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Fuel dilution's effect on oil viscosity etc #4778075
06/05/18 11:18 AM
06/05/18 11:18 AM
Joined: Apr 2018
Posts: 576
Canada
nap Offline OP
nap  Offline OP
Joined: Apr 2018
Posts: 576
Canada

Download it while it lasts:

https://hrcak.srce.hr/file/75680

Re: Fuel dilution's effect on oil viscosity etc [Re: nap] #4778138
06/05/18 12:37 PM
06/05/18 12:37 PM
Joined: Feb 2003
Posts: 7,425
Jupiter, Florida
Cujet Offline
Cujet  Offline
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Posts: 7,425
Jupiter, Florida
The elephant in the room is not just the raw fuel dilution. It's not unusual for most of the the fuel in the oil to evaporate, leaving behind various additives and heavier components of fuel. It's entirely possible, for example, to start and end with 5 quarts in the sump. 5 quarts of oil at the start, and 4.5 quarts of oil at the end, along with 1/2 quart of contaminants.

A great example of this would be the diesel "veggie" fuel users. The sumps are seriously contaminated with waste veggie oil. Often leading to oil failure and engine failure.

Last edited by Cujet; 06/05/18 12:39 PM.

People who count on their fingers should maintain a discreet silence.
Re: Fuel dilution's effect on oil viscosity etc [Re: nap] #4778143
06/05/18 12:45 PM
06/05/18 12:45 PM
Joined: Feb 2003
Posts: 7,425
Jupiter, Florida
Cujet Offline
Cujet  Offline
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Posts: 7,425
Jupiter, Florida
FYI, aircraft operators in very cold climates used to dilute the oil with fuel intentionally. This reduces viscosity for easy starting in severe cold. The fuel evaporates rather quickly after start, and oil pressure and temperatures remain normal.

In fact, some aircraft had a built in system, from the factory, that added fuel to the oil for cold weather starting. The requirement was that the oil reach 100 degrees F prior to takeoff.


People who count on their fingers should maintain a discreet silence.
Re: Fuel dilution's effect on oil viscosity etc [Re: Cujet] #4778176
06/05/18 01:31 PM
06/05/18 01:31 PM
Joined: May 2013
Posts: 2,093
Saskatchewan, Canada
Johnny2Bad Offline
Johnny2Bad  Offline
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Posts: 2,093
Saskatchewan, Canada
Originally Posted By: Cujet
FYI, aircraft operators in very cold climates used to dilute the oil with fuel intentionally. This reduces viscosity for easy starting in severe cold. The fuel evaporates rather quickly after start, and oil pressure and temperatures remain normal.

In fact, some aircraft had a built in system, from the factory, that added fuel to the oil for cold weather starting. The requirement was that the oil reach 100 degrees F prior to takeoff.


First of all, an airplane engine is not an automotive engine. It is a mistake to assume they are similar enough that various conditions or systems are interchangeable.

The airplane engines that did use fuel to dilute engine oil have sumps that are much, much larger than a typical automobile, or at least a typical post-WWII automobile. As in sump capacity is measured in gallons, not quarts.

Aviation oils in general are higher viscosity than automotive oils, for example Aeroshell 100 is equivalent to SAE 50 automotive viscosity.

Aviation oils until relatively recently had no winter rated oils and no multigrade oils that were legal to use, so using fuel dilution was not a 'good practice", it was the only possible practice to adjust viscosity.

By far the more common method of starting in cold weather is to tarp up the nacelle and provide heat under the tarp. The use of the equivalent of a campfire was hardly unheard of. The automotive equivalent is to tarp up the engine compartment and run exhaust from another running vehicle under the tarp to heat up the engine / sump, ground clearance being what it is making open fires difficult.

If you've never had to do either to an aircraft or a vehicle, you haven't been in a cold start situation that would benefit from oil dilution via fuel either.


