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- Ecosse
- Member Since: 13 Jul 2016
- Location: Grampian
- Posts: 35
Engine braking using gears?
With my D4 8-spd, using the paddle shifts to select a lower gear provided an engine braking effect that was excellent for slowing the car without using the brakes when approaching a corner/hill etc., and was especially useful when towing.
I'm struggling to get the same effect from the D5's gearbox - selecting a lower gear simply increases revs but does not appear to provide any obvious braking effect from the engine that I would have expected with the foot "off" the throttle. Is this normal?, or is there something to select (have tried the Sport mode & different TR settings but not the configurable one yet) to give engine braking? Thanks! -
- DieselRanger
- Member Since: 12 Oct 2017
- Location: God's Country, Colorado
- Posts: 793
If your D4 was a petrol engine and your D5 is a diesel that explains the difference. Diesel engines don't engine brake as well as petrol unless an auxiliary engine or exhaust brake is installed to create the vacuum necessary to limit the engine speed; or you select low range, which I would not recommend when driving on-road or while towing, because the low range gear box does not have its own transmission cooler and it's speed-limited anyway.
My 2017 D5 will limit its speed somewhat using the transmission in S mode and manually selecting the gears via the paddles. Typically 3 or 4 works to keep speed under ~60kph depending on the grade, but if the grade is steep enough, straight enough, or long enough it will gradually pick up speed and approach redline and I'll have to tap the brakes.
In a diesel, trying to shift down from a higher gear without first slowing down to match the speed for that gear will just cause the RPMs to spike. You need to first slow down to the speed you want to travel at, and then downshift to the proper gear.
My low range is far too low for anything but off-road, but when I am off road, the crawl ratio is so low that the off road speed control and HDC are superfluous. -
- Ecosse
- Member Since: 13 Jul 2016
- Location: Grampian
- Posts: 35
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Thanks, interesting!
I wonder if there was something fundamentally different with the D4 set up - my 8 speed (a TDV6 diesel) definitely created considerable engine braking through using the paddle shifts, but it was a pre-Euro6 model so there may be some emissions/fuel economy issue involved. I've got a LR Experience course coming up so will question the instructors there on the issue and feedback any input they provide. -
- DG
- Member Since: 27 Apr 2016
- Location: Surrey
- Posts: 445
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Which MY D5 do you have, Ecosse, and does it have a hi/lo range or only a hi range?
If you select Sport and then use the paddles to invoke manual transmission mode, it should hold the current gear indefinitely (unless you hit a safety override, e.g. redline it).
23 year LR veteran > D2 GS 2003 > D3 S 2006 > D3 HSE 2009 > D4 HSE 2013 > D4 HSE 2015 > D5 HSE 2018 > DS HSE R-Dynamic P300e 2021 > D5 HSE Dynamic D350 2025 -
- Ecosse
- Member Since: 13 Jul 2016
- Location: Grampian
- Posts: 35
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Hi DG, it's a 2023MY 300D mh, Hwith hi-lo transfer box, rear e-diff and config TR. Have tried S mode, using paddle shifts, then with foot off accelerator there is a slight slowing but it's more as if it's in neutral/coasting!, whereas in the 2012my D4 with similar spec and 8 speed, selecting a lower gear by paddles in either D or S brought in a very clear deceleration almost as if using the brakes! This was very useful on hills and if approaching a bend, and in particular when towing a moderately heavy trailer.
It's very much as if the car is coasting if I take the foot of accelerator on selecting lower gear although the revs show it is not.
Thanks. -
- DG
- Member Since: 27 Apr 2016
- Location: Surrey
- Posts: 445
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Thinking back to my own D4s, you are right, now you have mentioned it. I looked back at the SDV6 specs and compared them with the D300. For those of us who have had D3s, D4s and D5s, I don't think you are imagining it.
Engineering progress appears mainly to be to blame. The D4 was from an era where engines naturally dragged a bit, whereas the modern D300 is designed to roll as freely as possible. The old SDV6 had a fair bit of natural resistance. When you lifted off, the engine acted more like an anchor to help slow the motor down. The D300 is the opposite and designed to be very low-friction. It is allowed to spin very freely to keep the emissions system hot and efficient.
