Sould my rear differential be warm? Its not hot, but it is warm to the touch. I've never thought about, but mine seems to be warm when I come back from a drive. Just one of those dumb questions!

 

Warm is good. Even a little hot to the touch is okay. Completely normal. This is why they use a synthetic multi-vis oil.

 

OK, good! Just wanted to check. It just needs to hold in there for a month or so when I get it re-geared and can put my mind at ease.

 

There will be heat in the diff as there are moving parts and friction and also slipping of clutches around corners and whatnot.

 

You'd be warm to if you got thrashed around like that lube does between all those gears!
The amount of moving parts in the drivetrain is amazing.
The older I get the more amazed I am these trucks don't just blow up in a ball of flames!
I have a headache now.

 

I'm with you. I pulled apart a 5.0 Mustang motor a few years ago just for fun and I was amezed with the 1000s of pieces that make a car or truck run/move/not blow up.

 

yeah warm is ok. smoking is not ok like mine started doing. if youre worried about it check the level of fluid. just pull out the plug and start putting fluid into it till fluid starts coming out of the hole.

 

^^^

What he said. What kind of usage is the truck getting? Heavy towing all the time? What?

 

Already checked the fluid and it was perfect. Right to the top. Right now it is just getting regular daily driving, MAYBE upto 20 miles a day tops. In the spring it will be hauling my 7K pound race car trailer about 120 miles roundtrip once a week.

 

If you have any concern, now would be a great time to change the fluid and install the Ford aluminum cover.

 

I might be doing that. I'll have to see how quick I can save my gear swap money. hopefully in the next two weeks it'll have some new gears (and a DP Tuner and gauges!).

 

Being a data loving techno-geek, I stuck a temperature sensor in there. Modern differentials use hypoid gears, which have a "sliding" interaction, which shears the oil and generates heat.

Normal driving, minimal load: Rarely more than 50 degrees over ambient.

Towing: Usually 50 to 100 degrees over ambient

Grinding up long grades (20+ minutes) with heavy loads: I've seen 150 over ambient. 255 on a 105 degree day.... That's pretty stinkin' hot, and I don't recommend the touch test!

This is with Mag-Hytek cover and Redline 75W140 synthetic.

 

rear ends get really hot sprint cup cars have an pump cooler and fan to cool the oil

 

I might have to put a gauge on mine some day. That would be a cool feature to have.

 

I have a feeling the wheels in your sig don't help either. A Mag-Hytec cover or Ford Aluminum would be good for you. The Mag-Hytec actually has extended capacity along with a dipstick, a top fill port, and a bottom drain plug.