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Mercruiser 140 hp on Natural Gas


ron aerts's Avatar
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06-24-09, 02:11 AM   #1  
Mercruiser 140 hp on Natural Gas

I have an inboard Mercruiser 4 cil 140 hp engine. The former owner of the boat installed a natural gas installation. This saves costs specially at high speeds...
However, (like common I understand) the engine gets warmer on NG. I have NGK sparkplugs, type BR6FS, but sometimes the porcelain cracks and makes the engine run irregular, due to bad sparking of cause.
Is there a way to make this work better?

 
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06-24-09, 05:04 PM   #2  
That is interesting, I have never came across a natural gas boat. How large is your tank? I'm assuming it's removable to fill.

As far as running hot enough to crack spark plugs I would retard the timing a bit and get the coolest thermostat I could find.

Post a picture if you can I would like to see the setup. It sounds cool.

 
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06-25-09, 05:48 AM   #3  
NG on board

It is indeed not so common and it runs on both NG and leaded fuel, however loads of cars use NG here in holland, 70% of the gas stations sell it. I use 2 removable tanks of 40 liters. (exchanged w. eachother every time) 32 liters is enough for about 6 hours at 2400rpm. (maximum fill is 80% due to regulations)
Also forklifts, used indoors in industry are commonly equipped with NG-installation. So removable tanks and snap-on couplers are also easy to get. Nowadays you have the polyester tanks, which are much lighter than the old iron 'killers' and, as they are a bit transparent, its easy to see if your running out.
The NGtank is in the bow, this to balance with the 125 liter fueltank right behind the middle of the boat (6.5 mtrs)
As for the problem with the sparkplugs NGK advised me to use another heatrange of plugs. From NGK BR6FS to the R5673-7. These are a bit hard to get here and I can't find any specs to check if the physical dimensions are the same. Any Links.
I'm going to try to post some pictures.

 
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06-25-09, 06:46 PM   #4  
Is 2400 your top rpm with NG? If it is that is some of your heat problem and should drop prop pitch to get it up to 4000-4500.

I have never heard of plastic tanks, how thick are they?
We have cyl. exchange at a lot of gas stations most are for gas grills. Actually it is propane not natural gas that we use. We had a propane forklift and it was cool as the oil never got dirty when we changed it it looked like new.

Can you get the spark plugs from ngk?

It sounds like a neat setup.

 
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06-26-09, 12:18 AM   #5  
with NG it is 4200 tops, on fuel a bit more, I think 4400. And this wil make 58kph/31kts. We have only 2 area's nearby for highspeed boating but still taking a 2,5 hours trip...
So, long testing is not so easy.
Monday I have a mechanic looking at the engine and I will forward your tips to him. I am not so good yet with motors and terms, I'm an electrical engineer. If you or somebody have more Ideas please post them. (I'm about 8 hours ahead of your time) Thanks!
The spark plugs are available but double the price as normal. NGK informed me that the dimensions are identical. NGK has good service.

 
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08-06-09, 05:54 AM   #6  
Posted By: samuari I have never heard of plastic tanks, how thick are they? .
I can't find the right info yet but is already commonly used in campers etc. here is an example (in dutch) www.bpgaslight.nl

 
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08-06-09, 07:09 AM   #7  
Thats pretty wild..wish we had tanks like that here. Lightweight, no rust, can see the level inside....very cool.


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08-06-09, 08:47 PM   #8  
Ya that is cool, thanks for posting that.

 
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