The D300 tries to make up for some loss of engine braking with its Mild Hybrid electric motor. When it's regenerating, you get some electrical braking — but once that battery is fully charged on a trip, the drag will fade away, and it feels like it wants to coast even more. Add in the gen 3 8speed gearing and slightly larger rolling radius on the tyres (if you have 21" or 22") and it does feel much more 'slippery' than a D4.
You might take a slightly different approach when taking it downhill. Since you can’t rely on passive engine braking in the same way, you could drop it a gear earlier than you would have before, maybe one gear lower than feels intuitive. This might work best in Sport with the paddles so that it holds the gear.
Hopefully, it should become predictable again. IMO probably just needs a different approach.
23 year LR veteran > D2 GS 2003 > D3 S 2006 > D3 HSE 2009 > D4 HSE 2013 > D4 HSE 2015 > D5 HSE 2018 > DS HSE R-Dynamic P300e 2021 > D5 HSE Dynamic D350 2025 -
- DieselRanger
- Member Since: 12 Oct 2017
- Location: God's Country, Colorado
- Posts: 793
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Ecosse wrote:
Hi DG, it's a 2023MY 300D mh, Hwith hi-lo transfer box, rear e-diff and config TR. Have tried S mode, using paddle shifts, then with foot off accelerator there is a slight slowing but it's more as if it's in neutral/coasting!, whereas in the 2012my D4 with similar spec and 8 speed, selecting a lower gear by paddles in either D or S brought in a very clear deceleration almost as if using the brakes! This was very useful on hills and if approaching a bend, and in particular when towing a moderately heavy trailer.
It's very much as if the car is coasting if I take the foot of accelerator on selecting lower gear although the revs show it is not.
Thanks.
The mild hybrid might be the difference? However, I would think there would be some regenerative braking force generated...perhaps it's not enough....
Wish we could get that powertrain in the US...thanks for nothing, Volkswagen. -
- Mole HD
- Member Since: 18 Nov 2024
- Location: Orkney Islands
- Posts: 677
I've been watching this with interest. Mainly from the perspective of coming from a 2015 SDV6 D4 onto a 2017 TD6 D5 and noticing the lack of engine braking in comparison...nothing to do with hybrids in my case, but the effect is the same.
I had to change my driving style to being more brake reliant as a result of the low friction powertrain, even with my early (March 2017) TD6 D5 with the same 8 speed ZF gearbox as the D4...it did initially throw me off a bit and I found myself hammering the brakes approaching corners, belatedly realising the engine braking on the TD6 D5 was practically non existant. It took a few weeks to sink in.
As of now after a year of driving the D5, I've got used to it but the transition is especially noticeable when I occasionally jump into my old TD5 D2...even though that has a manual gearbox and almost legendary engine braking as a result, it certainly becomes a factor when judging corner approach speeds as I find myself over braking as a result of now being used to driving the D5.
That's just with normal day to day driving...towing a livestock or general use double axle trailer on and off road has opened a whole new experience of using the hill descent control button I never used with the D4, mainly due to it's engine braking...amongst other uniquely D5 towing and off road traction control settings that I rarely ever used on the D4 like launch assist and others.
My D5 has the capability plus pack with the centre and rear E-Diffs and advanced tow assist etc...which I admittedly have never used apart from trying it out because it was there. I'm constantly hooking and unhooking trailers, not just on the D5 but on tractors and other farm machinery so the additional faffing about when towing or reversing a trailer using the tow assist/trailer reverse assist isn't really a practical consideration in my case.
Anyway, the engine braking...or lack of it... is certainly a thing with the 3.0L diesel D5's in general, not just the newer hybrids... especially noticeable coming from a D4 used in the same context.
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- DG
- Member Since: 27 Apr 2016
- Location: Surrey
- Posts: 445
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Some interesting notes on the MHEV system
Technical Overview: Discovery D350 MHEV System
Vehicle: Land Rover Discovery L462 2025
Engine: D350 (3.0L Inline-6 Twin-Turbo Diesel - Ingenium AJ300D)
System Type: 48-Volt Mild Hybrid Electric Vehicle (MHEV) - "P0" Architecture
1. The Hardware: What is actually installed?
The D350 uses a P0 Topology, meaning the electric assistance happens at the front of the engine via a belt, not inside the gearbox or on the axles.
