Monday 23 March 2015

On maintaining the Mercedes 5 cyl engine in Classic Hymers

Engine. Most Classic Hymers have either Mercedes or Fiat engines. Mercedes are generally accepted to be the "classic" engine, becasue the OM602 5 cylinder diesel engine is probably one of the most iconic diesels in history. Known as the "million mile" engine, they powered merc vans and cars all through the 70's 80's and 90's. They have a mechanical timing chain which last much longer than a belt. They have no electronics to go wrong. They just go and go and go. Nothing wrong with Fiats - maybe somebody else can sing their praises - I have never owned one,
Do not be put off by a high mileage - 100k is nothing for these engines. Mine has done 346,567km as of today! And still sounds like the day I bought it. If faced with a high mileage example, by all means use it as a bargaining chip, as would anybody, but don't worry about the engine. Turn the key, let the heater lights go out, and it should start first turn, every time. A cold engine rattles for a minute or so, and a bit of smoke is OK, as long as it clears after 10 minutes of driving. There is nothing to adjust on these engines - they just go and go.
Commonest problems are usually fuel related - there are 3 filters to check, and one of them hardly ever gets changed!
Don't be afraid of a bit of oil, especially on an old high mileage engine - obviously you don't want it making pools on the drive, but a bit is OK - have it checked if you are unsure. Don't confuse engine oil leaks with diesel leaks, which are much more common - there are many little rubber fuel return pipes and they do perish - it's an easy fix.
Oil change every 10,000k no excuses, and no cheap oil - this is the most important thing by far to keep your Merc going for 30 years. Check the service history if there is one, but regular oil changes are what you want to see.
Expect glow plugs to go after around 10 years or so - easily fixed.
Brakes - discs on the front and drums on the back. The back brakes need regular service. There is a load balancing valve under the chassis which needs regular attention - every year or so. They are not heavy on pads and shoes, and cost is reasonable. I have had my back brakes serviced twice in 15 years.
Gearbox - also bombproof, but it has "character". You can't ram the gears around like a ford escort - you have to drive it like an old style truck - which it is. Most people struggle with first gear, which is left and back....it takes practice. It is worth learning the ancient almost forgotten art of "double de-clutching" ! The syncromesh can get worn on certain gears, causing a slight crunch occasionally. This is not terminal, and can be minimised once you are used to driving it. Don't be afraid of the automatics - they are reliable too, if basic. Everything on this chassis was designed in the 60's and 70's - you don't buy one of these for Rolls Royce silence! But they purr along at 55 all day....all year long! 5 cyl mercs return about 22 to 25 mpg. They will do 70mph if pushed, but you feel guilty afterwards. I once drove from Brussels to Calais, foot to the floor - I murdered it, I actually hit 85 down one hill. When I got to Calais it was like a sweating horse - you could hear it creaking with the heat - the engine cover was hot to the touch, as were the tyres. No lasting damage, just carried on......

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