Over revving at 70mph

[Dean3452]

Hi. I bought my MG HS PHEV 4 weeks ago.
I started to have trouble when driving on a flat or slight decline where the engine in HEV mode would sit a 3000rpm.
Even when letting go of the accelerator the engine would not change gear.
I have since taken the car back to the main dealer who reconfigured the software. Who immediately informed me the gearboxes are very lazy and not much good.
This didn't install me with much confidence about the MG Brand.
They have informed me that the car now, will have to learn my driving style ??, and that the car would perform even worse for a short while.
This was over a week ago.
Now when driving at 70mph the car in HEV is revving at 4000rpm constantly without changing gear, and I am averaging 18MPG.
I am driving down to Newquay in a couple of months in a car I have no confidence what so ever in.
I had a doubt in my head about buying a SUV that was 10k cheaper than other leading brands.
My doubts are becoming my nightmares.
Has anyone else experienced anything similar?

 

[salty]

Dean, sorry to hear about your new motor, giving you problems. It's well documented on other threads on here, about this problem. Same problem with the MG3 and ZS Hybrids. Have a look at them.
You've found out quickly that MG dealers are next to useless. Good luck.

 

[BoJoUK]

Hi. I bought my MG HS PHEV 4 weeks ago.
I started to have trouble when driving on a flat or slight decline where the engine in HEV mode would sit a 3000rpm.
Even when letting go of the accelerator the engine would not change gear.
I have since taken the car back to the main dealer who reconfigured the software. Who immediately informed me the gearboxes are very lazy and not much good.
This didn't install me with much confidence about the MG Brand.
They have informed me that the car now, will have to learn my driving style ??, and that the car would perform even worse for a short while.
This was over a week ago.
Now when driving at 70mph the car in HEV is revving at 4000rpm constantly without changing gear, and I am averaging 18MPG.
I am driving down to Newquay in a couple of months in a car I have no confidence what so ever in.
I had a doubt in my head about buying a SUV that was 10k cheaper than other leading brands.
My doubts are becoming my nightmares.
Has anyone else experienced anything similar?

TBH I think that the engine is running at that speed only because it is charging the battery, it will not be driving the wheels, they are being powered by the electric motor.
There are other entries in this forum that explain how the drive system works on the new HS PHEV. It only gets power from the ICE when applying full acceleration. At other times the engine just acts as a generator.
Very clever and very good.

 

[Dean3452]

TBH I think that the engine is running at that speed only because it is charging the battery, it will not be driving the wheels, they are being powered by the electric motor.
There are other entries in this forum that explain how the drive system works on the new HS PHEV. It only gets power from the ICE when applying full acceleration. At other times the engine just acts as a generator.
Very clever and very good.

I believe that is the case with the ZS, not in the HS PHEV.
I can not possibly accept that in HEV mode on a motorway cruising at 70mph, the engine should be screaming at 4000rpm to charge a battery.
This is constant and my fuel economy drops to 18mpg. This is neither economical or effective.
Its going back in on Monday as in the last half hour its also developed an engine management fault due to emissions.
Oh and I am now unable to scroll through my navigation, tyre pressure and Mileage info.
By the way I would be most grateful if you could point me in the direction of an explanation on how the HS PHEV engine works that would be amazing.

 

[Dunkie59]

The Roewe D5X-dmh is the Chinese version. They have an interesting video about the PHEV on their web page (https://www.roewe.com.cn/vehicles/d5x-dmh/#) Try visiting it via Chrome browser and letting Google translate the page for you. I believe it uses the Miller petrol engine cycle (as opposed to Atkinson or Otto)

 

[Dean3452]

Thanks. I have done a bit of research on Parallel and Series Hybrid set ups.
I agree, very clever. But do other HS PHEV owners experience such high RPM's at cruising speeds?
I could live with the engine firing up at 2000rpm to charge the battery, which would be far less intrusive than thrashing away in the background at 4000rpm for over an hour.

 

[BoJoUK]

I believe that is the case with the ZS, not in the HS PHEV.
I can not possibly accept that in HEV mode on a motorway cruising at 70mph, the engine should be screaming at 4000rpm to charge a battery.
This is constant and my fuel economy drops to 18mpg. This is neither economical or effective.
Its going back in on Monday as in the last half hour its also developed an engine management fault due to emissions.
Oh and I am now unable to scroll through my navigation, tyre pressure and Mileage info.
By the way I would be most grateful if you could point me in the direction of an explanation on how the HS PHEV engine works that would be amazing.

I do believe that this is how the HS PHEV works, and there is quite a good posting from user “aerofurb” called:

2025 MG HS Trophy PHEV v 2020 Skoda Superb iV Sportline PHEV​

As the title describes, he is comparing the 2025 HS PHEV to his older Skoda, but he explains quite well how the drive train works.
However, you are now getting more problems and it is booked into the garage next Monday, please keep us updated as I am sure that you are having more problems with your car now.
I tend to only use the EV mode so haven’t seen if the engine revs are much higher when using the HEV mode. Mine normally starts at about 2200 revs, then 2400, sometimes higher and then down to 1400 revs before going back to 0 revs. The other thing I have noticed is that mine runs the available mileage on battery, down to Zero before the engine starts up. As I say, this might be because I use it in EV mode.
Good luck and I hope they get it sorted for you.

