Today's Message Index:
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1. 02:32 AM - Re: Aviation Oil Vs Motor oil (Synthetic) (Philip A. C.)
2. 06:53 AM - Re: ENGINE OIL (Gary Casey)
3. 08:41 AM - Re: Aviation Oil Vs Motor oil (Synthetic) (Lowell Fitt)
Message 1
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| Subject: | Aviation Oil Vs Motor oil (Synthetic) |
--> Engines-List message posted by: "Philip A. C." <philipac@suncraftgroup.com>
Pete,
The difference in EGT may be due simply to the difference in specific
gravity between Avgas and Mogas. The float in the carburetor will not ride
at the same level, thus leaning or enrichening the mixture, which of course
would change the EGT.
What would be significant is the PEAK EGT. Check your peak EGT on one fuel,
go back to your original mixture setting, change tank, and then recheck the
peak.
If you do the experiment, I'd be interested in knowing the result. Thanks.
Philip Chollet
-----Original Message-----
From: owner-engines-list-server@matronics.com
[mailto:owner-engines-list-server@matronics.com]On Behalf Of Pete
Marshall
Subject: Engines-List: Aviation Oil Vs Motor oil (Synthetic)
--> Engines-List message posted by: Pete Marshall <wpetermarshall@shaw.ca>
I know of at least one Canadian fellow using AMSOIL series 2000 20W50
synthetic oil in an aircraft engine, this info from one of our Canadian
AMSOIL Dealers. This fellow buys a case every couple on months and has
been doing so for about a year. My distributor was telling me that AMSOIL
synthetic burns with less ash formation than ashless dispesant aviation oil
because of the very few additives used in Amsoil. It is true that AMSOIL
synthetic will run about 30 degrees cooler than normal oil. I have proved
this to myself by instrumenting my offroad dirtbike oil temperature and
recording the temperatures.
Getting back to the fuel selection dilemma; an engine builder in Kamloops
told me recently that Aviation engines do not have the hardened (stellite)
valve seats that are necessary to burn unleaded fuel. He recommended a
50-50 mix of 100 LL with unleaded regular mogas in our O-235 Lycoming. He
said that he had had a few engines recently requiring top end overhauls
after100 to 200 hours of unleaded mogas. The valves had pounded out the
valve seats and tuliped into the heads. We switched back from straight
mogas to a 50-50 mix. I notice Lycoming do not mention the use of mogas in
their bulletins.
It is also true that mogas runs 20 to 30 degrees hotter than even 80 octane
AVGAS, and of course 100 LL AVGAS. I have verified this on my Cessna 180
by loading one tank with mogas and the other with pure AVGAS. When the
tanks were switched in cruise flight while observing the EGTs, there was a
noticeable drop when the tank is switched to AVGAS.
For your information.
Cheers, Pete Marshall
Message 2
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--> Engines-List message posted by: "Gary Casey" <glcasey@adelphia.net>
<<My distributor was telling me that AMSOIL synthetic burns with
less ash formation than ashless dispersant aviation oil because of the very
few
additives used in Amsoil. It is true that AMSOIL synthetic will run about
30 degrees cooler than normal oil.>>
Just a little clarification from my previous post: Note that "ash" is NOT
carbon. Ash is by definition non-combustible as is basically rock, like in
a lava flow. As mentioned above, an "ashless" oil will still leave carbon
deposits, but these will be essentially carbon, soft and combustible and
they will eventually burn or flake off harmlessly. The amount of ash that
builds up on the combustion chamber and spark plugs depends on the amount of
oil that burns. Also, I would think that running a 50/50 mix of ashless
aviation oil (Aeroshell, straight viscosity?) and Mobil 1 would be
equivalent to running Aeroshell 20/50, which is about a 50/50 mix of mineral
and synthetic oil. Why not just do that? The reduced oil temperature
associated with synthetic is due to the reduced viscosity, not the fact that
it is synthetic in origin. The idea, as I understand it, is that since a
synthetic has a much higher viscosity index it can be formulated at a lower
viscosity and still have the required viscosity at the extremely high
temperatures that might exist locally between the piston ring and wall or
the cam and follower.
