6MT, which gear for mountain grades?

[BroncoAZ]

Should I be in 5th or 6th gear for best efficiency on the grades?

I’ve had my Passat for a couple years and I’m curious is I’m driving it wrong. My regular commute includes I-17 between Flagstaff and Phoenix, this road includes a couple long 6-7% grades that I drive at 72 mph (speed limit 65) or 80 mph (where speed limit is 75). I’m usually the one passing everyone on the hill because I have a diesel Since purchasing my car I’ve run these in 6th gear without issue, I figured the torque of the TDI is happily shoving me up the grades. It appears that the consumption reading supports my decision as it doesn’t drop below 20mpg in 6th, but hits teens in some spots in 5th. I don’t believe I’m lugging the engine or anything in 6th, and the car never indicates a downshift on the gear indicator. When I get slowed down by traffic or dualing truckers I downshift to 4th gear and floor it up to 80-81 mph and then shift back to 6th and resettle at 79 mph.

My 2011 Touareg would usually downshift from 8th to 7th on these same grades, but the ratios are closer there than my Passat.

 

[Tom in PT]

Stay in 6th gear.

I've paid a lot of attention to the instantaneous mpg readout in my 2013 Passat TDI DSG and it always indicates that running at a higher gear (at lower RPM) for a given speed produces better fuel efficiency.

So, in your situation leave it in 6th and let the transmission select the best gear given the load if you need to pass.

By the way, your economy is taking a big hit going 80 instead of the speed limit but I am sure you know that.

 

[BroncoAZ]

Stay in 6th gear.
I've paid a lot of attention to the instantaneous mpg readout in my 2013 Passat TDI DSG and it always indicates that running at a higher gear (at lower RPM) for a given speed produces better fuel efficiency.
So, in your situation leave it in 6th and let the transmission select the best gear given the load if you need to pass.
By the way, your economy is taking a big hit going 80 instead of the speed limit but I am sure you know that.

Tom,

Thanks for confirming what I was thinking. My car is a manual, so the selecting is up to me.

As for the mpg hit at 80, my lifetime average is in the fuelly link. 40.9 mpg is good enough for me. I don’t know how much better it might be at 75 vs 80, but I’m guessing I lose much more mpg accelerating from 55 to 80 in 4th gear at full throttle after getting cut off by idiots going up the hill.

 

[Graham Line]

Difference in fuel economy in a 6MT Golf can be a 10% loss at 80, rather than 75. The Passat is heavier but has better aero.
Up long grades, I frequently drop the Golf down a gear. It depends how much I'm carrying in the car. Optimum seems to be around 1900-2000 rpm.

 

[IndigoBlueWagon]

The only thing I'd worry about is that running under a heavy load (steep grade) at relatively low RPMs can drive EGTs pretty high. At 75 you're probably right around 2000 RPM. I'd be inclined (pun intended) to drop it down to 5th. I don't think the instantaneous FE readout is that useful: I don't think it would materially affect FE.

 

[BroncoAZ]

The only thing I'd worry about is that running under a heavy load (steep grade) at relatively low RPMs can drive EGTs pretty high. At 75 you're probably right around 2000 RPM. I'd be inclined (pun intended) to drop it down to 5th. I don't think the instantaneous FE readout is that useful: I don't think it would materially affect FE.

I had considered the EGT aspect enough to ask my buddy (shop foreman at VW) about it. His answer was that the cars are sophisticated enough that it would reduce power before I could cause any damage. On my diesel truck I set my hill speed by the EGT gauge when towing, but there is no gauge in the Passat or Touareg. If I read it right, the dieselgate warranty covers the engine block/rotating assembly itself, so if I grenade something they replace it. I will not be keeping these cars past the warranty.

You’re spot on with the RPM. On the tack it looks like 2010 at 75, 2070 at 80. I could use my Bluetooth scan tool and get an accurate RPM, but I think it’s close enough. I’ll check the RPMs in 5th at those speeds, I want to say they’re about 300 higher.

 

[BKmetz]

What IndigoBlueWagonsaid.
​

I have a ScanGuage-II and monitor EGT. Even on moderate grades the EGTs can get quite high, over 1300F. 1300F+ is OK for short durations as zipping through the gears but not as a sustained load.

For climbing grades I drop a gear and it lowers the boost and EGTs. I drove out to Denver last year for a wedding. On some of those grades I even dropped to 4th. What I do while climbing a grade is keep the RPM between 1800 and 2000. That takes enough load off the turbo and keep the EGTs down a bit.

Yes, the ECM will cut boost if the EGTs get too hot for too long, but then that forces you to drop a gear anyway because you're also loosing power.

Drive more and worry less.

 

[BroncoAZ]

What IndigoBlueWagonsaid.
​

I have a ScanGuage-II and monitor EGT. Even on moderate grades the EGTs can get quite high, over 1300F. 1300F+ is OK for short durations as zipping through the gears but not as a sustained load.

