MHEV or not...

Fred9193

New Member
Hi all, new to the forum. Existing S3 owner and got an A3 35TFSI S-Tronic on order for the other half. Ordered early-Feb, being told a June delivery expected (let's see).

My question... as a 2021 35 build, will it by default have the MHEV system?

If anyone has had a delivery with the MHEV system, it would be good to hear if it improves the car at all.
 
Hi all, new to the forum. Existing S3 owner and got an A3 35TFSI S-Tronic on order for the other half. Ordered early-Feb, being told a June delivery expected (let's see).

My question... as a 2021 35 build, will it by default have the MHEV system?

If anyone has had a delivery with the MHEV system, it would be good to hear if it improves the car at all.
Hi Fred. Welcome to the forum :)

All 8Y A3s with an S-Tronic gearbox are MHEV. Key advantages are:

1. The auto-stop-start system is very much smoother than conventional 12V systems (because the higher power motor in the MHEV can restart the engine instantly). So you can avoid pumping out pollutants when at a stand still without any inconvenience.

2. The MHEV allows the car to switch the engine off when coasting, which improves your mpg a little (and is more environmentally friendly). This is seamless, you can only really tell what the engine is doing by looking at the rev counter.

3. The MHEV uses regen under light braking, which improves fuel economy and reduces brake wear.

4. The MHEV uses the electric motor to fill in gaps in the engine’s torque curve. This improves the response of the 35 TFSI at low rpm (before the turbo has kicked in) like a low power supercharger.

5. In theory at least, the MHEV has a much bigger battery, which should reduce the chances of a flat battery. And I’m assuming that, because the load on the 12V battery is reduced, it should last longer than the one in the manual car and be cheaper to replace. (The 48V battery should last the life of the car.)

6. I haven’t tested this myself but, since the air con compressor is electric, the car can run the aircon with the engine off (eg in stand-still traffic.)

This all from my experience of owning the MHEV for a few weeks and a long interest in hybrid systems.
 
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KXL

Active Member
As far as I know, all S-tronic petrol engines are MHEV. I will let those who have received their S-tronic petrols comment if they improve the car or not. Myself, hopefully sometime in the next month or two, I will receive my 30 TFSI MHEV S-tronic. From the paper fuel consumption specs, it seems to improve by and handful of mpg, acceleration on paper, no difference, maybe the extra weight of S-tronic and MHEV negates any boost
 

KXL

Active Member
Hi Fred. Welcome to the forum :)

All 8Y A3s with an S-Tronic gearbox are MHEV. Key advantages are:

1. The auto-stop-start system is very much smoother than conventional 12V systems (because the higher power motor in the MHEV can restart the engine instantly). So you can avoid pumping out pollutants when at a stand still without any inconvenience.

2. The MHEV allows the car to switch the engine off when coasting, which improves your mpg a little (and is more environmentally friendly). This is seamless, you can only really tell what the engine is doing by looking at the rev counter.
Question for you @AdamInKent if in start stop traffic, can the MHEV system make the car crawl/creep or it would still need to restart the engine to do that. Understand that if traveling on a slight downhill the MHEV can turn off the engine and somewhat maintain the speed?
 

Fred9193

New Member
Thank you v. much @AdamInKent. Couldn't have asked for a better response.

Those advantages are pretty extensive. I know most are negligible but seems like they all add up to a better package. Puts some of the doubts of buying the 1.5 to bed.

I'm also interested in @KXL 's question on the ability to creep under electric power only.
 
Question for you @AdamInKent if in start stop traffic, can the MHEV system make the car crawl/creep or it would still need to restart the engine to do that. Understand that if traveling on a slight downhill the MHEV can turn off the engine and somewhat maintain the speed?
Hi KXL. A key distinction between the current crop of MHEVs and HEVs is that the former can’t drive the wheels without the engine (ie they can’t creep on the motor). For that, you would need the 40 TFSI. That said, in start stop traffic the MHEV restarts the engine instantly and without fuss.

On a slight downhill, the MHEV allows the engine to be turned off whilst coasting (so the car coasts further than one that leaves the engine engaged). The car seems to make intelligent decisions about whether to engine brake or to coast based on where you are and what’s in front of you (using the satnav and sensors).
 

Santiago

Registered User
Hi Fred. Welcome to the forum :)

All 8Y A3s with an S-Tronic gearbox are MHEV. Key advantages are:

1. The auto-stop-start system is very much smoother than conventional 12V systems (because the higher power motor in the MHEV can restart the engine instantly). So you can avoid pumping out pollutants when at a stand still without any inconvenience.
2. The MHEV allows the car to switch the engine off when coasting, which improves your mpg a little (and is more environmentally friendly). This is seamless, you can only really tell what the engine is doing by looking at the rev counter.
3. The MHEV uses regen under light braking, which improves fuel economy and reduces brake wear.
4. The MHEV uses the electric motor to fill in gaps in the engine’s torque curve. This improves the response of the 35 TFSI at low rpm (before the turbo has kicked in) like a low power supercharger.
5. In theory at least, the MHEV has a much bigger battery, which should reduce the chances of a flat battery. And I’m assuming that, because the load on the 12V battery is reduced, it should last longer than the one in the manual car and be cheaper to replace. (The 48V battery should last the life of the car.)
6. I haven’t tested this myself but, since the air con compressor is electric, the car can run the aircon with the engine off (eg in stand-still traffic.)

