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Smoking on start-up


Richot1989

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Apparently, Porsche fit a similar device as standard to the GT3.

 

I don't think it is an alternative or 'cure'  for worn valve guides.  Basically, all it does is to stop the migration of oil back from the oil tank into the crankcase when the car is left for a period of time which is more prevalent in some engines than others.

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The answer is 'yes' Graham.

My guage only used to register once the engine has warmed up - say after 10mins of driving. I presume this is because  it takes a while for the oil pump to clear the excess oil out of the crankcase which has, on standing for a while, seeped back into it from the oil tank

However, with 'the valve' fitted, as there is no migration of oil back from the oil tank through the pump into the crankcase, the oil tank still retains the level of oil in it that was there when the engine was switched off. Thus, when switching the ignition on, the tank is still 'full' of oil and  the guage reading is what ever it was when the engine was switched off.

Once you start the engine, the guage will drop as the oil pump pumps oil round the engine etc, opening the valve and sucking  some oil out of the tank. 

Whether your guage gives a correct reading, does, of course, depend on how accurate you guage is in the first place! 

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I guess the main thing is it’s not smoking at idle or on deceleration (?)

If it’s still being run in, I’m guessing it’s using a mineral oil so 15w40 or 20w50, so the right viscosity for these engines.

Im not saying the valve is a bad idea, I would have delayed fitting it until you’re more certain of the cause. 

Does it need to go back for a valve adjustment pretty soon?

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2 hours ago, Richot1989 said:

However, with 'the valve' fitted, as there is no migration of oil back from the oil tank through the pump into the crankcase,

Sorry to be Mr Negative on this, but ----- as you say the only way for oil to drain into the engine from the oil tank is through the oil pump. Most significantly it is also the pressure side of the oil pump rather than the scavenge side. If the oil pump is good/in spec this will not happen to excess in a short period of time. The characteristic of a "puff" of oil smoke on startup should not be excessive and should only be noticeable after extended periods of standing, e.g. more than a week.

My 3.2 has +130K miles on it with no recorded rebuild and if I park it up red hot (i.e. very thin oil) the "puff" is only noticeable after stand for a month or more. My SC with +80K miles and no recorded engine work also only noticeably "puffs" after standing for a month or more. In both cases there is no sign of burning oil after the initial starting "puff".

What you describe is not what I would expect on a newly rebuilt engine. The valve you have added is only preventing the symptoms, not curing the problem.

Sorry :door:

 

Mark

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2 hours ago, SilverWT said:

Sorry to be Mr Negative on this, but ----- as you say the only way for oil to drain into the engine from the oil tank is through the oil pump. Most significantly it is also the pressure side of the oil pump rather than the scavenge side. If the oil pump is good/in spec this will not happen to excess in a short period of time. The characteristic of a "puff" of oil smoke on startup should not be excessive and should only be noticeable after extended periods of standing, e.g. more than a week.

My 3.2 has +130K miles on it with no recorded rebuild and if I park it up red hot (i.e. very thin oil) the "puff" is only noticeable after stand for a month or more. My SC with +80K miles and no recorded engine work also only noticeably "puffs" after standing for a month or more. In both cases there is no sign of burning oil after the initial starting "puff".

What you describe is not what I would expect on a newly rebuilt engine. The valve you have added is only preventing the symptoms, not curing the problem.

Sorry :door:

 

Mark

+1
Adding a check valve is a compromise and not something required on a recently overhauled engine.

You have checked all the basics? 
Oil level, viscosity etc.

 

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Thanks for all you comments, whether positive or negative.

The engine has done 56k verified miles.

Top end rebuilt about 600 miles ago (with new rings etc).  Two of the valve guides were badly worn and it smoked on tickover, when really hot and excessivley on start up after a weeks layup.

Following the top end rebuild, it still smoked badly on start up if left for a week or so but otherwise all is fine.

After standing for a week, on draining the crankcase, several litres of oil would drain out, evidence that the oil was slowly migrating down from the tank.

Oil pressure when hot is good.

Oil is fresh Shell Helix 5 (10w-40) as advised by Matt, and level (when hot and idling is on around 3/4 mark (not that it has a 3/4 mark!)

Anyway, I'm very happy with the result.

 

Thanks again for your comments.

 

PS my son's '79 SC has done almost 200K with only minor work to the engine and it has never smoked on start-up 

 

 

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On 23/07/2020 at 15:13, Richot1989 said:

PS my son's '79 SC has done almost 200K with only minor work to the engine and it has never smoked on start-up 

 

 

Mine has done 128k and never smokes on start up even when left for 3-6 months over winter!

I did have a boxster that used to smoke when left for long periods. Almost gave me a heart attack first time it happened.

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