Diesel Air Lock Volvo 2010 - Help!

[DaveParry]

Last Weekend we got an airlock in our Volvo 2010 fitted in our Oyster 26. Not being savvy with diesels, we had trouble starting it until some kind chap at Kip marina sorted it out - very quickly and with a burst of black smoke. Unfortunately he was working and had to dash off so didn't have time to show us what he did! Can anyone enlighten us so we can fix it ourselves if it happens again? Thanks.

 

[hlb]

Well of course, first you have to find the air leak and stop it but presuming that has been done. The quick way to bleed the system is to loosen a couple of injector pipes. (Nuts on the pipes as they join to the injectors). Turn the starter motor. As the engine starts to fire, tighten the injector nuts up. Keep a rag over the injectors or you will have diesel every where. It's not the prescribed method, but much quicker.

No one can force me to come here-----------
----- I'm a Volunteer!!!

Haydn

 

[vyv_cox]

To an extent it depends where the airlock is. As Haydn says, the first step is to identify and fix the source of the incoming air. If your lift pump is airlocked it will have difficulty in sucking fuel, so you need to eliminate this one first. Easy if the tank is higher than the pump, just unscrew the discharge pipework and gravity will drive the fuel through. If the tank is low, operate the pump. There is often a lever that will do this manually, otherwise turn the engine over on the starter motor.

Once the lift pump is delivering fuel to the metering pump, in theory the engine will start eventually as all the air is driven through. In practice, only a very small amount of fuel (or air) is driven through on each engine revolution, so the battery will be flat before fuel arrives at the injectors. To short-cut this process, the manufacturer may put bleed screws in various places, like on the secondary filter. Open these one at a time, working from upstream to downstream, turning the engine over on the starter motor and closing the bleed screws when fuel emerges. Unscrewing the supply pipe on the injectors is the last step, to dispel air from the pipes. Once you have fuel here and have re-tightened the unions the engine should go.

Many modern engines do not need bleeding, according to the manufacturers, but this does assume you have lots of battery power. I find it is usually much quicker to do at least some bleeding. Be careful of high-pressure squirts of fuel, there is some evidence to show that they can penetrate your skin and enter the bloodstream.

 

[pvb]

While you\'re doing this...

If you're going to try to cure a starting problem by turning the engine over using the starter motor, it's often wise to close the intake seacock first. Otherwise, you can gradually fill up the exhaust with water which, in the worst case scenario, will get into your engine and create a far worse problem. Open the seacock as soon as the engine fires.

 

[hlb]

Re: While you\'re doing this...

Dont understand that one?? Vyv,s right though. Thats the long way round. There is also a little hand pump on the lift pump, but takes for ages. Taking the filters off and filling them with fuel might speed the job up. Depends where its air locked though. But as I said undo injector pipe and the engine will be running in seconds. But dont forget the rag over top or you will spray diesel every where.

No one can force me to come here-----------
----- I'm a Volunteer!!!

Haydn

 

[vyv_cox]

Re: While you\'re doing this...

We had some discussion about this last week. What happens to a rubber impeller when subjected to almost full vacuum on the suction side? Can the vanes invert? Pump manufacturers are silent on this, but they do put a limit of 30 seconds on dry running.

 

[pvb]

RNo, they can\'t invert...

If you think about the way the pump works, you'll see that the vanes can't invert. And if you've simply turned the seacock off, there should be enough water in the pump to lubricate it for a time. "Dry running" applies when a pump is empty of water and is trying to attain prime. The possibility of filling up the exhaust with water has to be avoided at all costs!

 

[vyv_cox]

Re: RNo, they can\'t invert...

I come to my hypothetical boat after a week away. Water level is lower than the pump, so impeller is probably dry. My engine doesn't start on the starter and the dry pump remains dry because it doesn't suck enough at cranking speeds. Following Volvo advice (although I don't have a Volvo) I then turn it over for 30 seconds before giving up, wait a while, and try again. Another 30 seconds. Still doesn't start. I start bleeding at intervals and turning over the starter motor. After a period (1 minute?) total turning time the engine fires. I check for fuel leaks, listen for unusual noises, check the exhaust and realise I've forgotten to turn on the seacock. Running time another minute? Total time more than three minutes, some of it at 1000 rpm.

How's my impeller?

 

[Trevethan]

Re: RNo, they can\'t invert...

Starting procedure for Gayle Louise according to previous owner (and builder) is

check oil etc.

Set battery selector to both.

Set boat in neautral with 3/4 throttle.

Turn key. when engine fires drop to tickover, nip down into salon and turn on seacock for raw water. (Boat has a heatexchanger and raw water cooled freshwater colling system.


Shut down procedure is to turn off seacock. wait til exhaust runs dry (maybe 30 seconds) and then kill engine.

Seems I might be buggering up the impellor this way. But it does make sure there is no water in exhaust that could get back into engine.

 

[pvb]

Get real...

Don't know what you sail, but most boats I've been on have a raw water filter. In order to facilitate cleaning this, it's usually mounted above the waterline. The raw water pump can't therefore empty unless the engine is started when the boat is dried out, ie the water outside is below the seawater seacock's opening. But, of course, if you have a poor memory, you can easily bu**er up an engine.