So I'm still a bit green when it comes to 4wd. I am just now really getting in to wheeling. I just bought an 86 4runner that I will be taking on a 2600 mile road trip this coming weekend, and I am noticing that my rear dif is getting rather hot. After about an hour of highway driving the other day I got out and touched it and it was pretty hot. I think I could have left my hand on it, but not for more than a few seconds. I am not getting any warning lights in the cabin, so I don't really know what to do. I am having trouble finding anyone that can tell me how hot is too hot. Can you please help!!!

 

You won't get any warning lights for that. They're supposed to be hot and if you could hold your hand on it, I'd say it's probably perfectly fine. Think about what's going on in there and you will realize it's going to get hot.

If you're worried about it, remove the fill plug and check to see if the fluid is good. Might not hurt to add some until it flows out of the fill hole.

 

Yeah, no warning lights. Instead of just checking the differential oil, I would go ahead and change the fluids, front and rear.

 

The only time i ever saw a rear diff get so hot you couldn't keep your hand on it was in a brand new dodge and the rear end was toast at 40k ( kms ).

Check your fluids, look for any metal shavings in them and report back.

 

Go for a drive then touch your diff. It should be hot.

When in doubt, drain the fluid, check for shavings and refill with a nice gear oil. Make sure the breather is working properly (great time to extend it)..

 

Just change the fluids.



If you're really worried, you could throw some lucas in there. I threw about 3/4 a bottle in my ass end because of a leak... seems to have smoothed it out a little bit, and it should keep things cooler.

 

Check the fluid. There should be enough to be level with the bottom of the fill hole. the fluid shouldn't be dark or opaque nor should it smell like the worse gag-inducing flatulence you've ever smelt. New fluid smells a bit like pine cleaning products (ie: Pinesol).

My diff gets about as hot as you described if I'm going up a steep grade for a while, or I'm driving hard onthe throttle. So there should be no immediate cause for alarm. There will never be any warning lights for anything driveline-related but the engine and the automatic transmission.

 

my transfer case smelled like that when i changed it and gagged hah

 

Thread hijack

What oil do you use for the diff? 75w-90?

 

75-90.... 75-140... 80-90....



diffs are very forgiving when it comes to fluid.

 

80W140 to keep my locker quiet.

 

Gotcha. I think ill bust out some 80-90. Temps around here dont get too cold or too hot.

 

that sulphurous smell from hypoid can be a bit overwhelming...

but I use an 85w140 in mine.

 

I can see why, California gets really hot, dont you live in the southern half?