Oil to gas ratio for idling

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KC_Jones

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So this question came to mind as a result of another post I made a while ago, at this link:
https://tinboats.net/forum/viewtopic.php?f=4&t=46840

The engine in question is from the VRO series, but the system has long since been disconnected by a previous owner. First, I have no intention of hooking that system back up, but the concept of that system got me thinking.

Since I run at idle for several hours for my crabbing, couldn't I run a small tank ~3 gallons of a mix with much less oil in it say 75:1 or even 100:1? I could switch to this tank during my crabbing, then onto the regular tank close to the end so I get the stronger mix in the lines for the faster run back to the ramp. This honestly isn't a big deal as it takes me about 30-45 minutes to pull the troline in and de-bait it, which would be plenty of time after switching for the fuel to run through the line.

It seems to me this would help with the crud in the lower unit, which would make me happy.

Thoughts? Has anyone actually tried this?
 
Why do we think that an engine can safely run on less lubricating oil at idle? Maybe it can, I've just never heard that before.

Typically, the slower two surfaces slide across each other, the higher the viscosity of the lubricating oil should be. Slower = thicker lubricant needed. It seems that less oil in the gasoline means a lower viscosity mix, the opposite of what would be needed at idle.

However, there may be information that I'm missing or haven't considered.
 
That's exactly what the vro engines did and what the etec engines do. Interesting idea.

Sent from my CLT-L04 using Tapatalk

 
maintenanceguy said:
Why do we think that an engine can safely run on less lubricating oil at idle? Maybe it can, I've just never heard that before.

Typically, the slower two surfaces slide across each other, the higher the viscosity of the lubricating oil should be. Slower = thicker lubricant needed. It seems that less oil in the gasoline means a lower viscosity mix, the opposite of what would be needed at idle.

However, there may be information that I'm missing or haven't considered.

What you describe is exactly the opposite of how engines work. Higher viscosity at lower RPM can happen as a function of heat, but it is definitely not a requirement.

A pressure feed oiling system is less pressure and volume at lower RPM and more at higher.

As stated this is how all variable oiling systems on 2 stoke engines work.
 
The VRO system is different. It does not increase pressure, only volume. It always operates under less pressure than what it takes to blow the needles off their seats. It is a simple fuel pump that happens to deliver oil in a separate chamber of the VRO pump that is operated by a piston rather than a typical diaphragm.
Now....as far as your question goes?
You would do well to check and service a few things before you go and add a totally separate fuel tank into your boat.
Thermostats should be in the engine and operating properly. OMC engines like to be nice and warm at idle to help atomize and burn the incoming mixture.
OMC engine tuner or equivalent should be run through the engine yearly or even more often in a commercial application such as yours. This will free the rings up and help combustion.
Air fuel mixture should be looked at as well as your fuel recirculation system. The recirc valves in older engines tend to leak or get plugged up. Again this will help burn off the excess fuel at idle and off idle.
Trim angle.....what??? Trim up a bit when running your traps and you will notice a higher idle and less smoke. This will, in effect, lean your engine out a bit. Don't believe me? Do it for about 90 seconds to a couple minutes then fully trim under. Your engine will drop RPMs drastically and fast and you will see quite a lot of smoke. Your engine may also stall. This is partly due to all of the above factors I have written above.
Remember this if you go ahead with your lean ratio fuel tank. When you are done with a trap line and romp on the throttle to get to the next one your engine will have to burn all of the lean ratio fuel from the entire fuel line, bulb, engine lines, pump, and carb bowls before getting the needed oil to protect it at the higher RPM and loads you just placed on it.
 
Pappy said:
The VRO system is different. It does not increase pressure, only volume. It always operates under less pressure than what it takes to blow the needles off their seats. It is a simple fuel pump that happens to deliver oil in a separate chamber of the VRO pump that is operated by a piston rather than a typical diaphragm.
Now....as far as your question goes?
You would do well to check and service a few things before you go and add a totally separate fuel tank into your boat.
Thermostats should be in the engine and operating properly. OMC engines like to be nice and warm at idle to help atomize and burn the incoming mixture.
OMC engine tuner or equivalent should be run through the engine yearly or even more often in a commercial application such as yours. This will free the rings up and help combustion.
Air fuel mixture should be looked at as well as your fuel recirculation system. The recirc valves in older engines tend to leak or get plugged up. Again this will help burn off the excess fuel at idle and off idle.
Trim angle.....what??? Trim up a bit when running your traps and you will notice a higher idle and less smoke. This will, in effect, lean your engine out a bit. Don't believe me? Do it for about 90 seconds to a couple minutes then fully trim under. Your engine will drop RPMs drastically and fast and you will see quite a lot of smoke. Your engine may also stall. This is partly due to all of the above factors I have written above.
Remember this if you go ahead with your lean ratio fuel tank. When you are done with a trap line and romp on the throttle to get to the next one your engine will have to burn all of the lean ratio fuel from the entire fuel line, bulb, engine lines, pump, and carb bowls before getting the needed oil to protect it at the higher RPM and loads you just placed on it.

Thank you for the feedback. Just to be clear, this isn't a commercial application. I crab like some people fish, its for recreation. I don't run traps it's a trotline, do a youtube search and you can see how it works. So I don't have the worry of throttling up between traps, just slow steady idling all day. Almost like trolling for crabs, but the baits don't move.

Thermostat is brand new, I replaced it when I did the water pump just to be safe. I've indeed tried the tilt up you suggest and have seen what you said. I will try that on the next trip out.

