S40 V40: Oil - sludge?

[morrismen]

I read something today from a new zealand person who said that Castrol 10W/40 Magnatec Oil sludged up his engine when used infrequently.

However, this person also said that using Castrol GTX 10W/40 was better because it had 25% anti-sludging agent in it and therefore has never had a sludged engine since, even when it sits for 1 month or more.

Now, we know that these V40/S4 cars don't like thicker oil re VVT etc, so is GTX semi-synthetic mineral oil actually better than Magnatec synthetc oil for the S40/V40?

[skyship007]

Any oil can form sludge, it's just a matter of how long you use it for. Magnetec has a slightly better base stock than GTX, but they both lack high enough levels of detergent and dispersant type additives (Calcium and Magnesium compounds) or the ability to resist high temperature shearing that results in a drop in viscosity during use, in comparison to Castrol Edge.
A classic case of, "You get what you pay for".

Sludge forms when the detergents and dispersant additives that help clean the oil passage ways and keep the Carbon that gets into the oil from the rings (Often called Blowby) in suspension, is used up. In technical terms the failure point is when the TBN (Total base number) equals the TAN (Total acids number).
When the oil passes that key marker, the Carbon atoms start clumping together and drop out of suspension forming the dreaded "Black death". Only ultra fine bypass oil filter systems used by big trucks can filter out the Carbon directly, a normal oil filter will not prevent sludge formation.

Anti freeze contamination of the oil kills the detergent additives real fast and even with the best German long life full synthetic oils in use, you will still get sludge, so leaky head gaskets are one big cause of sludge problems, although a lot of owners blame the oil if they get sludge.

If you ignore sludge the first direct warning is a flickering low oil pressure light at hot idle after a good run. The second warning will probably be a turbo charger bearings failure, which can result directly from a blocked oil pump intake screen or longer term varnish deposits in the turbo feed line. Varnish forms in hot spots because of either the long term use of cheap conventional oils or overheating resulting from sludge slowing down the oil flow rates. So one problem can lead to another.

My favourite oils list:
Liqui Moly High Tech Synthoil 5/40
Castrol Edge 0/40
Mobil Turbo Diesel 0/40
Shell Helix Diesel Ultra 5/40 (Seems cheaper at present)

PS. Sludge does not form just because the oil sits around not being used, just about any modern oil is good for 2 years in the pan. The one year limit is more to do with what can happen in corrosion terms if you ran an oil too long, so it became acidic and the detergents that have a secondary function in corrosion reduction terms, stop preventing corrosion. If you did that in the first few months and then left the oil, it's not good news. That's why you should change the oil before storing an engine. Major brand full synthetics are better at corrosion protection than older oils, so the change every year rule is now every 2 years for most new cars.

[Dog_Book]

I was just about to say......

[Darlo 1]

Originally Posted by skyship007

Any oil can form sludge, it's just a matter of how long you use it for. Magnetec has a slightly better base stock than GTX, but they both lack high enough levels of detergent and dispersant type additives (Calcium and Magnesium compounds) or the ability to resist high temperature shearing that results in a drop in viscosity during use, in comparison to Castrol Edge.
A classic case of, "You get what you pay for".

Sludge forms when the detergents and dispersant additives that help clean the oil passage ways and keep the Carbon that gets into the oil from the rings (Often called Blowby) in suspension, is used up. In technical terms the failure point is when the TBN (Total base number) equals the TAN (Total acids number).
When the oil passes that key marker, the Carbon atoms start clumping together and drop out of suspension forming the dreaded "Black death". Only ultra fine bypass oil filter systems used by big trucks can filter out the Carbon directly, a normal oil filter will not prevent sludge formation.

Anti freeze contamination of the oil kills the detergent additives real fast and even with the best German long life full synthetic oils in use, you will still get sludge, so leaky head gaskets are one big cause of sludge problems, although a lot of owners blame the oil if they get sludge.

If you ignore sludge the first direct warning is a flickering low oil pressure light at hot idle after a good run. The second warning will probably be a turbo charger bearings failure, which can result directly from a blocked oil pump intake screen or longer term varnish deposits in the turbo feed line. Varnish forms in hot spots because of either the long term use of cheap conventional oils or overheating resulting from sludge slowing down the oil flow rates. So one problem can lead to another.

My favourite oils list:
Liqui Moly High Tech Synthoil 5/40
Castrol Edge 0/40
Mobil Turbo Diesel 0/40
Shell Helix Diesel Ultra 5/40 (Seems cheaper at present)

PS. Sludge does not form just because the oil sits around not being used, just about any modern oil is good for 2 years in the pan. The one year limit is more to do with what can happen in corrosion terms if you ran an oil too long, so it became acidic and the detergents that have a secondary function in corrosion reduction terms, stop preventing corrosion. If you did that in the first few months and then left the oil, it's not good news. That's why you should change the oil before storing an engine.

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