Noisy engine after cheap fuel fixed with better fuel.
Discussion
There has been much discussion on various forums about the quality of fuel from some supermarkets usually without a definite conclusion, however :-
I recently bought a tank of Diesel from well know food retailer and within 20miles or so the engine was sounding quite different. The best way of describing it is to say it sounded “diesely” and the performance seemed to have fallen off slightly. It is a reasonably current 3000cc V6 Merc and normally makes fairly muted diesel murmur but not after that particular fill up. It was so bad I had the cover off the engine in an attempt to track down the source, thinking it may be a leaking manifold gasket or the like. A poke about with a listening tube showed that all cylinders seemed to be clattering.
Yesterday I refilled from fuel rather than food supplier and the engine has gone back to its normal subdued purring and eager self, it no longer sounds like a Transit van.
Could just be coincidence I suppose.
Now I don’t really know much about the workings of a diesel engine but had it been petrol I guess I would have been worrying about detonation and thinking that the fuel was significantly lower octane than normal.
Does diesel fuel have the equivalent to an octane rating and if not what property of Compression engine fuel would effect the noise it makes. Anybody know ?
I recently bought a tank of Diesel from well know food retailer and within 20miles or so the engine was sounding quite different. The best way of describing it is to say it sounded “diesely” and the performance seemed to have fallen off slightly. It is a reasonably current 3000cc V6 Merc and normally makes fairly muted diesel murmur but not after that particular fill up. It was so bad I had the cover off the engine in an attempt to track down the source, thinking it may be a leaking manifold gasket or the like. A poke about with a listening tube showed that all cylinders seemed to be clattering.
Yesterday I refilled from fuel rather than food supplier and the engine has gone back to its normal subdued purring and eager self, it no longer sounds like a Transit van.
Could just be coincidence I suppose.
Now I don’t really know much about the workings of a diesel engine but had it been petrol I guess I would have been worrying about detonation and thinking that the fuel was significantly lower octane than normal.
Does diesel fuel have the equivalent to an octane rating and if not what property of Compression engine fuel would effect the noise it makes. Anybody know ?
Do you think there is horse poo in their fuel ?
Fuel quality is a hard one to quantify. But I did have issue a year or so ago where fuel consumption dropped suddenly by about 15-20% fro a supplier I had used many times before ( I go through a tank a day or more )
After switching to a bigger brand name, only because it happened to be cheaper that day, all was restored.
Ive pretty much stuck to big brand names since.
Despite the massive increase in fuel consumption, there seemed to be no difference to performance.
Only oddity from time to time had been an occasionally loud idle and slight miss, which on the better brands seems to happen very rarely.
IMO supermarket fuel saves almost nothing....but is it any good for your engine ?
I'll stick with branded stuff.
Fuel quality is a hard one to quantify. But I did have issue a year or so ago where fuel consumption dropped suddenly by about 15-20% fro a supplier I had used many times before ( I go through a tank a day or more )
After switching to a bigger brand name, only because it happened to be cheaper that day, all was restored.
Ive pretty much stuck to big brand names since.
Despite the massive increase in fuel consumption, there seemed to be no difference to performance.
Only oddity from time to time had been an occasionally loud idle and slight miss, which on the better brands seems to happen very rarely.
IMO supermarket fuel saves almost nothing....but is it any good for your engine ?
I'll stick with branded stuff.
Because diesels run lean all the time (unthrottled) any fuel that is injected pretty much burns immediately. This creates a very rapid rate of rise of cylinder pressure. This is the characteristic diesel "knock" or "clatter" that you hear. These days, with very high precision (and pressure) common rail injection systems, the EMS can effectievly put in loads of little pre injections before the main injection. This enables the system to reduce the knock and results in a more refined engine noise. The latest systems monitor crank acceleration and actively control the fuel mass and timing to maximise smoothness at all times. The penalty for this pre injection is a reduction in fuel economy (as the charge burn occurs at a bigger cylinder volume so more heat is lost to the walls than if injected later (at a lower Chamber volume for a faster but noisier burn). As a result the engine calibration is a trade off between fuel economy and noise. For example BMW engines tend to sound a little less refined than say the PSA CR diesel, because they have pushed fuel economy harder and sacrificed a little economy for refinement. Now, your engine will not always operate with pre injections. When it is cold, or at a high load it will revert to just a main injection to make the best FE / Torque. If you start you engine from cold with the bonnet up, you can easily spot the moment the system switches to Pre injection (usually at about 60degC coolant) by the sudden quietening of the engine combustion noise. You'd be amazed how obvious the switch is when you know what to listen for ;-)
So, finally getting to the point, your engine was noiser on the supermarket fuel, suggesting two things:
1) Are you sure the engine was at both points fully warmed up and under the same load? (A/C & alternator load at idle is important too, as they can be quite large). I.E is it possible the EMS was not operating in the same mode for both tests
Or, and equally as likely
2)I suspect that the supermarket fuel could have had a higher cetaine rating (possibly a winter grade?) Being more volitile, this fuel blend ignites and burns faster, which leads to a quicker rate of rise of CP and a louder "knock". If you EMS was adapted to the previous fuel, it will take it a little while to spot this change and modify the Pre injection timing to suit. Typically winter grades of diesel have a lower calorific value (as the anti-sludging additives take up some space) and so fuel economy is degraded when running on them. Depending on the blend this can be up to 5-8% worse.
So in summary the commercial grade fuel isn't necessarily "better" as such!
So, finally getting to the point, your engine was noiser on the supermarket fuel, suggesting two things:
1) Are you sure the engine was at both points fully warmed up and under the same load? (A/C & alternator load at idle is important too, as they can be quite large). I.E is it possible the EMS was not operating in the same mode for both tests
Or, and equally as likely
2)I suspect that the supermarket fuel could have had a higher cetaine rating (possibly a winter grade?) Being more volitile, this fuel blend ignites and burns faster, which leads to a quicker rate of rise of CP and a louder "knock". If you EMS was adapted to the previous fuel, it will take it a little while to spot this change and modify the Pre injection timing to suit. Typically winter grades of diesel have a lower calorific value (as the anti-sludging additives take up some space) and so fuel economy is degraded when running on them. Depending on the blend this can be up to 5-8% worse.
So in summary the commercial grade fuel isn't necessarily "better" as such!
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