 

[aerofurb]

I had a run down the M40 to work yesterday, in HEV mode (game plan is to save the EV for the trip home to get there with 6 miles or so estimated EV range to avoid the ICE kicking in).

Going up Stockenchurch cutting, it changed down (ie into first gear) and at 60 mph, it was showing 3000 rpm. In second when on the flat, that tends to be around 2000 rpm. So that will be with the ICE directly driving the wheels.

The only time I feel the car changing gear is at around 2500 rpm when it sometimes is undecided which gear it wants for a couple of seconds. It was more noticeable with the cruise control on - but that's inop awaiting (hopefully a software upgrade).

It sounds to me @Dean3452, that yours isn't changing up into second, but staying in first (remember it is a two-speed gearbox).

Have you looked at the live power/drive distribution display on the screen? That should show if the ICE is driving the wheels, or the battery is, or both, ICE charging the battery etc.

It's a great shame that some dealers try to fob people off talking complete rubbish. I wish they would do their research so they can advise their customers accordingly. The supplying dealer 'after sales' person told me that the reason my car wouldn't charge from a wall charger was that it can only be charged from a granny charger. When I showed him the charging options in the MG manual on the MG iSmart app he was still sceptical and said he would have to ask a colleague. Idiot. At least he did accept my diagnosis of the windscreen wipers not working after he got in, tried them and told me they didn't work....

I haven't driven another PHEV MG, so can't say if they had a lazy gearbox but the 2025 is unlike its earlier counterparts in pretty much every way apart from the number of wheels. Perhaps MG UK don't provide training for the sales staff.

Badger the dealer - or call MG customer service. Do persevere, because when it's fixed (or replaced!) you will love the car. I called MG customer service when trying to get my car looked at by 'not the supplying dealer' as they had serviced it rather than stating it had had a Pre-Delivery Inspection, MG answered the phone within a couple of rings, was very helpful and responsive to emails after the call. Hopefully, mine will get a software update next week to fix the lack of road speed limit recognition and crise control. I now have a new closer, very helpful dealer in Banbury that opened (well changed from Citroen) after I had bought the car from somewhere else (MK...).

 

[Haza]

Hi. I bought my MG HS PHEV 4 weeks ago.
I started to have trouble when driving on a flat or slight decline where the engine in HEV mode would sit a 3000rpm.
Even when letting go of the accelerator the engine would not change gear.
I have since taken the car back to the main dealer who reconfigured the software. Who immediately informed me the gearboxes are very lazy and not much good.
This didn't install me with much confidence about the MG Brand.
They have informed me that the car now, will have to learn my driving style ??, and that the car would perform even worse for a short while.
This was over a week ago.
Now when driving at 70mph the car in HEV is revving at 4000rpm constantly without changing gear, and I am averaging 18MPG.
I am driving down to Newquay in a couple of months in a car I have no confidence what so ever in.
I had a doubt in my head about buying a SUV that was 10k cheaper than other leading brands.
My doubts are becoming my nightmares.
Has anyone else experienced anything similar?

Yes same problem nightmare

 

[WAC 768]

Thanks. I have done a bit of research on Parallel and Series Hybrid set ups.
I agree, very clever. But do other HS PHEV owners experience such high RPM's at cruising speeds?
I could live with the engine firing up at 2000rpm to charge the battery, which would be far less intrusive than thrashing away in the background at 4000rpm for over an hour.

I've got the MK1 HS PHEV, and the only time the car revs up slightly is when the car switches from pure EV -> Hybrid, after that it revs just like a normal ICE car at motorway speeds, even when trying to maintain the traction battery.

 

[aerofurb]

The earlier HS PHEVs have a completely different 'drivetrain' set up to the '2025' model. It is both a parallel and series hybrid set up with dual (electric) motors.

 

[JPR Drive]

I gathered information from online links, fed it to chat AIs, and then asked them questions. However, please take the following with a grain of salt, as AI responses may not always be accurate. Here's what I got.

1. “The gearbox tends to hold onto lower gears longer, especially around 30 mph…”
In hybrid mode, the MG HS PHEV’s transmission sometimes stays in a lower gear (like 1st or 2nd) longer than expected. This means:

• The engine revs higher (you hear it working harder) even though the car isn’t accelerating quickly.
• This is especially noticeable around 30 mph (48 km/h), where many traditional automatics would have already shifted to a higher gear for smoother, quieter cruising.

Why does this happen?

• The hybrid system is trying to optimize power delivery between the petrol engine and electric motor.
• It may keep the engine in a lower gear to maximize torque or to prepare for a power boost if you press the accelerator more.

2. “The system prioritizes speed-based gear changes rather than load-based ones…”
In traditional automatic transmissions:

• Gear changes are based on engine load (how hard the engine is working) and throttle input (how much you're pressing the pedal).
• For example, if you press the pedal hard, it downshifts to give you more power.

