Petrol in your Diesel the Truth

The Facts

 It has for a long time been the myth that Petrol in your Diesel tank will “kill the engine”, “destroy the fuel system” and “cost a fortune”

Yes of course prolonged running of a modern diesel engine with petrol contamination will and does cause extensive damage to the engine and fuel system, but note the word prolonged.
There are plenty of good honest skilled technicians out there who will go the extra bit try to keep your costs down, but there are others who will see this as an opportunity to make a packet at your expense.

Let me give you the facts:
Diesel systems B.C. (Before Common rail), It was normal practice and even recommended by the F.I.E. (Fuel Injection Equipment) manufactures to add Petrol to you Diesel tank in the winter to avoid the fuel freezing (Waxing). This practice became frowned upon by the motoring organisations for the safety aspect.
To fully understand the implications of miss-fuelling you first of all need to understand the fundamentals of how the diesel system and more importantly how the Diesel engine works, let’s keep this simple.
When the piston rises in its cylinder an increase in temperature occurs, this temperature is somewhere between 550c- 800c. Diesel fuel is injected into this hot chamber at precisely the right time. An explosion occurs which in essence forces the piston back down the cylinder, that is as simple as I can put it. Diesel fuel flash point is between 52c & 96c so at 800c at these internal temperatures there is no problem combusting this fuel.
Now let’s inject petrol into the cylinder, we now have vapourised petrol entering the hot chamber, as soon as the fuel leaves the Injector nozzle tip pre-ignition occurs and the temperature within the cylinder quickly begins to rise, prolonged running will see the piston crowns and the nozzle tips begin to melt. This pre-ignition usually results in a loss of power, white smoke emitting from the exhaust and eventually coming to a stop as the nozzle needle seizes in the Injector causing a full system shutdown.
So you have put Petrol in your pride and Joy what can you do. I will split this into options A & B

Option 'A' Engine Not Started

First find a reputable garage to carry out the work. They will have the facility to remove and dispose of the petrol safely.

Request a draining of the fuel tank, the petrol will also need to be drained out of the supply and return lines followed by the supply pump, rail, Injector pipes. Have the Injectors flushed through at your local diesel specialist. If there is anything wrong with these, they will soon put them right at a fraction of the dealer’s price. Now all traces of petrol have been removed, a new fuel filter and replenishment with Diesel should be OK. A word of caution, If the high pressure pump is not belt driven (ask your garage)keep an eye on your oil level for a few months, damage to the pump’s drive seal can occur but not manifest itself immediately. If a rise in oil level does occur, have the pump removed for drive seal replacement.

Cost for all of this work would be in the region of £500 (One days labour and Injector flush/test)***

Option 'B' Engine Started

As above regarding cleaning and also: Request that the Injectors and pump to be tested. Worse scenario if engine has been run for a short period would be, glow plug failure, new nozzles on Injectors, Pumps that have run for a short period do not usually suffer major component failure* however insist the pump drive seal is replaced as damage to this seal does not always show immediately. *The Delphi pump can fail due to lack of lubrication, an inspection of the fuel filter for metal debris is a quick way of confirming pump break-up.
Request a compression and cylinder test, why would you want to spend good money on the fuel system if the engine has suffered major component failure ?. If these are around 350p.s.i.** and leakage test shows all cylinders are over 90%. Then it’s pretty safe to say the engine has not suffered any serious damage. **Guideline pressure, this varies but you’re looking for conformity.

Cost for this would be in the region of £1250.00 (£500 labour + 4 Injectors @ £125 each = £500, Pump inspection and seal replacement £250.00***

So if you’re getting quotes of £2000+ at the dealers start asking questions and shop around.
***This is based on a four cylinder engine operating a typical common rail system, more cylinders and more obscure vehicles may cost more.

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