Jerkiness/Lurching from stopped when cold - Infiniti QX30 Forum
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post #1 of 9 (permalink) Old 06-04-2019, 02:54 PM Thread Starter
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Default Jerkiness/Lurching from stopped when cold

Hello,

Been trying to search the internet for this issue I discovered with my wife's '17 QX30, to no avail.

Happens in the winter time, when I come to a stop light and then start to get going again, the car lurches forward, hesitates, and jerks forward to get going. After about 10-15 minutes of driving it doesn't do that anymore. It doesn't matter if I let the car warm up for 10-15minutes before starting to drive, it still does it. Also doesn't matter if I have the auto shutoff feature off, it still does it.

I live in Ontatio, Canada so our winters are fairly cold.

The only explanation I found online is that it could be caused by the Dual Clutch Transmission, and that it's just the characteristic of it, however I refuse to believe that for the kind of money these cars are worth, a car could behave this "violently". I've tried researching if anyone might have this issue with their GLA250 as it's the same engine and tranny, but I haven't found any insight online either.

Any thoughts would be appreciated.
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post #2 of 9 (permalink) Old 06-04-2019, 05:22 PM
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It's a DCT, and it is just how they are.

The 7G-DCT uses dual wet clutches. They're called "wet" because the clutch is in a bath of oil (transmission fluid). When the fluid is cold, the clutches are a bit "grabby" and that leads to the jerky motion that you describe. Once the transmission fluid warms up, then operation is smooth.

Letting the engine warm up in a stationary position does little to warm up the transmission fluid. There is a heat exchanger in the transmission that transfers waste heat from the transmission fluid into the coolant circuit; however, it is designed only to cool the transmission fluid -- not to warm it up.

The easiest way to warm the transmission fluid is to drive the vehicle.
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post #3 of 9 (permalink) Old 06-04-2019, 08:21 PM Thread Starter
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It's a DCT, and it is just how they are.

The 7G-DCT uses dual wet clutches. They're called "wet" because the clutch is in a bath of oil (transmission fluid). When the fluid is cold, the clutches are a bit "grabby" and that leads to the jerky motion that you describe. Once the transmission fluid warms up, then operation is smooth.

Letting the engine warm up in a stationary position does little to warm up the transmission fluid. There is a heat exchanger in the transmission that transfers waste heat from the transmission fluid into the coolant circuit; however, it is designed only to cool the transmission fluid -- not to warm it up.

The easiest way to warm the transmission fluid is to drive the vehicle.
Thanks for the explanation...
I don't know much about oils and weights of oil, but I know some engine oils are more viscous in the cold than others...does the same apply to transmission oils?
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Thanks for the explanation...
I don't know much about oils and weights of oil, but I know some engine oils are more viscous in the cold than others...does the same apply to transmission oils?
Yes. I looked up the specs of Amsoil DCT, which Amsoil claims meets MB 236.21 specs, so it should work well in a QX30. The viscosity data shows the transmission fluid flows better when warm, and is more viscous when cool.

Kinematic Viscosity @100°C cSt: 7.7
Kinematic Viscosity @40°C cSt: 38.8
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post #5 of 9 (permalink) Old 06-04-2019, 10:37 PM Thread Starter
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Thanks.
I will have to talk to the Infinity Service dept next time I take it in and see what oil is OEM in there and if they could put that one in.
I am surprised that more people don't complain of this issue. I looked up that transmission model code, at 65% of C-class Mercs have that transmission.
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Thanks.
I will have to talk to the Infinity Service dept next time I take it in and see what oil is OEM in there and if they could put that one in.
I am surprised that more people don't complain of this issue. I looked up that transmission model code, at 65% of C-class Mercs have that transmission.
Factory oil is Shell DCT-M1. It is incredibly difficult to buy that EXACT fluid. I tried to quote the viscosity specs of that fluid, originally, but I couldn't even find a Shell technical data sheet. That's why I fell back to the Amsoil fluid. However, I am confident that the Shell fluid has similar viscosity characteristics -- since both claim to meet MB 236.21 specification (MB Specs are strict).

