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Volvo AD31XD Back pressure problem

edwardbcardona

New member
This is my third year with the same problem of oil splashing out of the pipe parallel to the dipstick which is used to make an oil change.
Two years ago when launching my boat I noticed after my first run and after the winter season that oil was coming out from
the dipstick pipe splashing onto the engine cover and the engine itself when using the engine at high revs. I called in the
mechanic /s and all agreed that either a piston ring was stuck or broken or something to do with the bore. The engine still reached its
maximum revs of 3900.
Anyway took the engine out and bought new liners and pistons, oil pump, bearings, oil seals, pressure relief valve, valves, fuel pump,
breather c/w cover etc... Meanwhile took the head, crank and turbo to be checked and all were found to be OK.
basically everything has been replaced with no expense to spare including the injectors which were serviced.
Engine bench tested and worked well.
When the engine was first opened all pistons and rings were in working condition and nothing was broken or damaged.
Then in May of last year I took the boat down and on slightly increasing the speed I noticed that oil was splashing out of the pipe parallel
to the dipstick. Needless to say I heart stopped... not another Summer ruined.
Took the boat up and engine once again was dismantled. Spoke to local Volvo agent who kindly sent one of their best mechanics to inspect
the engine. Pressure test was done, crank checked including cylinder head and all was fount to be in order. Turbo and injectors were also re-
checked. On the Volvo's engineer recommendation I also replaced the some copper guides located in the c/head and seals etc..
Engine was assembled and tested and it ran well. Compression was perfect on all four cylinders.
Yesterday I took the boat down again on the mechanics recommendation I drove it for more than an hour not exceeding 1500 revs.. very slow
indeed. No oil was evident and all went well untill the moment I arrived at my berth I noticed oil bubbling out of the pipe. No not again.
How can it be that back pressure is once again being present in the sump....
I really would like to hear from someone who has passed through the same experience maybe, he may direct me to the probem.
 
Other than excessive blowby about all it could be a blockage in the crankcase vent system. Is there a oil trap for the breather that needs service?
 
Is it possible the engine compartment is not ventilated properly. The air intake should be larger than the vent. Maybe keep the engine compartment cracked and take it for a run and see if the issue goes away? Have you recently upgraded the blower from the bilge?
 
You can get a cheap manometer the engine compartment should have a slight negative pressure .05 inches of water column is all thats necessary. My guess would be the fresh air intake or combustion air intake is not sufficient with the turbo roaring.
 
It has worked without any problem for twenty years before this
Fault surfaced. I thought that with a full engine re condition it
Would be back as new..
It seems I was wrong to assume this.
 
Are you sure that the dipstick is indicating the correct oil level and that the engine isn't over full? What happens if you try to run it with the oil sitting on the low level instead of full level? A competent mechanic should be able to remove the oil filler cap and tell you if there seems to be excessive blowby. If there is, then you know that there is an internal problem. If there isn't then you may have breather issues or oil level issues etc. The other question is why isn't there a cap or similar on the pipe that oil is coming out of? It may be a quite normal thing that is normally suppressed by a cap or similar.
 
There is a plastic cover which sits onto the pipe no screw on but this is blown off with the pressure coming out, hence oil splashing out of this pipe
 
So the engine has run many years previously in exactly the same configuration without this problem? If you have just done a full rebuild it is hard to see how you are still getting excessive blowby unless there has been something changed in the engine. If your compressions are at spec on your fresh rebuild then it is unlikely to be a rings problem. Have you checked that your breather system is unobstructed? I assume that it is one of those Volvo 'can' breather filters? If so, can you feel the blowby with the can removed? Does the problem still happen if you run the engine with the can removed? The first step now is to determine how much blowby you really have. At this stage it doesn't all seem to make sense which usually means that there is some information that is being missed at this point.
 
Start with the valve cover hook a clean hose up to it and see if you can easily blow and suck on the hose. It could be the port on the cover is just gunked up?
 
All oil seals were replaced with original Volvo parts. The breather system is from the rocker cover to the air filter. A small in diam pipe with two rubber elbows..
I intend to make the pipe wider in diam. I was told that these engines tend to suffer hence will do the modification.
My oil extraction tube also had a small plastic cover but was forced out due to back pressure n oil splashing out.
Many thanks to all for your help.
 
You might want to try a modification of the turbo drain elbow. I did this thinking I was smart, and in my case was unnecessary.
In your case it would force pressure on the crankcase to vent via a racor filter, trapping the problematic oil overflow.
This would be useful for you until the source of the problem gets corrected. Your problem has to do with something pressurizing
the crankcase. Maybe somehow the turbos exhaust?
 

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In fact I m in the process of increasing the width of the breather pipe to the air filter similar to the second image. Hopefully this will improve the vent and correct the problem.
 
Has you mechanic removed the oil filler and commented on the amount of blowby? Someone with experience will have a view on how much blowby you are getting. With the oil cap off you can feel whether it is an issue with too much blowby or a blocked breather etc causing pressurisation.
 
There is a bit of blow by... I am using the engine at max 1200 revs to allow the piston rings to bed it n also increasing the width of the breather pipe... Hopefully this will work.
The mechanics have given up on the problem n no one knows what to do next. I m refusing to take the engine out for the third time n spend more money...
 
Some blowby during the run in period can be normal but it sounds like you may have more than normal. If the engine is otherwise performing OK you could get a proper air.oil separator like some Cats use and fit it or mke up a simple one for yourself if you have a few tools.
 
Looking at the schematics it seems unlikely the pressure relief route would be the oil extraction tube unless every other
drain hole was blocked or already flooded. Just wondering if the oil is foaming in the crankcase or if there is a missing baffle ?
My next step would be to connect a hose to the oil extraction tube and run it into a open air bottle to see what it is doing.
This way you can measure and replace the lost oil without mess and see if more run time helps with the pressure build up.
 
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