What is an acceptable value for silicon for you?

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658
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EU
Just read a UOA here for a Corvette on Mobil1 5w-30. Blackstone said that the 16ppm Si was "fine". I've read other posts, though, in which some have stated concerns at Si levels in the high teens. At what level does the red flag go up for you? Are there trends associated with engines? Manufacturers? Aside from the problems occasionally evidenced by use of oiled elements like the K&N, in a stock air system with a new or clean paper filter, what range of Si values do you hold as acceptable?
 
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922
Location
Ontario , Canada
I personally don't get alarmed with 15ppm or less per 3000 mile oil change interval. Thus up to 30ppm on a 6000-7000 mile interval. Once it goes above that then I would start being concerned. I think on average 7ppm for 3000 miles is a good number for the average vehicle in normal driving conditions. It also depends on how old the engine is as well as gaskets do leach silicon. Also many oils have silicon in their virgin form to reduce foaming, such as Mobil1 and Redline for example - anywhere from 4-14 ppm in some oils. Just my personal estimtes here.
 

Patman

Staff member
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21,989
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Oakville, Ontario
Maybe I'm super picky but in my own opinion, I like to see under 1ppm of silicon per 1000 miles. I also keep in mind that with certain oils like Redline, they have silicon right out of the bottle though, so you have to take that into account. On my wife's 5000 mile interval with Mobil 1 last year, she only had 4ppm of silicon, with a Fram air filter. I just put one in my Firebird too, so I'm hoping to see results similar to this.
 
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47,693
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Duvall WA - Pacific NW USA
I'm with Pat, man. [Cheers!] I may be a leetle more liberal and say if it's coming from an external (air) source then I would draw the line at 1.5 ppm/1000 (15ppm/10K)....so IF you were to go 25K miles - 38-40 ppm MAX. I had a whopping a 4 ppm Si in 20K in one test. In my turbo with miles of intake plumbing 13ppm in 10K seemed OK. [ May 04, 2003, 05:54 PM: Message edited by: Pablo ]
 

YZF150

Thread starter
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658
Location
EU
IDMO, quite right about the age of the engine. I should have included a disclaimer in my original post that new engines don't count due to the RTV gasket seals. For example, I posted a UOA for an oil in an engine that went in at fewer than 3000 miles on the clock, and the Si was 36ppm--12 per 1000 when I sampled and changed it. I'm not even considering that particular metric as significant at that stage. Let's refocus the thread on engines that have enough miles to have reached equilibrium on the seals--however many that may be. Good point. Thanks.
 
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3,693
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Chattanooga, TN
First, the assumption for me is that the engine has gone at least 25,000 miles. Based upon my experience that is where the silicon gaskets/seals have had time to break in. Then, I like to see under 15 ppm at my interval which is 7500 in most cases. This equates to about 2 ppm per 1000 miles. However, if the iron numbers are low and have not spiked and the other wear numbers have not spiked the silicon is probably immaterial to wear and it is coming from other then dirt. My 92 Camry has 155,000 miles now and over a dozen lab samples at 7500 mile intervals. The silicon has consistently been in the teens and at times considerably higher. You really have got to look at the trend and miles etc. etc. there is no magic number. Like the copper number on GM engines, kind of relative. I would normally freak at 90 ppm of copper if I did not know that this is common for the engine in question. Maybe I live in a dirty climate but most of the time my silicon is in the hgiher teens at 7500 miles. Most labs, I believe, cut off at about 30-35 ppm of silicon regardless of mileage on the oil and then they flag it as high.
 
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