Too much octane ?

[jackrg]

I have a 1984 ,140 hp 4 cyl mercruiser.<br />The higher octane that I use, clears up the rattle<br />in the engine, but is there any concern that this higher octane could do any damage to my engine over time? <br /> Thanks,<br />Jackrg

 

[Buttanic]

Re: Too much octane ?

No, but incorrect ignition timing could be the cause of the rattle and that could do damage.

 

[jackrg]

Re: Too much octane ?

I've adjusted the dwell to spec. and the Idle.That cleared up alot of the rattle but, there is still alittle rattle. The higher octane seems to clear up the rest of the rattle. I was just concerned that the high octane might have some bad long term effect. I've noticed a big difference when I run 87 octane vs 91-93 octane.<br /><br />Thanks, Jackrg

 

[QC]

Re: Too much octane ?

Octane is ONLY knock protection, so you cannot hurt it, sounds like you need it . . .

 

[LubeDude]

Re: Too much octane ?

Maybe you are over propped just a little, what are your WOT #s

 

[Scaaty]

Re: Too much octane ?

Originally posted by LubeDude:<br /> Maybe you are over propped just a little,

I kinda leaning this way too, or when was the last time you cleaned out the 2000 pounds of "stuff" that a boat collects. You had better get rid of the "Rattle", or your gonna toast the motor...detonation is a motor killer. If nothing else, back the timing down until its gone

 

[jackrg]

Re: Too much octane ?

I currently have a 19 pitch prop on and I can easily get 4500 rpm, there's more throttle but I have never run beyond 4500 rpm. Approx. How far can I adjust the timing ? This is exactly the type of advice I was hoping to get. Thank you

 

[waterone1@aol.com]

Re: Too much octane ?

You are "easily hitting 4500 rpm's"....OK, you are not over-propped. As for engine timing, set it to the factory spec. If you still have a "rattle" in the engine....find out why. Use an advance timing light and check your advance curve...you might have some stuck advance weights.<br />You could also have a lean condition from the carburator. Set things to factory, then post back with your results.

 

[Dunaruna]

Re: Too much octane ?

Simply adding higher octane may have adverse affects such as running hotter and LOWERING horsepower.<br /> <br />Follow waterone1's post.<br /><br />Aldo

 

[jackrg]

Re: Too much octane ?

Waterone1, I have been using a dwell meter and timing light so far. The "advance Timing light" is something I'm not aware of and have not used.<br />Can I check the advance with what tools I have ?<br />Thanks , Jackrg

 

[pine island fred]

Re: Too much octane ?

If all else fails, retard the timing a small bit. Rotate the distributer slightly in the same direction that the rotor spins. fred

 

[jlshields]

Re: Too much octane ?

My daughter had an '84 Olds Cutlass with that same engine and it sounded like a diesel. Rattled even at idle. Turned out it had bad timing gears.

 

[Liquid_force]

Re: Too much octane ?

Originally posted by jlshields:<br /> My daughter had an '84 Olds Cutlass with that same engine and it sounded like a diesel.

The 140 ci is a ford block isn't it?<br /><br />My t-bird has the turbo 2.3 and with anything less than 90 octane it knocks horribly, and occasionally even with 90. With 91+ it's as smooth as can be. Even with 250k+ miles, 15 psi, and a couple degrees advanced timing.

 

[QC]

Re: Too much octane ?

Originally posted by Liquid_force:<br /> The 140 ci is a ford block isn't it?

The 140 is a 3.0 liter, 181 cu inch GM block . . .

 

[Bondo]

Re: Too much octane ?

Ayuh,...........<br /><br />Whatever you set the Timing too,...........<br />Back it Off a Degree or 2.......<br /><br />There's No Reason in the world you should have to run High-Test Gas in that little 3.0,.........<br />Unless somebody has taken a pretty fair Slice of Iron off that Head...........<br />

but is there any concern that this higher octane could do any damage to my engine over time?

Ayuh,..........<br />It'll Destroy your Bank Account........

 

[waterone1@aol.com]

Re: Too much octane ?

Jack, you did not say when this "rattling" occured? Is it while accelerating, or only at high rpm's, or ?? You asked about an advance timing light. You can get one for under $75.00 at any auto parts store. With it, you can verify that your timing advance on the engine is following the manufacturer's curve. Even if your base timing is correct, if your distributer is applying to much advance to soon, the engine will detonate or "rattle".

 

[Liquid_force]

Re: Too much octane ?

Originally posted by Quietcat:<br />

Originally posted by Liquid_force:<br /> The 140 ci is a ford block isn't it?

The 140 is a 3.0 liter, 181 cu inch GM block . . .

Ah, my bad, I saw 140 and for some reason immediately thought ci.