Engine braking on manual

[LakesPuma]

Has anyone else found that the engine provides very little braking when you lift off the accelerator?

 

I'm not saying its a problem just very noticeable compared to my old Mondeo, which I could drive on the motorway pretty much without using the brakes at all.

[RickTT]

I too have noticed that the the engines provide less resistane when holding a gear compared to other cars i have had in the pass, however comparing it to other modern cars on the market its around the same..

 

Wonder if its the engines are so refined now for emissions etc that theres less compression needed resulting in less resistance?? i have no idea lol ...

[Sec8200]

mainly depends on the engine volume, what is yours?

[glosrich]

Also your 'old mondeo' may have had dodgy brakes binding a bit, so slowing it down when the throttle was lifted...lol

[KenONeill]

This might not seem directly relevant, but my 15 year old Octy TDi is still freer rolling on over-run than a lot of cars, to the extent that have to brake to hold distance when they're just on over-run.

[Gerrycan]

I'm surprised to hear that new diesels also experience low engine braking (not driven one)

The retardation provided by the petrol 1.4tsi in my mk3 Octavia is almost non-existent.

 

A hill I could take in 4th gear (only 5 gears) in my old 1.9pd, I now have to still dab the brakes when revving its heart out in 2nd gear.

 

Of course it does benefit economical driving once you get used the extra distance anticipation required.

[psycholist]

Diesel engines have no engine braking to speak of as there's no throttle butterfly to block intake air. It's artificially added on some cars by including a valve in the exhaust system (I don't think VAG cars have this mostly because I've never of one failing) or by changing the valve timing in the case of retarders on trucks (The downside of this is that the engine sounds like a jackhammer while the retarder is on because it's effectively doing the same thing - letting the piston make full compression and then releasing the built up pressure instead of allowing it to push the piston back down as it would on a normal 4 stroke cycle).

 

This lack of drag for air going through the engine is part of what makes diesels inherently more fuel efficient. Modern cars can increase the power generation from the alternator to increase engine braking on overrun, but for the most part any slowing you see when you get off the accelerator is due to friction.

[MCG1975]

I get some braking particularly in lower gears, but come to think of it not so much in 5th or 6th...will have to look at this on the way home tonight.  Definitely get some if I drop to 4th approaching a roundabout and lift the clutch...

[Lol6]

Perhaps lower rolling resistance tyres is the cause of this. I have Pirellis on the Superb. On my previous Mazda 6 I had Michelins and the car slowed much quicker on overrun. I will find out whether I am right when I switch from Pirellis to Michelins on this car as IMHO they are a superior tyre in every other respect.

[MCG1975]

I get some braking particularly in lower gears, but come to think of it not so much in 5th or 6th...will have to look at this on the way home tonight.  Definitely get some if I drop to 4th approaching a roundabout and lift the clutch...

 

OK I take it all back - on my drive home last night there was minimal resistance when releasing the accelerator in all gears - the braking effect I do notice is when I drop down to 4th or 3rd approaching a roundabout so it's a bit more pronounced than just letting the power off...

[mastersteph44]

What rpm u are when changing gear,

Best engime break is after the torque rpm

So u need to be first up of this point before put down a gear and then u will be more higher after changing

Like 2000 rpm in 3rd and then 3000 in 2d

And of course more the gear is low ( direct ) more the brake is strong

If u are in 6 and at 1200rpm u will not have rake when changing to 5 at 1900rpm

No torque and too much long geared box

Edited 19 November, 2016 by mastersteph44

[KenONeill]

MasterSteph has a point; these cars are very long geared (but I don't agree "too long" necessarily) and long gears mean poor engine braking in the high gears until you're going very quick.

[Trevormw]

Hi,

 

Just bought skoda superb estate 2015 2l diesel. Also noticed lack of engine braking. Also after stopping car will idle at 1000 revs if I apply the brake it drops to 750 if I release the brake it returns to 1000. Completely

repeatable.

[boydeee]

5 hours ago, Trevormw said:

Hi,

 

Just bought skoda superb estate 2015 2l diesel. Also noticed lack of engine braking. Also after stopping car will idle at 1000 revs if I apply the brake it drops to 750 if I release the brake it returns to 1000. Completely

repeatable.

DSG? If so, the revs will sit idle at 1k as it's effectively slipping the clutch waiting for you to lift off so it can creep.

 

If you dab the brakes a bit harder, autohold kicks in if it's enabled (green brake symbol on instrument panel) With autohold on, the clutch(es) are disengaged so the revs drop to 750

 

If it's a manual box, I've no idea I'm afraid! 

 

My petrol dsg only really engine brakes when in sport mode.

[Trevormw]

Hi,

 

Yes its a DSG, I thought it must be intended but as have 2 weeks left on warranty I thought asking the question was worth it. Driven loads of automatics including my wife's Q5 2014 with DSG and have never experienced this.

