[Archived]

Sounds perfect to me. Just hot enough to boil out any moisture(condensation) that is in there.

The synthetic gear oil I use has a flash point of 400+ degrees f.

[Michael]

Don thanks for the reply, i have been thinking about changing to synthetic oil,did you notice mucb of a reduction in temp after replacing with synthetic

Thanks Gordon

[gordon]

Synthetic will run cooler and 230 is fine for synthetic; probably ok for regular. I’m happy to keep mine down at 250-260 but I approach 70,000# gross. I run synthetic and change at about 25000 but that’s unnecessary unless you do heavy towing and high speeds. You’ll find the temps go up at higher speeds.

[Bill]

Thank you for that info, once i return home and before my next trip i will try to change to synthetic, i dont usually travel much over 60 mph but a lot of my driving is mountain terrain in western canada, good info thank you

Gordon

[Dick]

How do you guys know your differential temps? Prevost gauge? Converter installed gauge? One that you installed? We don’t have one. Interested in what you’re using.

Synthetic gear lube will typically have a higher safe max temp than semi-synthetic or dino-based lube. I’ve learned to ask both the gear lube manufacturer and the gear provider (rear end manufacturer in this case) where they want the temps.

Disclosure: I’m not an engineer or chemist or truck driver. All I know is what I’ve learned being around airplanes and race cars over my life, reading stuff on the Internet, and talking to a few knowledgeable. Like I say in my signature … I try not to make stuff up.

As mentioned above, we don’t have a differential temp gauge in our coach. Its my understanding that larger trucks (like semi’s) have differential temp gauges (often one for each differential in the truck).

Through my 550 hour aviation career and now with the racing I’ve done, I have come to understand, like, and count on temp, pressure, and electrical info gauges. While a few temps are pretty easy to understand (water boils at 212*F at atmospheric pressure) … others are more specific to the device and the type of fluid and hence a little more involved to properly understand.

The load on a mechanical device is based on the amount of pressure being exerted on it and the weight that is being moved, I think the differentials in our coaches have a tendency to be subjected to a significant load. Most of us 45 footers are 48,000# to 52,000# plus a 3,000# to 6,500# toad. Some of us pull trailers that weight between 10,000# and 20,000#. All of that goes through a single differential being pushed by our what … 475hp, 1,600ft-lb Detroit Diesels. So with my race trailer I’m right around 60,000#.

Typical max load of an eighteen wheel, five axle semi is 80,000# (apparently without special permits and/or more axles and wheels). Those trucks usually have two differentials and are powered by engines similar to ours. So 40,000# for each differential on the semi versus 48,000# to 60,000# per differential on the coaches.

I presume that not all differentials are equal. Some differentials are likely engineered to take a higher load than others. I wonder what the load capacity is of the differentials in our coaches compared to most differentials in a semi tractor rated to 80,000# max load. When I say “load”, I mean load to pull versus weight on the axle.

Back to gauges. I watch gauges and look for trends. The “oil temp” gauge (which I understand is really trans lube temp; not engine oil temp) in our coach normally says 200*F when I’m running 63mph on level ground and pulling the HHR. If one day I look down while on level ground and see 250*F, I know I probably have a problem somewhere. 250*F is “not typical”.

I also use the various temps gauges to help me know when the various components (especially the engine) has adequately warmed up before I start to move and more importantly when its safe go to wide open throttle with a load.

So those are my thoughts about differential temp gauges. I would like one, especially once we start to travel more in the mountains during the hot summer months and pull a heavy trailer.

[Archived]

Dick

My 95 Marathon left Prevost with the diff temp gauge installed ,it is the same gauge in terms of temp range as the transmission oil temp gauge and sits directly beneath it in dash.

I was under the coach 2 weeks ago servicing it, the axle temp sender is screwed into casing a little below the height of the level plug, this is my first lengthy trip with the coach in summer temp so i was interested in what is normal operating temp for oil, i contacted a trucker friend of mine after posting here, he runs an 18 wheeler a nd loaded at 80,000 275 deg is normal and can go up to 325 on a long grade in summer, so i am now assured that 230 is an ok Temp.

Whats interesting driving and tracking the diff temp is that climbing the mountains in western Canada do not seem to make a huge difference to the increase in temp, that seems to happen over time, for example my temp will go to 230 after approx 4 hours running and will not cool down on long flat or downhill sections, but will drop 30 to 40 deg soon after stopping, so i think its just the heat soak effect into the oil.

My trans temp stays at 190 regardless of terrain, thats pretty close to engine temp and has cooler.

I may at next service fill diff with synthetic and see how much cooler it will run

I am pretty sure you could get an aftermarket gauge and sender unit, running the wires might be a bit tricky but worthwhile as i think is a useful gauge to monitor.

Regards

Gordon

[al]

Thanks Gordon! Next time I’m under the coach with it safely supported, I’ll look for the bung.

[DON]

Dick: My 1990 came with diff temp gauge. I installed one in the 1999; bung is in the diff.

Interesting that your trucker friend thinks 325F is ok. I’d like to know what meritor thinks…maybe I’ll bum around their website.

At 60,000#, 110F outside and 75mph on level ground, I guarantee you can get yours up close to 300F.

Because I kept going through drive axle seals, I went on a quest to get my temps down. I try never to exceed 260…mountains don’t seem quite as bad as high speed.

I:

1. removed full width flap across rear to help airflow under coach.

2. went to synthetic oil

3. replaced drive duals with 455 super singles which opened the area around the bearings and drums to more airflow. (I hope, didn’t test in a rolling wind tunnel!)

All this seemed to help but the seal problem seems to have been helped with a change of brand. Current seals are approaching 100,000…knock wood, previous averaging 50,000.

These diffs are still touchy though if you are heavy and fast. I was at Prevost when they were replacing one in the old Newman-Haas XLV at about 100K. They always towed a stacker style hospitality trailer that I believe had a full kitchen.

At 200K, I was changing out the Amsoil 90w-140 that had 50K on it. Pulled the drain plug and got NOTHING. Stuck my finger in to dislodge a big chunk of powdered iron which had been adhering to the magnetic drain plug and out came the oil! Installed Redline 85w-140. Changed at 210K with an oil analysis of high iron (expected). Changed again at 230K with a good oil analysis. I’m going to try to get back to 50K change intervals but I’m taking baby steps. I’m generally 65000-70000 gross.

[Jeff]

Joel, check your email.

[Tim]

Gordon: My gauge is aftermarket VDO. I had a front and rear radar detector when I bought the coach which I don’t use and stole a wire from the rear detector.

[Richard]

Joel, good idea to use the wires, if Dick reads this i was thinking that there are some spare wires run from rear junction box to steer compartment maybe he could use those for additional diff temp gauge, would only need short wires from diff to rear junction box, maybe easier than running new wires from axle to dash ?

[Pat]

Thanks for reminding me about those spare wires. I hope there are some left.

[Kirby]

You only need one. I grounded the axle to the frame with a ground strap. One wire goes from sending unit to gauge, then gauge needs hookup to ground in front as well as dash lamps for illumination.

BTW, I couldn’t find anything on the Meritor website re max oil temp, but I still have 260 stuck in my head and my VDO gauge designed for diff temp only goes to 300. Lo and behold, I was just on another forum searching for an answer: Peterbilt has a gauge with warning light illumination at 270.