Advice on Buying a Colvic with OM636

[James Rowe]

I am off to see a Colvic 21 fitted with a Mercedes OM636 42HP tomorrow.
Being a bit of a newbie and not knowing too much about these engines, does anyone have any advice about what to check for and if there are any common faults?

Thanks in advance

 

[pcatterall]

No knowledge I'm afraid, someone will come along soon though.
Is that a very large engine for a 21 footer?

 

[SHUG]

The Mercedes 636 is a terrific engine and was widely used in cars and commercial vehicles as well as being marinised for boat use. It is well supported by Westfield Engineering who stock spares.
See here http://west4x4.demonweb.co.uk/OM636/index.html

 

[DownWest]

Both the Merc and Perkins engines were licence built in Spain by the same company a while back, can't remember the name now (I had one of their Perkins 4-108s) Might be worth a search as a back up for spares. If they are still in busness.... Cors, the experts (Lisbon taxi driver) didn't rate the Spanish ones.

But it is a BIG engine for a 21ft, as said above. More in the 30ft range and up.
DW

 

[Bobobolinsky]

Good engine for a Colvic (Seaworker?). Spares are plentiful, I was offered one for £100 recently. You don't want a seaworker with a Hatz single.

 

[G12]

Great engines. Check for play in freshwater pump - pump requires filling with oil if I remember..... ummmm what else.....I think that's about it other than what you would normally look for.
The glow plugs may have been upgraded - there's a 12v kit, I think the originals were 6v with a massive resistor fitted for 12v operation.
Simple maintenance.... oil strainer rather than spin on filter, washable air filter.

 

[ffiill]

Mine is 34 years old still delivers about 70psi pressure when warm and uses no oil between 100 hour services.
Modern heater plug set from Westfield worth every penny.
That water pump oil reservoir is important-got my boat as far as Crinan Canal on its delivery trip up north and it siezed solid. Easy to get reconned or replacement from Westfield -modern sealed unit.
Often fitted with a steel shim oil filter which you just wash out.
Also inline fuel injector pump which again in some cases needs topping up with oil-in some versions fed from the engine oil supply.
Used in the origional Merc Diesel cars up to mid 60s;Unimog 4x4; and most recently in Thermo-king compressors on refrigerated container artics.
Love the engine!

 

[James Rowe]

That's brilliant guys, Thanks very much.

I will let you know how I get on!

Cheers!

 

[davey]

Both the Merc and Perkins engines were licence built in Spain by the same company a while back, can't remember the name now (I had one of their Perkins 4-108s) Might be worth a search as a back up for spares. If they are still in busness.... Cors, the experts (Lisbon taxi driver) didn't rate the Spanish ones.

But it is a BIG engine for a 21ft, as said above. More in the 30ft range and up.
DW

It all depends on whether you want to tow or trawl. Not quite the same engine but very similar is the Perkins 4.108 These are excellent in British waters but they can be very problematic in the Tropics where the sea can be like a warm bath. Its the heat exchanger that causes the trouble but the cure is to fit a Perkins 4.236 heat exchanger. The other problems in warm seas are octopus and jellyfish getting sucked into the cooling water intake. Good strainers are essential as is an engine overheat alarm. Without these it is possible to get a burnt exhaust hose, melted water-lock and a blown head gasket.

 

[elenya]

Great engine. We have one in our saltram saga 40. Runs forever at 1800 rpm at 2 litres per hour. We have had ours about 12 years and done about 2500 hours with it. We gave it a full rebuild when we got the boat. Spares are easy via Westfield 4x4 and we have had great service from Manfred there.

 

[macd]

James: we had the Merc OM616 (built in Spain and marinised by Sole) in our boat. Being 20-odd years later in design it isn't really comparable, but there were impending issues with heat-exchanger corrosion and other non-Mercedes bits. The bottom line is that marine diesels typically decay from the outside-in rather than wear out. So, whilst not wishing in any way to deride what is basically a great little engine, I'd suggest you arrange a particularly thorough check-out on one as old as the 636.

If you google "Mercedes OM636 ybw.com", you'll get a host of threads about the engine, in addition to the good advice on this one.