<<It is also true that mogas runs 20 to 30 degrees hotter than even 80
octane AVGAS,
and of course 100 LL AVGAS.>>
I don't understand this, as there are really only three things that can
effect the exhaust temperature - the inherent burn rate of the fuel and the
heating value. The burn rate shouldn't be a function of the octane or lead
additive, but it could be related to the structure of the hydrocarbon and I
don't know about the difference there. A slower burn rate would produce a
higher EGT as the burn would happen later in the cycle and more heat would
remain at the end of the stroke (less being converted into work). The
heating values are probably different and I would guess that the heating
value of a no-lead fuel might be higher than for an aviation fuel. Was the
mixture adjusted to get the same effective mixture? What would be
interesting is a chart of exhaust temp vs. fuel flow so we could see the
peak and the slope on either side. I wonder if we would see something
different. The vapor pressure of automotive fuel is higher (less so
recently) than for aviation fuel and that would effect the mixture
distribution within the cylinder, the higher vapor pressure fuel more
completely mixing with the air. That would increase flame speed and reduce
exhaust temperature, the opposite of what was reported. On the other hand I
have read reports where local mixture gradients in the cylinder enhance
flame travel, the fire leaping from one rich pocket to the next, but this
effect is primarily related to very lean mixtures.
Not a simple subject.
Gary Casey
Message 3
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| Subject: | Re: Aviation Oil Vs Motor oil (Synthetic) |
--> Engines-List message posted by: "Lowell Fitt" <lcfitt@inreach.com>
Hi Pete, I am definitely not an expert on these matters, but this summer I
heard the Amsoil guy at Oshkosh say that there is no connection between
combustion chamber and the oil system and the non lead scavenging properties
is a non issue because lead from the fuel won't find its way into the oil.
I argued this a bit as I will use 100 LL on cross countries and can see the
deposits in the bottom of my remote tank - I drain, open and wipe with every
oil change.
Also another pilot I know has his oil analyzed with each oil change.
According to him the lead content is so high it exceeds the test limits.
We are using Rotax engines and Rotax specifically discourages full synthetic
if 100 LL is used in significant amounts, but does recommend a
semi-synthetic blend with 100LL use.
Keep in mind that our engines have water cooled cylinders, but the
scavenging qualities of the pure synthetic is an issue in either case.
Lowell
----- Original Message -----
From: "Pete Marshall" <wpetermarshall@shaw.ca>
Subject: Engines-List: Aviation Oil Vs Motor oil (Synthetic)
> --> Engines-List message posted by: Pete Marshall <wpetermarshall@shaw.ca>
>
> I know of at least one Canadian fellow using AMSOIL series 2000 20W50
synthetic oil in an aircraft engine, this info from one of our Canadian
AMSOIL Dealers. This fellow buys a case every couple on months and has
been doing so for about a year. My distributor was telling me that AMSOIL
synthetic burns with less ash formation than ashless dispesant aviation oil
because of the very few additives used in Amsoil. It is true that AMSOIL
synthetic will run about 30 degrees cooler than normal oil. I have proved
this to myself by instrumenting my offroad dirtbike oil temperature and
recording the temperatures.
>
> Getting back to the fuel selection dilemma; an engine builder in Kamloops
told me recently that Aviation engines do not have the hardened (stellite)
valve seats that are necessary to burn unleaded fuel. He recommended a
50-50 mix of 100 LL with unleaded regular mogas in our O-235 Lycoming. He
said that he had had a few engines recently requiring top end overhauls
after100 to 200 hours of unleaded mogas. The valves had pounded out the
valve seats and tuliped into the heads. We switched back from straight
mogas to a 50-50 mix. I notice Lycoming do not mention the use of mogas in
their bulletins.
>
> It is also true that mogas runs 20 to 30 degrees hotter than even 80
octane AVGAS, and of course 100 LL AVGAS. I have verified this on my
Cessna 180 by loading one tank with mogas and the other with pure AVGAS.
When the tanks were switched in cruise flight while observing the EGTs,
there was a noticeable drop when the tank is switched to AVGAS.
>
> For your information.
> Cheers, Pete Marshall
>
>
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