: Difference between Petrol an Diesel Oils?


r44712
19-11-2003, 22:36
Simply, what is the diffrence between petrol and diesel oils. I guess its something to do with additives and combustion by-products?

MartinW
19-11-2003, 23:09
Very simply the three main areas are:
Higher dispersancy to deal with higher levels of soot
Higher detergency levels to minimise depositing on components and as a result a higher TBN which will minimise the risk of Sulphuric Acid formation from diesel dilution.
Diesel engine oils, as compared to petrol oils, do not have very good low temperature sludge formation resistance.

Diesel oils are useable in petrol engines, but if signs of low temperature sludge formation are seen, then switch back.

Petrol engine oils are not suitable for diesel engines in the long term because of the lack of detergency/dispersancy predominant in a diesel, and also a lack of high temp sludge formation.

HTH

r44712
19-11-2003, 23:47
Originally posted by MartinW
Diesel oils are useable in petrol engines, but if signs of low temperature sludge formation are seen, then switch back.

Thanks for your advice. I have some "left over" diesel oil(Magnatec & Mobil 1), but as I am selling the ZR to be replaced with a brand-new ZT 1.8T I wasn't sure if I had to let the stuff go to waste, esp. the Mobil 1?

MartinW
19-11-2003, 23:53
A brand new 1.8T K series, won't take kindly to the Mobil 1 until you have 10k on the clock. In fact, MG R reccommend, for some reason I have yet to fathom, a semi-synthetic, but it is good practice to accumulate 10k miles before using a fully synthetic like Mobil 1 in your 1.8T.
However, given the price you are paying for the car, using a diesel oil seems like a false economy, so why not sell the leftover with the car, or offer it to other TD owners cheap in the for sale section. The 1.8T is a relatively highly stressed unit, and we have already seen one HGF reported today on the forum on this engine. Don't take chances!

curious
20-11-2003, 22:00
Check the specs on the bottles. API S* (where * is a letter) is the gasoline spec and API C* is the diesel. Most gasoline oils have a diesel spec and often the reverse is true. So long as the specs suit your engine, go for it.

A dedicated heavy duty diesel engine oil will have too much detergency for a gasoline engine and a gasoline oil will have not enough for a big diesel, but in terms of 'typical' car engines and oils, they are pretty much interchangeable.

MartinW
20-11-2003, 22:21
Curious
I always understood S to mean Spark ignition and C Compression Ignition, but I am also told it can stand for Service and Commercial. What's your take on this? the Spark/Compression makes more sense to me.

curious
20-11-2003, 22:47
You're right with spark and compression.

[EDIT]
I'm wrong. I always thought it was spark and compression, but according to the API website... (http://api-ep.api.org/quality/index.cfm?objectid=74E2BB59-910D-11D5-BC6B00B0D0E15BFC&method=display_body&er=1&bitmask=002001005000000000)

The letter "S" followed by another letter (for example, SL) refers to oil suitable for gasoline engines. The letter "C" followed by another letter and/or number (for example, CH-4) refers to oil suitable for diesel engines. These letters officially stand for "Service" and "Commercial."

How embarassing.:blush

r44712
20-11-2003, 23:14
A quick trip to the garage reveals:

API CF & ACEA B3 (Magnatec)

API CF/SL & ACEA A3/B3/B4 (Mobil 1)


Now to find that chart....

r44712
20-11-2003, 23:32
While I think of it, which is better quality A3 or B3?

I see that the Magnatec has no API S* classification, but the Mobil 1 does. The Mobil 1 conforms to ACEA B3, as does the Magnatec, so does that make it the 'same'?

Of course if A3 is better than B3, then no it won't be the same.

MartinW
21-11-2003, 01:23
API Ci-4 was released as a spec in Sept 2002 to conform to the rigours of exhaust gas recirculation (egr) and the challenges posed by the soot loading inherent with this technology. It has a greater soot load capacity than previous CH/CG/CF.
I believe ACEA is more vigorous in taking into account the fuel economy and emission levels imposed in Europe.
Chris Longhurst's site is excellent resource (http://www.chris-longhurst.com/carbibles/index.html?menu.html&engineoil_bible.html)
The information below is from the site which also includes a history of the API ratings.
The ACEA standards are prefixed with a 'G' for petrol engines and a 'D' or 'PD' for diesel. Coupled with this are numerous approvals by car manufacturers which many oil containers sport with pride. ACEA replaced CCMC in 1996 primarily to allow for greater read-across in test programs (eg for viscosity, viscosity modifiers and base oil). The CCMC specifications were G (1 to 5) for gasoline, D (1 to 5) or heavy duty diesel and PD1 and PD2 for passenger car diesel. ACEA though have a slightly different nomenclature they can be summarised as A for petrol, B for passenger car diesel and E for heavy duty diesel. The ACEA grades may also be followed by the year of issue which will be either '96, '98 (current) but coming soon is 2000.
Full ACEA specs are:

