Low oil pressure-Heavy Blow by causes oil loss-and Smoke!

[Ken Fry]

Originally Posted by Scubaseas

If you feel no pressure with your thumb over the hose the crank pressure is probably OK. Most people can feel 1/2psi or so. But to measure blowby you need either a leakdown tester and an air supply (and know how to use it) or a manometer to measure how much pressure you are building up.

A leakdown tester is particularly nice, because you can tell by listening where the air is leaking: intake valve, exhaust valve, rings. Then you know what you are getting into before you tear things apart.

[Scubaseas]

https://dieselpartseurope.com/media/...-M42600_en.pdf Page 13 "bonnet" part images #5 and #18 are probably interchangeable with your engine. If I am wrong and your problem is too much blowby (which a manometer would tell you) you can probably get around it by moving the breather housing from where it is now back to the top of the valve cover. Then move the cover plate to cover the oil pump.

Note my theory only works if the oil pressure relief valve in the oil filter housing is stuck closed not stuck open.

[Rotten Ricky]

Gauges are great as you can tell that there is a future problem developing, but as you are not always watching your gauge, always install AUDIBLE alarms for water temperature, oil pressure and voltage. They will alert you instantly that there is a problem that could otherwise create much greater issue if not noticed. You might include one on your transmission as nothing kills a tranny quicker than excessive heat.

Audible alarms are inexpensive and usually easy to install, so please include.

Cheers, RR.

[Ken Fry]

Yes indeed!

[Scubaseas]

Keep in mind the oil pressure switch usually comes on after the engine seizes as most are set to turn the light on at 3.5psi to 7.5psi. They are designed to let you know if you have oil pressure after the engine starts. You can not rely on the light or any sound alarm to save you once you loose pressure when running. Diesel with good splash lube in a boat might tolerate it once in a while but most cars cruising at speed won't. Gauges are good.

[Juggerknot]

Originally Posted by wingssail

I am doing research in old threads and elsewhere but I'd like any ideas you guys might have.

My Yanmar 3JH with 6500 hours has been running fine since earlier this year when I changed the rear main seal and the oil pressure has been fine since I changed the oil pressure sending unit (and installed a secondary mechanical gauge).

Today when we advanced the throttle to 2500 to motor up the coast we got massive smoke (oil smoke, not steam, not carbon) out the exhaust. Of course we slowed to idle.

We found oil had also flowed out the dipstick, the oil level was down about 1/2 quart, and clean.

But oil pressure was OK, and at low speeds there was no smoke and no oil loss out the dipstick or anywhere else.

Advancing the throttle again the problem re-occurred and now the oil pressure became low, almost zero.

During all of this the engine continued to sound perfect, smooth (as smooth as any three cylinder engine sounds) started easily, idles smoothly. No excessive or strange noise.

I thought of a broken ring allowing oil to be burned or a damaged valve guide allowing oil to go down the valve, but neither of these would result in loss of oil pressure.

So we're back at the dock. My plan for next moves is to check the oil breather system, remove the injectors and check for low compression or an oily injector.

Any other possibilities?

If it is a stuck ring or lifter, fill a fresh fuel filter with seafoam and run it through, it'll clean and free things up as well as lubricate your pump and injectors.

[Nicholson58]

I suggest you enlist a reputable diesel mechanic. Lots of maybe possibilities have been suggested but you may be in a position to avoid a really huge bill by acting now.

[Ken Fry]

Originally Posted by Scubaseas

Gauges are good.

Rotten says "Gauges are great". I might say gauges are wonderful.

However, in the aircraft industry, where engine failures can mean dead people, there are an abundance of warning lights and sounds in addition to gauges. They are proven to help pilots react more quickly to abnormal and emergency conditions. Same is true in industry: lights and horns help people react to conditions more quickly, because invariably the machine operator is busy doing things other than staring at a particular gauge that could be indicating an impending failure.

[CassidyNZ]

Originally Posted by Scubaseas

Keep in mind the oil pressure switch usually comes on after the engine seizes as most are set to turn the light on at 3.5psi to 7.5psi. They are designed to let you know if you have oil pressure after the engine starts. You can not rely on the light or any sound alarm to save you once you loose pressure when running. Diesel with good splash lube in a boat might tolerate it once in a while but most cars cruising at speed won't. Gauges are good.

I have on several occasions been warned of irregularities in pressures/temperatures on my engine long before failure occurs.

On one occasion I had a very rapid loss of oil from a failed frost plug in the back of the engine (other threads posted posted by me outlined this failure) and the oil pressure buzzer alerted me to imminent failure of the engine.

On more than one occasion the temperature buzzer alerted me to an imminent overheat condition which in most cases were the result of failed raw water impellers.

With all conditions having been corrected according to normal convention, the engine continues to provide excellent service. To say that once a buzzer is heard it is too late and a buzzer only comes on after the engine seizes is just plain wrong.

The premise that a buzzer alert is “too late” implies that in order to be safe from engine failure, one must have one’s eyes permanently glued to the gauges which is also just plain wrong.

To suggest that “splash lubrication” will prevent engine failure caused by a loss of oil pressure (which the alarm senses) even for a few moments is also just plain wrong. Splash lubrication will maybe help a piston seizure for a short while but in no way protects crank or cam bearings.

I have for several decades, both in my vehicles and my boats, depended on alarm buzzers precluding engine failures and that reliance has most always been rewarded with a timely notification.

