New Live aboard with OM636

[CraigandHan]

Cheers mate, one of the main reasons we have gone for this boat is because we have managed to find the ideal owners and ideal boat, I’m sure the owner will make sure I’m fully up to speed with the engine prior to his departure. Thanks once again for the reassurance!

 

[LandyAndy]

The MB OM636 is a strong engine provided it is maintained adequately. Manuals etc are all available online if you dig around a bit! Spares are available online from Westfield4x4.
In my experience with these engines, the biggest problem is that people use the wrong oil - they should use straight 10 (10W) by the manual, although I have found 30W to be better. The tell-tale of having the wrong oil is that the oil pressure will be really high - in fact, it will likely open the relief valve when cold (around 75 psi). While a higher viscosity oil, say, 15W40, will make the flow a bit sluggish to get around the engine till everything warms up, the real problem is that the relief valve is on the discharge of the oil pump, and it the relief valve is open the flow will take the path of least resistance and most of the oil will just be dropping back to the sump rather than flowing around the engine! Obviously not good.
Other than that, there’s a defuser in the pre-combustion chamber that can break loose and rattle, which if not addressed can cause wear and drop debris into the bores - again, not good.
All of that said, if the engine has been re-built (properly!) and is still running smoothly after 40+ years, then I wouldn’t worry about it. In truth, it’s probably got more life in it than a modern engine ?
If you’re still worried about spares etc, then buy up some critical spares before you travel[Deleted quoted content removed]

 

[CraigandHan]

The MB OM636 is a strong engine provided it is maintained adequately. Manuals etc are all available online if you dig around a bit! Spares are available online from Westfield4x4.
In my experience with these engines, the biggest problem is that people use the wrong oil - they should use straight 10 (10W) by the manual, although I have found 30W to be better. The tell-tale of having the wrong oil is that the oil pressure will be really high - in fact, it will likely open the relief valve when cold (around 75 psi). While a higher viscosity oil, say, 15W40, will make the flow a bit sluggish to get around the engine till everything warms up, the real problem is that the relief valve is on the discharge of the oil pump, and it the relief valve is open the flow will take the path of least resistance and most of the oil will just be dropping back to the sump rather than flowing around the engine! Obviously not good.
Other than that, there’s a defuser in the pre-combustion chamber that can break loose and rattle, which if not addressed can cause wear and drop debris into the bores - again, not good.
All of that said, if the engine has been re-built (properly!) and is still running smoothly after 40+ years, then I wouldn’t worry about it. In truth, it’s probably got more life in it than a modern engine ?
If you’re still worried about spares etc, then buy up some critical spares before you travel - I have a full engine for sale, and know of another that was a complete runner until July 2020, but has now had the head removed for spares on another engine.
Andy
07545 347510

Andy, thanks for this!

interesting read and I will send you a message on here in due time to chat, we do have some serious plans, and a spare option to cherry pick the parts we take with us may be worth it. Thank you once again

 

[Graham376]

Many good posts above. If the oil pressure, compression and temperature are OK and it runs fine, then engine appears OK. Remember that surveyors like to limit their potential liability by warning there "may" be a problem with X,Y or Z.

 

[CraigandHan]

Yep totally understand, thanks!

 

[GTom]

The OM636 is indeed legendary as others have said

It's based on a 1930s petrol engine (believe it or not) and was in continuous production from the early 50s until the late 90s (and i think beyond under license)

It was used in Mercedes cars, vans and small trucks, the original Unimog, Thermoking trailer fridge / freezer units, plant machinery, generator sets and boats amongst other things

Parts are readily available, including the marinisation parts (mainly the aforementioned Bowman heat exchanger) and Manfred at West 4x4 up Liverpool way is a fount of knowledge and supplier of anything and everything you might ever need up to and including fully reconditioned part exchange engines

The 636 is virtually bomb proof and will pretty much run forever with due diligence and frankly the surveyor, unless he had specific reasons to doubt the longevity of that particular engine, was talking out of his bottom!

The downsides? It's not the most economical noise maker ever installed in the bowels of a boat. In our W33 (exactly the same hull as the Discus) if pushed hard, say battling down channel into the teeth of an F5/6, it will gobble up about 3.5l to 4l an hour (ouch) and cruising at 5 knots in decent conditions only improves that by a litre or so

Long and short of the matter is i wouldn't worry about the OM636. It's no more or less likely to cost you money down the line than an engine half its age or less (and parts are substantially cheaper than Volvo or, especially, Yanmar)

You might want to visit a prop doctor to improve efficiency. IIRC the W33/discus engine-prop match is not ideal, someone could correct me if it is.

I have this engine, run fine so far but due to it's age and the corrosion on the injection pump I decided to get it rebuilt. Injection pumps are difficult to find, I only found a centrifugal/mechanical governor, hope it will work...

 

[Bru]

You might want to visit a prop doctor to improve efficiency. IIRC the W33/discus engine-prop match is not ideal, someone could correct me if it is....

Since we have a Darglow Featherstream feathering prop, the merits or otherwise of the original prop are kinda irrelevant

The prop was too finely pitched when we bought her. I changed it to a coarser pitch and now get the performance I'd expect. A fixed three blade prop of the right dimensions would give us a little more speed flat out (half a knot at the most) and likely save a little on fuel (but not a lot)

The fuel consumption is what it is. It is, after all, a 40 odd year old example of a 70 year old design. Just think of the dramatic improvement in vehicle fuel consumption over that period

In fact, if you look at the power curves for a suitable modern engine (say Beta35 or Beta38) they're not a great deal more economical, certainly nowhere near enough better to make replacement economically viable