Interesting different oil/ratio observation today

[slimbo3006]

So not directly chainsaw-related but definitely oil related and I know how everyone loves to talk about oil and mix ratios

anyhow so today was a pretty day and I took my 15hp evinrude outboard for a quick run... I mixed up 2 gallons of fuel for the boat. I used XD100 oil. mixed it around 45:1 or so. I also took my gallon of mix for my saw/trimmer with me just in case. It is amsoil Saber at 50:1. (got a small bottle from friend to try) both cans are from the same fuel. 92 Ethanol free. maybe 2 weeks old. Possibly 3 at most. Anyhow took the boat out and it ran great. It tached out steady around 5,920-5,960 RPM at WOT. This was on the XD100 outboard oil at ~45:1. Then for no real reason whatsover, I decided to switch to the other can with the amsoil saber at 50:1. I did this while idling and it never missed a beat. Went another couple hundred yards to give the new fuel time to get to the engine and I noticed the rpms were only hitting 5,740. It held around this for the whole time on the fuel. I then switched back to the XD100 mix and shortly after the rpms were back up to 5,940.

Just thought it was interesting that RPMs fluctuated by 200rpm with nothing more than a different oil/mix ratio. That being said, If I did not have the tach on the motor, I would have never know the difference..

Both of these brands are quality oils. mix ratio is slightly different but pretty close.. same batch of fuel... not sure what the flash point difference is between the 2 oils


I know it is minor...but.....wonder what the difference is??

 

[ammoaddict]

That is interesting. So you didn't notice any power difference, just lower rpm?

 

[slimbo3006]

That is interesting. So you didn't notice any power difference, just lower rpm?

not at all. didnt have a gps so don't know if I lost any mph or not. but it couldn't be much if I did

 

[Tomos770]

So 200rpm difference between TCW-3 and FD oil....

 

[ericm979]

So 200rpm difference between TCW-3 and FD oil....

Its due to the very slightly leaner fuel:air ratio from the 45:1 vs 50:1 fuell-oil ratios. The carb meters fuel+oil. Adding oil means less fuel gets to the engine.

It takes a while for the oil that's stuck on the inside of the engine to be replaced by new oil. (SAE papers indicate about 30 minutes for full replacement). You would not see an instant change like the OP did.

 

[Tomos770]

Meh...

If that would be a 25-35ccm strimer I would belive you....

15Hp outboard engine is usually of 250ccm size......way less susceptible to any changes...

I would put my stakes towards.....that he has fastened tank cap differently when refilling (from batch to batch)...ie if cap was fastened more tightly....there was more lean ratio (vacuum in fuel tank obstructs fuel flow)

 

[HansFranz]

Was there a different load on the engine when you got different max rpms (upwind/downwind, upriver/downriver, uptide/downtide, etc.)?

 

[Patrick1903]

Try the experiment using same oil at two different ratios. Ie isolate the variables.

 

[slimbo3006]

I believe the displacement is 15.6 CI with is 255CC. 2 cylinder with a single carb.


So yea I might try this with the same oil/fuel but at different ratios.

As for variables... wasn't really planning on doing this as an experiment originally. just something I noticed. but as to the fuel cans, there was no cap on either of them. just a 3 foot fuel hose with a bulb and an inline filter that I pulled out of one can and put into the other. didn't even use the boat tank because I didnt plan on going too far.

as for water conditions, it was within the same 1/2 mile stretch of the creek. Wind/tide were the same. even had similar reading when I turned back and went back up. I literally just pulled the hose from one tank and stuck it in the other. Just held the throttle at full WOT on both tanks.

I will update everyone if I get around to trying this again. might be a while though. it is just a little 14ft boat and we do not get many days this time of year where the wind is calm enough to take it out. (BIG WATER!!!)

 

[tJKrider]

I took my 15hp evinrude outboard for a quick run

Try the experiment using same oil at two different ratios. Ie isolate the variables.

Agree we need to know a bit more here first, and then reduce the variables.

What size boat and is it empty or loaded? If the engine is really working/loaded an air/fuel ratio change will have a different impact then if it is working with relatively little load.

There also could be multiple variables here. Not knowing anything except what was given, I could envision three variables at play:

Ratio, current, engine temp

45:1, with current, cold engine = high rpm
50:1, against current, cold engine = low rpm
45:1, against current, warm engine = high rpm

Point being it could not be just one dominant factor...

 

[tJKrider]

@slimbo3006 just saw you posted again while I was typing. Thx for providing addl information. I was just using current as an example but see that it probably didn't have an impact. If your 14' boat was relatively empty I can see how it could be just an air-fuel impact. As an example, by tuning the "H" screw on a chainsaw at WOT you are changing the AFR and impacting max RPM, albeit within a given range.

