Engine Servicing - Fuel Venting Issue

[grazbo]

I have completed a DIY service on my Volvo/Perkins MD2010, replacing both the fuel filters.

Once replaced, I then proceeded to bleed the system - by the book(s) - and loosened the vent screw on the main/2nd filter while I pumped with the lift pump.

As I pumped (a lot) I realised that nothing was happening - not a drip of diesel at the vent screw after at least 20 mins (The glass bowl on the pre-filter was full, but I assumed gravity did that for me.) The books told me how to rotate the cam to "engage" the lift pump better - so I did. No change.

As a desperate effort, I spun off the main/2nd filter (which proved to be totally empty) and started to pump again. Nothing happened. No diesel came out the filter "socket".

I concluded the manual lift pump was not working - or had a major block.

To help things along, I decided to fill the filter with diesel and then screw it in again. Went through the same motions as before, but still nothing at the vent screw.

So, I decided to turn the engine and it started after a few turns - pushing the fuel through, I assume - and seems to be running sweetly.

However, in my mind I am not sure all is well, since I know I am meant to vent the filter, get rid of any bubbles, then I am meant to vent the injectors.

I have done neither.

To put my mind at rest:

- If the engine works and sounds happy, is the job done ? Can I relax ?

- How long to run a diesel engine before I pass the "if it's gonna go wrong" mark ?

Thanks

Graeme

 

[garvellachs]

bleeding filters

Graeme - you posted a link to here from the other post on leeding filters so I thought I'd try to help.

First, it's essential to turn off the fuel with a valve between the tank and the primary filter. Otherwise the fuel in the feed pipe may drain back into the tank or syphon out of the filter.

Secondly as you've found, it's worth filling both filters with clean diesel before screwing them back on - saves a lot of pumping. I keep a bottle of it on the boat in case I need to do it at sea in a hurry.

Thirdly, my guess is that filling the second filter gave the engine enough fuel to pump the air and diesel through the system itself - by chance did it cough and splutter a bit on the way?

As others mention, using the engine to pump it through is OK if it's quick, but there's a risk of overheating the starter motor (not built to run continuously) and/or of filling the exhaust with so much raw water (the engine isn't firing so it is being pumped in but it doesn't get blown out) that it comes all the way back up into the engine through the exhaust manifold. If water gets into a cylinder then it will bend the con-rod or similar because it is incompressible/not imflammable. Bad news.

It should be possible quickly to pump fuel and air through using the hand primer on the fuel pump, bleeding at the secondary filter first then at the injector pump. My experience suggests usually the injectors won't need to be bled - the engine will cough into life quickly once fuel is in the injector pump. If fuel won't come through, it may be that there is a leak somewhere and air is getting in - a symptom of poor starting too. Worth checking anything you've undone is tight again? Or just possibly the fuel pump diaphragm is leaking - not enough to stop the engine running but enough to stop it pulling fuel through by hand? The latter can cause diesel to get into the engine oil - evidenced by a rising oil level.

 

[YachtAllegro]

Once replaced, I then proceeded to bleed the system - by the book(s) - and loosened the vent screw on the main/2nd filter while I pumped with the lift pump.

If that means you loosened the vent screws on both the primary and secondary filters, and then pumped with the lift pump, I think that's your problem. The lift pump (in my setup at least) sucks fuel from the primary filter and pushes fuel into the secondary filter. So if the primary filter bleed screw is open when you're operating the lift pump you're likely to just suck air in through it, which then gets pushed out at the secondary filter.

You need to bleed the primary filter first (via gravity or a fuel feeder pump if your system has one), then tighten the bleed screw here and bleed the secondary filter with the lift pump.

But maybe I've misunderstood what you were doing...

Cheers
Patrick

 

[Stork_III]

I have completed a DIY service on my Volvo/Perkins MD2010, replacing both the fuel filters.

Once replaced, I then proceeded to bleed the system - by the book(s) - and loosened the vent screw on the main/2nd filter while I pumped with the lift pump.

As I pumped (a lot) I realised that nothing was happening - not a drip of diesel at the vent screw after at least 20 mins (The glass bowl on the pre-filter was full, but I assumed gravity did that for me.) The books told me how to rotate the cam to "engage" the lift pump better - so I did. No change.

As a desperate effort, I spun off the main/2nd filter (which proved to be totally empty) and started to pump again. Nothing happened. No diesel came out the filter "socket".

I concluded the manual lift pump was not working - or had a major block.

To help things along, I decided to fill the filter with diesel and then screw it in again. Went through the same motions as before, but still nothing at the vent screw.

So, I decided to turn the engine and it started after a few turns - pushing the fuel through, I assume - and seems to be running sweetly.

However, in my mind I am not sure all is well, since I know I am meant to vent the filter, get rid of any bubbles, then I am meant to vent the injectors.

I have done neither.

To put my mind at rest:

- If the engine works and sounds happy, is the job done ? Can I relax ?

- How long to run a diesel engine before I pass the "if it's gonna go wrong" mark ?

Thanks

Graeme

I have never been able to bleed using the lift pump, always turn engine over and it will self bleed. If not starting soon, turn off seacock, and try again. Always works for me, MD 2020 & 2030.

