I use Mobile 1 extended performance in my HHR 2.4 and used it in my 2006 Saturn 2.2. I sold the Saturn at 230000 miles and I expect to get at least that with my 2011 HHR. I change the oil when the indicator says so, but I change the filter every 3000. I use the Wix filter. I drive the interstate about 3000 miles a month.

 

I recently purchased a 2007 HHR LT2 and switched it over to Mobile 1 full synthetic oil about 500 miles ago. I had a small oil leak, not sure where appears to mabe be main bearing seal, after changing over to Mobile 1 it is a big leak. I am waiting for the weather to clear tomorrow and draining it out and going back to Dino oil. I had heard stories of the Mobil 1 causing small leaks to become large leaks but didn't believe it until now. I change my oil often so the benefits of synthetic oil is of no concern. Thought I was doing a good thing but live and learn, just hope the new oil slows the leak until I can find someone to repair it.

 

I use M1 High-Mileage formula partly for that reason. It's supposed to have some seal-swelling capability (could be rumor-only).

I now have 108K. Started that stuff at about 85K. It costs the same at Wally's Mart, so why not?

 

Working as a technical writer, I've spent a lot of time researching and testing engine oils.

There are a couple of points I'd like to make based on some of the posts above.

First, on blends of synthetic oil and petro-base oils. Be careful...very careful. Currently, there are no FTC requirements for labeling of "synthetic oil" blends. The actual amount of synthetic base stocks in a "blend" varies widely. Some of them have amounts of synthetic base stocks too little to offer much of the benefits of a synthetic oil but just enough for the vendor to say it's a blend of synthetic and petroleum based oils. Also, there maybe just enough synthetic in it to justify the higher price. Bottom line, there is little practical benefit to the user in a synthetic blend compared to a good petroleum-based oil, but there is benefit to the oil refiner in that they can charge a higher price.

As for the small molecule vs. large molecule issue in synthetic vs. petroleum based engine oils? What a bunch of BS.

If that were really true...all us folks who use synthetic would have engines which like sieves.

I've been using synthetic oil in my 2007 since the first oil change at 3000 miles. It's now got 120,000 on it. The first 101,000 were with Red Line 10W40. The last 15,000 have been with Gibbs Driven LS30 (which is a 5W30). The engine has never leaked any oil. If it were true that synthetic oil has "small molecules" which get by seals and gaskets, I'd have been constantly fixing oil leaks. Many car makers now use synthetics as factory fill. You think GM, Porsche, Mercedes, BMW, Audi and others would use synthetic engine oils if they all leaked. What in the heck are you guys smoking, anyway?

Reality is the oil molecules, be they petroleum-based or synthetic are all really small but the relative differences are not that one can get by seals and gaskets and the other can't.

 

Thanks, Hib.....

I was going to comment on that as well, but decided it would become an argumentative issue and decided, "what the hell!!".

So obviously, I concur

 

High mileage oils have more ZDDP (zinc ) than conventional oils. That is the anti wear agent that swells the seal a bit among other things. However each brand is different.
Check out bob is the oil guy for more info.
In my experience, I switched to high mileage oil on my chev express van, and noticed higher oil pressure at idle, and more left in the engine at oil change time. So there is a difference for sure. Mostly because of the higher zinc. Racing oils have a ton of zinc, but for daily driving, too much is a bad thing.

 

ZDDP is not an issue with a OHC engines like the 2.0T, the 2.2 and the 2.4 in our cars. Where zinc, and more importantly, phosphorous, are an issue is in engines with pushrods and flat tappet cams.

Also, just the existence of more zinc will not raise oil pressure.

Seal softeners, when blended in oil, are just a bandaid fix, IMO, but I'll admit, in the case of a short-term need to swell a slightly shrunk rubber seal, maybe they help. If you've got an engine with rear main or front seals which leak like sieves or valve guide seals which leak due to bad guides, I wouldn't put much faith in "seal softeners".

 

Five Common Engine Oil Myths
http://dropculture.forumotion.com/t5...-synthetic-oil
http://www.mne.psu.edu/chang/me462/syn_vs_min.pdf
http://www.mpgenhance.com/syntheticf...orsepower.html

 

So, who and what to believe.
I copied the quote below from the article that 2005HHRauto had a link to.

"The smaller molecules of synthetic oil are able to pass through very small cracks and crevices that the larger molecules of petroleum-based oil cannot. Eventually, those small cracks and crevices can lead to bigger problems — with or without synthetic oil."

 

And remember: if you use a "high mileage" or "seal swelling" oil you must stay with it, or the seals will shrink and start to leak.