* BiSG (Belt Integrated Starter Generator):
* What is it? A 48-volt water-cooled electric machine bolted to the front of the engine where a standard alternator would sit.
* Drive: It connects to the crankshaft via a heavy-duty, reinforced 7-rib belt and a specialized bi-directional tensioner system.
* Power: Produces up to 14kW of power.
* Torque: Generates ~55Nm at the machine, but due to the pulley ratio (approx 3:1), it delivers roughly 150Nm of instant torque assist directly to the engine crankshaft.
* The Battery (Energy Storage Module):
* Location: Mounted in the rear load space (usually under the floor or behind the trim).
* Specs: Lithium-Ion (Li-ion) 48V battery.
* Capacity: Approx 0.2 kWh (200 Watt-hours).
* Note: This is a power battery, not an energy battery. It is designed to charge and discharge extremely fast (high C-rate), but it has very low capacity (roughly the size of a cordless drill battery array).
* DC-DC Converter:
* Steps down the 48V power to 12V to charge the standard 12V AGM battery and run the car’s lights, screens, and ECUs.
2. How the D350 uses it
The electric motor doesn't drive the wheels directly. It acts as a "torque manager" for the diesel engine.
* Torque Fill (Anti-Lag):
The D350 has large turbochargers that take a moment to spool. When you touch the throttle, the BiSG instantly fires 150Nm into the crank. This bridges the gap for the split-second before the turbos wake up, giving that "instant" throttle response.
* Regenerative Braking (The 'Drag'):
When you lift off, the BiSG flips to generator mode. It puts a magnetic load on the engine to harvest kinetic energy. This is what you feel as "engine braking."
* Stop/Start 2.0:
Because the BiSG is permanently connected by a belt, it can spin the engine to idle speed (800rpm) in under 600ms. This eliminates the "chug-chug-start" of the old starter motor. It allows the engine to shut off while you are coasting to a stop (below ~10mph).
3. Pros & Cons (Real World)
The Pros:
* Refinement: The Stop/Start system is virtually seamless. The shudder found in the old SDV6 is gone.
* Response: It makes the diesel feel like a naturally aspirated petrol V8 off the line by masking the turbo lag.
* Efficiency: It allows the D350 to meet Euro 6d emissions standards without strangling performance.
* Auxiliary Power: The 48V system powers the electric supercharger (e-SC) on some models (though D350 relies on sequential turbos) and supports high-load electrical accessories.
The Cons:
* Inconsistent Engine Braking: Because the 0.2 kWh battery is so small, it fills up very quickly on long descents. Once full, the regenerative braking must cut out to protect the battery. This causes the "disappearing brake" feel where the car suddenly surges/coasts.
* FEAD Belt Maintenance: The front engine belt is no longer just running a water pump; it is transferring drive torque. It is under immense stress. This belt is a critical service item—if it snaps, the car is dead (no charging, no cooling).
* Wading Risks: While JLR seals the units for 900mm wading, a belt-driven system is inherently more vulnerable to slip if mud or grit gets between the belt and pulley during deep water crossings compared to a sealed transmission hybrid.
* Complexity: Diagnostics are harder. A failure in the 48V system (battery or DC-DC converter) can sometimes throw the car into a "limp mode" even if the diesel engine is fine.
The D350's MHEV system is a brilliant piece of engineering for on-road refinement and emissions compliance. However, for towing and off-road users coming from the older D4, the "Battery Saturation" issue (loss of braking effect) and the reliance on a drive belt are valid trade-offs to be aware of.
23 year LR veteran > D2 GS 2003 > D3 S 2006 > D3 HSE 2009 > D4 HSE 2013 > D4 HSE 2015 > D5 HSE 2018 > DS HSE R-Dynamic P300e 2021 > D5 HSE Dynamic D350 2025
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