[Scubaseas]

Originally Posted by CassidyNZ

I have on several occasions been warned of irregularities in pressures/temperatures on my engine long before failure occurs.

On one occasion I had a very rapid loss of oil from a failed frost plug in the back of the engine (other threads posted posted by me outlined this failure) and the oil pressure buzzer alerted me to imminent failure of the engine.

On more than one occasion the temperature buzzer alerted me to an imminent overheat condition which in most cases were the result of failed raw water impellers.

With all conditions having been corrected according to normal convention, the engine continues to provide excellent service. To say that once a buzzer is heard it is too late and a buzzer only comes on after the engine seizes is just plain wrong.

The premise that a buzzer alert is “too late” implies that in order to be safe from engine failure, one must have one’s eyes permanently glued to the gauges which is also just plain wrong.

To suggest that “splash lubrication” will prevent engine failure caused by a loss of oil pressure (which the alarm senses) even for a few moments is also just plain wrong. Splash lubrication will maybe help a piston seizure for a short while but in no way protects crank or cam bearings.

I have for several decades, both in my vehicles and my boats, depended on alarm buzzers precluding engine failures and that reliance has most always been rewarded with a timely notification.

Switch closes at 3.5psi to 7 psi. Run engine at 3000 rpm with 10 psi oil pressure which won't make the light come on but it won't do the engine any good either. If you are low on oil you can have a situation where you have enough oil pressure to keep the light off but not enough pressure to adequately supply your bearings. So even though you have a light and a buzzer you can ruin your motor and never know about it until after the damage is done. If you had a gauge it may be a different story.

What I am saying is a lot of time when an engine seizes from lack of oil or lack of oil pressure the light doesn't come on until well after the damage is done or on many occasions the light comes on seconds after the motor locks up. A rapid loss of oil will set the alarm off in time. Very low oil pressure for extended periods won't and without a gauge you would never know until after you have done damage.

Splash lube in regards to cam shafts depends a lot on where your cam is located. If you have OHC no it won't work at all. I am not saying you can not run a bearing with splash lube (unless it's ball or roller and the motor is design for splash lube (see Sabb Motor or pretty much any lawn mower) I am saying having oil splash around helps mitigate any instant damage from loss of oil pressure. If a motor is designed to operate with a minimum oil pressure it should have that pressure or you start to damage the bearings.

I appreciate your anecdotal evidence. Mine is based on 50+ years as a mechanic and busy repair shop owner and people telling me the oil light came on AFTER the engine seized which has happened about 20 times if memory serves and that's just the seized motors. I would estimate I have seen maybe 200+ seized or severely damaged engines and do not recall any of them where the customer said the oil light came on until after it seized or started making noises. Just saying. Most motors will start to knock long before the light comes on. Granted a car/truck/suv engine is under a lot more demanding service than a boat but a gauge will tell you more than a switch with a set limit of 3.5 to 7 PSI. Not saying an OP switch is useless, I'm saying a gauge works better for me and that there are times when an OP switch only tells you that you have a problem after the damage is done. OP switches are great to tell you that you have oil pressure after you start the motor. They don't tell you w hole lot about what your oil pressure is after the motor is running unless that oil pressure is below the switch set level.

[markic]

To dump oil out the dip tube means something is pressuring the crankcase.

As its only above 3000rpm and you get a drop in oil pressure when it happens and it stays low when revs are reduced Id chase the following,

Im chasing over filled crankcase. The oil pump relief valve wont cause the crankcase to pressurise as the to total oil volume in the sump etc dosent change do to a stuck relief valve etc.

Blow by doesnt just happen at high revs and then go away, it will increase with revs and load though but not an instant change. I would how ever make sure any crankcase ventilation hoses, pcv valves etc are clear. I'd even run with the crancase vent line to a small catch bottle or similar so there is no chance to build crankcase pressure.

I think you mentioned a rear oil seal issue earlier, crankcase breathing or lack of is probably what cased this, age and blow by also had its place here

Dump the oil and do an oil and filter change, take a sample for testing, only fill to between the upper and lower marks on the dip stick, NO higher.

I believe that your crankcase is overfilled and the higher revs are thrashing the oil to foam, the increased volume of the aerated oil is why you are getting the crankcase pressure and purging oil out the dip tube.

Also the air will stay in the oil for quite a while as small bubbles, you can compress air so cant get oil pressure which is why you have a drop in oil pressure. Let the engine sit for 30min shut down and I bet your oil pressure is back to normal or at least significantly better, till you raise the revs and foam the oil again.

An oil analysis as mentioned earlier is deffinatley worth the $30 to check for oil diesel dilution which can be the cause of the over filled crank case and to check if any damage has been done. Also diesel foams a lot easier than oil so if the level is high due to dilution I'll bet my left coconut this is your problem.

[CassidyNZ]

I’m not going to perpetuate this discussion except for two points.

1 - my experience is not “anecdotal” - I too spent 50 years of my life in automotive and heavy transport workshops.

2 - My present car which is a high-end performance model, does not have any gauges at all, it only has sensors that report things like low oil level, low oil pressure, low coolant level, high coolant temp, low charge rate, tyre pressure variations. Funny that.

[Scubaseas]

Since the topic is about oil pressure not TPS monitors, coolant, coolant temp, oil level etc. maybe I could make you happy by reparsing my statement to say lights are good but gauges will give you more information. If you need to be right, fine you're right.