I've been using Mobil 1 in my cars since the late '70s; I still have a copy of April 1976 Popular Science that addresses synthetic oil. I had a '76 Rabbit that I had used Mobil 1 in since 2000 mi. I changed its oil every 100,000 miles and added a quart every 27,000 miles. It had the head gasket fail at 198,000 miles, and the hone marks were still in the cylinder and there was NO ridge at the top of the cylinder; nein, nichts, nada. My question for those with some expertise with oils is if I mixed Mobil 1 on a 1-for-2 or 1-for-3 ratio with my Aeroshell 15-50 semi-synthetic, would that create a problem? Opinions, please!
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Mobil 1
- Thread starter elippse
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mikegraycmg
Well Known Member
Hunch
This doesn't rise to the level of an opinion, because I really don't know -- it's just a hunch. I wouldn't mix synthetic oils with anything else. I suspect it won't work very well. I am using Phillips 20W-50 XC for that very reason (Aeroshell multi-viscosity oils contain synthetic elements). I suspect that the loose tolerances in airplane engines mean that synthetic oils don't work as well -- they are too slippery/
This doesn't rise to the level of an opinion, because I really don't know -- it's just a hunch. I wouldn't mix synthetic oils with anything else. I suspect it won't work very well. I am using Phillips 20W-50 XC for that very reason (Aeroshell multi-viscosity oils contain synthetic elements). I suspect that the loose tolerances in airplane engines mean that synthetic oils don't work as well -- they are too slippery/
Guy Prevost
Well Known Member
Exxon & Shell moved away from fully synthetic aviation oils because they were causing engine problems. They both now offer semi-synthetic blends. I wouldn't mess with the ratio they've worked out--it is based on experience. Also, there is no guarantee that the Mobil 1 will actually mix with your Aeroshell.
Just an opinion, worth what you paid for it....
Guy
Just an opinion, worth what you paid for it....
Guy
My understanding (I was actually reading about synthetics this afternoon for my Lotus) is that all the synthetics now blend fine with conventional oils. There used to be some additives in the synthetics that did not play well with regular oil. None of those additives are used any more. I would not mix my own blend of oil, but if you are running the semi synthetics you can add a quart of regular oil to top off if you run low.
Kyle Boatright
Well Known Member
Pure synthetics don't suspend lead particles very effectively. Which means serious sludge accumulates in the engine. That was the issue which caused the demise of Mobile 1 aviation oil.
Mobile ended up tearing down/rebuilding/replacing quite a few engines over that one.
Aeroshell 15-50 and Exxon Elite 20-50 both contain synthetic stock, but there is sufficient non-synthetic to suspend lead particles. I'd bet those companies properly researched the ratio of synthetic vs semi-synthetic bases to create high performance oils that can handle the lead.
Mobile ended up tearing down/rebuilding/replacing quite a few engines over that one.
Aeroshell 15-50 and Exxon Elite 20-50 both contain synthetic stock, but there is sufficient non-synthetic to suspend lead particles. I'd bet those companies properly researched the ratio of synthetic vs semi-synthetic bases to create high performance oils that can handle the lead.
Paul - Kyle has the correct answer. Exxon originally marketed a fully synthetic aircraft oil "Mobil 1" that did not scavenge lead. The lead sludge plugged up oil pick-up screens causing starvation and loss of oil pressure. After paying for lots of repairs,they laid low for a few years, then brought out their semi-synthetic oil labeled "Exxon" (company name) rather than "Mobil 1" (trademark). Ben Visser, former AeroShell "Oil Guru" published several articles about the the lead scavenging issues - you might try googling his name and see if they come up. I have a lot of respect for the R & D people at Exxon. Mobil 1 aviation oil is the only one I can recall on which they stubbed their collective toes.
BTW,I run Mobil 1 in all my cars, which run on unleaded gas, of course
LarryT
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MrNomad
Well Known Member
Exxon Elite composition
Kyle, When I bought my Superior engine in 2007, Exxon had a promo on their Elite for $2.50 a quart & I bought a bunch. Is it safe to assume that the Elite sold in 2007 has the composition "there is sufficient non-synthetic to suspend lead particles" you mentioned?
It's been 230 hours and all oil samples come back great!
Barry
Kyle, When I bought my Superior engine in 2007, Exxon had a promo on their Elite for $2.50 a quart & I bought a bunch. Is it safe to assume that the Elite sold in 2007 has the composition "there is sufficient non-synthetic to suspend lead particles" you mentioned?
It's been 230 hours and all oil samples come back great!