For climbing grades I drop a gear and it lowers the boost and EGTs. I drove out to Denver last year for a wedding. On some of those grades I even dropped to 4th. What I do while climbing a grade is keep the RPM between 1800 and 2000. That takes enough load off the turbo and keep the EGTs down a bit.

Yes, the ECM will cut boost if the EGTs get too hot for too long, but then that forces you to drop a gear anyway because you're also loosing power.

Drive more and worry less.

The RPM while climbing grades at 80 mph in 6th gear is 2080, so above the range you suggest. If I get slowed by traffic I downshift to 4th gear to get back up to speed, I don’t just floor it in 6th and hope it gets back to speed. I’ve been driving the grades in 6th for the past 32K miles I’ve had this car. I’ll have to see if I can monitor EGT on the Torque app. Please don’t take my response as blowing you off, I completely understand where you are coming from and appreciate the answer.

Sustained 1350+ in my Cummins will melt the aluminum pistons, which is why I drive it by the EGT gauge when towing.

 

[IndigoBlueWagon]

You did ask our opinions, right?

I posted about dropping down a gear because I have an EGT gauge in my ALH and have seen them get high when accelerating at low revs in 5th. Even if your car has a limiter that will reduce power, I would think that by the time that kicks in you've already risked damage to the turbo. These cars have tiny turbos that run hot already, and Borg-Warner turbos in older VWs have proven fragile at high altitudes. There an active thread here now about a BEW owner on CO who only got 25K out of a replacement B-W turbo on a tuned car.

I don't baby my car, but I'll give the hardware a break when I can. Dropping down a gear is an easy way to do it. Of course you should do what you want. But if you ask...

 

[turbobrick240]

5th gear on the steeper slopes. Pay no heed to the shift indicator on the dash.

 

[BroncoAZ]

You did ask our opinions, right?

I posted about dropping down a gear because I have an EGT gauge in my ALH and have seen them get high when accelerating at low revs in 5th. Even if your car has a limiter that will reduce power, I would think that by the time that kicks in you've already risked damage to the turbo. These cars have tiny turbos that run hot already, and Borg-Warner turbos in older VWs have proven fragile at high altitudes. There an active thread here now about a BEW owner on CO who only got 25K out of a replacement B-W turbo on a tuned car.

I don't baby my car, but I'll give the hardware a break when I can. Dropping down a gear is an easy way to do it. Of course you should do what you want. But if you ask...

Yes I did ask and I do appreciate the responses. I hadn’t read about turbo issues at high elevation on some models, but seeing as one of my grade climbs goes from 3500’ to 7000’ it is pertinent to the question. I’ll try 5th gear on the hills on the next trip and see if it feels much different.

I kind of wonder what a DSG car would do on these climbs, would it downshift itself or would it stay in the higher gear? It’s been so long since I had the DSG Jetta that I don’t remember.

 

[BKmetz]

5th gear on the steeper slopes. Pay no heed to the shift indicator on the dash.

Indeed, it would have you upshifting at 1200 RPM. I like to be around 2000 RPM when I upshift.

Before I bought my 2014 I had a 96 Passat with a 1Z engine and a 5-speed. The 2014 Passat with the CKRA engine and 6-speed was so quiet and smooth I forgot to upshift all the time as I was used to the gearing, power band, and engine noise of the 1Z. Also, the sweet spot for the 1Z was 1800 to 2000 RPM, a bit higher than the CKRA (and now my CVCA) which is 1500 to 1800 RPM. Many times I had driven miles in 4th or 5th gear before I noticed the upshift arrow on the gauge cluster.

Drive more and worry less.

 

[740GLE]

What IndigoBlueWagonsaid.
​

I have a ScanGuage-II and monitor EGT. Even on moderate grades the EGTs can get quite high, over 1300F. 1300F+ is OK for short durations as zipping through the gears but not as a sustained load.

AFAIK the EGT safety limit of the ECU is up around 1600F at least that's what I've seen in our '15 Passat trying to pass up hill at 85+ before temps started to fall, which was right when I backed off. I've only done that once or twice and its not an every day commute experience. If I had the OPs commute, I would prob drive in 5th and not thing twice about it.

1300 is right around regen temps so can't be that bad for it.

 

[tdiatlast]

BroncoAZ: I have a ScanGauge II I'd be willing to part with. I always had mine velcroed to the steering housing. It really was useful.
Let me know via PM.

 

[Jetta_Pilot]

The rule of thumb is/was to use whatever gear you'd be in going uphill, use the same going downhill and let your engine do some braking. Using your brakes only is not a good idea. Some very steep hills have emergency ramps going down because overheated brakes do not work very well.

