Missfiring Vr6 due to oil deposits on plugs. Oil questions

[was8v 0]

The oil consumption was due to a missfire/poor spark produced by a faulty coil pack NOT bore wear / head wear as suspected!!

 

 

My car is a 106k Vr6 and has a plug fouling problem due to oil deposits I believe due to bore wear / head wear on cylinders 1 and 6.

 

When I first got it I ran it for 3000 miles on 15w40 halfords semi synth with only the occasional puff of blue smoke on overrun and the plugs (1&6) got black deposits though no missfiring, prob consumed 500ml of oil.

 

1.5k ago I changed to 10w40 synta silver semi synth and i've been getting bad problems with drinking lots of oil (1.5 litres in 1.5k) and the plug 1 badly fouling up to the extent that it doesn't spark.

 

 

 

 

My question relates to oil weights: My understanding is that both the oils I have used are the same viscosity when at operating temperature (90-110deg), the 15w40 being slightly thicker than the 10w40 when cold. Now I understand oil also gets thinner as it gets hotter.

 

So ignoring any other factors, why the difference in oil consumption and plug fouling - if the oil is thinner when hot surely this is when the oil gets past the seals and fouls my plugs? So the 2 oils should be no different being the same 40 weight equivalent? I don't understand why there is a difference.

 

 

 

 

Also I need to do something about this oil consumption and plug fouling - (a rebore/head rebuild in an ideal world) - a thicker oil?

 

I've read on here that mobil 1 fully synth 10w50 is used for cars driven hard so presume that weight is safe for the Vr6. Now I don't want to waste that cash if it is just gonna go to foul my plugs up. Will there be any ill effects from running cheaper 15w50 non synth oil?

 

Is there actually any benefits of using semi-synth other than increased period between changes? I usually change every 4k so are the benefits of semi synth negated when changing so often?

[rmn 0]

i had simular issues with my golf

what i did was replace the plugs, leads and use a slightly thicker oil 15w40 or there abouts

It is due to ware to be honest and not much can be done

[dr_mat 0]

I think there's some good threads regarding experimentation with oils, have a dig around with the searchy thing ...