Hydrolocking through too much oil?

[Arcady]

Technically not hydrolocking, as it’s the engine oil I’m thinking about. Maybe oleo-locking??

Within the last few weeks we’ve experienced a problem whereby after a lively sail we’ve been unable to crank the engine, despite a good (brand new) fully charged battery. Typically it’s been after a downwind passage with much rolling and some surfing, or when sailing hard on the port tack (which puts our exhaust underwater). My initial thought was hydrolocking due to back pressure in the exhaust system, but it’s not been a problem in previous years.

Today I checked our engine oil level and found it a - not huge - but noticeable amount above the maximum notch. The engine runs fine and starts perfectly before sailing, but I am wondering whether when heeled, excess oil might find it’s way into a cylinder somehow. Has anyone else experienced this? Is it a documented problem? The engine is a Yanmar 4JH80 and we’ve been heeling as much as 25 to 30 degrees immediately before experiencing this problem.

I haven’t dismissed conventional hydrolocking as a possibility, but as stated it’s not previously been a problem, and this is the first time we had too much oil in the engine.

Thoughts and suggestions would be welcomed!

 

[mikegunn]

Did you consciously overfill the engine’s sump with oil?
If when you did the last oil change the sump was only filled to the upper mark I would suggest that there may be seawater as well as oil in the engine. Oil, being less dense than seawater will float on top of any water in the engine’s sump. The easiest way to check is by extracting a sample of the sump’s contents using a vacuum pump with a tube of small enough diameter, to be inserted through the dip stick tube to the bottom of the sump.
It is conceivable that sea water has entered one of the cylinders through an exhaust valve. Attempts to start the engine might push seawater past a piston and its rings into the sump.
I would suggest that you don’t attempt to start the engine until eliminating this possibility. Should an engine be fired up with water in a cylinder’s head the resultant hydraulic forces can be sufficient to bend a con rod. That can be expensive to rectify.
Mike

 

[AntarcticPilot]

It may not be relevant, but my Volvo 2003 won't start if overfilled with oil. No idea why - it turns over perfectly freely - just won't start until the excess oil is removed!

 

[Arcady]

Did you consciously overfill the engine’s sump with oil?
If when you did the last oil change the sump was only filled to the upper mark I would suggest that there may be seawater as well as oil in the engine. Oil, being less dense than seawater will float on top of any water in the engine’s sump. The easiest way to check is by extracting a sample of the sump’s contents using a vacuum pump with a tube of small enough diameter, to be inserted through the dip stick tube to the bottom of the sump.
It is conceivable that sea water has entered one of the cylinders through an exhaust valve. Attempts to start the engine might push seawater past a piston and its rings into the sump.
I would suggest that you don’t attempt to start the engine until eliminating this possibility. Should an engine be fired up with water in a cylinder’s head the resultant hydraulic forces can be sufficient to bend a con rod. That can be expensive to rectify.
Mike

I thought I had been pretty careful when filling with oil, but it’s possible I measured the dipstick too quickly after adding oil and before it had all drained to the sump.

We’ve had an engineer aboard who checked the oil (and other things). No emulsification, still pretty clear golden colour and although he noted the modest excess of oil, he wasn’t too worried about it.

The engine starts fine and runs well, and undoubtedly will until the next incident! It’s a bit of a mystery,

 

[mikegunn]

Glad you’ve eliminated hydraulics as the cause.
One further question. Is the failure to crank the engine because the starter motor won’t function?
Mike

 

[Arcady]

Glad you’ve eliminated hydraulics as the cause.
One further question. Is the failure to crank the engine because the starter motor won’t function?
Mike

No, I don’t believe so. I can start it repeatedly and easily every time on the mooring or when calm. It’s just after sailing as described earlier.

 

[footsoldier]

Today I checked our engine oil level and found it a - not huge - but noticeable amount above the maximum notch. The engine runs fine and starts perfectly before sailing, but I am wondering whether when heeled, excess oil might find it’s way into a cylinder somehow. Has anyone else experienced this? Is it a documented problem? The engine is a Yanmar 4JH80 and we’ve been heeling as much as 25 to 30 degrees immediately before experiencing this problem.

I am not familiar with this engine and I have never seen any drawings of its internal layout.

But what you say above is - in theory - feasible. (Although I have never heard of it occurring).

You do not say - or I have missed it - that you have removed oil to bring it to its correct level. As a first step I would advise you to do so. There are sound reasons why all engine manufacturers advise against over-filling. It may be that for marine engines you have identified another one.

