Using diesel oil in petrol engines, advice please

28 Jun 2005
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United Kingdom
Hi, I have the chance to buy some of that Shell Helix Ultra synthetic oil for Diesels but I have a petrol car.

I have been told that this oil has such a specification that it is so good that it is easily adequate for a petrol engine. As this could be an expensive mistake I would like to ask if anyone can confirm this and maybe point me to a link on the net that may confirm this is ok to do and as to how well it performs ie in relation to the correct Shell Helix Ultra synthetic stuff for petrol engines.

Any help appreciated.
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I have been offered it cheaper due to friend selling diesel car, thats why.
yes you can. For some purposes (e.g. motorcycles with wet clutches) it is even recommended, if you can't get the special oil.

However diesel engine oil is highly detergent. If you have neglected oil changes and your engine is dirty and sludgy inside, the diesel engine oil will loosen all this sludge and send it circulating round the engine. It will probably not cause a blockage because it will be ins suspension, but it might clog your filter, and you would need an extra oil change to drain it all out (which seems a waste of money)

BTW all the oil companies have consumer advice offices which are very helpful, you can email or phone. Try and have a look round/

Have a look at the label on the back. the oil will probably have two ratings, one beginning with a "C" for Compression-Ignition (diesel) engines, and one beginning with an "S" for Spark ignition (petrol engines). In this cse you can look up the "S" rating and see if it meets or exceeds that recommended by your car maker (I think you will find it does). For example it might me marked CF/SJ where SJ is the petrol-engine rating and was introduced something like 5 years ago. the second character is in aphabetical order, so SG is an older specification than SH which is older than SJ

edited: I just had a look, and unlike some of the other "Ultra" dieseloils, it does not say "OK for petrol engines" so there is a chance it is incompatible with the catalytic converter - so best to ask Shell.
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The additives in the oil are different. the basic oils are similar, and you wont destroy your engine by using the wrong oil.
Oil gradually thins or becomes diluted over time, with contaminats from the fuel. Also an engine produces acids from the combustion process and impurities in the fuel. The oil contains chemicals to nutralise these and stop your engine wearing out more quickly. These are different for petrol and diesel engines.
Dont try to run for a long time -12K miles or more services intervals with the wrong oil, but for short term use it will be fine.
Why not just use the right oil. I am sure you are not saving more than a few £ by doing this.
I think it's to do with temperature rating of the engine(?) Diesel being a lower heat engine then petrol.

I used to work for Mobil Oil and Mobil 1 is one of the best and is use in F1 racing, it not even an oil base, top secret so I have been told