Hi folks,

New guy here, but not new to trucks. Have owned a bunch and currently ditched the diesel for a 2000 V10 F350 CC DRW Laredo. Don't ask what my other truck is for now, but I'm pulling horse trailers, a quad trailer and a 30' 5th wheel.

I've seen a lot of comments about rusted differential covers and most folks shrug it off due to high heat and then blast and repaint - or replace the cover. But, what I have not seen is any comments on the source or intensity of the heat. I understand that with any friction, you're going to generate heat, but it occurs to me that if it's enough to peel paint, then that's too much!

I say this because I've noticed that after running - even not pulling - my F350 (4.30:1 open) gets hot enough that you don't want to hold your hand on it. I can't help but think that's too hot. Or is it? Do they all run this hot? I've never seen a Dana (oops) run that hot . . .

Thanks for any comparison information . . .

Arizona truckin . . .

 

Hmmm, interesting question. I'm not an automotive expert, but I'll take a stab at it, just for fun. Here's some numbers that I just pulled out of, er, thin air, to use for an example. I could be WAY off. But here goes:

Let's say it takes 25 HP to keep your truck moving down the road at 70 mph, unloaded. It's probably more than that, but anyway 25 HP would be 18650 watts. Now let's say that your differential is 95% efficient (another guesstimate). That means it would dissipating 932 watts. That would generate a fair amount of heat. Of course, there is quite a bit of surface area, and a lot of cool air moving over the housing, but I would think it would still be hot to the touch.

If someone thinks I am way off on any of these estimates, plug in your own numbers and see what kind of heat we'd be talking about. 1 HP = 746 watts. I used watts because everyone knows how hot a 100 watt lightbulb gets, or a 1500 watt space heater.

In any case, if you are able to hold your hand on it for any amount of time at all, that's not very hot. And the synthetic diff oil should be able to withstand even higher temps than the conventional stuff. I would think that if there was really a problem, you would notice it in the mileage and power (and possibly noise).

Again, just taking a stab at it, for fun. Feel free to correct me if I missed the mark.

 

Rotten diff covers were around from the factory, without any heat The paint was crap, and flaked off. Or just rusted underneath it.

I used a high-temp engine enamel that I baked at about 200 degrees, it's still on there...

And don't be afraid to mention Dana - our front-ends are Dana's ...

That sounds strange, that it would be that hot without pulling anything.

Pull the fill plug, it has a magnet on it - see how much crud is stuck to it, and see what the fluid smells like.

If you haven't already checked the fluid, there's a possibility it's contaminated with water - or there's not much left - which ain't good.

 

Oh, and WELCOME to FTE! I missed that it was your first post



Hmm... going into Mechanical Engineering? If not, you should

I'd put the diff at a higher than 95% efficiency... especially at such a low load.

Now I'm going to have to go around feeling rear-ends...

 

Fluid level is fine and was not burnt. I know this because I just replaced the pinion seal - whadda pain that was. (I won't detail the agony). But, I did replace the fluid.

(And I don't have a Dana up front, just I-beams and spindles).

Thanks for the comments so far - and I like putting a bit of science behind the analysis. Now, if we could only find a rule-of-thumb to use for a dissipation factor off this big mass, so I'd know if my "heat" is normal . . .

 

desertrefugee -- You have a very valid question. IMHO...it appears FORD has recognized this issue with the all new '08 models. They seem to have finned aluminum rear diff covers now. Not sure if they added capacity to that also, but would make sense if they did.


That's what I'm talkin about!!!


biz

 

Why thank you! I think I know just enough to be dangerous :-)


I suspect that you are right.


Would the efficiency decrease with load? I would think that the efficiency would be higher with heavier loads, because the inherent (no-load) loss would be a smaller percentage of the total dissipation. It would certainly get hotter, though.


LOL!

 

Yes it is normal for the diff to (almost) burn your hand if you touch it after driving around awhile and especially after towing. The friction of the gears generates heat... the gear lubricant oil keeps the gears at a viable operating temp as well as lubed. All in all, it's normal.... that's why they have exhaust vents as well, to let some heat escape... make sure your diff exhaust hasn't broken off too. Water will also cause the housing to run extremely hot and will ultimately sieze your gears. If the gear oil is pure and level is fine, heat is not really a problem.

 

Check out this great article at http://www.fourwheeler.com/techartic...vetrain/129_06 .It looks like 200 is about as high as you want to go. They did some tests pulling some real weight and took numbers.
Keith

 

Thats supposed to be www.fourwheeler.com/techarticles/drivetrain/129_06

 

You can get the Mag-Hytec covers that are finned and has room for more fluid. I think thats why they have them on the 08's now like stated above .

Yes they will get hot and you can see the fluid line on the cover if its hot enough when you stop. It will burn the paint off to that level.

Don't ask me how I know...........

I would look into the Mag-Hytec cover . They really keep the temps down.

 

Checked mine (05 F350) with an infrared non-contact thermometer after running unloaded for 45 minutes on the highway. It read 180 degrees.

 

PupnDuck - I was actually hoping someone had an IR gauge! That is good information - as is all the rest! I don't know what my threshold for pain is, but I'm thinking that what I felt was 180 to 200 degrees. I actually do feel better.

Wait . . . did I hear a slight whine on the way home ? ? ?

I'd better go back and feel my rear end again.

Never mind.

 

Um, I gotta ask an obvious question.

How did you determine the correct torque on the pinion nut (and likewise, the correct preload on the bearings) ??

because too much preload on those pinion bearings, and bango!

And might be a cause for more heat than normal too....

 

Most of the time, you can put the yoke back on at the torque you took it off with.

I am not a rocket surgeon, it seems like the fluid would contain the bulk of the heat. The rate the fuild transfers heat to the axle tube and the tube convects outward should be the dissipation your looking for. Using a high quality synthetic should help reduce your temps, and I would imagine transfer heat better.