Reduction Gear Oil Change - Benefits for Range

I've got over +4k miles on my gear oil change, no issues (well at least nothing I can hear) yet. I plan on changing it next month since I've already put it through plenty of abuse with my lead foot driving and several +600 mile trips now on the vehicle.
I am curious to see if the next oil analysis shows anything to worry about. :mrgreen:

so to put in a data point - running 75w90 for the last week and few hundred miles, and my average is at 3.9, which is what it was with the low viscosity gear oil. This is telling me that the temperature switch from colder to warmer did the large majority of the efficiency gains and gear oil really seems to have very little effect. Granted this is not many thousands of miles of data but it's enough to not be a total fluke, and the 75w90 is many times thicker than the ATF the Leaf usually uses.

It's good to know. Good science is about accepting the data and less about hoping for the data :lol:
I'm about to try the same thing, going to swap back in the Nissan Matic S, send the old gear oil in for analysis (to see if it was causing gearbox damage for example) as I have nearly +5k Miles on it now.

I've been able to narrow down my extra efficiency boost to tire pressure when the temperature was climbing this month on top of the boost I got from my gear oil change. The temperature efficiency boost has no effect on the high speed driving, but does have an effect on the lower (under 55 mph) type of driving. Probably just rolling resistance related, I can feel it in the vehicle handling, the tires being inflated to 48 PSI when hot are real bouncy. :shock:

I've lowered the tire pressure this week to 40 PSI (in ambient 72F temperature) so that when the day gets hot, they top out at 44 PSI to try to eliminate that low speed boost I'm seeing. It's a slow process keeping track of all this data and I wish I had a way to monitor the gear oil temperature real-time or LeafSpy like, but don't have the time or resources to drill a temperature probe into the gear box. Of course my conclusions are not finished yet, but if I had to take an educated guess based on the data I have, I would say using the ULV gear oil seems to negate the mileage loss using the AC/Heat during a trip. The effect seems to show itself more when the temperature is colder and then slowly decrease as the temperature gets warmer. I suspect it is something more thermal related in the system as a whole and the benefit of the ULV is more about it's lower viscosity at colder temperatures than how well it keeps the gears lubricated. It could also be that just changing out the gear oil period is the key, regardless of what type of you choose, you will see a benefit. Maybe it's not so much a gain of efficiency but a return to the "original" efficiency when the vehicle was brand new from the factory. I think I learn more towards that than anything, but I don't have a brand new 2021 Leaf with 0 miles on the odometer to test with, unless someone wants to send me one? :mrgreen:

I'm going to find a way to start recording my gear oil temperature to add to the pile of data. I want to get some good readings with trips and efficiency so that when I make the switch back to Nissan Matic S, should the efficiency actually change, I want to know if the gear box temperature is changing as well. Just making a note here for future reference.

The Nissan Matic S finally came in today. Now I can prepare for the reduction gear oil change back to "factory" standard. Once I get the temperature sensors installed for the gear oil and coolant (had an extra sensor, why not?), I can start recording what the ULV is doing temperature wise and then when I put the factory oil back in, I can see what difference (if any) it makes for both efficiency and operating temperature.

Temperature probe bolt for reduction gear oil complete. Move on to Level 3...

are you putting this in the fill hole? will you have it pointed down into the oil or i suppose air in the gearbox will be much the same temperature as the oil?

Ok, first readings today. Drove around for about half an hour in 85F Sunny temperatures, high humidity :?
The coolant and gear oil temperature started at 90F so I had do a lot of stomp the pedal acceleration to heat up the gear oil because casual stop and go driving was never getting it above 120F :lol:

First interesting thing I noticed, the coolant temperature (Probe 2) never gets over 100F. Another interesting thing, as the temperature of the gear oil increases past 140F (Probe 1), then coolant temperature starts to rise up to +100F (cooling motor and stuff my guess) until gear oil temperature gets below 140F and then coolant temperature starts to gradually decrease from air cooling.

estomax said:

are you putting this in the fill hole? will you have it pointed down into the oil or i suppose air in the gearbox will be much the same temperature as the oil?

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I'm using the fill hole on top, probe is pointed straight down into the gear oil. I made sure it wouldn't touch any gears and locked it into place with some straps and sealed the hole around probe with liquid electrical tape even though drill hole and probe are already a tight seal. I didn't want any water to get in, but at the same time, this isn't permanent. It should hold for a few weeks so I can run some before and after test.

After my first test today, no leaks (thank goodness) :lol:

This is interesting data. Thanks for sharing

Ok, had a full day to really play around with this. It is interesting data.

Normal, stop and go traffic, AC running, kind of hot and humid day, the gear oil temperature stays right at around 140F. The coolant temperature never gets above 100F, usually goes between 90F and 100F, on the high part with AC going, hangs around the low 90s with the AC off (makes sense). Highway/Interstate driving (+70 MPH), now that can raise it all the way up to 160F, especially if you drive aggressive, it's easy to quickly reach that temperature. Oddly enough, I could never get it to go *past* that temperature no matter how much I aggressively raced down the highway. That also raises the coolant temperature right up to the 100F mark, but never more.

Now, the interesting part. I exit the highway from my +70 MPH (10 mile) test run, waiting at the stop light on the exit ramp. During that 1 minute wait the gear oil temperature drops from 160F to around 140F in that short of time. I'm not moving, so I'm not plowing air into the front of the car. It's still 85F outside, sunny too. I don't know how much thermal mass the whole "motor/inverter/charger" block has, but my gut feeling tells me some aggressive cooling is going on under the hood.