 

[johnalison]

I was told by my engineer that the lift pump (on 20n0s) will only function when the engine is in the correct position, with a yellow mark (unless it has worn away) in line with a mark at the front. If this is correct, you will be able to feel the pump working and in other positions the lever action is much softer to the touch. This is opposite to the older 2000 series which was the reverse in that it would pump in all except one position. I can usually bleed mine without difficulty.

 

[grazbo]

Graeme - you posted a link to here from the other post on leeding filters so I thought I'd try to help.

First, it's essential to turn off the fuel with a valve between the tank and the primary filter. Otherwise the fuel in the feed pipe may drain back into the tank or syphon out of the filter.

Secondly as you've found, it's worth filling both filters with clean diesel before screwing them back on - saves a lot of pumping. I keep a bottle of it on the boat in case I need to do it at sea in a hurry.

Thirdly, my guess is that filling the second filter gave the engine enough fuel to pump the air and diesel through the system itself - by chance did it cough and splutter a bit on the way?

As others mention, using the engine to pump it through is OK if it's quick, but there's a risk of overheating the starter motor (not built to run continuously) and/or of filling the exhaust with so much raw water (the engine isn't firing so it is being pumped in but it doesn't get blown out) that it comes all the way back up into the engine through the exhaust manifold. If water gets into a cylinder then it will bend the con-rod or similar because it is incompressible/not imflammable. Bad news.

It should be possible quickly to pump fuel and air through using the hand primer on the fuel pump, bleeding at the secondary filter first then at the injector pump. My experience suggests usually the injectors won't need to be bled - the engine will cough into life quickly once fuel is in the injector pump. If fuel won't come through, it may be that there is a leak somewhere and air is getting in - a symptom of poor starting too. Worth checking anything you've undone is tight again? Or just possibly the fuel pump diaphragm is leaking - not enough to stop the engine running but enough to stop it pulling fuel through by hand? The latter can cause diesel to get into the engine oil - evidenced by a rising oil level.

Thanks for thinking about my issues... a problem shared....

Luckily I turned the tap off before I did anything....and once I filled the 2nd filter, I had only intended to turn engine over a couple of times to pump fuel through. But after the first turn it just sounded like it wanted to catch - so I gave it another push and with the 3/4 turn it coughed and spluttered and just started to idle nicely.

Thanks for the tip on starter motor and water in exhaust - especially the water in the exhaust cos it sounds nasty, very nasty.

Sounds like I should relax, with no fuel leaks and a nicely idling engine.

From other threads and posts, next time I'll try more crank positions to get lift pump going (I tried a few, but maybe I should have tried in increments until pump felt 'right'). Also read about using oil pump to pull it through - maybe a good option as a back up.

Ta

 

[grazbo]

I was told by my engineer that the lift pump (on 20n0s) will only function when the engine is in the correct position, with a yellow mark (unless it has worn away) in line with a mark at the front. If this is correct, you will be able to feel the pump working and in other positions the lever action is much softer to the touch. This is opposite to the older 2000 series which was the reverse in that it would pump in all except one position. I can usually bleed mine without difficulty.

There was a reflective sticker on the 'wheel' and I tried to line that up with TOP on the crank case - but no idea if the sticker was relevant or just a mark for a strobe.

Anyway didn't work for me, but that is probably because I didn't try the lift pump as I turned the crank. I should have thought of that - makes perfect sense that the pump would feedback.

Good tip for next time - I'll definitely try.

Ta

 

[Graham_Wright]

If that means you loosened the vent screws on both the primary and secondary filters, and then pumped with the lift pump, I think that's your problem. The lift pump (in my setup at least) sucks fuel from the primary filter and pushes fuel into the secondary filter. So if the primary filter bleed screw is open when you're operating the lift pump you're likely to just suck air in through it, which then gets pushed out at the secondary filter.

You need to bleed the primary filter first (via gravity or a fuel feeder pump if your system has one), then tighten the bleed screw here and bleed the secondary filter with the lift pump.

But maybe I've misunderstood what you were doing...

Cheers
Patrick

+1. Nice to have a pushing pump at the tank;- makes bleeding much easier.

 

[ianj99]

+1. Nice to have a pushing pump at the tank;- makes bleeding much easier.

Yep, I fitted an electric one next to the fuel tank outlet. Makes bleeding quick and easy and clicks away quietly whislt the engine is running. ASAP Supplies or Thornycroft Engine sell them for about £40 and just needs wiring to the ignition key.

I've left the engine lift pump connected but I can bypass it with no adverse effects either way.

 

[Stu Jackson]

+1

Always.

We have an electric pump that always runs when the engine is running (ignition key on). The first time i bled my engine I used the finger pump on the primary filter. My finger still hurts and that was 13 years ago!

Fit an electric pump, switch it as you choose, and bleeding will always be easy.

You can get a diesel pump at a truck stop for a lot less than a "marine" pump.

 

[DaveS]

And don't forget the low tech solution - a squeezy in-line manual bulb pump (as per outboard motors) between the tank and the primary filter. Makes life a lot easier when filling the primary filter, bleeding fuel lines etc. It also acts as a useful temporary quick fix if you get a tiny leak in the suction line letting air in and letting the fuel (with the engine off) run back to the tank.