Merc Thunderbolt 50 fuel and year

[Grant Manning]

Have purchased 50 hp thunderbolt. Serial number is 4417206. Would like to know year and do we use leaded or can we use unleaded fuel please?<br />Brisbane, Australia.

 

[riverebel]

Re: Merc Thunderbolt 50 fuel and year

1976 model....not sure on the fuel, but think if would be ok to use unleaded

 

[Spidybot]

Re: Merc Thunderbolt 50 fuel and year

Unleaded and min. 91 RON/87 oct. is right for it. (Notice that octane is stated by two different definitions:<br /><br />

The US/Canada uses a different Octane rating system at the <br />gas pumps than most other countries.<br /><br />They use the U.S. Cost of Living Council (CLC) index<br />which is the average of the Research Octane Number (RON) and<br />the Motor Octane Number (MON):<br /><br /> <br /> CLC = (RON + MON) / 2<br /><br /> RON = Research Octane number (ROZ in Germany)<br /> MON = Motor Octane Number<br /> CLC = U.S. Cost of Living Council<br /><br />This translates to (roughly):<br /><br /> 91 RON = 87 CLC (Regular) <br /> 95 RON = 91 CLC (Premium<br />

And always use TWC-3 oil as it is rated for marine use and specifically designed for such conditions.<br /><br />Except from you paying more, there will be no difference if you use higher octane.

 

[andrewkafp]

Re: Merc Thunderbolt 50 fuel and year

You can use ordinary lead free mixed 50:1. My 81 Merc uses this and the octane exceeds the manual octane requirements. Lead free super or Optimax will not give you any benefit on these motors.<br />Whack a few drops of fuel stabiliser in each fill to eliminate moisture, retain octane and remove gum. Something like petrolpower or fuelset. This will help keep those carbs clean and prevent a meltdown . I run mine dry between trips, but this is a debatable subject.

 

[WillyBWright]

Re: Merc Thunderbolt 50 fuel and year

Lead in gasoline was to improve the octane and lubrate the valve stems of a 4-stroke. 2-strokes never needed lead.

 

[Grant Manning]

Re: Merc Thunderbolt 50 fuel and year

Many thanks to those who replied. Have now run the motor on the water twice. Went very well the first time. I had already striped and cleaned both carbs and'Devcon'patched the small corrosion holes in the water jacket. Second time out yesterday could not get full power. On inspection lower carb was leaking milky mixture of what looks like water and fuel mix? Will inspect today but any ideas?

 

[andrewkafp]

Re: Merc Thunderbolt 50 fuel and year

Check the plugs for 'Steam cleaning" effect of water in cylinder. You say you have plugged some water jacket leaks. Perhaps water has decided to leak from inside the plug threads into the cylinders. This wouldn't explain the "Milky" substance, but would explian rough operation. If you find that water is getting in, you may have to remove the jacket. This means you will likely snap bolts,and may be necessary to remove the powerhead and re-drill new ones. Don't want to sound negative, but head and exhaust areas are notorious for corrosion on early Mercs.

 

[Grant Manning]

Re: Merc Thunderbolt 50 fuel and year

Merc 50 water in fuel. Have striped water jacket cover and gaskets exposing pistons which confirm water in lower combustion chamber. Also removed carbs and something is very loose inside crankcase aperture! Looks like a casting might be cracked. Having trouble removing lower engine case section? Do I need to take engine off boat and drop case section off over shaft? Thanks Unicorn for previous advice. Intend to completely rebuld now I've come this far. Will probably need a manual. Are they available?

 

[andrewkafp]

Re: Merc Thunderbolt 50 fuel and year

You didn't waste any time... You can either buy a SELOC or Clymer manual for around $90.00<br />AUD. Or borrow from most libraries.<br />Good luck with your Merc..