 

[Ammonite]

Doesn't sound like an issue with the oil to me. It can happen when you lie an outboard on its side the wrong way but I'm assuming you are not sailing the boat on its side. Most engines are designed to cope with something like 30 degrees of heel, although that's with the engine running. Stopped it would be higher than this.

If it's not happened before, do you have a vented loop in the raw water circuit that has become blocked? If this is the case it could be siphoning water while heeled and back filling the exhaust. It would be helpful if you could add a sketch of the raw water intake and exhaust arrangements relative to the waterline. I'm assuming the engine is probably well below the waterline given its size/power?

 

[Biggles Wader]

If by "unable to crank the engine" you mean you press start and nothing happens, the engine does not turn or make any attempt to turn then I would be looking at the electrics. Maybe a loose connection or bad earth or a faulty starter motor which is intermittent and only becomes a problem after bashing about to windward.

 

[Ammonite]

If by "unable to crank the engine" you mean you press start and nothing happens, the engine does not turn or make any attempt to turn then I would be looking at the electrics. Maybe a loose connection or bad earth or a faulty starter motor which is intermittent and only becomes a problem after bashing about to windward.

....which then fixes itself and works repeatedly until you go sailing again. Seems very unlikely

 

[Arcady]

If by "unable to crank the engine" you mean you press start and nothing happens, the engine does not turn or make any attempt to turn then I would be looking at the electrics. Maybe a loose connection or bad earth or a faulty starter motor which is intermittent and only becomes a problem after bashing about to windward.

No. The engine will make perhaps a half revolution and then stop.

 

[Arcady]

If it's not happened before, do you have a vented loop in the raw water circuit that has become blocked? If this is the case it could be siphoning water while heeled and back filling the exhaust. It would be helpful if you could add a sketch of the raw water intake and exhaust arrangements relative to the waterline. I'm assuming the engine is probably well below the waterline given its size/power?

We do. It’s a Vetus type anti-syphon loop. I’ve checked it and it’s clean and apparently functioning.

 

[Arcady]

You do not say - or I have missed it - that you have removed oil to bring it to its correct level. As a first step I would advise you to do so. There are sound reasons why all engine manufacturers advise against over-filling. It may be that for marine engines you have identified another one.

We’re about to do that. We are currently cruising so I don’t have the usual extractor pump aboard - but we’re in a marina with full boatyard support. I plan to have the yard remove some oil (which will also let us sample the bottom of the sump) and reposition the exhaust outlet from under the transom to exit higher up, through the transom and fitted with a one-way flap.

 

[mikegunn]

Personally, I would resist making too many changes otherwise you will never know what fixed the problem. I suggest one step at a time. From your account it would appear that the sole difference between the engine behaving and misbehaving is the oil level. Sort that out and see what happens.
Mike

 

[MoodySabre]

Moodys have the exhaust below the transom with no problem.

Do you sail with the boat in gear? This might be causing the gearbox to lock up. I know that’s not the engine but all things need to be eliminated.

The starter motor is my prime suspect. Try turning the engine over a little with a spanner to see if that frees it up

 

[Ammonite]

To lock the engine with oil it would need to be grossly overfilled, although this did happen to me on a holiday delivery job at a garage in my teens. One of the mechanics had removed a broken dipstick and replaced it with a shorter one off another model and stupidly reconnected the warning light. Another mechanic topped up the oil for me (from my hazy memory it took around 3 litres) and I came to a grinding halt a few yards up the road. However I'd be surprised if this is the issue in your case given it normally takes less than a litre to raise the oil from min to max, dependingon the size of the engine but it is possible. How far over the top mark was it?

 

[nevis768]

I had to deal with an over filled MD2030 which caused excessive smoke at high revs, rectified by removing the extra oil. No starting issues despite there being a pint of extra oil in it. So, I doubt it's too much oil in your case.

 

[thinwater]

Is something getting wet, resulting in insufficient voltage to the starter to get it over the compression hump? Something different about the starting battery side from the house side?

The oil level is most likely a red herring (not a all related). In post 4 water in the oil was ruled out.

 

[Arcady]

Personally, I would resist making too many changes otherwise you will never know what fixed the problem. I suggest one step at a time. From your account it would appear that the sole difference between the engine behaving and misbehaving is the oil level. Sort that out and see what happens.
Mike

Yes - I agree that methodical elimination of possible causes one by one is the best way to do this. However, our next leg might not find us in such a well-equipped marina.

 

[Arcady]

To lock the engine with oil it would need to be grossly overfilled. How far over the top mark was it?

About 10 mm.

I had also wondered about fuel. It’s common rail diesel. Is there any way that fuel in the common rail could get into the cylinder(s) when not running??