Technical How hot should a rear end get

I'm getting ready for a 800 mile round trip this weekend and doing last minute checkup on my 41 Plymout before I drive it that far. The only other trip was about 400 miles round trip and it did fine.

However, I think I keep hearing a bit of a roaring noise in the DS rear. The exhaust is not touching the frame, so thats out. Everything runs fine but I did notice that the rear end is fairly warm, maybe 140-150 degrees after a 30 minute run. Is that typical?

Ive never paid any attention to rear end temps in all my years but I did weld perches on this axle twice and have not checked it for straightness.its a Dodge 8 1/4".

Thanks for your help. I hope I'm just being paranoid.

 

I am guessing here, if the axels slip in and out your rearend without force it is probably ok.

 

you made me look....

I just got back from a 20 mile drive in wife's later model pickup, the rear cover near the bottom is about 120 degrees, the air is 80 degrees.

 

Where were you recording 140 to 150 degs? Is that oil temp or a surface temp? For oil temp, you should be just fine. If that is a surface temp, far away from the wheel ends, brakes, or seals, that may be problematic.

 

How hot can a rear end get ?...........( nope, I'd probably get in trouble !!! )

 

If you run synthetic it will make a huge difference...


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I just shot a temp on the rear cover. I have about 1800 miles on this rear end already.

 

I think I will go for one more drivr and check it again.

 

I think up to 200 under prolonged why driving is fine, especially under a load. I.e. mountainous driving or carrying a high load or pulling a trailer. The gears are going to create a lot of heat. The gear oil will do fine at that temp, though the hotter it runs the faster the oil will oxidize (age). Over 250 is too hot. Over 300 and you'll burn it up.

 

Depends on how hard your spankin' it!

 

Better take your sunscreen

 

155 on the cover after cruising around for 20 minutes. Seems high for just cruising. Ugh. I hate it when I get paranoid on taking an old car for a long trip. Being broke down on the road sucks.

 

The noise sounds like it could be a wheel or carrier bearing, but it could also be an acceptable noise--meaning nothing is wearing abnormally, and it will last a long time.

Changes in the noise are a concern!

 

I only notice the noise at about 70 mph. I used to hear a similar noise in my 54 Chevrolet and I drove it many thousand miles. It could be my hearing playing tricks on me, thats why I checked temps.

 

What does the gear oil look like?

 

I checked the 9” in my 55 Chevy the other day after its maiden journey around the block. After 10 miles the back of the housing was 135 F, the bottom was the same, and the pinion support was about 160 F. I haven’t gotten to check it since but I hope it will be a little less as time goes on.

 

Don't know... You'd have to ask my wife....

 

I am going to punt and drive my 57 Chevy. I need some time,with this car in hotter temps.

The engine temperature gauge seems wonky, too. My infrared indicates 185 while the temp gauge says 200. I know I have to go through some construction delays and I'm nervous. I will drive this one later.

Thanks for your help, everyone.

 

the best way to find out if it is going to be a problem would be to take an 800 mile trip.

 

That approach would work but I'm retired and not into stress any more. I've done road trips watching the temp gauge. Its not fun.

I will do some local due diligence in hot weather before hitting the road this summer.

 

If I had your problem I'd have the car on a lift running and be all over it with a mechanics stethoscope. If there's anything bad going on you'll hear it.

Saw a link thing here somewhere showing the adverse effects of poorly designed so called performance aftermarket rear end covers where the fluid flows were messed up causing excess heat and I think oil starvation issue too. But I'll surmise that's not the case here?

Chris

 

It's a stock open diff 8 1/4" Mopar but it has been welded on a couple of times. I will get to the bottom of it. I just don't want to find out it's screwed up 400 miles from home.

 

drain and replace the oil wont break the bank.it will run smoother

 

Have you tried turning the radio up?

 

Why don't you check the housing temp at each wheel bearing, and at the pinion bearing and see if any one of them is hotter then the others? A bad axle bearing will heat up a rear end, as would dragging brakes.

Maybe you should also check the temps of the rear end on the 57, maybe the temps on the Plymouth are not out of line. I suspect different road conditions can effect the rear end temps, as well as how much air flow is present, and how close the exhaust runs to the rear end.
I've never checked the temp of the rear end on any vehicle I driven, and I've put a lot of miles on old hot rods the past few years.

As for the water temp, what gauges are you using? Are you checking the temp with your infrared tester at the same location as the water temp is reading? If the gauge is submerged in coolant like its suppose to be, and the probe isn't bottoming out, its reading the coolant temp. The infrared tester is reading the outside metal, I would expect those temperature readings to be different. Gene

 

It is normal for a diff to get warm, how warm is another question. I know on newer cars and pickups they can get hot enough to burn the lubricant and break it down, this is one of the factors they take into consideration when setting limits on the weight a vehicle can tow. If I were you I don't think I would worry about 140 - 150 degrees.

As for the engine now you know your heat gauge reads a little high. Are you checking with a laser thermometer and did you check the temp at the temp gauge sender? It could be slightly different than at the thermostat housing.

What thermostat do you have? Your temp sounds normal for a 180 stat and should be no problem if you have a pressure cap on the rad. Even a low pressure one like 7 pounds. If you use a 50/50 antifreeze mix and a 7 pound cap your boiling point will be around 240 degrees. If you have a 16 pound cap it will be 257.

 

Check this out:
https://www.thebestsyntheticoil.com/pdf/TSB_differentials.pdf
Bottom of page 3 has temps for a common auto rear.

I wouldn't be concerned with your temps. I would drain and switch to a good synthetic. When we switched to synthetic (Valvoline 90/140) in our dirt late model quick changes, the temps dropped 20-30* across the board.

SPark

 

Take another drive and check the temperature at the wheel bearings. That will tell you whether the welding you did on the axle housing may have affected how true you housing is.

 

I had a rear end noise like you describe in my 55 Chevy , which I´m driving daily for the last 25000 miles. It got a little louder lately so I replaced the pass side wheel bearing which was running pretty rough ( but did that for 25k miles since I got the car! Imagine that!) On the test drive I noticed, the pinion bearing and driver´s side wheel bearing were noisy too. The pass side bearing was so loud, I didn´t notice the other two bad ones... Anyways, fixed all and now I can hear the OD whine, hahahahahaha
If you are concerned going 800 miles, just put a few tools and spare bearings in your trunk, and go. As Jim said, if the noise changes it´s tune things are getting interesting.

 

Drove my "bullet proof 57" and wouldn't you know it, I have a problem with the ignition switch. It cut off on me in traffic several times today, including heavy Nashville traffic. I was sweating bullets. Danchuk is FedEx'ing me a new one tomorrow. Jesus, I could do without all the drama.

Thanks for all the suggestions. I will sort the P12 out when I get back. I wish I didn't understand this stuff so well. It often causes me to create worry, if you know what i mean.