Diesel vs Petrol oils

obi_waynne

obi_waynne

Administrator
Staff member
Moderator
Points
1,157
Location
Deal, Kent UK
Car
A3 1.4 TFSI 150 COD
What are the differences between these and is it safe to use a diesel recommended oil in a petrol engine.

Or should we view each make/grade as unique and each case should be considered on its own merit?
 
Just about all oils these days are for petrol and diesel despite what marketing may be written on the can. All you need to do is go for an oil that meets or exceeds the correct specs for the car and these specs can be found in the hand book.

Cheers

Guy
 
oilman said:
Just about all oils these days are for petrol and diesel despite what marketing may be written on the can. All you need to do is go for an oil that meets or exceeds the correct specs for the car and these specs can be found in the hand book.

Cheers

Guy
Click to expand...

One point to add here is that diesels that utilise particle filters need to be filled with a low sulfated ash oil. As far as I am aware neither the SAE or API specs can be used to determine this so you'd have to use something that meets or exceeds the manufacturers own internal rating, for example VW's 5xx.yy labelling.
 
be989 said:
I've heard that diesel engine oils have more detergents in them, is this true?
Click to expand...

Yes, diesel specific oils do generally have higher levels of detergency. Largely I think to hold soot particles in suspension and prevent their deposition where they might otherwise provoke circulation problems.

Yet many diesel specific oils have very strong API petrol engine ratings anyway and will work perfectly well in a petrol engine.

However, if your car's maker has a list of approved oils then use one those.

Oil manufacturers spend huge amounts of money developing their oils. They also spend huge amounts getting the oils approved specifically by car makers. Matching the spec letter by letter on the data sheet is not necessarily the same thing.

(And they (the oil makers) also spend quite a bit on marketing, although this seems to be dying, at least in the public consumer domain - how many times do you see engine oil ads on the telly now? Compare with the mid 1980s and Castrol's GTX 'liquid engineering' marketing blurb. That was a marginal oil at the time anyway - the birth of the sludge era. Duckhams bright green Hypergrade was worse still. I think there's more trade specific marketing/advertising for engine oils now, than there is direct to consumer marketing).

The other thing to consider is that petrol is a fierce solvent and will wash oil away readily, diesel is much kinder in that respect and so diesel oils possibly require less assistance to stay 'in grade' throughout their service life from fuel contamination, despite the need for greater detergency.

Things move on relentlessly but I do advise using an approved oil for your car. If the maker's approved oils are both derv and gas compatible then there's no need to worry. They will have been thoroughly tested by the manufacturer of the car and at the expense of the oil manufacturer.

However, the really really good and worthy answers can be found from Guy of Opie Oils.

He posts on here as Oilman and his knowledge is astounding.
 
If you look at the label on a can of oil (unless it's either a top end race oil, some American oils or total rubbish) there will be an ACEA A spec and B spec mentioned. The A spec refers to petrol and B to diesel. Most oils will say something like ACEA A3|B3 or A3|B4 meaning that they meet the equivalent petrol specs and diesel specs, or are at least close to them. Except in some odd engines, like some generators and a few other random things, you don't get a diesel only oil, you don't just see a B spec on the can.

A lot of it comes down to development costs, why make two oils and pay for one to be tested for ACEA A specs and other for B specs? It's cheaper to make an oil that covers both and then market it as a 'petrol' and 'diesel' version, usually putting a couple of quid extra on the diesel version(Castrol did that with the Magnatec 10w-40 and I'm pretty sure it's the same with the Edge 5w-40 as well). If the name of the oil contains the word 'Diesel', it's only there for customer confidence.

Consider the manufacturer specs like VW504.00 and VW507.00, BMW LL98/01/04, Merc, GM, etc etc etc. Part of the requirement of each spec will be to meet ACEA specs. If you have a BMW from 2008, that car will use an LL04 oil, regardless of whether it's a petrol or diesel. A VW on a long life schedule will use a 504.00 (petrol) or 507.00 (diesel) oil, but with those ones, if the oil meets 504.00, it also meets 507.00 and vice versa.

