blue smoke and mot

[JaneHibbert]

my car has started on blue smoke now! from reading i guess its the piston rings - will this get worse? dont fancy trying anything as complex as changing those! my question is the old girl needs to go in for an mot, will it pass with a smokey exhaust?

[MarkyB]

If it only smokes when first started it's the valve guides/seals.
If on the over run then it's probably the rings.
Worth checking the breathers are all clear too.

Potentially on MOT fail depending on your tester.

[Dean]

Don't quote me, but I'm sure MOT testers only look for smoke after the car has been idling for a while and at normal running temperature. If it doesn't smoke once warmed up, I think you should be ok.

[bmcecosse]

For Minors - it's a visual test for smoke. They will let it idle while they check the lights/brake lights/flashers etc - then they will rev it up. Blue smoke = fail....... So do that test yourself - does it puff blue when you do that? As suggested - connecting breathers directly to the carb (or inlet manifold!) sucks the oil down the bores and can greatly improve a blue smoke situation.

[JaneHibbert]

no its still blue smoke even when it is at temperature. god

[Dean]

Did it start blowign blue smoke recently? Was it after a service or oil change? Another one to check (as well as the above), was the correct oil put in at the last oil change?

[mike.perry]

Keep the oil level in the sump low.
If the tester starts coughing and spluttering and the garage has to be evacuated then it is a fail!!

[JaneHibbert]

I changed the oil the other day - i used 2050 oil as recommended. but today when i tried to start it it was only running on cylinders 1 and 2 and so i took out the plugs and cleaned them then it ran on all four. but the opil level is high, well on the max mark anyway. ill lower the level and see what happens.

[JaneHibbert]

how much would it cost for somebody to change the piston rings if it failed its mot?

[bmcecosse]

Max mark is fine - don't drain any out. When you filled it with new oil - the rocker gear would be completely flooded and oil probably ran down the guides - hence the two fouled plugs. I would give the engine a good running - up to temperature and then hold it at decent revs for at least a minute - and see if the oil haze disappears. When it's hot and idling - take the oil filler cap off and rev up - is there a plume of smoke/fume?

[JaneHibbert]

i did run it up to temperature today on the drive and then revved it a bit and there was smoke, but didnt hold it on high revs for any length of time. ill try that tomorrow. i hope i dont have to learn how to change rings yet!!

[kennatt]

what do you mean by well on the max mark,is it over cos if you have overfilled it it will smoke untill the level has gone down,if this has just started after an oil change, likely to be the cause,rings wear gradually so don't, overnight,let oil past.The blue smoke just starts off as a haze and gets slowly worse after many.many, miles. Unless a ring has suddenly broken of course.But it sound to me that you have overfilled the engine.

[Dean]

I think BMC and Kennatt have it.

1) You have probably overfilled it.
2) When you changed the oil, the oil ran down the guides.

Like the other says, check all your pipes going to the carb are not bloked. Take it for a nice big blast and get some of that oil consumed.

When is the MOT due?

Mine blows a bit of blue smoke at start up, it's a similar thing, the oil runs down the guides and settles. Once running though it's clear again.

[JaneHibbert]

hope that's the case. the mot is due now! it has just run out and was going to get it done at the weekend, ie next weekend. might have to drain a little oil as will not get a chance to run it in use!

[JaneHibbert]

drained a little oil so it is just below max, used the haynes to adjust the carb so the mixture is, i think, right, made sure petrol was clean etc. all well in the actual running department, sounds fine though a little bit of what i think is timing chain rattle, but still that smoke on acceleration. just hope it passes the mot... otherwise im def walking from now on!

one final question, how much would you think a garage charge to change the piston rings?

[MarkyB]

Don't even go there!
Pound signs will light up in their eyes and they will start planning exotic holidays.
I'm sure it will be fine for many years to come.

[bmcecosse]

It's not a huge job to change the rings - head off, sump off - push the pistons up and away. Clean them up - fit new rings and reassemble. All going well it's a morning's work........ say 5 hours at whatever they charge /hour. Best by far to DIY it!! However - the bores will be glazed (and may be worn) - so it would be wise to inspect before ordering rings (and you don't know what size they are anyway) - and new rings may not make a huge difference anyway - especially as they will need to bed in before they give of their best. You don't report on the 'remove oil filler cap' test ?

[JaneHibbert]

sorry, there were just a few small wisps of smoke / fumes - nothing else at all. everything seems okay except for this smoke on acceleration... or rather on is it called over-run? anyway, will HAVE to get a garage to do it i think, as can't do it myself yet, only just mastering the simpler things...

[Dean]

It may be cheaper to get a replacement reconditioned engine than to get a garage to do the rings. That's if you can find a garage these days that is interested in doing it.

[JOWETTJAVELIN]

If you want a quick fix for the smoke situation pour in a can of Wynn's super charge oil treatment. It is some gloop which thickens the oil and quietens knocks, bangs and reduces smoke. I speak from experience - it works.

The long run answer is indeed new rings and possibly a re-bore (by which stage you might as well overhaul/renew everything else) but as other members have pointed out, rings do not wear out over night.