In the MG HS PHEV:

• The hybrid transmission uses a speed-based logic: it shifts gears based more on vehicle speed than on how hard you're accelerating.
• This can feel less responsive or less intuitive to drivers used to conventional automatics.

3. Because the transmission is speed-based, not load-based – on scenarios where you’ll likely want to accelerate quickly to merge safely or expect the car to respond immediately when you press the pedal:

• The car might hesitate slightly before downshifting or delivering full power.
• It may stay in a higher gear or rely on the electric motor briefly before the petrol engine kicks in.
• This can feel like a lag or sluggish response, especially if the battery is low or the system is transitioning between electric and hybrid modes.

Why This Happens

• The hybrid system is trying to balance efficiency and performance, not just give instant torque.
• It may take a moment to engage the petrol engine, shift gears, and deliver full power.

Tips to Handle This

• Anticipate - press the accelerator slightly earlier (could be easier said than done - requires really getting to know the car)
• Switch to “Sport” mode if available — this should hopefully sharpens throttle response and holds lower gears.
• Keep the battery charged — a well-charged battery allows the electric motor to assist more effectively. - i think this is key to keep the RPMs low

Just sharing the above - again please take the following with a grain of salt, as AI responses may not always be accurate.

@Dean3452 - your's still revving too much with 80% battery seems very odd. i thought having a very good charged battery would solve it but seems like its not the case. keep us posted on how you got that sorted! thanks!

 

[Dean3452]

Hi guys.
A quick update.
After 3 days of emails back and forth to MG Uk.
They insist that my car even though fully charged will intermittently rev at up to 4000rpm to recharge the almost fully charged battery for over 30 minutes.
I find this hard to believe.
What I have noticed is that at 70mph with the ICE at 4000rpm the energy flow graphic shows the ICE supplying the power to the wheels but even though the EV is showing 30% demand there is no blue on the wheels on the car in the graphic.
I even (although breaking the law out of frustration) sent the car up to 80mph.
The revs jumped to 4500.
Are MG saying that if I happen to take my car abroad. I could potentially be sat at 80mph with the engine revving at 4500rpm for over 30 mins. I dont call this a refined driving experience at all.

 

[aerofurb]

Hi

All I can say is that I haven't seen mine rev to that level when on motorways/dual carriageways (or at any other time).

Have you dried setting up a video camera showing the display (including power, rpm, energy flow etc)?

Obviously, I can't say yours has a fault as all my experience has been on mine.

Perhaps you could ask them to lend you another car and see how that behaves over similar routes?

 

[Dean3452]

 

[Dean3452]

The above photo is cruising on a level gradient road.

 

[aerofurb]

I'm thinking now (from memory), that in your picture, the yellow shading shows that the ICE is driving the wheels and charging the battery.

The EV side is not showing as driving the wheels. Correct me if I'm wrong but that would show up as blue and sometimes, it will show blue and yellow together.

The power output overall (in this case from the ICE) is 35%. That seems a bit high for level 70 mph cruising to me.

I won't be running the ICE until Wednesday but I'll pay more attention and report back.

 

[Dean3452]

Quick update.

The below is a email response from MG UK.
I would love to know if anyone else experiences this, so I can put my mind at rest.


Once the EV battery has been depleted past 90% the engine can decide to put power back into the EV battery to extend the range and so the revs can jump to 3800 to charge the EV battery.

 

[aerofurb]

On my ICE engine running on the M40 and A34 this week, the highest rpm I saw whilst in the cruise was 3000 and that was when heading up Stokenchurch Cutting onto the Chilterns rather than anything else. I presume it changed down into first at that point and was only for a short period - 20 seconds or so. The batteyr would have been under 90% charge at the time.

For the most part, mine sits at 2200 rpm (around 15% power) in HEV mode at 70 mph, 1900 (8-10% power) at 60 mph. Aerodynamic drag increases as the square of speed - double the speed, four times the drag. That's particularly noticeable when in EV mode at speed.

As I mentioned before, the powertrain (and the power flow display) pretty much does what ever it thinks is best - far more active than the simpler Skoda Superb iV setup.

So at times the ICE is just powering the wheels, but may also charge the battery and drive the wheels at the same time, and similarly, the battery might drive the wheels on its own, or together with the ICE. Then there's regen charging of the battery from braking and/or decelerating. All of course depicted on the power flow display in real time.

Personally, from my experience, the way your car behaves is not the same as mine. I still think you should go into another dealer as a secret shopper and take another HS PHEV out for a decent test drive and see how it behaves.

 

[Dean3452]

Thank you so much for the feedback.
I am starting to believe this is ECU/software related.
Today I have made a 75 mile trip over to the east coast.
On the motorway cruising at 70mph.
My car was behaving exactly as you describe above.
After 30 miles the engine increased to 3800rpm, still driving on a level road.
It remained like this for over 30 minutes until I could nt take the noise any more. The graphic was showing full ICE power to the wheels.
I pulled over, turned off the car and waited a couple of minutes before turning back on.
The car behaved itself for the rest of the journey. Something, whether it be software or the gearbox is stopping the car from going into the higher gear, end of !!!
I will be back onto MG Tuesday.