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Metal Guru
911nut's Avatar
Join Date: May 2001
Location: Michigan
Posts: 2,513
Originally Posted by Flieger View Post
Why is ethanol so "corrosive" to both rubber and metal?

The molecules don't seem all that different from gasoline. Instead of all C-H bonds, it has a couple C-OH bonds thrown in. What is the harm?
I'm not a chemist but from the Corrosion class I took in E-school I seem to remember that oxygen in compounds is corrosive.

Goran, the varnish you speak of are the plastics and rubbers breaking down and ending up in the filter.

E 10 can be an issue in older cars due to it's hygroscopic nature, as mentioned earlier.

Paul B.
'91 964 Turbo
Port matched, SC cams, K27/K29 turbo, Roush Performance custom headers w/Tial MV-S dual wastegates, Rarlyl8 muffler, LWFW, GT2 clutch & PP, BL wur, factory RS shifter, RS mounts, FVD timing mod, Big Reds, - 210 lb
Old 01-10-2009, 04:02 PM
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Manassas, VA
lucittm's Avatar
Join Date: Apr 2007
Posts: 1,211
What I read is that rubber parts were manufactured with a very thin coating of varnish to protect them on the shelf. The 10% ethanol will dissolve this varnish over a very long period of time, not the rubber though. The difference to your CIS will so slight, it will not be perceptible.
In your engine, oil breaks down over time and leaves a varnish deposit inside the engine. It is the brown coating you see when you split the cases on a high mileage engine. The tiny amount of ethanol in the blow-by gases will eventually clean the varnish coating from the parts and you will dispose of this when you change your oil. Good, no?

I maintain that 10% ethanol will do no harm to our cars other than reduce the mileage slightly.

This thread was never really about E85 but "beepbeep" added that as an aside in the third posting. Goran has shown that in Sweden E85 is a fact of life. Here is a bit of trivia from wikipedia nonetheless:
As of 2008, there were an estimated 7 million Flex-Fuel capable vehicles on the road in the United States. A recent GM study found that roughly 70 percent of its flex-fuel vehicle owners didn't know they could use E85, and fewer than 10 percent did so.

1991 964 Polar Silver Metallic Turbo Coupe
Old 01-10-2009, 04:22 PM
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MEMBER # 930
waynesco1's Avatar
Join Date: Dec 2007
Location: Olympia Wa
Posts: 347
I have jist filled my 1978 930 with the 10% ethanol for the first time , also a fresh fuel filter.
This will be a good start point for how long it takes to glog the new fuel filter.
At the time I filled up the tank , and started it up at station the RPMs fluctuated abnormaly up and down 900-1200 rpm at start up. The car had not had this symptom before the 10%ethanol fuel. Any one have any Ideas ,has this fuel made a lean condition with the CIS?

Well with about 100 miles the RPMs setteld 900 steady , all seems fine !!

MEMBER # 930

Last edited by waynesco1; 01-12-2009 at 08:23 PM..
Old 01-10-2009, 04:54 PM
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