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Tips & Advice

How To Bleed Your Engine

Often, engine starting problems, are caused by small amounts of air in the fuel. A common cause of this problem is when you run out of fuel, if this happens you will need to know how to “bleed” your engine, which rids the fuel lines of air, so the engine can start.

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If you are an owner of a diesel engine bleeding is an essential skill. If you are familiar with the manufacturer’s recommended procedure for bleeding your engine, follow it, but generally, the procedure is as follows.

When bleeding the fuel line, especially when the starter motor is used to operate the fuel lift pump, wrap rags around all venting units to collect excess diesel fuel that splashes out.

Open the fuel supply valve, (usually located near the fuel tank this is the on/off switch) and use the manual fuel pump (found on most diesels at the side of the engine).

  • Pump the fuel into the lines.
  • Do this until you just see fuel bubbling out of the bleed nipples of:
  • The secondary filter (diesel filter-usually located on top of the filter housing)
  • The fuel injection pump (located on the side of the engine – follow the fuel pipes down from the injectors)
  • The connection points (bolts) at the top of the injectors.

    (The process is similar to bleeding your central heating radiators)

  • Try to pump until you get clear fuel without bubbles from each fitting. If you succeed, and there is no longer air visible in the fuel system tighten each connection in turn. Starting at the filters, then at the pump and then the injectors.
  • If you are fortunate enough to get all the air bubbles from the fuel, flowing out of each and every injector your ready to start your engine. Make sure all bleeding points are tight before trying to start your engine. If you are still having problems try the following.

Expel air from the filter, then the pump as in the last paragraph. Make sure that all the injectors are tight in their bases and all of the fuel line connections at the top of the injectors are loose, this will allow the fuel and air to spurt out of them when the starter motor is engaged.

Have the correct size spanner in hand, ready to tighten the fuel line connections when the fuel runs clear without air bubbles.

  • Now, turn the engine over with the starter motor, and with the throttle open.
  • At first you should see fuel and air bubbles coming from the injectors.
  • Look at the number one injector. (Check your manual for guidance)
  • When it shows clear fuel with no bubbles, tighten the connection and look at the second injector.
  • Again, when it shows no air bubbles in the fuel, tighten it and go on to the next one.
  • Continue this process until all injectors are cleared of air.

    Your engine may start before you all injectors have been tighten. This is completely normal so don’t panic. Just release your pressure on the starter button or key and let the engine run while you continue to monitor the fuel flow from the remaining un-cleared injectors.

  • Do not crank the starter motor for more than 30 seconds at a time, as this will cause wear on your starter motor.
  • WARNING This method can cause the battery to become flat whilst the engine is ‘wound over’, so CARE should be taken.

    As an alternative to using the starter motor you can also put the decompression lever in its decompressed position and hand crank the engine to move fuel to the injectors. When all injectors are cleared of air and their fuel connections tightened down, you are ready to start your engine.

  • In all cases Don’t over tighten the nuts, and it is always prudent to check for leaks when the engine is running.
  • When the engine is running look at the exhaust if it is “puffing white smoke” this is a sign that air is still present in the fuel – keep the engine running and if this doesn’t eventually clear, re-bleed injectors whilst the engine is running.