oil change--does the oil cooler drain?
 

Just did the first oil change on my 77 300d. I am curious, does the oil cooler drain when the oil is changed? I had read somewhere that there was a thermostat in the oil cooler lines. Wouldn't this stop that oil from draining? If so, wouldn't it be advantageous to make sure that the oil did drain out of the cooler? If it doesn't drain normally, does anyone know what to do to cause it to drain?

kerry edwards,

Used to be that the oil coolers had drain plugs on them and you would pull the plug to make sure the oil in the cooler came out. I think that was given up with the W123 body cars (like yours) because only a cup or so of oil came out and it was usually cool, so it took forever to drain out.

So, I think the MB engineers changed the design to save time and money. By the record of the W116, W123 and W126 cars with the same engines, leaving the little oil in the cooler in there had no net negative effect on the engine life.

Hope this helps, Jim

Kerry,

As Jim said, some oil remains in cooler unless it is drained by removing oil cooler lines. Some debate on the value of doing this given the small amount of oil involved and possible issues associated with oil cooler lines. But some very qualified people on this site argue hard that the cooler should be drained.

Search and you'll find those threads.

I don't do it.

Nic
'85 300CD