Hey guys,

I have a 1974 D6C with a powershift, and I was wondering if I can run a multigrade oil safely in both the engine (3306) and the transmission ?  Something like a 10w30 so that I could use it in the winter the odd time if needed without having to swap out oils but heavy enough for summer use...  Thoughts or experiences ?

Thanks for the help

you don't say where you're located Xtremist....or the temperatures you're dealing with roughly...

-my D6c, i use 5w30 in everything (standard trans)
-located in Northern Canada, so i can run in the summer and optional winter use as well (-40 to +40C)
-i don't operate at either extreme...i get lazy...

Northern Canada you say, where abouts ?  Im in central Alberta so we are lookng at the same rough temps id say....  I ended up ordering 10/30 for it....mine is a powershift.  Thanks for the reply !

Pouce Coupe BC (Dawson Creek)

yes our weather is very similar... 5W30, 10W30 and you're golden
i forgot, my finals are 80-90 gear oil

yep went with 80/90 in the finals as well

that is exactly what multigrade oils were developed for so you dont have to change them just becuase of the weather.
now if your some where that gets real extreme swings of temp than a suitable multigrade may not be available. ask your chosen oil company for a reconmendation they know there products and can advise you.

yep absolutely i was just more wondering if it was safe to run it in a machine that was originally supposed to have a straight grade oil in it.

perfectly fine. multi grades are often the better choice as they give a more consistent oil thickness and thus more consistent lubrication. they are also cheaper.

As trainzkid88 says multi-grade oil is nearly always better to use.  It gives the best of both worlds as it behaves like a lightweight oil at low temperatures (starting) and behaves as a heavyweight oil at higher temperatures (operating).  For example 10W-40 viscosity is similar to 10 weight at 0 degrees F and has the equivalent viscosity of a 40 weight oil at 212 degrees F.  
Another consideration is the API service rating.  Many countries use the API rating and some use their own rating system.  Never use an API rated oil below that specified for the particular requirement.

note some engines cant use modern high detergent oils. and must use low or non detergent oil. hence why you get a recommendation from the chosen oil company as they will have this info. a point to remember with old cat gear is they have bronze gears and bushes in the finals and trans and cant use zinc fortified oil in those areas. the zinc compound can attack the bronze parts