How much oil leak is acceptable

[lilianroyle]

I have a 20 year old BMC diesel which runs perfectly. It does however leak oil. Not a huge amount and I can't work out where it is coming from, but it is enough to worry me and to make the bilges filthy. I'm going to fit a drip tray but I'm interested to know how big a problem or indication of a problem this is.
Thanks

 

[Mel]

I would suggest that you try cleaning the engine down with GUNK or similar cleaning agent to find the source of the leak. It might be easy to cure and then the problem is solved.

However, the quantity of oil lost (so long as it is not gushing out) should not be a problem to the engine if you always maintain the correct oil level in the engine. Minor leakage could become a fire hazard but is usually only a nuisance with smell and mess.

 

[Mel]

I would suggest that you try cleaning the engine down with GUNK or similar cleaning agent to find the source of the leak. It might be easy to cure and then the problem is solved.

However, the quantity of oil lost (so long as it is not gushing out) should not be a problem to the engine if you always maintain the correct oil level in the engine. Minor leakage could become a fire hazard but is usually only a nuisance with smell and mess.

 

[Twister_Ken]

None, if you pump it over the side with the bilgewater.

 

[Gordonmc]

I would go with the notion of cleaning off to find the source. I have a 35hp BMC and had similar problems. The culprits appear to be the oil filter head... might be worth considering buying an adaptor which will take a modern spin on cannister and dumping the paper filter set up.
Another loss of oil was on the port side of the block below the exhaust manifold, covers for the push rods which tend to leak through the centre fixing bolt holes. Easily fixed with new fibre washers.
My rocker box is oil tight, but a new gasket would sort. That leaves the sump gasket. Oh dear... probably an engine out job.
I previously used a bag of cat litter to soak up the drips. The whole lot could be shovelled up from the tray occasionally. Now I use an oil/water seperator mat which is still white after half a season.

 

[stretch33]

I have a Thorneycroft T80 which does much the same, it caused some alarm when l first noticed it but it looks a lot worse than it is.(i hope) I checked the oil level every time l run the motor and as yet havent added any as level has remained fine. I think my little leak is from the back of the engine but i to cannot find the source as yet. Will keep looking though. The tip about cleaning it up is a good one but did'nt help in my search.

 

[lilianroyle]

I don't. If I did the problem would be much less irksome.

 

[Col]

Diesel engine oil is so black, that a little goes a long way. Probably not as bad as it appears.

 

[oldharry]

Minor oil leaks are rarely more than a minor nuisance, provided the engine always has enough oil. Never let it drop more than about 2/3rds of the way between the dipstick marks as the engine oil levels were determined for road use, and not being rolled around as in marine applications.

It is important to find the leak source to ensure it is not in an external oil way that is about to fail and dump all the oil into the bilges. Many engines have rubber oil pipes which may leak for a while before finally breaking down, particularly if an external oil cooler is fitted. It only takes around 30 seconds to empty the sump altogether if one of these fails at crusing speed!

Cleaning off with engine cleaner such as Gunk or Jizer is the first step, then carefully check round all the various engine gasket joints when the engine has warmed up and run for half an hour at normal speeds.

Far more difficult to identify - and the commonest source of oil leaks on older engines are the main bearing seals, where the crankshaft comes out of the engine front and rear. A leaking front seal is fairly easy to detect, but the rear seal is right inside the gearbox adapter plate, and the source of the leak is quite difficult to detect as the oil may finally surface in an unexpected place!. As a rough rule, if there is oil dripping from anywhere near the back end of the engine or gearbox and is not running down from further up or further forward, then its a good bet the rear seal has failed.

Unless it has been disturbed the sump gasket rarely develops leaks, but it is worth going round and checking that all the bolts are still tight.

Did you replace the copper drain plug washer last time you changed the oil? They should be replaced every time, although you can often get away with it 2 or 3 oil changes. Once the surface is scratched it becomes impossible to get an oil tight seal at the drain plug, however tight it is done up, and there is a constant slow drip.

Engines will continue to run quite happily with leaking main oil seals, and until the oil loss itself becomes a hazard can be safely ignored - provided there is some means of collecting the spill.

DO NOT PUMP SPILLED OIL OVERBOARD!

Twister Ken please note: any UK harbour authority detecting oily bilge discharge WILL prosecute, and the courts can and do award huge fines for marine pollution. We are talking big money. A 40 footer in Brighton some years ago had an engine oil spill. The owner mopped up, then pumped the last little bit out with the bilgewater. The fine levied was in the region of £15,000. Unfortunately the bilge discharge outlet gives the game away as an oily streak rapidly develops down the side of the boat!

There are various proprietary oil absorption pads that can be cleaned off and re-used, and various oil elmusifying agents which will break down oil residues so that they neither harm the environment or your pocket!

 

[ccscott49]

Just as an aside, don't use gunk, you will never get rid of the smell of the stuff, use a detergent based degreaser, which can be disposed of, as it breaks down the oil and is certified for discharge, fishermans supplies have it. You can also use it to clean the bilges, we use a product in the oil industry, which is wonderful stuff, I always liberate a couple of litres when I go home, lasts for ages, super concentrated, but fishermans supplies have a similar stuff.

 

[johnt]

dont discount that it could be worn bores and rings, that will make the engine "pant" throught the crankcase breather! and the tiny amount of oil that is discharged will get everywhere.

I fairly recently changed my old YSE8 for a new yanmar, and the engine bay was like the black hole of calcutta!

check the breather pipe ...if its oily ..that most likely it !