Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGF Technical - Smoke coming from Oil Filler cap?!?!?

Engine was replaced last year and has been fine since... However took car to Barcelona this summer and found that when I had a sustained 3-5min blast on the autoroutes in VVC territory at >4000RPM it would really suddenly overheat….L

Moreover, I stopped at the service station noticed smoke coming from the oil filler cap! The oil was low so put in approx 1.5L. However, engine sounds fine and pulls well and you can drive around all day in +35C heat in slow traffic and it'll never overheat... However it will overheat in a cool evening if you have a 5 min >4000RPM blast on the motorway. English speaking AA type guy checked it out in Bordeaux said the system looked OK…

Had the system pressure tested in Barcelona and it all checked out OK, however on the way home I had to fill it up with coolant so many times as air locks started in the system it got worse and my average speed had to come down to 40MPH for the last 100miles to keep the temperature in the middle. Every time the engine temperature went up, I immediately pulled over allowed it to cool down… So there was lots of sunbathing and swearing at the side of the road!

When I got back the local MRG garage pressure checked the system, flushed and refill the fluids. However, I still notice this smoke coming out of the oil filler cap! I really don't want to go through the hassle of another engine...

Please my question is, has anyone ever heard of smoke coming from the oil filler cap and had a similar problem with overheating?

Please any suggestions would be welcome as this has me stumped!?!?!

Sorry this is happening to you. What oil are you using ?

What do you mean by overheat - the temperature gauge climbs towards the red, or coolant boils out of the system ? How's your oil temperature at this point ?
There should be no smoke from the oil filler cap - this smoke should be recycled anyway, but shouldn't be coming out of what's really the dipstick hole.
Personally I would get the car thoroughly serviced, paying especial attention to an oil / filter change (perhaps an oil flush too), and flush the cooling system and check all components - especially the radiator and coolant bottle cap. Refill with fresh coolant. Investigate the oil smoke, and the cause of losing so much oil - why did this 1.5L disappear so quickly ?

Good Luck

I've had this car for nearly 7 years... Its been cherished the whole time with regular services, extra oil changes, etc. No expense has been spared with this car, virtually every component has been replaced with new! When I was in Barcelona I had an Oil/Filter change done as well as the pressure check!

It seems that excessive heat is generated when engine goes above 4000RPM and if sustained for longer than 2 mins the cooling system cannot cope and it will overheat. Strange thing s that you can stop/start around town in 37C and it'll never overheat.

The smoke coming from the oil filler cap just scares me and I don't understand how that is possible. I have always used the standard MGR recommended Oil

Cheers Steve

Check One:
Open bonnet and remove plastic coew (some plastic screws and some plastic 10 mm nuts) (scarlet? pics?)

Under the cowel you should see two pipes running front to back near the washer bottle, these are the radiator pipes. When you overheat do you get:

One hot pipe: not enough water flow, the radiator or metal colling pipes may be silted up restricting flow, possible damaged water pump or sticky thermostat, thermostats can get sticky and only open half way, this would give you this problem, old water pumps, as in on older cars had a problem of cavating the water, this is wher the pump spins so quickly that air pockets open up around the pump impellers, so older cars had better cooling at mid RPM ranges, but very little at high RPM. I suppose it is posible that the pump has deterioated such that it causes this effect.

Two hot pipes: Not enough cooling, the radiator may be silted up restricting certain water paths or the fins on the radiator may be rusted away (very lightly on a 7 year old, at least in part, although this might not be your actual problem). The fan fuse may be gone or the fan stuck, or a sensor problem (although I would expect this to be less of a problem at speed and more a problem around town)

No hot pipes: Quite unlightly, thermostat almost compleatly stuck, or no water flow due to the impeller blade comming off the drive staft at high temp (lots of I know a bloke who knows a bloke stories about this)
Will Munns

We could be looking at more than one problem here Steve - so bare with us...

Just to clarify: when the car is over heating, it is the WATER temperature gauge that is climbing, NOT the oil temperature? Or are both climbing when you use more than 4k rpm?

