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Old 05-22-2008
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Post Tutorial: Bleeding your Yanmar Engine

Introduction and Disclaimer:

This is a picture tutorial of how to properly bleed your Yanmar Diesel engine. It will also cover other maintenance issues as well, and is provided with no warranties or thought of accuracy. Use this information at your own risk, and is merely provided to assist others that are like me, a bit mechanically challenged. A good portion of this tutorial is from knowledge gleamed from "You can call me David", and other forum members.

When do you need to bleed your Diesel?

1. When you change out any parts related to your fuel system. Such items may be, fuel lines, various fuel filters, mechanical pump, injector pump etc.

2. When you have run out of fuel and refill after such. Note: If you run out of fuel, you will positively realize the effects of algae and other sludge in your tank, keep an eye on your Rancor fuel filter, and I personally recommend when re-fueling after exhausting your tank - do it with the pump handle set at the slowest pump selection possible as not stir up residual sludge at the bottom of the tank.

3. Anytime that the engine appears to cut-out, as this may be an indication that there is a leak in your system that air can be introduced.


Anytime that your engine is not able to turn over after 2 or more tries, and if you have not done so - locate your water inlet valve for your Engines water intake and TURN IT OFF - until the engine is running. If you do not you RISK ruining your engine as it will be likely that you will siphon water into your engine and since water is not easily compressionable by your engine - you will blow out gaskets, ruin cylinders and if water sits in there - will rust out your engine quicker than you can say duh.

When starting the engine, it is important that the water shut off is done, but also do not try to start the engine for more than 2-5 seconds at a time, without allowing it (the starter) to cool down in between. Trying to make it start by holding the starting button for long periods of time will cause your starter to overheat, and you risk a possible explosion or start of a electrical fire. Patience is the virtue that must be practiced with this procedure.

Starting at the front of your Engine.


In the picture above, you will note one item that probably is not part of your normal Yanmar engine setup. That will be the Facet electric diesel fuel pump. This is a mod I added to the fuel system, to allow me to bleed the fuel lines without requiring me to run up to the cockpit to turn the engine over, or manually depress the mechanical lever on the Yanmar's fuel pump like a crazy man.

This particular pump is easy to install, and when not powered is passive, which means it can remain inline of the fuel line going to the engine as it will not restrict the flow of fuel once powered off. In the installation pictured, there is a push / pull switch that I installed into the bilge (not pictured) that allows for easy access for powering it on and off, when I am required to bleed the system or in the event that the mechanical fuel pump fails underway.

The part is $124 from Napa, and the push / pull switch is about $9. You may also need additional fuel line and adapter barbs if you locate the pump elsewhere. But for less than $170 bucks, less than an hour install time, a worthwhile mod to make to your system.

You will notice that the picture above, also denotes where your water intake valve is. On my vessel it is located forward of the engine. SHUT IT OFF and do not turn back on until engine is running.

I also annotated where the bleed valve for the Rancor is. Water is heavier than fuel so it is important to check the Rancor filter to make sure that the bottom of the clear portion of the filter is not filled with debris etc. To drain any water there is a little twisty at the bottom that you unscrew. Unscrew and keep a fuel/oil mat or rag underneath, and it will drain. When red dyed diesel comes out - screw back in.

At the top of the Rancor is a vent valve. I find with the electric pump installed there really is no need to open this, but officially, this is the first place to start.

Starboard side of the engine:


In the picture above, you will see that I have annotated fuel related components. Starting aft (the left in the photo), we see the Yanmar mechanical pump. This is the part I replaced because the outlet side was leaking and the outlet screw piece was stripped on the original part. The part is around $70-130 depending on your make and model of your diesel. MAKE SURE, you get a gasket with the new part as they do not come with one. The gasket is around $2, and you can not re-use the old one. If you simply bolt it on without one, you will find that your engine will run well once bled but will leak oil like a banshee into your bilge - and it won't be long before you get oil warning lights and alarms.

Forward in the photo (to the right) is the injector and it also has a small fuel filter as well, located at the bottom of the unit. If you are changing out your Rancor, this would be a good time to replace this one as well.

In the photo I have numbered the bleed points for quick visual identification.

NOTE: Place a fuel / oil absorption mat or rag under the areas as you bleed to catch fuel.

To pressurize the system, manually cycle the mechanical fuel pump lever up and down or turn on the electric pump (if you have installed one). Starting with #1 to #3, one at a time, crack them open using a crescent wrench of proper size. When I state crack, just enough to unseat the bolt. You will see air bubbles escape through the fuel. Keep cycling the fuel pump lever until nothing but fuel comes out. Once you have nothing but fuel coming out - tighten the bolt - be careful not to over tighten them as if you strip them, it means replacing the part.

#1 through #3 are part of your low pressure fuel system. If these are bled successfully, most of the air that you should be worried about will be in your HI pressure system, which I will cover next.

HI Pressure System.

In the same picture above, note where the HI Pressure relief valve is. WARNING - wear protective goggles and loosen slowly as fuel can spray when under pressure and cause injury.

Use a properly sized crescent wrench or flat head screw driver and crack this nut ever so slowly. You will get a bunch of air escaping and remember this is under pressure. Remember you have to manually depress the fuel lever to pump fuel or rely on the electrical diesel pump if you have installed one. Be patient as it will take some time. Use a large fuel / oil absorption mat under it as more fuel than not will come out with the air. When no more air is escaping re-tighten.


Next locate the other hi pressure relief point on the starboard side - forward of your engine. This one is illustrated in the photo above and will be on the top right of the photo. Using a phillips head screwdriver or crescent wrench - repeat the same process you did with the previous one.

Now, we need to move to the port side of the engine. Repeating the same processes as before, and release the air out of the fuel intake of the cylinders (again HI Pressure).


Locate the three HI Pressure nuts on the port side of the engine as per the above photo. Notice that I annotated the LO pressure side as well, you will most likely not need to touch these as they are fuel return and do not impact air in the fuel / starting or engine running problems. Repeat the same process we did on the previous ones, starting with the most forward one (#1) and working your way back to #3, ONE AT A TIME. Remember - this is the HI Pressure side and protective goggles are suggested.

Wahoo! Am I done now?

Maybe. Now is time to crank the engine. Keep the water intake valve SHUT for now. Try starting the engine.

1. It doesn't start after 2 tries.

Repeat the above process on the high pressure locations only. Start on the starboard side of the engine and work your way around. We may need to repeat this process several times as you will be surprised how much air is in the system.

2. It runs. Turn on the water intake valve now. Check to make sure your are getting water out of your exhaust. Now put your engine under load by putting your boat in forward or reverse and give it throttle. If you are tied up at the pier, prior to make sure your lines are properly properly secured. Run under load for 5 minutes or so.

If its hums along, you may be done, but if the engine sputters and dies out. Repeat the process again, shut off the water intake valve down below, and bleed the hi pressure locations described starting on the starboard side working around to port.

So, there you have it. A pictorial tutorial that should allow the true mechanic in you to come alive.

I hope you find this helpful and that the mysteries of "bleeding" a diesel are de-mystified. You should probably print this out and keep it on your boat in the event this happens while you are underway.

NOTE: I may have made some technical labeling errors in some areas, and will correct as needed, however - this document gives a very elementary overview of how to do the task.
-- Jody

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Last edited by artbyjody; 05-23-2008 at 10:10 AM.
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