else.

2. All such motors already sold need to be fitted free of charge with Grommet D, Lower Cowl Part # 346-76161-0 at their next service. All customers need to be sent a letter to inform them of this.
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Old 10 December 2010, 10:18   #2
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Interesting, i have seen this lots, although as far as know all the Mercury/ Mariner's have this grommet fitted as of abou 2 years ago, if not we fit the grommet when we PDI the engine.
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Old 10 December 2010, 13:41   #3
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Interesting, i have seen this lots, although as far as know all the Mercury/ Mariner's have this grommet fitted as of abou 2 years ago, if not we fit the grommet when we PDI the engine.
No issues like this on my 50 is there?
I regularly spray my opti's with this stuff called "Shield", it's an oil that dries leaving a residue, going to put a good few coats on the 50 since it's brand new
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Old 10 December 2010, 16:11   #4
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No issues like this on my 50 is there?
I regularly spray my opti's with this stuff called "Shield", it's an oil that dries leaving a residue, going to put a good few coats on the 50 since it's brand new
No just on the 2 cylinder block engines.
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Old 11 December 2010, 06:17   #5
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Interesting. Not all seams to agree about this issue? http://forums.iboats.com/showthread.php?p=3042236

Haven't seen any water, excessive moisture or corrosion inside the hood or engine bay on my 25/30. The inlet in the cowling is pretty well protected, don't see any issues there.

Anyone have a picture of this mentioned grommet, maybe its already installed and that's why I haven't any issues?

What about the heat inside the hood from the engine, would not that dry things up pretty fast anyway?
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Old 11 December 2010, 07:27   #6
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Interesting. Not all seams to agree about this issue? http://forums.iboats.com/showthread.php?p=3042236
Always a bit worrying when a first post is a carefully scripted gripe on multiple forums
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Old 12 December 2010, 15:57   #7
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I was little curious about this so went to the garage to check the engine. Yes indeed, the mentioned aperture is there and its not obvious. Difficult to spot without knowing( i had no idea). Still dont know if there is any practical disadvantage of this design.

When the engine is running don't think any blow would go around the block, what ever air goes in will be sucked by the carb. Then again, when the engine is stopped warm air will go out from the upper vent in the hood and cold air will be going in through the aperture.
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Old 13 December 2010, 04:10   #8
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Item number 10 on the attachment is the grommet!.
Attached Files
File Type: pdf 25mgrommet.pdf (109.5 KB, 126 views)
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Old 14 December 2010, 17:44   #9
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Item number 10 on the attachment is the grommet!.
Thanks! Is this a metal part or rubber /plastic?
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Old 15 December 2010, 16:15   #10
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Thanks! Is this a metal part or rubber /plastic?
Rubber grommet, Never seem to fit to well, so put some RTV on it!!
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