I'd be curious to see if you could even buy that exact fluid at your local Infiniti Parts Department. I expect they'll try to sell you an "equivalent" from another brand, instead.

Unless you have reason to believe someone changed your fluid to an incompatible one, then you should still have the factory fill in your QX30. The maintenance schedule says the transmission fluid and filter should be replaced every 60k miles or 5 years, whichever comes first. If you want to do it sooner, then that's your call. Shifting quality can degrade as the fluid wears out. But if shifting feels "good" when the transmission is warm then I'd suggest that new fluid is not likely to improve shifting.

I have serious concerns that many dealers will not be following the manufacturer-prescribed process for transmission fluid changes on the QX30. The Infiniti Service Manual is quite clear that the DCT filter MUST be replaced as part of the periodic maintenance. However, I have seen too many dealers cut corners, and I fear many will simply use a fluid-exchange machine and call that "good enough". I do not think those machines are a good idea -- especially not on a DCT. They've been known to cause problems with conventional transmissions, and I think they're an absolutely terrible idea on a DCT. Dealers who use the machine do so purely to save their own time, and end up ignoring the transmission filter. There WILL be clutch material caught by the filter, and it MUST be changed, otherwise flow will become restricted and if you let that go on too long you're asking for a failure. Replacement doesn't seem particularly difficult, but it is time consuming. The following parts must be removed to access the filter:
  1. ECM
  2. Engine Air Duct and Air Cleaner Housing
  3. TCM Harness (Connector)
  4. Left Charge Air Tube
  5. Engine Under Cover
  6. Oil Pan

Before you have a dealer change your fluid, make sure to confirm their pricing, and whether they change the filter. I would ask them lots of questions, and don't let them wiggle out with a non-committal answer like "we change it if it needs it, or we change it if it has one". I would make sure they confirm the QX30 does have a filter, that they're aware of and familiar with how involved it is to access, and that they will change it. Expect to pay several hours labor for them to do it right. This is not a "cheap" service.


MB 236.21 DCT ATF lists for $31 per quart. Online it goes for around $23.
The QX30 requires 5.125 qt of ATF (2WD) or 5.5 qt of ATF (AWD).

For labor, I'd expect around 4 hours of billable labor, plus/minus an hour.

Ultimately, I wouldn't be surprised to see a $600+ estimate for a dealer to PROPERLY perform a transmission fluid service. It would be even more if you're in a high-COL area with a shop that charges a premium.

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post #7 of 9 (permalink) Old Yesterday, 07:01 PM Thread Starter
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Originally Posted by Krystian View Post
Thanks.
I will have to talk to the Infinity Service dept next time I take it in and see what oil is OEM in there and if they could put that one in.
I am surprised that more people don't complain of this issue. I looked up that transmission model code, at 65% of C-class Mercs have that transmission.
Factory oil is Shell DCT-M1. It is incredibly difficult to buy that EXACT fluid. I tried to quote the viscosity specs of that fluid, originally, but I couldn't even find a Shell technical data sheet. That's why I fell back to the Amsoil fluid. However, I am confident that the Shell fluid has similar viscosity characteristics -- since both claim to meet MB 236.21 specification (MB Specs are strict).

I'd be curious to see if you could even buy that exact fluid at your local Infiniti Parts Department. I expect they'll try to sell you an "equivalent" from another brand, instead.

Unless you have reason to believe someone changed your fluid to an incompatible one, then you should still have the factory fill in your QX30. The maintenance schedule says the transmission fluid and filter should be replaced every 60k miles or 5 years, whichever comes first. If you want to do it sooner, then that's your call. Shifting quality can degrade as the fluid wears out. But if shifting feels "good" when the transmission is warm then I'd suggest that new fluid is not likely to improve shifting.

