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Old 28-04-2017, 08:11   #1
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Brown streak on Yanmar 3YM30AE

I found some water under my engine 3YM30AE (about 1 cup) and while checking the engine saw some brown streaks in the engine body. Not sure if this is rust or oil. Does not feel too oily on touch though. The picture is attached. What would you suggest to use to clean this? WD40? Any guess what is it?

Thanks
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Old 28-04-2017, 08:14   #2
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Re: Brown streak on Yanmar 3YM30AE

Sure looks like light rust to me. I keep my engine wet with Corrosion-X and wash it off once a year and re-apply.

Need to find source of water though leaks rarely do anything but get worse
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Old 28-04-2017, 08:35   #3
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Re: Brown streak on Yanmar 3YM30AE

Like a64pilot said, clean it up and check where it's coming from. It seems like engines come with very thin coating of paint from the factory. You can buy a spray can of matching engine paint for touch up.
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Old 28-04-2017, 08:43   #4
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Re: Brown streak on Yanmar 3YM30AE

What's the best product to clean this light rust?
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Old 28-04-2017, 09:09   #5
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Re: Brown streak on Yanmar 3YM30AE

On a side note... I wonder why there is no wire on the oil pressure warning switch.

Edit,... or maybe it's the water temp switch, since it's next to a drain fitting.
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Old 28-04-2017, 09:10   #6
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Re: Brown streak on Yanmar 3YM30AE

I don't think you can clean it.
If it is rust stains on top of the paint maybe you can, but if it's the metal rusting, then you treat with osphoric acid and paint.
I butchered the spelling, its an acid that chemically changes iron oxide I believe into iron phosphate which stops the rust, then paint over it.

I have heard that Coca Cola will clean light rust stains and cause no harm to anything
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Old 28-04-2017, 09:13   #7
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Re: Brown streak on Yanmar 3YM30AE

Bad news is Yanmar paint is not of the higherst quality in my opinion.
Good news is you can buy a can of spray paint that matches it perfectly, I spray it into a container then use a brush to touch up areas like this after killing the rust, you will not be able to tell.
I do not trust myself to spray it and not make a mess

I wondered myself about the missing wire
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Old 28-04-2017, 09:25   #8
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Re: Brown streak on Yanmar 3YM30AE

Thanks, the missing wire is an oil pressure sensor. Per our mechanic it is faulty and a replacement was ordered. The oil sensor was giving low oil alarm although the oil level seems to be ok. So it was temporary disconnected.

I have to admit that I also feel uneasy a bit about this.
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Old 28-04-2017, 09:34   #9
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Re: Brown streak on Yanmar 3YM30AE

Quote:
Originally Posted by jserge View Post

I have to admit that I also feel uneasy a bit about this.
Unscrew it, go to the auto parts store a buy a cheap oil pressure gauge kit, take the switch so you can be sure to match threads, then temporarily install the cheap oil pressure gauge to verify you have good oil PSI.
Remove it and put it all in a zip loc bag and keep it, you or someone else will need it one day to diagnose if their alarm system is bad or if they have low oil PSI.
Rarely do the alarms systems go bad, and it seems most of the times when they do it is they fail to alarm, that is why you listen for the alarm every time before you start the engine, it alarms, you start the engine it and it quits, you have just checked the alarm system
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Old 29-04-2017, 08:30   #10
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Re: Brown streak on Yanmar 3YM30AE

That looks suspiciously like extended life anti freeze. worry about the paint after you find out where that is leaking from. Was the head re-torqued at the specified interval?
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Old 29-04-2017, 10:33   #11
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Re: Brown streak on Yanmar 3YM30AE

i replaced a oil press switch on a friends yanmar engine with a kabota oil press. switch. think it was around 15.00 us
same one that I use on my universal engine
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Old 29-04-2017, 13:59   #12
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Re: Brown streak on Yanmar 3YM30AE

Thank you, one other version I got was "the water under the engine likely came from the bleed vent for the air conditioner pump".

We are still looking at this. Will post if the culprit is identified.

The water under the engine was sort of clear. It is possible that the rust/marks on the engine and the water under the engine are unrelated.

The engine is brand new, only 55 hours so far.
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Old 10-04-2019, 14:41   #13
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Re: Brown streak on Yanmar 3YM30AE

Hi Jserge,

the Engilne Oil alarm of my Yanmar 3YM30AE with 220 hours started to chirp when revving over 2,100 in gear.

Of course Engine Oil and filter are perfect.

I wonder how you fixed the problem with your Engine oil alarm.

Thanks!
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Old 10-04-2019, 16:06   #14
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Re: Brown streak on Yanmar 3YM30AE

Havoline 7994 extended life coolant recommended by Yanmar is orange in color, could be time for a replacement cap if you use this coolant?
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Old 10-04-2019, 16:30   #15
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Re: Brown streak on Yanmar 3YM30AE

Looks very clean and inconsequential...
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