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Changing oil type - can it release some old sludge?

I recall having been told this in connection with changing from Exxon Elite to Aeroshell 15W50, or maybe the other way round...

One would expect to see bits of it in the oil filter, or under the rocker covers, but probably not in the oil analysis because it isn't metallic.

Administrator
Shoreham EGKA, United Kingdom

Certainly Aeroshell state this when you switch to their oil. They claim its due to its superior cleaning effect. Whether this is true or not i have no idea.

I've also heard hanger chat that if you switch to aeroshell you should top up with aeroshell in the first instance before making a complete switch.

Our aircraft get 15/50 at service and then we top up with the cheapest single grade oil I can get my hands on Total) and we use 80 in winter and 100 in the summer.

The exception to this is the 172n which gets topped up with aeroshell 15/50 all year round due the lycoming soft camm additive.

I've not reported any difference is sludge from our maintenance company. Personally I suspect the time interval between oil changes would have the biggest effect. none of our Cessna 150s went more than 30 days between oil changes this summer.

Can’t guarantee to the accuracy of the information as it was relayed many many years ago when I had to take a course in metallurgy. One of the pieces of info that the lecturer passed on was that one of the ways to protect the cyl. from premature wear was to let glazing build on the cyl. walls. He also said that when different make/blends of oil are used the fresh X oil will cause the old Y oil glazing to fall off .

Cylinder glazing does however result in massive oil consumption, which is why one does the engine running-in at a high power setting, to bed in the piston rings.

Once a cylinder gets glazed, it is unlikely to un-glaze by itself, and need to be re-honed. I did manage to glaze 1 or 2 cylinders after the SB569 rebuild (most likely by doing some high altitude flights on which the engine didn't develop enough power) and it took maybe 100hrs before the spark plugs stopped being full of oil.

Administrator
Shoreham EGKA, United Kingdom
4 Posts
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