runaway engine

J

joeh

Well-Known Member
Joined
4 Feb 2003
Messages
204
Location
asia
Visit site
hi all
over the weekend the green monster decided to pick up revs and refuse to stop after boat has parked. lots of white smoke from exhaust and leak of lube oil from filler cap and could see more lube under engine. it stop after closing fuel valve.
any expert diagnosis before i have time to look at it tomorrow pls ? thks.


<hr width=100% size=1>
 
oh dear. White smoke suggests water suggests blown head gasket. Oil leak suggests crankcase over pressure, again cylinder head gasket. The over run could be worrying as a diesel can be fed with sump oil blowing past the pistons or via a bad head gasket, depends on the engine design. The best non intrusive test is a compression test. Good luck

<hr width=100% size=1>
 
Caused by over pressure in the crankcase forcing oil into the combustion chamber, which the engine then runs not very happily on. Oil below engine, and at the filler means the pressure was sufficient to blow past the seals.

Likely Causes: worn engine suffering 'blowby' where combustion gasses are leaking past the rings into the crankcase and building up pressure - can also be caused by damaged or broken rings.

OR Blocked crankcase breather allowing pressure to build in the crankcase. (Some Volvos have a very small breather which is easily blocked).

OR Damaged head gasket allowing gasses to escape in to the tappet chest.

Most engines vent the crankcase back in to the inlet manifold so that crankcase fumes are burned off. High crankcase pressure blows lube oil in to the inlet manifold, effectively giving the engine a second source of fuel.... I know of an old van which used to do this, and ran for quite a while with the breather tube disconnected and emptying into an oil can, which was then returned to the sump every 50 miles or so. It even passed its MOT ! Kept going for over a year until the owner finally saw sense...

A simple (if messy!) test for excess crankcase pressure: block the breather system, remove the oil filler cap, start the engine. Block the filler orifice with a rag and rev the engine to around 2000rpm for 10 seconds, then release it. If there is a whoosh of air (fumes) from it, then that confirms excessive pressure build up. Check that the breather system is clear and functioning normally. If it is, the engine has a major problem as outlined above.

Dont waste time doing a compression test - it very rarely tells you anything about this kind of fault. Basically if the breathers are good then the engine needs to be stripped and examined, and is probably BER.

<hr width=100% size=1>
 
Does the lube oil smell of diesel? Are there any fuel pipes INSIDE the engine caseing (Lister) ?

If either answer is yes, then you have oil dilution from. Smoke from burning oil, Oil leak from what is effectively an "overfilled" sump.

First change the engine oil and retry engine. If it does not smoke and leak oil, you have to find the fuel leak. If all the fuel pipes are external you coudl have a badly worn/faulty lift pump or more rarely injector pump IF the injector pump is directly bolted to the engine rather than being driven through a little "shaft coupling".

Tony Brooks

<hr width=100% size=1>
 
i found 3 litres of diesel in the lube. changed the oil seal at the fuel injection pump ( seal is 3 years old ) and changed the lube. engine started and ran ok . will be monitoring closely.
 
Joeh
I had this problem with my Yanmar 1GM10 last year.
The cylinder head gasket had failed - the white smoke was from the coolant and the engine ran on by burning engine oil.
The only way I could shut the engine down was by the operating the pressure release valve on the head.
Rebuild of the head and having the injectors serviced - she now runs as sweet as a nut.
Phil
 
You were lucky. The early Golf diesels would sometimes do this when badly worn or if the oil level was too high and continue running at high speed even with the fuel turned off. In a car, unless you stalled them by braking to a stop in, preferably, top gear they would self destruct. I don't know how you could stall an engine in a boat unless you can find a friendly fishing line wrapped around the prop!
 
Whilst I have no experience of run away diesels, I believe the following should work. Basically, fire cannot burn without oxygen. So block the air inlet tube with damp cloth, pushed down hard, past any breather inlet. However, do remember, if there is a risk of the engine breaking up, get out quick. Some years age a steam turbine went out of control and killed several operators. It may also be possible that a con rod could go through the hull.

When my oldest daughter was a baby, we booked a self catering holiday in a wing of a large newly thatched cottage in Devon. (Probably worth nearly a million at today's prices). The owner had laid a fire in the grate, but had not realised that the jackdaws had filled the chimney up to the top with dry twigs! While my wife changed the baby upstairs, I put a match to the fire. It took off with a huge roar. As the chimney had a slate cover, all the sparks landed on the thatch. The dark rain clouds didn't drop any rain on that day! I ran to the stables, gathered some heavy cloths, soaked them in soapy water, and blocked the chimney. The fire stopped immediately. The fire brigade arrived 14 minutes later. I have used the same technique at home.

Philip
 
on hindsight i could have stop engine by lifting the decompression lever as scubafill had earlier suggested
 
Thats (one of) the problems with internal fuel pumps. If the lube level is too high it has the same effect as the causes I outlined, and lack of space in the crankcase creates the high pressure effect.

Good luck! Lets hope that seal was the cause.

Decompression levers are invaluable in these circumstances: but as someone said - if you cant stop the thing - get away fast! When (not if) - when the engine starts to break up it is extremely dangerous as the disintegrating parts can fly off at fantastic speed.
 
You must log in or register to reply here.

Share this page

Top