I have serious concerns that many dealers will not be following the manufacturer-prescribed process for transmission fluid changes on the QX30. The Infiniti Service Manual is quite clear that the DCT filter MUST be replaced as part of the periodic maintenance. However, I have seen too many dealers cut corners, and I fear many will simply use a fluid-exchange machine and call that "good enough". I do not think those machines are a good idea -- especially not on a DCT. They've been known to cause problems with conventional transmissions, and I think they're an absolutely terrible idea on a DCT. Dealers who use the machine do so purely to save their own time, and end up ignoring the transmission filter. There WILL be clutch material caught by the filter, and it MUST be changed, otherwise flow will become restricted and if you let that go on too long you're asking for a failure. Replacement doesn't seem particularly difficult, but it is time consuming. The following parts must be removed to access the filter:
  1. ECM
  2. Engine Air Duct and Air Cleaner Housing
  3. TCM Harness (Connector)
  4. Left Charge Air Tube
  5. Engine Under Cover
  6. Oil Pan

Before you have a dealer change your fluid, make sure to confirm their pricing, and whether they change the filter. I would ask them lots of questions, and don't let them wiggle out with a non-committal answer like "we change it if it needs it, or we change it if it has one". I would make sure they confirm the QX30 does have a filter, that they're aware of and familiar with how involved it is to access, and that they will change it. Expect to pay several hours labor for them to do it right. This is not a "cheap" service.


MB 236.21 DCT ATF lists for $31 per quart. Online it goes for around $23.
The QX30 requires 5.125 qt of ATF (2WD) or 5.5 qt of ATF (AWD).

For labor, I'd expect around 4 hours of billable labor, plus/minus an hour.

Ultimately, I wouldn't be surprised to see a $600+ estimate for a dealer to PROPERLY perform a transmission fluid service. It would be even more if you're in a high-COL area with a shop that charges a premium.
Thanks for all that insight. I would have never imagined so many issues could be involved around a transmission!

The sad part is that for a lot of these repairs/scheduled maintenance...you're at the mercy of the mechanics, because there probably is absolutely no way of knowing if the filter has been changed, only to take their word for it.

I have a feeling that they won't be much help with the jerkiness issue. I'll have to wait till next winter in order to recreate that on a test drive with them.
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I also live in SW Ontario and once in a while experience this during the cold months... after a few minutes of driving it goes away; this is a normal behavior of a DCT while the oil warms up. You are overthinking it, just keep in mind the first few min of driving until the transmission gets a little warmer and that is it. Even if you change the oil for something thinner..... it does not guaranty that the DCT will not do it while warms up, might be a few minutes sooner but still......
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post #9 of 9 (permalink) Old Today, 10:02 AM
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The sad part is that for a lot of these repairs/scheduled maintenance...you're at the mercy of the mechanics, because there probably is absolutely no way of knowing if the filter has been changed, only to take their word for it.
Yes, if you choose to use a mechanic, then you must find one you trust. You can ask to be shown the used filter, after they replace it. It doesn't guarantee an absolutely dishonest mechanic won't still try to bamboozle you, but it would give you some peace of mind if your mechanic was mostly decent.

Personally, I'll probably DIY my transmission fluid service -- not that I really want to, but I want it to be done PROPERLY. No one will treat my vehicle better than I will.

I recently purchased a new Honda Goldwing. I saw it taken out of the crate. When I took delivery it had only 2 miles on the odometer. It should be PERFECT, right? When I started installing my foglights I realized the dealer techs were neanderthals and didn't install several bolts properly. The two bolts that attach the saddle to the frame were just pushed in the bore and not threaded in AT ALL. I was also missing a fairing bolt and clip, entirely. I'm currently waiting for my PartZilla order to ship so I can replace the missing fasteners. My point is that mechanics "know" what they're doing, but they're usually not careful, in my experience. They're always in a rush to get to the next job, because their pay structure incentivizes them to get vehicles out, quickly, rather than maintain high quality.

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Originally Posted by Krystian View Post
I have a feeling that they won't be much help with the jerkiness issue. I'll have to wait till next winter in order to recreate that on a test drive with them.
Even if you perfectly reproduce the issue I honestly don't think you'll get any satisfaction. By your description, it seems the transmission is behaving as-designed. The mechanics can't fix what isn't broken. But if you pester them enough, they'll fix it until it IS broken.

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