The oil cooler can't be absolutely necessary. I have a 1983 Mercedes 307d motorhome in the UK with the 616 engine that is basically the same as the motor in 240d's. It has no oil cooler on it and it came from the factory that way. It also does not have air conditioning. I suspect that the oil cooler is a bit of overkill unless you are running AC in west Texas. I'd be curious to know if anyone has done any experimenting to figure out how often the thermostat in the oil cooler opens to cool down the oil. Has anyone put an oil temperature guage on their engines?