Hey just wondering what grades off oil can ya use in an subaru 1400 motor?

I'd go with 10W40 in Winter and 20W50 in Summer.

would it be ok to use 10w40 castrol magnatec? cause thats what i use in most of my cars and im had no problems with that

For most engines, most regular 10-40 and everything between will do, though 10-30 seems to be standard. You might want to avoid synthetic as it can lube "too good" in an older engine and leak past things, so I hear.

First off, i'd say stick with 10-30, as the farther the low and high numbers are apart, the less oil and more additives there are, which won't make and appreciable difference, but as the oil ages, the bigger spread oils will have more breakdown than the smaller spread.

 

Second, 20-50 is way too thick, even in the summer, you'll have no oil on startup, which will cause increased wear, which is usually the cause for running the thicker oil, because a thicker oil is less likely to seep past rings and valve seals. Its a double edged sword.

 

Third, Synthetics don't lubricate "too good" they clean better than dino oils, so the sludge buildup that was keeping the oil in your motor will some times get cleaned away by the new synthetic oil, which could make your engine leak in new and exciting places.

My Dad is Mechanic, and says to avoid the use of synthetic oil in older engines, becuase the seals are not prepared for that, and will worn faster and leak.

As Noah said-it's not necessarily "old" engines that are worst off from the switch to synth-it's a combination of age and mileage. I'd be hesitant to use synth in anything over 5 years old or 50K miles if it's had dino oil in it previously (ie everything I own except my VW). I use Castrol 10W30 in summer in my '70s cars...no oil pump or leak issues so far.

im used 10w40 castrol magnatec in all my cars for an 82 1600 leone to xt6s and xt turbos and one of them had done 300,000kms was on origanal motor and turbo. found that the oil levels remained good. and im never had any troble with it.

its not the level, its the acids that build up in older oil.