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RIP (12/27/60-7/18/15)
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767 Posts
Discussion Starter #1
Im old school and have never used synthetic oil.
and wouldnt dream of using it in my GTO.
but, what are the advantages/disadvantages of it (if any)
thanks as always
 

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I only use it in vehicles that recomend it from the factory. Lots of european cars, our corvette, all subaru require it. If the owners manual require it use it. It is great stuff for those applications. I own a 2009 chevy cobalt and the owners manual does not require using synthetic oil, so why use it. I just use regurlar oil and change it every 3,000 miles.
 

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Former Moderator
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Interesting. Must timeout or something. It was just a link to the results of a search on "synthetic" in this forum. Redid the search and copied the link and it worked fine. Anyway, deleted it since I misunderstood what the OP was intially asking....
 

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There's lots of websites that cover conventional / synthetic pros & cons. I found Joe Gibbs site pretty useful. They sell some; e.g., the HR (hot rod) oils for (non-cat converter) high performance street cars in both varieties so they offer some good insights on pluses and minuses of each type.

Joe Gibbs Driven - Racing Oil and High Performance Products

A search on the GTO Forum site will also add insight. There are reasons not to use syn that some cite; e.g., possible incompatibility of the gasket sealants used. I also seem to remember reading years ago about issues with some types of rear main oil seals when changing from conventional to synthetic and/or back again because seals swelled and/or shrank, etc. I think you'll find this addressed on some sites Q&A's like maybe Mobil-1. I've had multiple rear main seal types...including the post-asbestos rope type replacement around 1992 that started leaking pretty good (on conventional oil) a few years ago...the cause for a rear main replacement last year with the newer viton type. I don't know if viton is especially good for synthetics, but I'm using synthetic, probably without the degree of expertise I should have to make the best decision. And I don't know if it's as big an issue potentially on the front seal.

As you'll see elsewhere...the zinc level is critical if you've got flat tappet cam / lifters setup, maybe the most important issue. High (enough) zinc synthetics are available in limited oil weights; e.g. Mobil-1 has a 15w-50 that is higher weight than I wanted. So I went with Joe Gibbs, who had the 10w-30 I wanted with enough zinc. Another option for me would be 10w-30 Mobil-1 and add ZDDP-Plus (that's what I do for my boat motor).

My motor only had about 300 miles on a partial rebuild, so my case does not prove synthetic won't cause me a problem.
 

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64-67 Expert
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peahrens, well stated. I went through the same thing with my '67's rear main. Running a Viton seal now. The 30 year old asbestos rope seal in my '65 is leak free, while the post-asbestos rope in my '67 started leaking soon after the rebuild in 1988. You will find that the new synthetics cause no harm to rubber seals or cork seals or leather seals, for that matter. I don't know about some sealants. Synthetic oil is superior to mineral in an engine. It has better lubricity, cling, and resistance to coking up at extreme temps. As long as ZDDP is added, it's fine. Is synthetic oil necessary? No. Is ZDDP? Yes.
 
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