'57 FL Straight 50 wt
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Re: Fuel dilution's effect on oil viscosity etc [Re: Johnny2Bad] #4778208
06/05/18 01:58 PM
06/05/18 01:58 PM
Joined: Dec 2005
Posts: 9,890
Upper Midwest
kschachn Online content
kschachn  Online Content
Joined: Dec 2005
Posts: 9,890
Upper Midwest
Originally Posted By: Johnny2Bad
Aviation oils until relatively recently had no winter rated oils and no multigrade oils that were legal to use, so using fuel dilution was not a 'good practice", it was the only possible practice to adjust viscosity.

But multi-grade oils have been available to GA for over 30 years and manufacturers have approved their use in via service bulletins, right?


1994 BMW 530i, 228K
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Re: Fuel dilution's effect on oil viscosity etc [Re: nap] #4778238
06/05/18 02:25 PM
06/05/18 02:25 PM
Joined: Mar 2017
Posts: 5,410
Soviet State of Washington
PimTac Online content
PimTac  Online Content
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Posts: 5,410
Soviet State of Washington
Originally Posted By: nap

Download it while it lasts:

https://hrcak.srce.hr/file/75680





Why? Whatís going to happen to it?


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Re: Fuel dilution's effect on oil viscosity etc [Re: nap] #4778242
06/05/18 02:29 PM
06/05/18 02:29 PM
Joined: Apr 2018
Posts: 576
Canada
nap Offline OP
nap  Offline OP
Joined: Apr 2018
Posts: 576
Canada
Internet rot. Interesting / useful info tends to disappear after some time.

Re: Fuel dilution's effect on oil viscosity etc [Re: nap] #4778358
06/05/18 04:36 PM
06/05/18 04:36 PM
Joined: Oct 2005
Posts: 4,965
Fredericksburg, VA
JAG Offline
JAG  Offline
Joined: Oct 2005
Posts: 4,965
Fredericksburg, VA
That is a good paper. Itís ironic that you posted it because I was searching on the same subject yesterday, and found that paper.

Another bad effect of fuel dilution is the oxidative stress that it puts on the motor oil. Itís particluarly bad in the case of bio-diesel due to its particularly poor oxidative stability.

Re: Fuel dilution's effect on oil viscosity etc [Re: Johnny2Bad] #4778627
06/05/18 10:01 PM
06/05/18 10:01 PM
Joined: Dec 2009
Posts: 25,355
Regina, Saskatchewan, Canada
Garak Offline
Garak  Offline
Joined: Dec 2009
Posts: 25,355
Regina, Saskatchewan, Canada
Originally Posted By: Johnny2Bad
Aviation oils until relatively recently had no winter rated oils and no multigrade oils that were legal to use, so using fuel dilution was not a 'good practice", it was the only possible practice to adjust viscosity.

Well, you could use a heater, or even better, heated storage, but ask the Regina Flying Club what they charge for heated hangar space. wink


Plain, simple Garak.

2008 Infiniti G37 - Shell ROTELLA T6 Multi-Vehicle 5w-30, NAPA Gold 7356
1984 F-150 4.9L - Quaker State GB 10w-30, Wix 51515
Re: Fuel dilution's effect on oil viscosity etc [Re: Johnny2Bad] #4779651
06/06/18 09:34 PM
06/06/18 09:34 PM
Joined: Feb 2003
Posts: 7,425
Jupiter, Florida
Cujet Offline
Cujet  Offline
Joined: Feb 2003
Posts: 7,425
Jupiter, Florida
Originally Posted By: Johnny2Bad


First of all, an airplane engine is not an automotive engine. It is a mistake to assume they are similar enough that various conditions or systems are interchangeable.

The airplane engines that did use fuel to dilute engine oil have sumps that are much, much larger than a typical automobile, or at least a typical post-WWII automobile. As in sump capacity is measured in gallons, not quarts.

Aviation oils in general are higher viscosity than automotive oils, for example Aeroshell 100 is equivalent to SAE 50 automotive viscosity.


Thin straight viscosity oils were allowed in cold weather ops. Lycoming aircraft engines can use a straight 20 below 10F.

Furthermore, many light aircraft hold 6 quarts, much like automotive applications.

The little bit of Alaska ops I've done include using thin oils, preheating and there was near universal talk of using fuel to dilute.

My point was simply that it was a procedure for cold weather ops. Not that it is good.


People who count on their fingers should maintain a discreet silence.

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