Hi:
I'm new to this website. I need advise on changing the oil in my transfer case to a heavier grade. I am leaking at the output shaft seal and at the parting surface. The output seal has been chanced already, the truck has 130,000 miles on it. Did not want to reseal the unit, can I run a heavier oil?

 

You need to fill out your sig so people know what type of truck you are talking about, mine is an 01 automatic and my T/C takes ATF, I dont know what a standard truck uses, but in my opinion pull the TC and re-seal it. thicker oil (if talking 80w90-75W140) is NOT going to stop/slow down leaking. A re-seal is cheaper than rebuilding/replacing a T/C that ran dry of oil

 

Welcome to the site! Depending on the year of your truck, if you put heavier oil than whats recommended in it, you might be pulling it for repair. My 1997 owner manual recommends ATF+2 or Mercon or Dexron III Automatic transmission fluid. My 2000 owners manual recommends DEXRON III Automatic transmission fluid or DaimlerChrysler Corp. ATF+3 Type 7176 automatic transmission fluid. Is it possible that where the seal contacts the shaft is damaged or rough? May be the case is over full? Was the new seal damaged when it was installed? Some things for you to consider.

 

My 01 calls for type 4 ATF. I am replacing the rear seal this weekend. I also have a small leak at the output housing to case junction but am not going to worry about it. Heavier oil wont plug a leak. The np241dhd requires a relatively light oil so if thats what you've got I wouldn't change grades. It would be cheaper to fix the leak correctly in the long run.