Diesel fuel starvation on a 308 HDi, a priming bulb that remains soft after a filter change, or a starter that spins without engaging: we’ve all experienced that moment when the engine refuses to start. The diesel injection system of the 308 HDi requires thorough air bleeding to restore fuel supply. Here’s how to do it effectively, without wasting an hour pumping into thin air.
Locate the priming bulb on the engine block of the 308 HDi
On the 308 HDi, the priming bulb is not always where the manual indicates. Depending on the versions (phase 1 or phase 2), it is either located between the two lower hoses of the diesel filter or slightly above the engine, to the left of the air filter. It is a black cylindrical piece made of rubber, connected to the low-pressure circuit.
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Before touching anything, locate the diesel filter. It is connected to three hoses and an electrical connector. The bulb is located between the two lower hoses, just below the filter housing. On some models, a plastic engine cover obscures it: simply remove it by pulling upwards.
If you are looking to prime the diesel bulb on a 308 HDi after running out of fuel, first check that the bulb is not cracked. Reports from independent workshops indicate a risk of micro-cracks on the original bulbs of high-mileage phase 2 308s. A split bulb draws in air instead of fuel, and you can pump for an hour without results.
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Bleeding the diesel circuit of the 308 HDi: the manual procedure that works
We start with a classic case: the tank has been filled after running out of fuel, and the engine won’t start. The circuit is filled with air between the tank and the high-pressure pump. The priming bulb is used to manually expel this air.
Concrete steps to bleed with the bulb
- Put at least ten liters of diesel fuel back into the tank. A small amount is not enough; the column of fuel must exert a minimum pressure to assist the suction.
- Squeeze the priming bulb regularly, without forcing it. Pump slowly, about one squeeze per second. The bulb should gradually harden after a few dozen squeezes, indicating that the diesel is replacing the air in the circuit.
- Once the bulb is firm, turn the ignition on without starting (accessory position) for a few seconds to activate the electric lift pump. Repeat two or three ignition on/off cycles.
- Start the starter in short bursts of a maximum of five seconds, with a pause between each attempt to avoid burning out the starter or overheating the high-pressure pump.
If the bulb never hardens, the problem is likely an air leak upstream: porous hose, loose connection on the filter, or a faulty bulb itself. Inspect each connection for wet traces of diesel, indicating a leak.
Common mistake to avoid
Pumping frantically for long minutes without checking the firmness of the bulb is pointless. If the bulb remains soft after about fifty squeezes, stop and look for the leak. Continuing risks sending air directly into the high-pressure pump, a component whose replacement costs significantly more than a simple bulb.
DIY alternatives when the priming bulb is missing or out of service
Some 308 HDi models, particularly the early versions or those that have undergone workshop interventions, may end up without a functional bulb. In the event of an electrical failure in the high-pressure system, the classic priming method no longer works. Here’s what you can try on the ground.
Gravity method and ignition cycle
Disconnect the diesel supply hose at the filter (the one coming from the tank). Place the end in a clean container, then wait for the fuel to flow by gravity. Once the flow is steady, reconnect the hose, tighten the connection, and restart the ignition cycles as described above.
This method only works if the tank is higher than the filter, which is the case on the 308. Reports vary on this point depending on the vehicle’s incline: on a slope, gravity may work against you.
Using a syringe or an external hand pump
A large syringe (like a veterinary feeding syringe, available at agricultural pharmacies) connected to a piece of flexible hose allows you to draw diesel from the filter and force the degassing of the circuit. Draw gently until you see fuel without bubbles in the syringe, then close the circuit.
A hand pump for transferring fuel (sold as an auto accessory or at boating stores) does the same job with more flow. The goal remains the same: to expel air from the low-pressure circuit before engaging the starter.
Preventing priming issues on 308 HDi
The majority of priming failures are related to the diesel filter or the condition of the bulb. Replacing the filter according to manufacturer recommendations (generally every two years or based on the mileage indicated in the maintenance booklet) limits air intake. After each filter replacement, always prime with the bulb before attempting to start.
On high-mileage phase 2 308s, a preventive replacement of the bulb with an original part (OEM) avoids the unpleasant surprise of discovering a micro-crack on the roadside. The cost of the part is modest compared to an intervention on the high-pressure pump.
Lastly, a point often overlooked: after any work on the circuit (drain, hose replacement, filter change), check the tightness of each connection. A connection that is a quarter turn loose is enough to let air in and make the next start impossible.