The standard cooling system is more than adequate to keep the engine cool even at ambient temperatures in excess of 40ºC - so there is a problem with the cooling system.

Failure of circulation:
1. Air lock
2. Thermostat failed
3. Water pump failing

Failure to dissipate heat:
1. radiator: corrosion damage can lead to loss of cooling fins and reduced surface area - efficiency is dramatically curtailed
2. grilles to radiator are blocked

Steve, does the heater itself still work (ie, turn it to hot: does hot air come out? Does this effect the coolant temperature when the engine appears to overheat?)

From what you've said so far, it sounds as though air is in the cooling system - so this needs to be thoroughly flushed (and remember to turn the heater setting to maximum heat when doing this).

The other likely problem is the condition of the radiator itself - and a significant loss of efficiency. Your car is 7 years old - when was the radiator last replaced? Indeed, has it *ever* been replaced?

I think that the oil smoke is something of a red herring - a symptom of a hot engine - hence the concentration on the cooling system itself.
Rob Bell

Thanks guys this is very helpful as I am becoming demented and losing some sleep!

The pump was replaced by MGR about 1yr ago, the long pipes under the car have been replaced by the Mike Satur aluminium ones about 1-2 yrs ago.

I haven't checked the thermostat and don't think that this has ever been replaced, does the thermostat control the flow of cool water from the front radiator coz I noticed that when the car overheated the radiator was often quite cool... However I put this down to airlocks in the system? So when I returned, MRG completely flushed and refilled the coolant at a cost of £100 however still the same problem!

Radiator has never been replaced, what are grilles to radiator?

Does the cooling system constantly recirculate through the radiator or can it survive without under low stress conditions? Reason thinking is that really is fine as long as you stay below 4K revs and only go above for very short periods... however this leads to very boring drive and I now get over 40MPG!

I really need to get this fixed however obtaining a diagnosis is the most difficult challenge.... From experience MGR will just keep putting in new parts and hope that it fixes the problem...:(

Cheers RichieR

The oil temperature increases as engine revs climb, have also noticed them climb quite high on a steady cruise at around 80MPH The Oil temperature looks quite normal considering ambient temperatures for time of year.

The thermostat sound like the bunney to me ! It basicly controls the flow back from the radiator, mixing the cold water from the radiator with the hot water from the bypass tube to create a steady water temp back to the engine of around 90 degrees. If the rad is cool then both the fins on the rad, and the grills in the bumper are both fine.
Will Munns

Steve (AKA RichieR?)

Wait a moment.... bit confused here, Steve = RichieR? So are you the RichieR who fitted the NOX.....?

tim woolcott

>> I haven't checked the thermostat and don't think that this has ever been replaced, does the thermostat control the flow of cool water from the front radiator coz I noticed that when the car overheated the radiator was often quite cool... <<

Steve, as Will says, the thermostat effectively regulates water flow through the radiator (it is located on the return pipe). So if the thermostat remains closed, then the rad will remain cool.

How have you determined that your radiator was cool? It is hard to get too to check this - Will suggestion on checking the temperature of the rubber pipes located under the sindscreen washer resevoir is an excellent suggestion, and a much more reliable indication of water flow to and from the rad.

>> However I put this down to airlocks in the system? So when I returned, MRG completely flushed and refilled the coolant at a cost of £100 however still the same problem! <<

Airlocks could readily cause this problem (and indeed lead to the top of the radiator being cool if the rad starts to trap significant quantities of air). Just because an MGR dealership has drained and bleed your cooling system doesn't completely exclude the possibility that air locks have reccured...

>> Radiator has never been replaced, what are grilles to radiator? <<

I'd definitely want to get the condition of the radiator assessed thoroughly - it could well need replacing. The grilles being blocked is highly unlikely - you'd notice if the radiator grilles (the mesh in the bumper) were blocked!!!

