Priming Diesel after filter change in an OM366LA


Gotta Be Nuts
Not sure if this is done in the trucking world but on the boat I installed a vacuum gauge after the filters. It has a sweep arm that stays with the highest reading so when I do an engine check I can see if the filter needs replacing. Better than just replacing the filter on a schedule and safer to boot. Racor offers this as an add on for the marine filters.


I've done some fancy plumbing so that I can transfer fuel between the two tanks through the filters. Ive picked up a tank or two of bad fuel and have saved a fair bit by filtering the 160 odd litres of fuel through the filters which cost me $5 a shot - I carry six of them and a couple of the glass bowls as well just in case. I tend to only change the filters when I notice performance drop on the hills, and I can start the electric pumps to push a bit more fuel through if I need to, but it doens't take long to change the filters. I would recommend it for anyone doing any remove traveling.

The other thing I have if I suspect the fuel is dodgy if a water separating funnel - it works great and the look on the servo owners face when you hand him back all the water out his diesel tanks is worth it :) I have the highflow version and it can handle the normal flow rate of a servo fuel pump.



Gotta Be Nuts
Hey Iain, what you describe sounds very close to what I did on the boat. I have 2 separate Racors with valves to switch from one to the other. If the engine starts to stumble I quickly swap to the other filter while the engine is running. I also have a "polishing" pump that can either just recirculate or transfer the diesel from one tank to the other. Works very well. We also pre-filter using the same filters you are using. One thing to caution people with those filters though is the "water block" wears out with use. The company recommends putting water in them every now and then to check if it is still working. In Asia we got fuel at times that looked a bit like coffee...


Tea pot tester
One thing I'm sure everyone does is fill up at the end of the day wherever possible?

AFAIK since the recirculated diesel ends up warming the tank and contents, if you leave it to cool when empty you get the condensation out of the air collecting on the metal sides and running down. Over time that builds up.

Filling up at the end of a run before parking up would be with possibly cooler diesel, and then there will be less air in there, and so less condensation.



Gotta Be Nuts
Another good thought about the condensation, thanks for that idea. We just last evening completed our run with our "new" truck from Florida to Vermont. All went reasonably well except for the fact that the existing fuel tank had junk in it. Had to replace/clean the filters twice in parking areas on the drive up. Bit of a pain, but now we are here I am going to begin the build and one part of that is the upgrade of the fuel system.


hi, brothers, I changed fuel filter on my U500, found so hard to tighten the filter cap back to the housing totally, I used over 40 N.M torque onto the hexagon bolt on the top, almost broke it, there's still one thread remaining, which makes a gap between the cap and the housing, I am confused...
I am definitely sure the filter element is the correct type, and the seal ring wasn't twisted. Is it caused by the air pressure inside the fuel filter housing?
And of course I can't start the engine now, though I pressed the pump button on the water/fuel separator 150times.
the engine type OM906LA, model 902.912
I think fuel comes from the tank to the water/fuel separator---prefilter---fuel filter----fuel pump--injector, am I right?
the problem is, so hard to get help locally, I called some diesel truck workshop, their answer is towing the truck to them. I called one mobile mechanic service, got answer is take off the air intake, and spray some WD40 into it, then start. Is this the right way to solve the problem?
The manual shows after fuel filter change, it is auto bleeding.
thanks guys.


Expedition Leader
Make sure it doesn’t have a grid heater before squirting anything down the intake. My 926 definitely has a heater and if you hit it with ether bad bangs can happen. I would not recommend it and if you must stick to something like WD40 (propane propellant) rather than ether.

Also make sure the batteries are fully charged. If the voltage is dropping too low due to prolonged cranking all sort of crap happens with the electrics.

I am not that familiar with your engine but most modern diesels will bypass excess diesel back to the tank.You may be able to pull the return line off the tank and keep pushing the priming pump until fuel comes out. That is where you also can check for air getting in the lines. If you have bubbles coming out the return you have a problem. Also there is a check valve somewhere in there I think. To stop bleed back. Make sure it is not blocked or constricted. I think there was an issue with some filters playing silly buggers with that valve. But do your own research. My memory is not the best.

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Tea pot tester
giantiger do you mean you have not tightened the fuel filter to get it to seal? So diesel is leaking out and air in? Maybe you cross threaded the fixing bolt?


giantiger do you mean you have not tightened the fuel filter to get it to seal? So diesel is leaking out and air in? Maybe you cross threaded the fixing bolt?
I am sure the thread is good, not crossed tighten. After I hand tightened the fuel filter cap, then used wrench tighten it, since I don't have that fittable size torque wrench for the hexagon bolt on top of the filter cap, I can't monitor the torque specifically. According to my poor experience onto other Merz gasoline cars oil change, I can feel what is 25N.M- hand tighten the cap, and use torque wrench for one more round, that is 25N.M. I put absolutely over 25 N.M onto it, there's still a gap between the cap and housing till the plastic hexagon bolt almost got broken. I can't see any diesel got seeping out, the o ring seal is good--I removed the cap, and tighten it, did this like 8 times, the thread on the cap is pretty good so far. Now I put the old seal ring and filter back, same story.

This is something confused me. possibly the resistance caused by air pressure inside the fuel filter housing, find the bleeding screw, release air, then tighten the filter cap? I don't know where it is...
from the picture attached you can see how hard force I put onto the hexagon bolt.
hereby I must say thank you very much to warmhearted Charlie, he explained quite a lot on how to priming the engine over the emails, like push the Racor button on the water/fuel separator 100 times, I tried, but just not working. I tried to find the bleeding screw on or near the fuel filter housing, or the fuel supply hose to the fuel pump, but the air intake and the main frame blocks everything, I can't see nothing-most important is, I don't know much, if some mechanic mentor me, believe me, I will be a good learner.
I called local workshops such as Firestone, and three truck workshops, their answer is "you have to tow the truck to our workshop, we don't provide to door services", " I am so busy, sorry" etc.
I also contacted a famous Mog specialist in Colorado, he would charge me $150/hour-- from and back to his location, plus accomodation, flights, parking in the airport, etc. I totally agree with his quote which is fair for his proficiency, wallet is too humble...

Today I am going to call other workshops to see if any mechanic would come for help. and towing the Mog to a workshop would be the last stupid option for a simple priming issue.



Have you tried installing the filter full of fuel? then pump the manual pump. Access looks a little tricky, may be messy.


nope. I didn't fill fuel into the filter, since the manual doesn't say so, and I changed it at midnight, hard to see well. After the cap being tightened, I just went to sleep. The next morning, I found the engine failed to start, only cranking. Then I tipped the cab again, saw the filter cap doesn't sit tightly onto the housing, so I untightened it, and put the old filter and o ring back, tighten again, same--got a gap between the cap and housing.
That's it.
Today I just drove to some diesel workshops nearby for help, they don't have "to door mobile services", they request me tow the mog to them for engine priming.........I don't get it, for a simple engine priming, towing? dumbbell.


This afternoon I got a mobile mechanic come to help : remove the fuel filter cap, take out the filter element and the receptacle, I kept turning to ignition, let the air bleed out from the housing, it could be seen there were so many bubbles come out of the housing through the fuel, then he kept spraying the engine starter fluid into the air intake from time to time, I kept turning ignition let the engine cranking. After 10 times maybe more attempt, the engine cranking and cranking, finally got it started!
lessons learned!!!! Newbie paid the tuition and made progress!
Better than towing to workshop!!!
Regards! brothers!