I guess my next research goal is the cooling pump and the fans for the grille, to see how much power they can use, do they have variable speeds. I know the fans do, I've heard them run on a low and high settings. I don't know if the coolant pump is variable or it if just has one on/off setting. The cool down time (from turning the car off) from 140F is a long time, like 15 minutes later and the gear oil temperature is still +120F with the outside temperature now 72F (night time)

More to come, this is interesting to observe...

It looks like your coolant temperature sensor is in the expansion tank. If so, that is likely why the coolant temperature increase lags the oil temperature. Most likely, the heating during aggressive or high-speed driving comes from high currents in the inverter and motor heating the metal and coolant in addition to the direct oil heating due to power transfer through the gear case. Since the coolant returning from the motor and inverter flows to the main part of the heat exchanger (radiator) where the heat is dissipated by air flow, you are not seeing true coolant temperature. Unfortunately, there is no easy way to add a temperature sensor to the main tank portion of the heat exchanger. It is good to see that the gear oil and the coolant (no matter how it is measured) both stay at very reasonable temperatures. I notice this in my climate because under hood temperature is always moderate even with stop/go or high speed driving on 110 F or higher days.

It will be interesting to see temperature comparisons between the low viscosity fluid you have now and the Nissan Matic-S (along with oil analysis).

GerryAZ said:

It looks like your coolant temperature sensor is in the expansion tank. If so, that is likely why the coolant temperature increase lags the oil temperature.

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Yeah, I knew it wasn't ideal. I was just trying to use the second probe for something. I did consider buying the hose and drilling it to put that sensor into since where it comes up to the tank, it's not under any high pressure but..... was trying to concentrate on the gear oil temperature. :lol:

Another interesting bit of data. Usually when I check the coolant and gear oil temperature, it reflects the ambient temperature outside when left sitting long enough. I checked it today before going on a trip and was surprised to see both the coolant and gear oil temperature was +120F. Then it dawned on me, the L2 EVSE was plugged in, has been charging for a few hours. I knew some heat was generated by the onboard charger and the water pump does run while it is charging, but I was surprised that so much heat was generated. I've never seen the coolant temperature over 100F, so my guess that since the radiator fans were not running, the whole system builds up a lot of heat. I did wonder at what temperature would the radiator fans finally switch on to start some active cooling, but someone else probably knows that technical bit of information.

Driving of course, lowered the coolant temperature back down to the sub 100F range after only a few miles.

More notes from today. Running the AC will actually lower the temperature of the gear oil by 10F, so instead of averaging about 140F during the day while driving, it hangs around closer to 130F, as long as speeds are under 55 MPH. Coming to a complete stop does further cooling if you stand still long enough in stop n' go traffic. Once you start fighting the air resistance and using more power, it brings the temperature back to the 140F range. Interstate speeds still keep it at around 160F, even with the AC running. My guess is that the AC keeps the radiator fans going constantly, so as a by-product, the whole charger/inverter/motor block gets additional cooling. A few more days of this, should give me a good baseline for how the temperatures work before I switch back to Nissan Matic S gear oil.

^^ Sorry if I missed it -- what have learned about ATF about the rise of temperature from ambient ?
I presume that efficiency gains will be most apparent at lower ATF temperatures.

We have to move you to a winter climate for some "real world" testing

SageBrush said:

^^ Sorry if I missed it -- what have learned about ATF about the rise of temperature from ambient ?
I presume that efficiency gains will be most apparent at lower ATF temperatures.

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It only takes a few miles of driving to warm up the ATF. My guess is most of the heat comes from the Motor. I'm still researching how much power the water pump uses, how much power the radiator fans use, when do they come on (if not using the Heatpump) temperature wise when the temperature is high enough, etc. I can watch LeafSpy to see how much power is on the 12V system, but I doesn't tell me which device is using the power or how much. I guess I could always just switch on the Leaf and just stick a "space heater" into the engine area to artificially make the radiator hot and just monitor the 12V power usage, fans, etc. to see how hot it has to be before they kick on. Hmm...

We have to move you to a winter climate for some "real world" testing

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Dry-ice the engine area.... maybe... :mrgreen:

I will make an attempt to measure the coolant temperature when the radiator fans kick on while charging the next time I charge. In my hot climate, the radiator fans do come on periodically while charging. I believe the coolant pump(s) run all the time when the car is on or charging (although at slower speed when coolant is cool). Since the radiator fans run whenever the heat pump compressor runs, it is normal for them to drop the coolant temperature when A/C is on even if the motor and inverter are not generating a lot of heat.

GerryAZ said:

I will make an attempt to measure the coolant temperature when the radiator fans kick on while charging the next time I charge. In my hot climate, the radiator fans do come on periodically while charging. I believe the coolant pump(s) run all the time when the car is on or charging (although at slower speed when coolant is cool). Since the radiator fans run whenever the heat pump compressor runs, it is normal for them to drop the coolant temperature when A/C is on even if the motor and inverter are not generating a lot of heat.

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I knew I read somewhere that someone can get the radiator fans to come on during charging, I just couldn't find it. Thanks for sharing here, it is greatly appreciated!

120F wasn't high enough, at least from what I measured today by accident. I bet I was close though. Tomorrow I might try a "let it sit in drive mode and feed it heat" experiment to see how hot the motor block has to get before the radiator fans kick on to simulate driving in some extreme heat. I have a heat gun, should be easy to switch it to low and just feed it right into the front of the car without melting anything (hopefully). I can monitor the coolant and gear oil temperature and LeafSpy real-time to know about where it triggers. This way I can tell when the cooling system is kicking into high mode under normal conditions but just can't tell because everything is so quiet under the hood while driving.

More interesting data... charging via L2 raises the temperature of the coolant, gear oil, everything connected by 10F per hour when the outside ambient temperature is 75F. This is on a 2020 Leaf, not sure how it would equate to the earlier Gen 1 version(s), but still data non the less.