This all from my experience of owning the MHEV for a few weeks and a long interest in hybrid systems.
That's ok but, to me, most of those claimed advantages are very 'marginal' or "in theory", so wouldn't persuade me to go for MHEV unless it came as standard (as for the auto 8Y A3)..
1. Any modern car with a decent 12V battery will work the start-stop system seamlessly. I know my current car does.
2. Maybe, but the saving would be minimal for the large chunk of the population that are now doing less than 7000 miles per year.
3. Maybe, but very difficult to quantify.
4. Ok, fair enough, if it works properly. Proven on a dyno (8Y A3 vs * 8V A3)?
5. Unproven
6. This is the one thing that would interest me, if it's true. I'm sure we've all had to wait for someone on a freezing cold night and not wanted to run the engine just to have the heater on.

There has also been a "suggestion" (no more than that) by some on here that the widely reported electrical/MMI faults may in some way be linked to the MHEV system? Nearly all the reported MMI problems are from people with s-tronic cars, but that may of course simply reflect that very few on here have manual A3's?
 
That's ok but, to me, most of those claimed advantages are very 'marginal' or "in theory", so wouldn't persuade me to go for MHEV unless it came as standard (as for the auto 8Y A3)..
1. Any modern car with a decent 12V battery will work the start-stop system seamlessly. I know my current car does.
2. Maybe, but the saving would be minimal for the large chunk of the population that are now doing less than 7000 miles per year.
3. Maybe, but very difficult to quantify.
4. Ok, fair enough, if it works properly. Proven on a dyno (8Y A3 vs * 8V A3)?
5. Unproven
6. This is the one thing that would interest me, if it's true. I'm sure we've all had to wait for someone on a freezing cold night and not wanted to run the engine just to have the heater on.

There has also been a "suggestion" (no more than that) by some on here that the widely reported electrical/MMI faults may in some way be linked to the MHEV system? Nearly all the reported MMI problems are from people with s-tronic cars, but that may of course simply reflect that very few on here have manual A3's?
I suspect that you are not alone in considering the advantages not to be worth paying extra for; which is, I guess, why VAG and others are not offering it as a separate option. (Mazda go one step further by making MHEV a standard feature in the latest models of their cars, eg the CX-30.)

1. This was one of the main selling points for me. And bearing in mind the number of people who say that they switch Auto-Stop-Start off because they find it annoying, I guess I’m not the only one. I suspect we have different concepts of seamless: I have driven quite a few modern cars with 12V start stop systems and I wouldn’t describe any of them as such. (12V batteries can’t supply enough power to make it work well: which is a reason why the 24V / 48V MHEV systems have been introduced.)

2. I agree that it’s probably not a big saving in and of itself and there are plenty of other things on the car that improve its fuel efficiency (COD, the S-Tronic box, the aerodynamics). But if, rather than considering just one car, you consider all the cars that could be using MHEV systems, the savings to the environment start to add up.

4. I haven’t compared it directly to a manual 150 PS 35 TFSI car, but I haven’t experienced any sign of the low torque that is typical of small turbo petrol engines at low revs. Has anyone done a direct comparison? (I’m pretty sure I read somewhere that the motor can add 50 Nm (which is 20% of the peak torque of the ICE); bearing in mind that motors apply their highest torque at low revs, that provides a good match to the characteristics of a small turbo.)

6. Unfortunately, the air vents get heat from the engine (though does anyone know if the water pump is electric, which would keep the air hotter for longer even with the engine off?) It’s the aircon compressor that’s electric, which should allow it to provide cooled air with the engine off.

Potentially good news for most of us is that it’s looking like the newer build cars are less likely to suffer the electrical glitches suffered by the earlier builds.
 
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I've been looking everywhere for info on how this works and how to best demonstrate it!

@AdamInKent - any ideas? Drop me a direct message if you can, we can exchange potential video ideas and how we can show the benefit to others.
Auzzam, to find tech info, have you tried googling for something along the lines of “48V car electrical system” rather than MHEV (which is a relatively new term for it)? Car manufacturers have been developing this tech for years.
 
Hi Fred. Welcome to the forum :)

All 8Y A3s with an S-Tronic gearbox are MHEV. Key advantages are:

1. The auto-stop-start system is very much smoother than conventional 12V systems (because the higher power motor in the MHEV can restart the engine instantly). So you can avoid pumping out pollutants when at a stand still without any inconvenience.

2. The MHEV allows the car to switch the engine off when coasting, which improves your mpg a little (and is more environmentally friendly). This is seamless, you can only really tell what the engine is doing by looking at the rev counter.

3. The MHEV uses regen under light braking, which improves fuel economy and reduces brake wear.

4. The MHEV uses the electric motor to fill in gaps in the engine’s torque curve. This improves the response of the 35 TFSI at low rpm (before the turbo has kicked in) like a low power supercharger.

5. In theory at least, the MHEV has a much bigger battery, which should reduce the chances of a flat battery. And I’m assuming that, because the load on the 12V battery is reduced, it should last longer than the one in the manual car and be cheaper to replace. (The 48V battery should last the life of the car.)

6. I haven’t tested this myself but, since the air con compressor is electric, the car can run the aircon with the engine off (eg in stand-still traffic.)

This all from my experience of owning the MHEV for a few weeks and a long interest in hybrid systems.

Thanks! I havent really paid any antention to the mild hybrid before. Still waiting for mine to arrive. Now that am reading other articles online as well to undestand it, indeed it makes the whole experience smoother and assist the ICE with the work it has to do.

I must admit that during the test drive in the highway, at one moment the engine was turned off and had no idea until the sales rep told me to look at the revs. The engine started again without even notice anything.
 
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