Technical 99 octane Fuel

[hugohh]

I don't know if any of you experience this, but my Panda seems to like the fancy drink of 99 octane.

My Panda has 99200 miles on the clock and the engine as far as I can tell is in good shape (1.2 petrol 60hp).

So here is what happened, yesterday I stopped for fuel and the 99 octane was just 1p extra, so I treated the Pandemonium to the fancy stuff, now I'm driving around and noticed how much quieter the engine seem to be running, it actually sounds smooth for a tiny engine.

When I use the normal 95 octane I can hear rattling from the engine, especially in 1st and 2nd gears, or going up hill, and no, it is not the heat shield from the exhaust manifold, I took that off long time ago. It sounds a bit like a diesel rattle or when you are in the wrong gear. But the rattling lasts only a couple of seconds then as you accelerate it disappears.

Is that something to worry about? or just the engine ageing?

Cheers :worship:

 

[chris3234]

I think it's just the placebo effect more then anything

 

[grantleyrich]

Rattling sounds like pinking, or pre-detonation.

Used to happen on a regular basis as cars used to build up carbon deposits which formed hot spots and let to the aforementioned detonation. This is one of the reasons why de-cokes used to be a regular past-time for garages up to late last century (I have done a few in my time). Modern fuel injection and ignition control to reduce emissions has largely made the need for this is a thing of the past.

If it were an older car I would start looking at the timing first. I guess that the modern equivalent is a misaligned crankshaft sensor?

Whatever the cause, pinking will eventually destroy your pistons. Stick to the 99 octane (you might even get better fuel consumption) or try using a lower gear to drive around the problem, after all these engines thrive on revs

 

[hugohh]

Rattling sounds like pinking, or pre-detonation.

Used to happen on a regular basis as cars used to build up carbon deposits which formed hot spots and let to the aforementioned detonation. This is one of the reasons why de-cokes used to be a regular past-time for garages up to late last century (I have done a few in my time). Modern fuel injection and ignition control to reduce emissions has largely made the need for this is a thing of the past.

If it were an older car I would start looking at the timing first. I guess that the modern equivalent is a misaligned crankshaft sensor?

Whatever the cause, pinking will eventually destroy your pistons. Stick to the 99 octane (you might even get better fuel consumption) or try using a lower gear to drive around the problem, after all these engines thrive on revs

So probably when time comes to do the timing belt again, the timing will be readjusted, no? Must look into this as I believe FIAT suggested doing the timing belt every 35k.

The problem with 99 octane is that it is usually 10p extra here where I live. Even though I regard my Panda as a mini Ferrari, I can't afford to go 99 all the time

 

[DaveMcT]

The engine power rating is specced using 97 RON. Lower octane can be used of course but causes retarded ignition so more energy gets lost down the exhaust = less power and worse mpg.

At slow town speed with 95 v 97 you may not notice much but the engine will be running less efficiently. At open road speeds you will feel the difference and with a low powered car you'll need all you can get.

The engine has a knock sensor so the effect of 97 or 99 RON over 95 RON is not placebo. However if you do not have a knock sensor (or it is not working) you absolutely should be using the high octane stuff or you risk engine damage.

I find that Tesco 99 costs about same per mile as Tesco 95. So it's a no brainer to have a car that's nicer to drive. I do not find that Shell Optimax is any better but their rewards system can make it viable if you use it enough.


On the motorbikes -

Yamaha 900 85bhp air cooled four with no knock sensor 95 was just as good as 97 or any other. Some people advanced the ignition for smoother running on posh petrol but they would pink badly on lower rated fuels. Not good.
BMW 1200 105bhp air cooled ran like a dog on 95. It would stall on the way out of a petrol station and gave poor mpg. Whenever possible, I used 97 or 99 RON.

Brother used to go all over Europe on an MZ 250 two stroke. In France he had to carry extra fuel because the low RON stuff usually available gave such poor mpg. He had to retard the ignition to prevent harmful detonation. One would expect a basic two stroke making just 21bhp (on 97) to cope just fine but that was not his experience.

 

[grantleyrich]

So probably when time comes to do the timing belt again, the timing will be readjusted, no? Must look into this as I believe FIAT suggested doing the timing belt every 35k.

The problem with 99 octane is that it is usually 10p extra here where I live. Even though I regard my Panda as a mini Ferrari, I can't afford to go 99 all the time

By timing adjustment I was referring to the ignition timing. Before modern engine control systems the spark used to be triggered and sent to the plugs by the distributor, which was usually driven by a gear on the camshaft. Timing of the spark was adjusted independently of the camshaft timing, which in those days of chain (or gear) drive was never the maintenance item that cam belts are today. So ignition timing could be adjusted independently of the camshaft timing. Being a mechanical setup there was potential for it to go wrong on a regular basis...

I wouldn't have thought that incorrect cam timing would cause pinking as the spark timing is controlled by the crank sensor. Unless the crank sensor has been knocked and is not in the right place, I struggle to see how the ignition timing could be out and cause pinking as you have described. Have you checked for leaks in the inlet manifold and other hoses?

 

[The Panda Nut]

Daughters Seat 1.416v suffers pinking at intervals. When it finally started stalling it was sent away for hospital treatment! It was returned with the throttle body having been removed and cleaned. It needs doing again now after 5 years. Cost of someone else doing it was £35 so worth it to avoid dirty finger nails! It was restored to first class running order. Seat said it required a new throttle body at £725 +VAT and fitting. I suppose it was sticking slightly and causing sensor conflicts and pinking as a result.

 

[GeorgeDamper]

I would make sure that the thermostat is working correctly. Running slightly cool can result in carbon build up.

Change the stat and do a few motorway runs to clear the soot.

 

[hugohh]

So I've been using 99 octane for now as the price's still quite good. Can honestly say the car is running better and I can drive more with one tank.

Normally I get 220 230 miles out of 1 full tank 95 octane till reserve. With 99 I'm getting 280 290 miles out of the full tank.

I always get heavy traffic during my week commute so my figures are pretty low I know!