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Holden Cruze 1.8L 2012. 63k miles odometer (15-03-2020).
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Discussion Starter #1
So I took my car to get the manual transmission serviced, using the Castrol VMX-80 for better gear shifting which it does especially when cold started. I wrote on the second bottle to pour 800ml, not the whole 1000ml but they poured the whole 2L anyway and I saw an oil stain down the front of the geabox housing suggesting some spilled out the fill hole and they cleaned it up.

Now the fuel economy is about 8% worse and I have noticed on routine routes the car does not accelerate down low gradient hills by gravity like it used to.

Anybody have experience with this?
 

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Is the new fluid the correct fluid for your transmission? I can't see 200ml extra fluid making that much difference. I could see using a heavier weight oil causing a decrease in mileage.
 

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Holden Cruze 1.8L 2012. 63k miles odometer (15-03-2020).
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Discussion Starter #3
It showed up in the oil matcher so I am assuming yes. It is a thinner oil, that is how the gears change smoother, no bunny hopping. I did read over filling can cause the gears to be immersed in oil so that it churns, which creates heat and reduces power because of extra drag. Apparently that loss of power is the cause of slightly worse fuel economy. I think I will syringe out the 200ml when I buy the tools to remove the filler cap.
 

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I can see being significantly overfilled causing that to happen. It just doesn't seem like 200ml would raise the fluid level enough to cause a noticeable difference, but maybe?
 

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Holden Cruze 1.8L 2012. 63k miles odometer (15-03-2020).
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Discussion Starter #5
I will report back when I take out the 200ml. Might get around to it this weekend and test the MPG for a week. It takes time after resetting the fuel consumption meter to average out.

The higher real time fuel consumption is mostly when accelerating hard into high rpms or when cruising above 35mph (50kph). The faster I cruise the worse the fuel economy. From what I read the faster the gears spin while in too much oil, the more drag and power lost as heat which makes sense to me.
 

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Holden Cruze 1.8L 2012. 63k miles odometer (15-03-2020).
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Discussion Starter #6
The situation is more complex than I think. I suspect they over filled it by 400ml! Because a Russian guide indicated that the fill capacity is not 1.8L like the manufacturer says, but 1.6L.

I posted here all about it. Videos and articles available.

Looks like I will have to buy a gasket, replacement oil and have it drained and filled again!
 

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Holden Cruze 1.8L 2012. 63k miles odometer (15-03-2020).
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Discussion Starter #7
I replaced the gearbox oil with 1.8L 75w85 synthetic from Penrite along with 50ml of MBL8. Solved the drag issue, I accelerate downhill now even with AC on. The MBL8 causes the transmission to reach operating temps after 30 minutes of driving. The VMX-80 had much smoother gear changing. Down or Up shifting.
 
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