 

[BroncoAZ]

The rule of thumb is/was to use whatever gear you'd be in going uphill, use the same going downhill and let your engine do some braking. Using your brakes only is not a good idea. Some very steep hills have emergency ramps going down because overheated brakes do not work very well.

What is this "engine braking" that you speak of? My Passat accelerates down the grades in 5th or 6th gear with no throttle, if I don't hit the brakes it will be exceeding ~100 mph at the bottom. The grades I'm on are 6% for 7+ miles. I don't want to run the RPM's up over 3500 in 4th going down the hill to try and slow it down, even then I'm not sure it will.

I just replaced my warped front brakes a couple thousand miles ago at 56K, they were warped since I bought the car at 26K but got noticeably worse recently. I don't ride the brakes down the hill, I let the car accelerate to ~83 and then do a firm brake application to get it back down to ~75 and repeat that cycle as necessary giving the brakes plenty of time to cool between applications. My new brakes are ceramic pads.

 

[Tom in PT]

In my car (2013 Passat TDI DSG) I downshift as necessary to hold speed on downgrades and run the engine fast (over 3000 RPM) if necessary. In my experience the engine develops a lot of braking force when the RPMs rise above 3000.

In my 2012 F-250 6.7 diesel, it has an exhaust brake built into it but the exhaust brake is not very effective below 2,500 rpm. However, when I tow and it downshifts to 3rd gear at 2,700 rpm it develops enough braking to keep my rig (~ 14,000 lbs combined) at ~55 \mph on a 6 percent grade. In this towing situation I climb the hills in 5th or even 4th but descend in 3rd.

I certainly don't worry about damage to the engine turning this fast in either engine.

 

[BroncoAZ]

I measured EGT on the Torque app on today’s drive. Pulling the grades at 73 mph in 6th gear the EGT hovered around 1200 degrees f with a couple spikes to 1325 degrees f. I downshifted to 5th and was seeing EGT around 1120 degrees f with a spike of 1225 degrees f. My return drive on Thursday will have more up grade driving and at 80 mph instead of 73. In 6th gear on flat ground, full throttle acceleration from 75 mpg to 85 mph showed a highest EGT of 1380 degrees.

I tried downshifting to 5th and 4th on the downhill. The car doesn’t hold speed in either gear. In 4th with the cruise set at 72 and RPM about 3200 the car accelerated to 79 mph before I hit the brakes. It certainly accelerated slower downhill than 5th or 6th gear, but it won’t hold speed downhill.

 

[740GLE]

now try accelerating from 70 to 90 in 6th climbing the hill

 

[Jetta_Pilot]

I tried downshifting to 5th and 4th on the downhill. The car doesn’t hold speed in either gear. In 4th with the cruise set at 72 and RPM about 3200 the car accelerated to 79 mph before I hit the brakes. It certainly accelerated slower downhill than 5th or 6th gear, but it won’t hold speed downhill.

Who the hell would use cruise control going downhill set for 72Mph ???

 

[BroncoAZ]

Who the hell would use cruise control going downhill set for 72Mph ???

Me, obviously...what am I supposed to set it for? I drive on fast mountain highways.

I set my cruise for 79 down the 75 mph grades and 72 down the 65 mph grades. I’m usually moving about the speed of traffic. In my 2015 Touareg TDI I set the cruise and manually shift to 7th gear, it holds speed perfectly at the set point all the way down the grade. My Passat accelerates down the grades, even in 4th gear. I did find that it seemed to top out the acceleration at 80 mph in 4th gear from a set point of 72 mph, RPM at 3331 on one of the grades from Sunset Point down to Rock Springs.

now try accelerating from 70 to 90 in 6th climbing the hill

I did some experiments on the way home Thursday night. Accelerating 70-90 mph in 6th gear up a 6% grade resulted in an EGT of 1463.5 degrees F at 2479 RPM with 9.9 psi of boost.

Here are some other results, I was taking screenshots of Torque when I saw the temps spike.
80 up grade in 6th: 2175 RPM, EGT spiked at 1309 degrees F, 9.1 psi boost
80 up grade in 5th: 2604 RPM, EGT spiked at 1290 degrees F, 7.8 psi boost
72 up grade in 6th: 1964 RPM, EGT spiked at 1238 degrees F, 10.3 psi boost
72 up grade in 5th: 2341 RPM, EGT spiked at 1176 degrees F, 8.3 psi boost
80 on flat in 6th: 2192 RPM, EGT settled at 780 degrees F, 0 psi boost
75 down grade in 4th: 3145 RPM, EGT at 246 degrees F, 0 boost

To me the temps don’t look that different in 6th or 5th gear when climbing grades. Yes, there is a 20-50 degree difference, but it’s not 100+ degrees difference at either speed. They all seem high compared to what the pre turbo gauge in my Cummins truck shows. My 7K truck towing 9K at 65 mph up the same grades as the car at 72 mph is about 1150 degrees F.