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Old 20-04-2016, 06:15   #1
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Low Hour Volvo Intermittently splutters And Builds Oil Pressure

I have two Volvo 55HP engines in my catamaran. The hours are very low at only 1050. One engine is problematic. It runs smoothly for many hours and then suddenly splutters as if fuel starved. We pump the manual fuel pump around 8 times and she suddenly runs smoothly again for a while. However, on a recent 5 day trip, after running smoothly for many hours, the engine started spluttering again, as if fuel starved. It built up pressure and when pulling out the dipstick, which popped up when removing under pressure and oil spat oil out of the dipstick housing. Furthermore, a lot of oil was seen lying in the bottom under my floorboards in the engine room and the oil level was low. Other than the oil which spat out of the dipstick housing, I'm not certain where the excessive oil that was found under the engine leaked from. We topped up. A colleague removed the spring out of the crankcase breather valve that sits right on top of the rocker cover. When the spring is removed, the engine operated very smoothly and there didn't seem to be a build up of oil pressure. Today, back in moorings, we returned the spring and the oil pressure build-up quickly returned. Whilst the motor seems to runs fine without the spring, Id rather it is returned and there is obviously a problem which I wish to resolve. The oil pressure is symptomatic of worn rings / sleeves etc but this seems very strange on such a low hour motor. Please can the experienced folk out there advise what could be causing this and what process we should follow. Are there a number of possible causes? Thanks for the anticipated replies.

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Old 20-04-2016, 14:52   #2
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Re: Low Hour Volvo Intermittently splutters And Builds Oil Pressure

Did you check the lift pump? A bad diaphragm on a pump can leak diesel into crank case. I don't know volvo but a too common a problem with many engines. spitting oil out of dip stick sounds like level way up or really bad rings. Hope for something simple!
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Old 20-04-2016, 17:53   #3
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Re: Low Hour Volvo Intermittently splutters And Builds Oil Pressure

A bad fuel pump seal or diaphragm makes it seem like more oil, not less.

Blow by is what you have. You don't have high oil pressure, you have high crankcase pressure probably caused by combustion gasses getting by the rings. You could have broken rings from using too much ether. It's unlikely but really bad valve guides can also pressurize the crankcase. It could be just one cylinder, but I doubt it.
And it could be a part failure that might be covered by Volvo. I doubt that, too.
Why do you have blow by with low hours? Running the engine hot. Running w/o oil. Running too high rpm for the engine/trans/prop setup. Many owners like to push the throttles all the way forward. High rpm/load creates much more heat in the cylinders and wears rings and sleeves/cylinders. Regardless of what the owners manual says.
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Old 20-04-2016, 17:56   #4
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Re: Low Hour Volvo Intermittently splutters And Builds Oil Pressure

Find the crankcase vent, I bet lunch it's clogged somehow


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Old 21-04-2016, 09:53   #5
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Re: Low Hour Volvo Intermittently splutters And Builds Oil Pressure

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Originally Posted by Lepke View Post
A bad fuel pump seal or diaphragm makes it seem like more oil, not less.

Blow by is what you have. You don't have high oil pressure, you have high crankcase pressure probably caused by combustion gasses getting by the rings. You could have broken rings from using too much ether. It's unlikely but really bad valve guides can also pressurize the crankcase. It could be just one cylinder, but I doubt it.
And it could be a part failure that might be covered by Volvo. I doubt that, too.
Why do you have blow by with low hours? Running the engine hot. Running w/o oil. Running too high rpm for the engine/trans/prop setup. Many owners like to push the throttles all the way forward. High rpm/load creates much more heat in the cylinders and wears rings and sleeves/cylinders. Regardless of what the owners manual says.
Plus one above. taking the spring out of CPV answered that question. the next step is a compression test, both wet and dry tests to see if its the rings or valve guides. Drain the oil too to see if it has excessive sludge build up..ie..rings/blowby

with bad rings...to a point...she can still start well and run fairly smooth to an untrained ear.

good luck
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Old 21-04-2016, 10:44   #6
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Re: Low Hour Volvo Intermittently splutters And Builds Oil Pressure

I think you found the problem-PCV valve-replace it

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Old 21-04-2016, 11:55   #7
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Re: Low Hour Volvo Intermittently splutters And Builds Oil Pressure

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Find the crankcase vent, I bet lunch it's clogged somehow


