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MG MGF Technical - Performance after a service

Hi to everyone,

My 1.8MPi has been in for its 40k km service. I don't think they have followed any guide to decide what they gonna do. A few things that they have done:
* oil change for engine and transmission (full synthetic) --> see further
* new oilfilter
* new fuelfilter
* new wiperblades
* a summer treatment for the breaks --> ???
* new part for the gearbox
* checking the valves --> they were OK
* new sparkplugs --> at 40.000 kms ???
* ....

1) they filled the oil up far above the max-indication on the dipstick. Almost as far as the distance between 'min' and 'max'. What shall I do ?
2) it looks like the car is slower than before, especially at lower rpm. It also sounds different. When accelerating from the 4th gear instead of 3rd gear, you normally hear a deep sound. But now, you don't hear that growl anymore. And when driving at higher rpm, the high pitch is gone. From time to time I even think we are driving without an SP, but with a standard exhaust system. What could have happened and how can I change it.

Thanks in advance,



The extra oil will be splashing all over the place and robbing your power- if you dont drain the excess, itll soot up your nice new sparkplugs.

fix the oil level, and then see how it feels.


The amount described seems to 1 liter.
This (as far as my mechanical skills alow) seems to me that you hare damaging your engine.
The oil pump is overworking!
The extra oil will expand and damage the "retentores"(Donīt know the english word... maybe seal or gasket)
Bruno Valadas

The oil pump won't be affected as it simply draws oil from the reservior, which of course will be at a much lower level during engine operastion as a fair quantity of oil will be in the upper part of the engine. However the residual level will be higher and is likely to cause extra splash which drags on the crank webs. This abosrbs power which is lost power for driving.

I doubt that the degree of overfil will lead to any significant combustion chamber effects, although some contamination will lead to poorer combustion. Of more concern would be the effect that the oil would have on the effect of the cat. Severe oil burning soon coats the inner surfaces of a cat and will kill it.

A change of plugs at this point is of little surprise, since I have advocated for a long time that the listed service interval is too long for maintenance of peak performance. A sudden and clearly obvious change in performance is certainly more than a high oil level will cause, so I wonder whether the plugs are gapped correctly??

I also wonder what the gearbox part was? A change within the box can increase the drag within it and so reduce performence. It won't have any effect on the sound of the exhaust and I wonder if there was a leak from a loose flange which has been tightened??

Checking the valves?? No mention of a cambelt change, but if the belt has been removed for whatever reason and either cam has been refitted a tooth out, then this will most certainly cause the sort of conditions you have.

Has the car been on Testbook? A reset can cause the performance to go 'soft' whilst it settles back to normal operation.

Lastly does the car roll easily with the brakes off? Any drag on the brakes kills performance, but doesn't affect the exhaust sounds.

Roger Parker

Roger's comments are spot-on, I especially like the Testbook idea.

However, I'd have to disagree when he says " [A noticeable loss of power is] certainly more than a high oil level will cause"

Overfilling with oil is surprisingly noticeable, especially if the driver was used to his car before the overfilling incident. It's the nasty combination of oil splash slowing the crank and oil wash contaminating the charge that makes overfilling sap so much power.


Looks like my problem is getting solevd by this board again.

>However the residual level will be higher and is
>likely to cause extra splash which drags on the crank
>webs. This abosrbs power which is lost power for
OK, like you guys are saying, the high level of oil has an impact on the performance of the engine. Before the service my oil level was on 'min' instead of far above the 'max' indication. So all parts are coming together.

>Has the car been on Testbook? A reset can cause the
>performance to go 'soft' whilst it settles back to
>normal operation.
I was thinking about that myself. A reset of the ECU is giving me a more civilised car. If it wasn't such a hard job, I would have tried installing the original airbox and standard exhaust, drive a few days and than change it back to the setup of today.
But Roger, what do you mean with 'normal operation'? A clean smooth running car with a higher priority for comfort, or the setup I was used to have.

>Checking the valves?? No mention of a cambelt change,
>but if the belt has been removed for whatever reason
>and either cam has been refitted a tooth out, then
>this will most certainly cause the sort of conditions
>you have.
Good point I think, I will tell it to the technician.

>Lastly does the car roll easily with the brakes off?
Yes, that's no problem.

I think the car will be in again on Friday.



Just like to back up grant, i slightly over filled my oil a few weeks back, and while there wasn't such a noticable drop in performance, i only just over filled it, certainly not a litre, there was a very noticable change in the noise from the engine. much quiter.

back to normal now, or i've got used to it.
Matt Lawrance

Good feedback Grant and Matt.

I have seen significant power loss from overfilling which is certainly felt when driving. With this instance I was thinking more of the overall change with this car, which I don't think is just down to a high oil level. I didn't make this very clear did I?

Roger Parker

But.... if there is significant loss with overfilling, and assuming when we are talking about overfilling we are talking the kind of over filling i did which wasn't to major, then over filling by a large amount could have huge effects.

Roger, how much difference to the engine can the clever electric bit make, i.e after testbook running and it being reset, and how long before its figured out that you want to drive like a nutter again?
Matt Lawrance

Just another thing I want to add to this thread.

I just had another quick look at the bill, and I saw the price of those four new spark plugs .... less than Ģ8 for four of them. IMO, these items couldn't be the original (platinum) parts.

The car is booked for another service tomorow.


haven't you got any description in that bill on the replacement partnumbers ?

This could IMO help Roger to identify the obviously wrong cheap copper sparkplugs (to cold?) and also the gearbox parts.


For 8 GBP, that should be copper plugs, but no worry, if they're of the right type, they are working as good as platinum ones. The only difference is that they will will last for approx 20.000 km instead of much more.
I remember that Rog said the gap must be adjusted.
If it hasn't be done, that could alter the performance ...
I will soon get OE platinum Champion plugs for a bargain price (1 GBP each ;) ... Roger, do you know if I have to adjust the gap on these plugs ? At what torque should they be tightened ?


The car has been in again since yesterday evening and ... they are changing the plugs again. Last Friday they removed some oil (no idea how much, but the amount they said was far too low, only 25cl). After removing the oil (well a part of it) the F sounded much better. Performance was still a bit low, so the technician decided to order the platinum plugs.

I'll keep this thread updated. Could be interesting if someone else has the same problem in the future.


My car came back from services a couple of time feeling a bit sluggish. I put it down to them reseting the chip. It always improved over the space of a week or two.

The car is back, and it sounds and drives like the good old one. Even better, it looks like the reving is much better now. After releasing the accelerator the rpm drops much faster. Good, that's the way I like to hear it. And when I hear the comment of Dot, it could only get better ;-)

Anyway, thanks for all your help.


The biggest influence here are the plugs. Did you actually get to see what were fitted? It sounds as though whatever they were they were simply 'thorn in' and not set. Copper cored items set correctly with the right heat range will provide indistinguishable performance from the OE platinum ones when new, if set correctly!! New plugs come with all manner of gaps, some preset others not. I ALWAYS check the gap and if need be reset it. Often the gap is fine out of the box, but some I find are set much too small at about 0.6mm rather than the ideal 0.9mm. Conversely some are set at 1.1mm, but the ignition system usually has the power to cope with this gap for a while.

I take on board the obvious effect of the overfill. I would also suspect that the garage would 'understate' the amount of oil they removed to reduce any implied error on their part. I suspect that they removed somewhat more than 25cl!

Dot's experience with the car settling over a couple of weeks use is about what I would expect. If the overfill of oil was higher than stated then it is possible that it may take a little longer for all the effects to wear off and return to normal.

Roger Parker

This thread was discussed between 19/06/2000 and 01/07/2000

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