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High silicone in oil analysis

rvator4twa

Well Known Member
Patron
I have changed the oil twice in my rebuilt O360 with mineral oil in each, once at 35 hours and again at 70. Both times silicone was high. That last time it was 34.5. I burn mostly 93 Octane ethanol auto fuel with some 100 LL as I have an 8.5/1 compression ratio. Any ideas if this is normal?
 
Silicon is usually a result of poor air filtration, letting dirt get into the engine. Check the status of your air filter and make sure it is well sealed in the air box.
 
With car engines, one technique is using starting fluid, small careful doses, but the fan on a car is much smaller and protected.

Just looking maybe should be expanded into some careful disassembly and searching for the slightest trace of incursion.
 
My Blackstone analysis usually gives me some reasons / ideas to look into. They also answer questions via email.

I too had silicone in my A-65 in my Champ. In addition to the air filter, any silicone sealants used in the rebuild can also find there way into the oil (not the problem in my case). Another option my A & P mentioned were the Real rocker cover gaskets that might have worn in since installation. I don't know about that one.

Dirt introduced during annual and the air filter cleaning / reassembly could be another source.

Yet another, but unlikely source is leaving the plug holes open for the 2 weeks of its last annual.

At any rate, my levels dropped without doing anything different.

When it comes to engines, cleanliness is extremely important.
 
Silicon and silicone are two very different things with different origins. Google and make sure you know which one was actually elevated.

Erich
 
A common source of elemental silicon in your oil analysis is from silicone grease (DC-4) used as a lubricant on the oil filter rubber sealing ring.

If you don't do your own filter changes, your mechanic may be too liberal with the grease. It should be applied sparingly.
V
 
I?m pretty sure that the various oil analysis firms use spectroscopic techniques, which only see silicon, copper, iron, etc., e.g., only elements. They cannot differentiate between sand (silicon dioxide) or silicone (a larger molecule containing the element silicon).
 
I still remember an inorganic class in grad school. Prof. Du Shriver opined that silicon chemistry is considered boring. It's the chemistry of concrete and caulk, mortar and ceramics, microchips and the micro-rocks (i.e. sand) from whence it comes. In other words, some of the most useful chemistry there is. :D
 
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