Unleaded vs Unleaded Plus

Honest John Back Room » Technical matters
What is life like with your car? Let us know and win £500 in John Lewis vouchers | No thanks
View Threaded
Sun 29 Jun 2003 21:47
Unleaded vs Unleaded Plus - msm
Hi,

I got a VW Passat 1.8T sport, was a company car done 64k, maintained real well. I've had it 3 months and I been using unleaded petrol however when the weather's warm I get a sort of plinking sound when accelerating. The noise goes away when I hit a comfortable speed for the gear.

Showed it to a mechanic and he said something about a pre-ignition problem and suggested I try Unleaded Plus (Super Unleaded) fuel. He said the change in petrol will sort out the noise (if I recall him, I think he was on about carbon in the engine or something like that).

I changed the fuel and so far the noise has been lessened dramatically. However, I'm having to floor the car hard to get any decent speed, something I didn't have to do when I was using normal unleaded petrol.

So I guess my question is would the use of Unleaded Plus petrol make some kind of difference to the performance of the car? Also, is there not an additive I could use with normal unleaded petrol to kill the noise instead of having to use the Unleaded Plus fuel?

Thx.
S.
Reply | Report as offensive | Link
Sun 29 Jun 2003 22:16
Unleaded vs Unleaded Plus - Ben79
An additive would probably end up costing more than super unleaded. Try using Shell Optimax, you may even end up with better fuel economy.

Ben
On my 3rd Citroen. Saxo, Xsara, C5.
Reply | Report as offensive | Link
Sun 29 Jun 2003 22:20
Unleaded vs Unleaded Plus - msm
Thx Ben. I'll try that on my next fill. Still interested to know if the fuel type would result in loss of performance.

S.
Reply | Report as offensive | Link
Sun 29 Jun 2003 22:50
Unleaded vs Unleaded Plus - james_60
hi

The ecu has a sensor that determines the octane and adjusts the ignition accordingly

if you use super plus you will get more bang for you're buck and it may clean ure engine much more efficiantly than a bottle of red water (redex)

Regards
J Stephenson
Reply | Report as offensive | Link
Sun 29 Jun 2003 23:31
Unleaded vs Unleaded Plus - v8man
I don't think such a sensor exists. The only sensors in the engine are a knock sensor and of course the lambda (oxygen) sensor in the exhaust. Look in the owners handbook for the recomended octane rating for your car, and use it. High performance engines are often designed to use plus and damage can occur if not. My Rover turbo has been running on Optimax for 2 years with a noticeable inprovement in economy and responsiveness.
Reply | Report as offensive | Link
Mon 30 Jun 2003 09:35
Unleaded vs Unleaded Plus - robZilla
I'll second that. I've been using Shell Optimax (98RON) in my 2.0 16v Vecra for about a year and it has improved fuel economy by about 10%. Not bad considering the fuel costs on average around 5% more than regular unleaded (95RON).

Not really sure if it has improved performance but it certainly hasn't reduced it! One other thing - I noticed a significant drop in fuel economy when using a certain supermarket's "Super" unleaded (97RON) - can't explain that one.
Reply | Report as offensive | Link
Sun 29 Jun 2003 23:32
Unleaded vs Unleaded Plus - Aprilia
Unleaded Plus has a higher octane rating and should not lead to drastically reduced performace. There is something wrong somewhere - possibly with the knock sensor, or its circuitry.
Reply | Report as offensive | Link
Mon 30 Jun 2003 09:21
Unleaded vs Unleaded Plus - msm
Thx for the info and advice.

S.
Reply | Report as offensive | Link

Looking for a garage you can trust? Honest John's Good Garage Guide has thousands of reader recommended garages, plus how-to guides and tips on servicing.

The Good Garage Guide

A guide to how much VED you will need to pay on your car.

Road Tax Bands and Rates