>> Does the cooling system constantly recirculate through the radiator or can it survive without under low stress conditions? Reason thinking is that really is fine as long as you stay below 4K revs and only go above for very short periods... <<

No it doesn't. However driving at engine speeds of 4k rpm means that there is less heat being produced, so if the radiator were not working at optimal efficiency, heat from a lightly loaded engine is most likely be 'coped with' - but driving harder overloads the limited cooling ability...

So the checks to do are:
1. Will's suggestion of removing the under bonnet shroud and checking the radiator pipe temperatures after a thorough thrash
This should give indication of whether hot water is actually reaching the radiator in the first place, and if it is, whether it is being effectively cooled.

If no hot water reaching the radiator
2. check the bleed nipples on the cooling system, and bleed as necessary
3. remove and check operation of the thermostat - replace if necessary

If hot water reaching radiator:
4. remove radiator bleed screw (when engine cold!!!) - if empty top up cooling system until water floods from bleed nipple)
5. remove front bumper and check condition of the radiator core.
Rob Bell

so what do you make of the 1.5L oil that suddenly disappeared ? Or was it not so sudden ?
It could also be due to a partial blockage in the main coolant system - flow would be sufficient at low revs, but insufficient at higher revs (higher power levels); hence the recommendation to (reverse) flush.
Do check your heater circuit, and make sure the system is bled with the heater fully ON ! - and check that the heater control fully opens the water valve


Have a decent garage to perform a compression test (measuring the value of the compressed air thru each spark plug hole while cranking the engine ).
Don´t want to be a pain in the a.. but CAN be a holed piston or blow by in the pistons ring-land....
Any smoke visible at the exthaust while the oil dissapered? Best of luck,

Carl Blom

Thanks everyone, I will hopefully get to the bottom of this soon...:)

Put car into MGR and asked them to look at the overheating problem again and the above as you so kindly suggested. Their so-called Service Manager just called and told me in the plainest of don't give a damn tones, that the head gasket looks like it may have gone...:( I asked the how this can be the case since it has been pressure tested twice by themselves last week and there were no indications of a head gasket problem then. He said that there seems to be leakage?? I reminded him of the fact that there is no mixture of water/oil. The car never overheats unless you run it hard. I asked him if they had checked the thermostat and he never even answered me instead saying in the same tone, "In our opinion it is the a head gasket problem and we cannot do anything unless you agree to £550 cost to look at it!!! What a nightmare some of these guys are! The guy I usually speak to is very helpful and understanding of the headaches that these cars can sometimes cause however it was apparent that this guy just didn't give a toss, and he was the Service Manager. I may speak to Tony White their Group Services Manager who I believe may care a little more.

They also put a bracket on the exhaust in June coz they said it needed one for the MOT however the exhaust fell down and has melted the valance... I guess they will find an excuse about how it isn't their fault and I should pay for a new Valance...

This is the same MG garage that attempts to charge 2Hrs labour to change an alternator belt...:(

Any suggestions please, I'm trying to get them to change the thermostat however they keep saying about this apparent strange leakage even though it passed all pressure tests and was charged for in last weeks invoice!

Mmm.. sorry to pee on your parade but it does sound like the beginnings of head gasket failure to me, when the engine is 'stretched' you will get blow by of combustion gases past the gasket fire rings into the coolant which will both raise its temperature and its pressure, as the coolant jacket is pressurised, local leaks blow through the sealing ring into the drainholes around the bolts and coolant leeches into the sump, when the oil gets hot enough you will see some of this as steam...

No amount of bleeding will get the 'airlocks' out because the 'air' in the coolant is in fact combustion gases.

Seen this before any number of times..

Dave Andrews

Hmm now if their service manager had put it that way...:) These engines are a challenge to say the least! The engine was replaced just over 12MTHS ago I guess they timed that perfectly!

Well here we go again £550 seems pretty darn expensive to me, since the car is not buggered and can be driven at 45MPG. I can shop around therefore does anyone know who can do a good quality Head Gasket replacement at a reasonable cost? There may be a gearbox replacement in it for them too.

