Several Automotive Questions

Have several questions here - anyone feel free to comment, thanks. 1. On a trip through Utah and Colorado I noticed a lot of 85 Octane (not Ethanol). Most car manuals I've read say 87 octane is the lowest (including mine). This is the first time I've seen 85 octane. Is it ok to use? It was noticably cheaper... [Razz] 2. For someone who has used synthetic in their engine would it be ok to use a semi-synthetic? I've heard going from synthetic to dino is bad but dino to synthetic is ok. What bout going from full syn to semi-syn? Had a friend ask. 3. In efforts to obtain an accurate UOA with a specific brand is it necessary to "flush" out the old oil by doing several runs of a new brand? I usually let my car drain for 30min-1hour. If I drain brand Y for 1 hour put Brand X in will Brand Y affect X's UOA? 3b. Due to oil add pack difference it would seem to me that running different brands of oils now and then should result in a cleaner engine due to the different add pack cleanings? Is this a correct assumption? Thanks, -Paul [Cheers!]
 

Kestas

Staff member
Messages
13,952
Location
The Motor City
1. The mountain areas can get by with lower octane because of the altitude. I forget the technical reason behind this. Some owners manuals address this. 2. You should be able to switch back and forth at any oil change with no worries.
 
Messages
1,979
Location
Dallas, TX
1) Oxygen density (lack of) at higher altitudes allows for less octane 2) From personal experience, switching to synthetic in old engines has brought on seal leaks after many years and miles of dino oil. Other than that, no harm done. Personally speaking, I don't see the point of synthetic blend oils. A pan of oil is only as strong as its weakest molecule. 3) I would skip the UOA on the 1st change, and do one on the 2nd change. 4) I've learned here that every brand of oil is a give and take. I subscribe to the school of thought that if you pick a high-detergent oil that provides the best protection available and perform reasonable OCIs, your engine is going to remain clean. For these reasons, I prefer full syn. Superior high-temp stability, sludge and varnish resistance.
 
Messages
936
Location
Pittsburgh,PA
If its one thing I have learned here its that most modern oils are really pretty good nowadays and given a fair OCI you will not have problems with lube related failures. This is pending you dont have a "sludge monster" engine. I know first hand that the Chrysler 2.7L engines were known for sludging up on anything short of full synthetic. There are others but thats the one that pops into my mind right off the bat. I would say choose a good oil(dino or syn) and unless you have a good reason to switch, dont. But nothing wrong with trying new things to see what your engine might like best. I did that with mine. I found Supertech makes my engine louder than say GTX. Both oils were 10w30.
 
Messages
3,329
Location
Bolivia
All we can buy in Bolivia is 80 octane, except for a few stations in 3 of the bigger cities where sometimes you can find 90. Our altitudes run from 1200 ft to 16,000 feet. My Grand Cherokee ran on 80 once I got it cleaned out with 2 techron treatments. Suzuki's have a lot of trouble with autoignition and not turning off. My BMW would not run on anything less than 90 when I had it at 1200 ft. Now I have it at 6000 feet and mix 50% 80 octane with 50% 110 octane aviation gas. Personally I do not believe in the blends. Either a good Group II or Synthetic, depending on yur driving and car. I would not switch off brands unless there was a significant reason. No sense in analyzing the first change with a brand. It has residuals from the other.
 
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