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I think he found the problem and doesn't realize it. Sounds as the spring is a relief mechanism on the crankcase vent?
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Old 21-04-2016, 12:01   #8
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Re: Low Hour Volvo Intermittently splutters And Builds Oil Pressure

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I think he found the problem and doesn't realize it. Sounds as the spring is a relief mechanism on the crankcase vent?
I don't know, the spring thing had me confused. I didn't know Marine Diesels had PCV valves, I'm used to just an open pipe plumbed into the intake, maybe with some screen wire in it to act as an oil separator, but no springs
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Old 21-04-2016, 12:12   #9
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Re: Low Hour Volvo Intermittently splutters And Builds Oil Pressure

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I don't know, the spring thing had me confused. I didn't know Marine Diesels had PCV valves, I'm used to just an open pipe plumbed into the intake, maybe with some screen wire in it to act as an oil separator, but no springs
I guess they are no longer our father's diesels?
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Old 21-04-2016, 13:48   #10
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Re: Low Hour Volvo Intermittently splutters And Builds Oil Pressure

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I guess they are no longer our father's diesels?

They are getting just like cars-full of black boxes,etc. Next generation won't be able to work on them.
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Old 21-04-2016, 14:00   #11
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Re: Low Hour Volvo Intermittently splutters And Builds Oil Pressure

Many Volvo models have crankcase breather filters which block up from time to time.
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Old 21-04-2016, 14:27   #12
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Re: Low Hour Volvo Intermittently splutters And Builds Oil Pressure

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They are getting just like cars-full of black boxes,etc. Next generation won't be able to work on them.
Maybe they will. I open a hood on a car and say what the hell is that and could care less. I will have to admit the new stuff runs longer. Just hold onto your wallet when a black box goes bad and they charge $100/hr. for labor.

Back to the OP. I think you may be right on the breather. The spring he was speaking of may be designed to maintain a certain amount of crankcase pressure? I would hope he can get, it is a common problem, replace a $5.00 spring or filter.
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Old 21-04-2016, 17:40   #13
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Re: Low Hour Volvo Intermittently splutters And Builds Oil Pressure

Sorry, not the breather. With the spring gone, allowing excessive gasses to escape as they build, the engine seems to runs normally. But allowing any flow carrying oil vapors into the engine room. Usually a breather has a type of filter that collects any oil vapor and allows it to run back into the oil system. The spring probably closes some simple valve that interrupts the flow of gasses allowing the oil drip off the filter, back where it belongs.
Without the spring, the air doesn't pause and gasses + oil vapor is going into the engine compartment. Removing the spring may have allowed the flow to bypass the filter. Maybe the filter is clogged?
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Old 22-04-2016, 10:39   #14
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Re: Low Hour Volvo Intermittently splutters And Builds Oil Pressure

ALL engines have some "blow by"(aka crankcase pressure. It should normally be very low (measured in mm/in of h2o). It doesn't take much to give the appearance of "high" and it will make a hell of a mess, when coupled with an engine making oil, as you've described.
Either the fuel supply pump (lift pump) is leaking into the crankcase, which is most likely, or the injector pump itself has begun leaking into the crankcase. Most probably it is the supply pump diaphragm.
The oil level increases to the point where the crankshaft is flinging oil around and overwhelming the breather, thus the clogged valve.
You need fairly sophisticated equipment to measure crankcase pressure properly, but this table should give you an idea of what is considered normal for new and worn engines.
Estimates of Maximum Blowby Rates (Actual Flow Rate)
Engine Blowby Estimate Reference
New engine Blowby [dm3/s] = rated power [kW]/180
Blowby [ft3/min] = rated power [hp]/120 [Caterpillar 2000]
Worn engine Blowby [dm3/s] = rated power [kW]/90
Blowby [ft3/min] = rated power [hp]/60 [Caterpillar 2000]
[Barris 2000]
Blowby [dm3/s] = rated power [kW]/60
Blowby [ft3/min] = rated power [hp]/40 [Powell 2007]
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Old 22-04-2016, 11:44   #15
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Re: Low Hour Volvo Intermittently splutters And Builds Oil Pressure

The pressure in the crankcase is cause by a clogged screen in the breather and that in turn is causing pressure behind the pump diaphragm to prevent it from pumping fuel. I expect you have another crank vent other than the one on the valve cover.
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