I will experiment. My old Chrysler Grand voyager had a brilliant box no matter how steep the hill whenever I stopped it never crept forward or slipped back.

Many thanks for the info.

 

T

[SuperbTWM]

On 18/11/2016 at 14:51, psycholist said:

Diesel engines have no engine braking to speak of as there's no throttle butterfly to block intake air.

 

throttle or not, diesel engines still have some (maybe negligable?) engine braking due to the high compression ratio. As long as the engine is turning then air is being drawn in and compressed which will generate heat etc. which consumes some energy.

 

 

Edited 29 November, 2018 by SuperbTWM

[Trevormw]

My experience with my Skoda is the fact that when you/I lift off the accelerator engine revs only drop to1000 but because the gearing is so high its enough to make the car feel is it

almost free wheeling. Revs don't drop to 750 until you stop and apply the brake.

[psycholist]

12 hours ago, SuperbTWM said:

 

throttle or not, diesel engines still have some (maybe negligable?) engine braking due to the high compression ratio. As long as the engine is turning then air is being drawn in and compressed which will generate heat etc. which consumes some energy.

 

 

Almost all the energy used to compress the air drawn into the engine during the compression stroke is returned to the crank shaft during the power stroke. When no fuel is injected all the engine is doing is compressing air and letting it expand again. Some of the energy is transferred to the engine oil and coolant as heat and some is lost to friction, but unless the engine is designed badly or engine braking is added afterwards diesels freewheel very well when no fuel is being injected. The high compression ratio means slightly more heat will be transferred to the coolant than a low compression ratio (Thanks to pressure times volume being proportional to Temperature for gases), but it's still happening too quickly for a significant amount of heat to leave.

 

Some diesel engines, especially those designed for off road use, do have an intake or exhaust butterfly to create engine braking, and to stop their brakes boiling on long descents, large trucks have compression brakes that open the exhaust vales at the end of the compression stroke to dissipate the energy stored in the cylinder rather than allow it back to the crankshaft (It sounds like a jack hammer, because what it's doing to compressed air is pretty similar).

[SuperbTWM]

48 minutes ago, psycholist said:

Almost all the energy used to compress the air drawn into the engine during the compression stroke is returned to the crank shaft during the power stroke.

I suppose it does, never looked at it that way before.

 

VAG could very easily implement some engine braking if they wish as pretty much all of their diesel engines in the last 15 years have had throttle butterfly's in the intake as part of the egr/anti-shudder but I guess in the interests of economy its better without.

[Stu-perb]

Don't forget that oils (both engine and gearbox) have been getting thinner in the quest for marginal gains in economy, emissions etc. These gains are yielded via a reduction in friction.

[Gerrycan]

3 hours ago, Stu-perb said:

Don't forget that oils (both engine and gearbox) have been getting thinner in the quest for marginal gains in economy, emissions etc. These gains are yielded via a reduction in friction.

'Marginal gains' is accurate. Low friction oil effects on engine braking reduction would be barely perceptible.

I have experimented with thinner oils in previous non VW type cars and never noticed a difference when driving.

[Stu-perb]

31 minutes ago, Gerrycan said:

'Marginal gains' is accurate. Low friction oil effects on engine braking reduction would be barely perceptible.

I have experimented with thinner oils in previous non VW type cars and never noticed a difference when driving.

I would agree completely, I just wanted to point out other factors that hadn't been brought up yet. If we're talking about motorway driving, the car's mass and drag coefficient are a couple more factors for consideration.

 

For those who hadn't considered the presence of a throttle being a factor on a diesel, the first 5 minutes of this video may prove interesting. This guy is making some great car diagnostic videos: https://youtu.be/yxjcBO4V8Uk

 

Personally, I don't mind a lack of 'engine braking,' because it can often be used for better economy when combined with good anticipation, and the rest of the time, modern brakes are more than up to the job.

[Gerrycan]

Has anyone else here really confirmed that the 2.0d engine offers lower engine braking than an equivalent from another brand?

If there is a difference then perhaps on other brands the throttle body position is (partially?) closed on overrun and VW defaults to (more) open?

 

I hired a 1.6d manual Kia in the UK last year with long gearing, and not a particularly light weight vehicle, the engine braking on offer seemed reasonable to me.

Coming down the steep narrow road from the Long Mynd, four up and using 2nd gear most of the way only required occasional supplementary use of brakes which would have been on full time in my 1.4tsi.

 

Thinking further on the 1.4tsi, mine does not have ACT so I wonder if the ACT version in the Superb offers even less engine braking presuming the deactivated cylinders are not doing any pumping at all, and the Superb is a heavier vehicle (although only about 30-40 kg I think).