Barry
Kyle Boatright
Well Known Member
I think everyone had learned the lessons from Mobile 1 by that time, so yes, I would assume Exxon Elite is properly engineered.
rocketbob
Well Known Member
I think you guys have based opinions on Mobil 1 based solely on what you've read. I have a friend who bought up cases of the stuff and still has some which he still uses in some of his airplanes and swears by it. No problems with sludge.
FWIW one of my best friends is testing new formulations for Phillips in his Rocket. And they are experimenting with automotive anti-wear additives.
Paul, I run Mobil 1 Turbo Diesel Truck in my VW TDI and have had the valve cover off recently for a timing belt change...after 200K miles the cam still looks new. I'm going to be using this oil in my Rocket. There's a lot of research I've done to determine the suitablity of this oil which I won't go into but am highly confident it will work fine. It is more expensive than aircraft oil, so the point is not to save money per quart but I would like to see it run 200 hours on an oil change.
FWIW one of my best friends is testing new formulations for Phillips in his Rocket. And they are experimenting with automotive anti-wear additives.
Paul, I run Mobil 1 Turbo Diesel Truck in my VW TDI and have had the valve cover off recently for a timing belt change...after 200K miles the cam still looks new. I'm going to be using this oil in my Rocket. There's a lot of research I've done to determine the suitablity of this oil which I won't go into but am highly confident it will work fine. It is more expensive than aircraft oil, so the point is not to save money per quart but I would like to see it run 200 hours on an oil change.
It's rumored LL aviation fuel days are numbered. I know of serious testing going on in Ada OKlahoma with auto fuel being used in Lycoming engines of all perfixes and suffixes and it seems to be working out okay. If the LL aviation fuel does go away would this open the door for pure synthetic oils? Don't for get the zinc issue mentioned earlier.
hevansrv7a
Well Known Member
200 hour oil change - bad idea
Extended drain intervals are usually not a good idea even in a tight engine like you would find in a modern auto. Aircraft engines have a lot of blow-by by design. The crankcase becomes (in the words of an oil expert I once knew) a chemical sewer. Oils even contain ph buffers for this reason. Those buffers become exhausted over time. If there is lead in the oil, how do you think it got there? For example, if you combine the sulfur compounds that blow past the rings with water you get H2SO4 - sulfuric acid. While it is true that straight grade and pure synthetic oils don't "wear out" in the sense of their long chains breaking and thus losing viscosity, they do become contaminated.
Extended drain intervals are usually not a good idea even in a tight engine like you would find in a modern auto. Aircraft engines have a lot of blow-by by design. The crankcase becomes (in the words of an oil expert I once knew) a chemical sewer. Oils even contain ph buffers for this reason. Those buffers become exhausted over time. If there is lead in the oil, how do you think it got there? For example, if you combine the sulfur compounds that blow past the rings with water you get H2SO4 - sulfuric acid. While it is true that straight grade and pure synthetic oils don't "wear out" in the sense of their long chains breaking and thus losing viscosity, they do become contaminated.
rocketbob
Well Known Member
My VW TDI has .002" piston clearance and has a change interval of 10K miles on synthetic oil. Kenworth trucks have a 90K change interval. Something you know that their engineers here don't? I can also tell you after putting together a half-dozen Lycomings and Continentals together that if you want to talk about design...nothing has changed or been improved upon since the 1940's. With keystone rings and .032" ring gaps its no wonder why they have a lot of blow by. Acceptance of the status quo is what keeps aircraft engines 50 years behind the times.
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hevansrv7a
Well Known Member
Change Intervals redux
10K is normal on my wife's Audi, too, but not if it sits around. Yes, that's about 300 hours, but not at high power settings and yes with tight clearances. I don't know about Kenworths but the big rigs A] use a lot bigger crankcase and B] rack up those miles in a big hurry where condensation is not an issue and thus have less acid development. I looked up the oil drain intervals on trucks in local service at http://www.peterbilt.com/pdf/PX6manual.pdf and found they are between 6k and 9k miles and they have special treatment systems for the recirculating oil. Next OSH, go to a lecture by the guy who invented CamGuard and you will be a believer.
10K is normal on my wife's Audi, too, but not if it sits around. Yes, that's about 300 hours, but not at high power settings and yes with tight clearances. I don't know about Kenworths but the big rigs A] use a lot bigger crankcase and B] rack up those miles in a big hurry where condensation is not an issue and thus have less acid development. I looked up the oil drain intervals on trucks in local service at http://www.peterbilt.com/pdf/PX6manual.pdf and found they are between 6k and 9k miles and they have special treatment systems for the recirculating oil. Next OSH, go to a lecture by the guy who invented CamGuard and you will be a believer.
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