A1 Fuel Economy Petrol
A2 Standard performance level
A3 High performance and / or extended drain
B1 Fuel Economy diesel
B2 Standard performance level
B3 High performance and / or extended drain
B4 For direct injection passenger car diesel engines
E1 Non-turbo charged light duty diesel
E2 Standard performance level
E3 High performance extended drain
E4 Higher performance and longer extended drain
E5 (1999) High performance / long drain plus American/API performances. - This is ACEAs first attempt at a global spec.

Basically A3/B3 is like saying API CF/SL meaning it is suitable for use in both types of engine.
HTH

r44712
21-11-2003, 01:33
Originally posted by MartinW
Basically A3/B3 is like saying API CF/SL meaning it is suitable for use in both types of engine.

HTH

It helps greatly, confirming my thoughts. I had a look at that website, too, as well as finding a Castrol one that described Magnatec as conforming to SL/CF & ACEA A3/B3

curious
21-11-2003, 14:03
Originally posted by r44712
A quick trip to the garage reveals:

API CF & ACEA B3 (Magnatec)

API CF/SL & ACEA A3/B3/B4 (Mobil 1)


Now to find that chart....

Are you sure you weren't looking at Castrol GTD Magnatec? GTX Magnatec most certainly does have an API S rating.

r44712
21-11-2003, 19:54
Originally posted by curious
Are you sure you weren't looking at Castrol GTD Magnatec? GTX Magnatec most certainly does have an API S rating.

The stuff I've got is GTD.

I had a look in halfords today. GTX is rated API CF/SL - ACEA B3 & A3, wheareas the GTD is rated API CF ACEA B3 only. Which is odd, becuase I thought diesel oil offers better protection than petrol oil (as described above).

So if the petrol is good for the diesel, then surely the disel is good for the petrol, if the diesel is better?

curious
21-11-2003, 23:29
The diesel isn't necessarily better. It's more marketing - typically, no-one looking for an oil for their gasoline will look at a diesel oil, so they don't bother putting the gasoline claims on it. However the gasoline oils do get used in diesels as a matter of course, so they put both claims on the bottle.

Furthermore, a dedicated diesel engine oil can have a really good diesel performance but not meet gasoline specs. This is because a true diesel oil has more additive in it, which means more metallic elements (Ca, Mg), which can form ash deposits in a gasoline and therefore fail certain gasoline engine tests.

r44712
22-11-2003, 01:52
Confusion is setting in for me at this point: use it/don't use it (I'm actually tending towards the don't).

MartinW
22-11-2003, 10:46
Matt
As I said above, don't use the Mobil 1 on your new engine until it has 10k miles. The Mobil 1 is formulated to work in the petrol or diesel.
The Castrol Magnatec you have is GTD formulated for diesels. Considering the lower cost of Magnatec I would suggest play it safe and don't use it. Buy some GTX for the running in. It's a semi-synth recommended by MG R.
It's not worth screwing up a new engine for the sake of some oil.
If your engine was already run in and you didn't plan to keep the car for a long period of time, then I don't suppose it is absolutely problematic.
Like I said in my second post on this thread, when I found out you were buying a brand new ZT 1.8T don't take chances.

curious
22-11-2003, 19:46
Originally posted by MartinW
Buy some GTX for the running in. It's a semi-synth recommended by MG R.

It may be recommended by MG-R, but GTX (with no suffixes or added words) is a mineral product - always has been.

Other than that Martin's advice is sound - run in with a good quality mineral or semi-syn and then switch to synthetic if you feel the need.

Going back to the very original question, you'll be OK running your left over GTD Magnatec in your new car and, when run in, the Mobil 1 will be OK too.

Byron
30-11-2003, 10:31
Idon,t think you you can mix the 2 oils together semi syn and fully syn,but i may be wrong.

curious
30-11-2003, 23:26
Originally posted by byron
Idon,t think you you can mix the 2 oils together semi syn and fully syn,but i may be wrong.

No offence or anything, but you are wrong. :angst

You can mix mineral, semi- and/or full synthetic. It's not ideal since you are diluting the good stuff with the less good stuff, so effectively wasting your money on the better one, but there are no incompatibility problems.