Engine Oil change

Pathfinder

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Changed the engine oil again today after 3000 miles. Don't understand why the manufacturers suggest 10k miles.

The drained Shell fully syn was wreaking of petrol and stinking black.
 
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S.Speed

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If petrol is getting into your engine oil then that's not good at all..
Petrol is the opposite of a lubricant..
What colour are your spark plugs?
Does your car ever get warmed up properly or is it just used for short runs?
 
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Maybe it's due to the high mileage, piston ring wear or something.
 

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I read extensively on oil changes/wear and unless you have engine problems repeated changes are counterproductive and a change of filter is better.
 

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I think there is something more serious with the car that needs addressed, a petrol engine should go ages before needing a change and petrol in the oil isn't good.

Head to Merparts, the Muzzoni brothers will help you.
 

television

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Petrol is not getting into the engine and that would only serve to dilute the oil.

If there is no smoke when left at idle for a few mins and you rev it up, if no smoke then the valves are good, if you get smoke on hard acceleration the rings bore problems, if you get no smoke from the above all is fine.
 

hotrodder

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Tired valve guide seals couldn't result in petrol diluted oil and knackered rings shouldn't unless something else is going on too. A leaking injector or other fueling problem could regardless of ring condition and, as said, be compounded by short journeys.

There's an SAE paper (2003-01-3119) on the subject of the antiwear properties of low phosphorous oils which AFAIK is the source of many of the 'frequent oil changes increase engine wear' thing. Never found a free source for the actual study the did, only forum discussions about it

How many MBs (or any modern cars for that matter) literally wear their engines out these days? MBs generally die of rust or other economic reasons like SBC pumps + rust for example. Over 200K on mine and it doesn't use enough oil to need topping up between changes
 
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I think it is probably piston rings and valve seals wearing out. High mileage, 160k.

Wife has done 3 trips to Kingston, London in the last month so that's the sort of mileage its been doing lately. Its not using up any oil, no smoke and on the motorway it's still managing to do 35 MPG.

There is nothing that Merparts can do that I can't do myself, so no gain there, other than advice.

Maybe the smell of petrol in the oil is due to the long motorway journeys, I don't know, but it is just aswell I changed it as it needed a change. It was not Shell fully syn, it was semi synthetic. Now ECP brand Triple Q fully syn. I will change it again soon to see what it smells like.

How often do petrol injectors fail, that's what I'm wondering.
 
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television

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It would fail the MOT if any problem with the injectors
 
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MOT'd in May, passed the analyser test. I seen the results. No, this is a new problem, I shall monitor and see what comes up.
 

oigle

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Petrol and diesel injectors are different. Doubt very much if a petrol injector would cause petrol to get into the sump like a diesel one can. You need to find the cause as those petrol fumes are very explosive - I know from experience. Normally a petrol engine has very little dilution in the oil if driven on long runs as the petrol will evaporate out with heat and be sucked into the manifold and burnt. Is your thermostat operating properly? A cold engine can prevent the petrol from evaporating out of the oil. Of course, short running will also do the same thing. If it had carbies, I'd say the dirty aircleaner would have made it run richer and possibly allow unburnt fuel to bypass the rings but, with injection and MAF, that shouldn't be the case.
Is your pcv system working properly? A split hose or blocked valve could break the vacuum that sucks out the fumes from the sump.
 

kth286

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long journeys can dramatically reduce the oil level due to evaporation of all that extra stuff which has accumulated.

It would be interesting to do an oil level check after you have been doing your normal short journeys, and just before doing a long one.

At end of long round trip, check if the level has dropped much; and if the smell of petrol is still there on dip stick.
 

hotrodder

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Petrol injectors have a pintle valve that's opened electromagnetically and shut with a return spring. All properly tiny and cycled very quickly. If the valve/orifice is gummed up with deposits etc it can mess with spray patterns and/or stop the needle seating properly. If the pintle valve isn't seating properly the injector will leak when it's supposed to be shut i.e. switch the engine off and the injector will dribble fuel until the fuel rail pressure has been bled off.

Obviously biased in that it's from the fuel injector cleaning/servicing industry but more detail here... http://www.ditex.it/news/asnupres.pdf

Again, worn valve seals cannot result in oil dilution- the seals are at the wrong end of the valve for fuel to find it's way past them. Tired rings will have a bigger effect on oil control than with fuel unless there's something wrong with the fueling and 160k hasn't been close to high mileage since the 1970s. Personally i'd say low mileage is more likely to result in premature wear with modern engines- relatively speaking lots of cold starts and short journeys where the engine never gets properly upto temperature
 
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Thanks all above for the suggestions and advice. On Friday, I am driving from Gourock to Wells, Norfolk, so I will check on arrival and report back.
 
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