At the end of the day it takes me about 45 minutes to pull and de-bait the line, so I would most likely switch tanks back to 50:1 before that. That should give plenty of time for the fuel to get to the engine before I run back in at speed.

I was planning new tanks next year, and with the idling and new tanks it got me thinking about this scenario. I will give it some more thought.

Thank you for the feedback.
 
KC_Jones said:
Pappy said:
The VRO system is different. It does not increase pressure, only volume. It always operates under less pressure than what it takes to blow the needles off their seats. It is a simple fuel pump that happens to deliver oil in a separate chamber of the VRO pump that is operated by a piston rather than a typical diaphragm.
Now....as far as your question goes?
You would do well to check and service a few things before you go and add a totally separate fuel tank into your boat.
Thermostats should be in the engine and operating properly. OMC engines like to be nice and warm at idle to help atomize and burn the incoming mixture.
OMC engine tuner or equivalent should be run through the engine yearly or even more often in a commercial application such as yours. This will free the rings up and help combustion.
Air fuel mixture should be looked at as well as your fuel recirculation system. The recirc valves in older engines tend to leak or get plugged up. Again this will help burn off the excess fuel at idle and off idle.
Trim angle.....what??? Trim up a bit when running your traps and you will notice a higher idle and less smoke. This will, in effect, lean your engine out a bit. Don't believe me? Do it for about 90 seconds to a couple minutes then fully trim under. Your engine will drop RPMs drastically and fast and you will see quite a lot of smoke. Your engine may also stall. This is partly due to all of the above factors I have written above.
Remember this if you go ahead with your lean ratio fuel tank. When you are done with a trap line and romp on the throttle to get to the next one your engine will have to burn all of the lean ratio fuel from the entire fuel line, bulb, engine lines, pump, and carb bowls before getting the needed oil to protect it at the higher RPM and loads you just placed on it.

Thank you for the feedback. Just to be clear, this isn't a commercial application. I crab like some people fish, its for recreation. I don't run traps it's a trotline, do a youtube search and you can see how it works. So I don't have the worry of throttling up between traps, just slow steady idling all day. Almost like trolling for crabs, but the baits don't move.

Thermostat is brand new, I replaced it when I did the water pump just to be safe. I've indeed tried the tilt up you suggest and have seen what you said. I will try that on the next trip out.

At the end of the day it takes me about 45 minutes to pull and de-bait the line, so I would most likely switch tanks back to 50:1 before that. That should give plenty of time for the fuel to get to the engine before I run back in at speed.

I was planning new tanks next year, and with the idling and new tanks it got me thinking about this scenario. I will give it some more thought.

Thank you for the feedback.

I think what you are proposing would work fine.

OMC actually advertised a 100:1 ratio at some point, and stopped because such a lean ratio did not leave enough of an oil film to protect the engine during storage, not because it would cause engine damage.
 
Informative post on the VRO system. Thank you for the explanation; it's completely different than what I'm used to. Yamaha's Autolube works in a much more efficient and almost failure-proof design, which is what I'm used to. On those, yes, the idling mixture might be 200:1, but as engine speed increases, the amount of oil (volume) increases and at full throttle it might be 30:1. There are a few exceptions, but those have a separate cable that runs from the carbs or throttle to a lever on the pump, the lever works a valve inside the pump that also adds in throttle position. The reason they did it is because even though the engine might only be under 1/4 load, the RPM might be 5000, thus it didn't need as much oil--and particularly on engines that had a catalyzer--such as jet ski's. Man I hated those things! Fun to ride, but no fun to work on/

Now some engines, the oil is "injected" into the carb bowls, and some have it injected into the intake manifold behind the carb(s). If yours injects into the carb(s), nothing further has to be done to the carbs, BUT if it's into the intake manifold, and you decided to disable the injection system, you'd need to increase the main and possibly pilot jet size slightly. Reason being, the little bit of oil that's in the gasoline is going to displace some of the fuel, so effectively the engine will run a slightly leaner air/fuel mixture. Most carbureted outboards run on the rich side anyway and it won't affect them, but where I see issues is on motors that sit a while and partially plug the main jet; then when they are "slightly" leaner, the combination of main plugging + leaner mix can cause some expensive problems.
 
Many years ago early mopeds had a cable to the throttle and would cut a lot of the oil down at low throttle settings. Problem arose when going down long hills with a lot of rpm and no throttle....

Just like the one ya love..keep her fed with good food...use often and keep er well lubed.
 
I'd have no problem trolling an engine at 100:1 with good oil.. I'd often thought about doing the same myself for down rigging lake trout.
As long as you have suffient time to get the engine back on 50:1 before revving up. You could actually rig your fuel line with a 3 way valve near the engine so you could just turn it rather than swap hoses.
Some Ski-doo engines actually run NO oil at idle as the engineers found there was enough lube in the fuel alone.

Sent from my SM-G903W using Tapatalk


 
GYPSY400 said:
I'd have no problem trolling an engine at 100:1 with good oil.. I'd often thought about doing the same myself for down rigging lake trout.
As long as you have suffient time to get the engine back on 50:1 before revving up. You could actually rig your fuel line with a 3 way valve near the engine so you could just turn it rather than swap hoses.
Some Ski-doo engines actually run NO oil at idle as the engineers found there was enough lube in the fuel alone.

Sent from my SM-G903W using Tapatalk

A valve setup is exactly what I would do. My plan (if it fits) is to convert to a single 12 gallon tank with an additional 3 gallon tank with the 100:1 mixture. Switch when I run slow, then switch back maybe 30 minutes before I end my day and throttle up. Sounds like the consensus is this shouldn't be a problem.

Thanks again for all the responses.
 

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