Lotus Elan

Unleaded Or Leaded That Is The Question

PostPost by: rgh0 » Thu Jan 13, 2005 8:58 am

>AVGAS has a different type of additive package and IT WILL turn your engine oil >into sludge.

I am a mechanical and chemical engineer with 30 years experience in petrochemical plant operation which has included manufacturing large volumes of gasoline . I have also used Avgas in my racing engines for over 15 years as does everyone else in Australia where they are still allowed to run leaded fuels.

In Australia at least and also elsewhere also I beleive there is no fundamental incompatability between Avgas and common car engine components and oils. Avgas is specially formulaed and tested to minimise these risks because the consequence of an engine failure due to poor fuel or fuel incmpatiability is so much more serious in an aircraft.

Any commnets on the lack of suitablitiy of Avgas is an urban myth or old wives tale as far as I am concerned. If you have data please send me the references as in all my work on gasoline I have never heard of this problem.

The most common reason for oil sludging is generally due to excessively low temperatures in the oil caused by multiple short trips not boiling the water out of the oil. Synthetic oils used with extended change intervals such as in modern BMW and Mercedes tend to form a mouse like sludge in these circumstances especially.

Rohan
Lots of avgas and no problems
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PostPost by: GrUmPyBoDgEr » Thu Jan 13, 2005 10:18 am

Hi Rohan,
I respect your qualifications and business experience. The use of this fuel in racing engines would not cause the sludging that I mentioned in my previous message because most racers change the engine oil after each event.
I work in the engine development department of BMW and have seen several engines that have been written off due to sludgy oil because the owners had used aviation fuel from their local flying club. Notably a high percentage of these engines were returned fom Australia.
No hard feelings but I still strongly recommend that fellow Lotus Elan owners steer well clear of this fuel unless they are prepared to make very frequent oil changes.
We've drifted off course from the poor guy with high coolant consumption
John
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Editor: On Sunday morning, February 8th 2015, Derek "John" Pelly AKA GrumpyBodger passed away genuinely peacefully at Weston Hospicecare, Weston Super Mare. He will be missed.
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PostPost by: rgh0 » Thu Jan 13, 2005 11:33 am

Hi John

Interested to see you worked at BMW on this problem. Did you investigate engine usage patterns in these cars and other fuel sources used ?

I worked on this problem in Australia where the gasoline feedstock we made was being blamed for problems in BMW's and Mercedes. It was a high octane feedstock with high olefinic components and Mobil had been over blending our feed stock in premium unleaded used by these cars as it was a cheap source of octane rating. Our feedstock was also used heavily in Avgas for the same reasons of its high octane rating.

The investigations I did could find no relationship to our feedstock in gasoline to engine oil sludging. However at the same time I suffered a cracked bore in my race engine that lead to high water levels in my synthetic mobil 1 engine oil. I experienced exactly the same sludging as observed in BMW's and Mercedes. Synthetic oils behave very differently to normal oils under water contamination either due to leakage or lots of short trips in egines with long recommended change intervals. The sythetic oil does not form a milky emulsion like normal oils but stays relatively clean because a thick mouse like sludge forms in the bottom of the engine that contains the water. Once this is thick enough it gets sucked into the oil pickup and the engine is stuffed. I dont think this water contamination risk with synthetic oils has ever been properly understood by many people. This is why I dont beleive Avgas is a risk in a normal car engine. Have you ever done any experiments on water contamination in sythetic oil to see its impact?

I change my race engine synthetic oil every 12 months in my car not after every race and would have done up to 3000 racing miles between changes and suffered no problems on Avgas over many years.


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PostPost by: GrUmPyBoDgEr » Thu Jan 13, 2005 12:00 pm

Hi,
my involvement at the time was as dev. engineer for lubrication systems. Another guy was responsible for the oils we use.
The multiuple cold start scenario is a well known factor for sludge forming. The engines that were returned to us from Australia had up to 6mm thick layer of black sludge on all of the stationary internal components. These engines had an original oil fill of synthetic oil. It was confirmed that aviation fuel had been used in the cars.
It is always very difficult to obtain reliable, honest vehicle usage information from customers who are trying to get a free or reduced cost replacement engine for their car.
Thanks for your interest but thats about as much as I can discuss on an open forum.
John
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PostPost by: rgh0 » Thu Jan 13, 2005 12:36 pm

John

Dont know when you experienced the problems with your BMW engines. The work I did was about 5 to 6 years ago

Just before the problem I worked on there was a separate problem wih Avgas in Australia due to incorrect over addition of additives being done. This stuffed up a lot of aircraft engines at the time and grounded all the piston engined aircraft in Australia while they were all checked. It was a major embarrassment and cost to Mobil. It may have been this that also stuffed car engines using Avgas at the time. The sludged caused by this excess additive problem was black. The sludge caused by water in sythetic oil is a dark grey and is was what was being identified when our feedstock was being blamed.

Use of leaded Avgas or race fuel in road engines has been illegal for many years in Australia now so your customers were breaking the law putting it in their BMW's anyhow. It can only be used in a limited number of historic competition classes on race tracks and now requires a special pemit to purchase unless you put it straight into a plane.

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PostPost by: GrUmPyBoDgEr » Thu Jan 13, 2005 2:49 pm

Hi Rohan,
yes the 5 to 6 years back would be about right. Those guys running that fuel would certainly have seen a perfomance advantage because the engines had knock sensors and fully variable camshaft timing.
However as I wrote previously you never get the full facts about the usage of our cars from the customers.
It is unfortunately a fact of life that durability testing cannot permit cold starting of engines ove a period of time. It would take far too long & we would never get into production.
I still have an oil pan baffle plate from one of those engines, in a perspex show case, that is totally covered in black Australian sludge.
In any case I think it is fair to say that one should not take petrol for granted, it has also caused many problems here in Europe even further back in time. ARAL caused chaos in the automobile industry with a fuel which led to black sludge.
Thank goodness that both the vehicle manufacrurers and the fuel companies have got together and generaly improved the fuel quality; Sulpher content was another major stepping stone
I think this website is very good, I only discovered it just before Christmas.

Well I think we both have done this one pretty well to death now.
Regards
John
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PostPost by: type36lotus » Fri Jan 14, 2005 1:23 am

But is was VERY interesting! PS I do not use avgas or sythetic oil in my Elan. Only dead dinosaurs.
Mike Geiger
66 S3 Coupe', no more :-(
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