 

[thenne1713]

So not directly chainsaw-related but definitely oil related and I know how everyone loves to talk about oil and mix ratios

anyhow so today was a pretty day and I took my 15hp evinrude outboard for a quick run... I mixed up 2 gallons of fuel for the boat. I used XD100 oil. mixed it around 45:1 or so. I also took my gallon of mix for my saw/trimmer with me just in case. It is amsoil Saber at 50:1. (got a small bottle from friend to try) both cans are from the same fuel. 92 Ethanol free. maybe 2 weeks old. Possibly 3 at most. Anyhow took the boat out and it ran great. It tached out steady around 5,920-5,960 RPM at WOT. This was on the XD100 outboard oil at ~45:1. Then for no real reason whatsover, I decided to switch to the other can with the amsoil saber at 50:1. I did this while idling and it never missed a beat. Went another couple hundred yards to give the new fuel time to get to the engine and I noticed the rpms were only hitting 5,740. It held around this for the whole time on the fuel. I then switched back to the XD100 mix and shortly after the rpms were back up to 5,940.

Just thought it was interesting that RPMs fluctuated by 200rpm with nothing more than a different oil/mix ratio. That being said, If I did not have the tach on the motor, I would have never know the difference..

Both of these brands are quality oils. mix ratio is slightly different but pretty close.. same batch of fuel... not sure what the flash point difference is between the 2 oils

I know it is minor...but.....wonder what the difference is??

THE 50:1 IS RICHER (more fuel/oil= more fuel/air) than the 45:1, as many have stated on various boards; the question then becomes "is the 50:1 too rich, or the 45:1 too lean", especially to a point that would cause eventual damage??? And you noted this with JUST a 5-point(+/-) difference. Interesting to prove/ disprove the point would be to switch, get the new fuel mix to carb, then retune, Noting HOW MUCH ADJUSTMENT required? (1/16, 1/8, 1/4-turn?) Certainly less than 1/4? Thanks for the experiment and feedback to group.

 

[Tomos770]

https://www.arboristsite.com/threads/changing-oil-mix-ratios-do-i-have-to-re-tune.363387/

 

[bwalker]

So 200rpm difference between TCW-3 and FD oil....

Amsoil doesn't make an FD oil.
And using an FD oil in a outboard is stupid.

 

[bwalker]

THE 50:1 IS RICHER (more fuel/oil= more fuel/air) than the 45:1, as many have stated on various boards; the question then becomes "is the 50:1 too rich, or the 45:1 too lean", especially to a point that would cause eventual damage??? And you noted this with JUST a 5-point(+/-) difference. Interesting to prove/ disprove the point would be to switch, get the new fuel mix to carb, then retune, Noting HOW MUCH ADJUSTMENT required? (1/16, 1/8, 1/4-turn?) Certainly less than 1/4? Thanks for the experiment and feedback to group.

It's a very miniscule amount in air to fuel ratio between 45 and 50 to one.
I would be more inclined to think the reason for the observation is that the engine was warmer when switching fuels. Either way 200rpm is miniscule and it could be caused by many things.
I've ran many outboards with tachs and using the same fuel. Rpms vary quit a bit and this is normal.

 

[thenne1713]

It's a very miniscule amount in air to fuel ratio between 45 and 50 to one.
I would be more inclined to think the reason for the observation is that the engine was warmer when switching fuels. Either way 200rpm is miniscule and it could be caused by many things.
I've ran many outboards with tachs and using the same fuel. Rpms vary quit a bit and this is normal.

For giggles/ grins and research few years back, I put 50:1 in my 4-cycle weedeater it would BARELY RUN, OR NOT START, from what I recall. Proper E-0 plain gas restored normal run.

 

[bwalker]

For giggles/ grins and research few years back, I put 50:1 in my 4-cycle weedeater it would BARELY RUN, OR NOT START, from what I recall. Proper E-0 plain gas restored normal run.

That's funny because when I owned a fishing lodge every motor on the place ran on 50:1 mixed gas. Including two trucks and several ATV's. Never an issue.

 

[HansFranz]

That's funny because when I owned a fishing lodge every motor on the place ran on 50:1 mixed gas. Including two trucks and several ATV's.

I often add 1 gallon of Lucas diesel fuel additive (I think it's castor oil-based) to 80 gallons of gasoline to feed my Chevy 350 marine engine (raw-water cooled) to keep the TBI injector happy, especially when using gasohol which I normally try to avoid,
Never noticed any change in the way that runs, either. I figure it can't hurt, might help, and might prevent a long walk home.

 

[sean donato]

For giggles/ grins and research few years back, I put 50:1 in my 4-cycle weedeater it would BARELY RUN, OR NOT START, from what I recall. Proper E-0 plain gas restored normal run.

I dump my old 2 stroke mix in whatever 4 stroke that's close at hand weed whacker or other wise they run just fine. that's e-10 as well.

 

[icontreeservice]

I've found some engines are far more sensitive than others...
Some seem to be able to run no matter what, while others can't start if the gas is even slightly stale... A lot has to do with what their heads are like, take the early Hemi racing v8, great power, but often didn't finnesh the long races because if the tune got slightly off the engine would detonate to the point of pre-ignition and fail. On the other extreme my flat head brigs will run on gas that had diesel accidentally put in. The lower compression engine with its swirly head allowed the engineers to time it differently (less detonation risk) and probably a lot of other things. it has a wider range where it works fine.
Our 2 strokes would face the same problems with the added complexity of the lube being in the fuel to boot!