Has anyone used Tech Speed? Are they better value for less money?

Tech Speed are brilliant, They are not cheap - but they are very cost-effective.
It could be a head gasket - if exhaust gases are escaping into the coolant then an MOT emissions sniffer in the coolant bottle would confirm. HGF does not always result in mixed oil/water.
HGF gets undriveable pretty quickly in the MGF - but this one appears to be stable - so it's worth pursuing the thermostat option until some better indicator of HGF


The head will undoubtedly need a skim which means stripping and rebuilding it. I would be wary about driving it in this condition, if you soften the head it will become scrap, you could also suffer a hydraulic lock and damge the bottom end.

Dave Andrews

>> Has anyone used Tech Speed? Are they better value for less money? <<

In short yes! Their basic quote for HG repair is in the order of 340 quid (ie 200 fewer notes than charged by your friendly neighbourhood MG garage).

If you chat to Roy or Marvin, they can arrange collection of the car on their flat loader - which as Dave suggests, running the car in its current state could result in much larger bills.

Best bit about Tech-speed is their approach to customer service. I know from experience that even when I come up with the most insane ideas, they'll listen and will do every thing they can to help. A complete contrast to the "don't give a damn" approach of your service manager...
Rob Bell

You still need to positively identify if in fact the head gasket is guilty. Remember, head gaskets can and do fail on ANY car usually as a result of neglect or as a bi-product of some other fault. Over on Scoobynet, one professional openly admits he changed several K series head gaskets before he realised that the real cause of the problem was something else. I suspect he, and a good few other "professionals" are equally guilty and no doubt some of those without ever realising their costly errors. The K series in all its various forms has a head gasket "They all do that mate" reputation which in some, maybe many cases, is not justified because the root cause was something else.

Get several opinions from those who really know their MGFs before deciding the course of action. Otherwise there's the possibility that expensive unnecessary work could be done on your car which may not even cure the real cause of the problem ..... and good luck.

There have been several K series cars in my family over the years which have given faultless service and still do .... bit superstitious so will now have to "knock on wood" ....:O)

John McFeely

There's more Steve:

You mention >>The engine was replaced just over 12MTHS ago I guess they timed that perfectly!<<

What SORT of replacement? Oil fumes from the Cambox, Oil Filler, breathers or anywhere connected with the crankcase/bottom end could indicate blow by in some/all bores? Not got time to read all this thread but, has a compression test been done?

These things on any car a rarely as simple as first thought. Worth checking.

John McFeely

Just spoke with them again... They can change the thermostat however feel that would be a waste of time and resources because they really think it's the head gasket! Would you believe they charge 1Hr labour to do it on a VVC, which comes to over £100!

I think that I might investigate the Tech Speed option...

In addition, the car was in with them in June for its standard service and MOT. However, they told me that it failed because of a loose o/s exhaust bracket on the MS Daytona. The Daytona has been on there for 2-3 years no problem at all... Well they supposedly replaced a bracket and it passed OK... However I went down to Barcelona and noticed that the exhaust had completely come off its mount exactly where they had refitted it.... worse still it has melted through the valance!

However, MGR now tell me that they can see the paperwork charging me for the job however cannot really see what they replaced and charged me for on the car! They are also trying to argue that the exhaust must have been like it before and its not a standard exhaust, etc. Which is complete rubbish MGR are turning into a nightmare… shoddy work, not taking responsibility for their clearly botched up job.

If the valance was melted and the exhaust wasn’t standard surly they shouldn’t have accepted the job to fix it for the MOT Moreover wouldn’t they have spotted the damage to the valance when doing the job!?!?!

>Would you believe they charge 1Hr labour to do it on a VVC, which comes to over £100!

For the thermostat? parts sould be less than a tenner, but do you know where the thermostat is on the K-series?
Will Munns

This thread was discussed between 12/08/2003 and 15/08/2003

MG MGF Technical index

This thread is from the archive. The Live MG MGF Technical BBS is active now.