Fuel octane levels

[Hannarj]

Not sure this is exactly the right place to post this so feel free to point me somewhere else!

I have a 2.1fuel injected petrol, watercooled engine in my camper. There is a sticker on the side of the drivers door which specifies she should only have fuel of 98octane. I've always just gone with it and avoided using anything with less Octane but actually this is a bit of a pain as it seems Tescos are pretty much the only place with 98octane super unleaded. Most other garages it's 97 octane. What would the effect of using a lower octane fuel be? I've obviously had to occasionally but I've never put in more than about £15 and then made sure to get to a Tescos to fill up next.

Just wondering if using a 97 octane fuel would mean she might cut out or similar running issues. Or have long term consequences for the engine.

Cheers

[bigherb]

You can run them on 95 octane if the timing is adjusted to 5 deg BTDC.
It might have already been adjusted, if it was still being serviced in the VW dealer network in the 90s we adjusted them as a matter of course.

[Hannarj]

Thanks Bigherb.

How could I check if she's already been adjusted? Would my garage mechanic be able to? She's booked in for a service next week so that could work well.

Would be great to save the few pennies on super unleaded, especially going into the summer!

The engine was newly installed a few years ago. The sticker, I had assumed had been added when the engine was, but not sure.

[bigherb]

Yes a garage should be able to check and reset the timing if necessary using the information above.

[Hannarj]

Great thanks! I'll print and take it in with me.

[California Dreamin]

The 2.1 DJ runs a higher compression (10.1:1) than the other 2.1's (the SS & MV which I believe are 9.5:1). The extra compression delivers more power but also heat. This additional heat has a tendency to cause abnormal combustion, pre-ignition/pinking. By retarding the ignition this heat can be reduced but with some power loss, so it sort of defeats the object of having the more powerful 112bhp of a DJ although not all is lost. Using higher octane fuel (and the 97ron is just fine BTW) means the fuel has a higher resistance to ignition so won't ignite before the spark plug starts the process, running nice and cleanly as intended.