REGARDLESS OF ADVICE, DON’T PUT UNLEADED IN WITH YOUR DIESEL
Peter read our recent article on the dangers of mixing fuels, and in particular petrol being added to diesel.
He has no argument with the article as it referred mainly to the more modern common rail diesel engines. He does point out, however, that his 1991 VW Golf (1.6 turbo diesel) is, according to the handbook, allowed up to 30 per cent petrol in the diesel tank.
He quoted from his original handbook Petrol instead of Diesel:
The diesel can be diluted up to a concentration of about 30 per cent with lead-free or leaded regular petrol (also premium with a maximum of 95 RON in an emergency). With the 44 kW diesel engine fitted with a catalytic converter, only unleaded petrol must be used for dilution.
I’m sure this would have been a global recommendation at that time of vehicle production for specific countries where temperatures were extreme. You can certainly rule out New Zealand as being one of those countries. What it does highlight however, is just how forgiving some of the older generation diesel engines actually were.
On the negative side, they produced far too many unhealthy tail pipe emissions to stay in production, hence the move to common rail technology.
Out of interest, Volkswagen NZ provided us with the wording from a 2011 diesel owner’s manual. It reads in part:
Vehicles fitted with diesel engines may under no circumstances be filled up and driven with petrol, kerosene, heating oil or any other fuels that have not been clearly approved for diesel engines. Do not under any circumstances start the engine if you have refilled with the wrong fuel.
Regardless of a vehicle’s age, the best advice is still to drain the fuel tank completely if the wrong fuel is added. An older diesel in New Zealand may tolerate a dose of petrol added by mistake, but just how much is the big question.
Here’s another email I received on a recent fuel-related story about whether a full fuel tank makes any difference to a vehicle’s fuel economy:
Greg writes: “I drive my car frequently over a repeat of the same 600km route and same loading. I notice the fuel consumption figure varies sometimes by a litre or more. That’s using the meter that shows litres per 100km. Maybe there’s a tail wind sometimes but probably not. Has there been any regular checking of the quality of petrol being supplied. And how does consumption vary between 91, 95 and 98 octane?”
Yes, there is a stringent fuel quality monitoring programme from the Ministry of Business Innovation and Employment which monitors the quality of our retail fuel with statistical sampling also used to detect any non-compliance.
That’s not to say fuel quality doesn’t vary. What the standards and testing do ensure is that fuel quality does not drop below the set regulations. On a given day it may well be exceeded.
Over 600km of driving it doesn’t take too much to alter the overall fuel consumption. It can be because of even the smallest increase in shorter trips on a cold engine, weather conditions, traffic congestion and traffic flow or even driver mood.
Regarding the octane ratings, I have always maintained there is no significant advantage in using a higher octane fuel if an engine was designed for the lower octane, and it was the manufacturer’s recommendation to use it.