Some oils have another ACEA spec, the C rating that does relate to diesel engines and if the car needs a C spec oil, you must use one as they are low ash oils, formulated for use in engines with diesel particulate filters. A C spec is part of the BMW LL04 and VW507.00 spec, meaning that they are the oils to use in those cars fitted with the DPFs, but they are also suitable for the petrol engined versions as well.

Cheers

Tim
 
Last edited:
Not at all, the Edge 5w-40 Diesel was called that to attract the likes of the VAG owners with the PD diesel engine, this requires an oil that meets the VW505.01 spec such as the Edge TD 5w-40. It is also approved for petrol, and its a good oil.

Cheers

Guy
 
Thanks,

Might switch to an ester based one when I've got some mods on it though, or when I do an engine swap, I've not decided yet,

Engine I would switch to is a 2.2 hdi engine from a 406
 
Also I've heard that you shouldn't change your oil too often because you risk damaging the engine, so i've been told, I was on some TDI forums and some of the people on there were really having a dig at the people who change there oil more frequently that the manufactures recommend, they said that there would be too much detergency in the engine at any given time and the engine internals will ware out quicker....

Personally I think this is a load of old .... well lets just say it comes of a shovel...

Would you care to clarify?

Cheers

Brett
 
The only shred of truth might be if the weekly oil change nut also insists on using a can of very savage flushing additive every single time he changes the oil.

But then it wouldn't be the oil change doing the damage, would it?
 
If they are using a flush all the time then harm could be caused, but then its not the oil change its the flush.

You could change your oil daily and it would do no harm.

Cheers

Guy
 
The only other thing I hate about oil changes is that first 'dry' startup.

If changing oil every day then you'd have to do something about partially filling the filter housing or filter 'can' with some oil. In some cars this is impossible because of the filter's location and orientation.

I shan't, however, be changing my oil every day, week or even every month so it's unlikely to cause a problem for me.
 
Where do you stand with oils with a high amount of detergent, being used in old high millage engines. I remember years ago being told it would strip all the carbon and build up of detritus about the engine off, leaving more wear in the engine, perhaps in the cylinders, and around the valves.

Ive got a tdi focus, 174k on the clock. i do oil and filter every 6 months(about 7k) with a ford rec mid priced oil from the motor factor. dont know if im doing the right thing, but the engine is sweet as a nut. smokes a bit, but sweet nevertheless.
 
Automotive oils these days are for both petrol and diesel, using one with an unusually high level of detergency isnt really going to happen so a non issue really. Only really flushes these days will cuase that kind of problem.

You Ford will be fine if you carry on as is, regular oil changes is very good.

Cheers

Guy
 
Thank you guy, ill carry on as before. And while we are at it, could i ask you, or the other chaps on this thread, I have an old honda generator that i picked up recently, the bloke reckons its kaput, i think it cut out cos of no oil, judging by the spec of sludge on the bottom of the stick. ive got some 5/30, but presume that will be a bit on the thin side. I dont know any1 else with a geny to ask. What would you rec guy.
thank you for any help.
 
I've just had mine filled with Castrol Edge Sport 0w-40 - this was before schedule as the previous service invoice (previous owner) showed me that 15w-40 had been used.

What a berk!

Strangely the tappets are a lot quieter at startup now.
 
I've used 0w and 5w weight oils for years and I have never ever had problems with engines despite the fact that I keep my cars for ages.

It's an old fashioned view to think that more viscous is better.

You only need to shake the can to see how 'thin' it is at room temperature.
 
You must log in or register to reply here.
Similar threads
Thread starter Title Forum Replies Date
R Petrol or diesel engine oil? Engine Oil 16
M Castrol Edge Diesel Engine Oil 5
H Engine oil for 8 valve Astra 1.6 (petrol) Engine Oil 12
E Kendall engine oils Engine Oil 1
oilman Opie Oils Autumn Competition Engine Oil 0
oilman 20% Off Millers NANODRIVE CFS Engine Oils Engine Oil 0

Similar threads


Please watch this on my YouTube channel & Subscribe.


Back
Top