It says in almost every engine or transmission manual DO NOT USE OIL ADDITIVES. The folks that wrote those comments know far more about the engine or box concerned than anyone reading this post.
There are a number of exceptions to the golden rule of not adding extra chemicals to a good quality engine or transmission oil and they are as follows:
1/ Maintenance procedures that require the use of a solvent to clean various engine parts, special pre assembly oils and anti corrosive sprays.
2/ Maintenance procedures relating to sludge prevention or minor cases of sludge, where a flush additive is used at idle only for 10 to 15 minutes just before an oil change. A number of dealers have approvals for such procedures, although I have not seen it mentioned in any maintenance manual, just in more local approvals.
3/ Type and product specific manufacturer approvals that relate to a specific design fault that requires an oil or fluid additive. These are very, very, rare and tend to relate to noise reduction in auto gearboxes or leaks. Some approvals were cancelled when new oils or fluids became available.
4/ Terminal phase engine or gearbox faults. When an engine is on its last legs and the bearings, rings and valve guides etc are failing the best course of action is to use a thicker multi grade race oil, like a 10/60, but if you also have serious oil leaks a high mileage oil containing seal conditioners should be tried. If you have a serious oil leak that is beyond economic repair, then it might be worth trying a can of stop leak rather than scrapping the engine. There are a few car or box manufacturer approved hydraulic fluid additives for specific failure issues, but they all require that the oil and screen filter be changed first and you need to follow the exact procedure listed in the approval.
5/ Experimental use. There are one or two new anti wear additives under test by major oil companies that might make a slight difference, but if you try one make sure you do a full UOA to see if the product is causing increased wear, as many do.
If you feel that you have to buy a can of additive get one from a major engine or hydraulic fluid company, as they have the facilities to test it fully and are far less likely to be selling a potentially damaging product.
Most folks that use additives would be far better off using a better quality or different viscosity range oil or an oil designed for their specific needs, like an HM oil, classic car or race oil.
Never forget, if in doubt, read the instructions not the advertising and that means the maintenance and users manuals in combination with any additional approvals.
There are a number of exceptions to the golden rule of not adding extra chemicals to a good quality engine or transmission oil and they are as follows:
1/ Maintenance procedures that require the use of a solvent to clean various engine parts, special pre assembly oils and anti corrosive sprays.
2/ Maintenance procedures relating to sludge prevention or minor cases of sludge, where a flush additive is used at idle only for 10 to 15 minutes just before an oil change. A number of dealers have approvals for such procedures, although I have not seen it mentioned in any maintenance manual, just in more local approvals.
3/ Type and product specific manufacturer approvals that relate to a specific design fault that requires an oil or fluid additive. These are very, very, rare and tend to relate to noise reduction in auto gearboxes or leaks. Some approvals were cancelled when new oils or fluids became available.
4/ Terminal phase engine or gearbox faults. When an engine is on its last legs and the bearings, rings and valve guides etc are failing the best course of action is to use a thicker multi grade race oil, like a 10/60, but if you also have serious oil leaks a high mileage oil containing seal conditioners should be tried. If you have a serious oil leak that is beyond economic repair, then it might be worth trying a can of stop leak rather than scrapping the engine. There are a few car or box manufacturer approved hydraulic fluid additives for specific failure issues, but they all require that the oil and screen filter be changed first and you need to follow the exact procedure listed in the approval.
5/ Experimental use. There are one or two new anti wear additives under test by major oil companies that might make a slight difference, but if you try one make sure you do a full UOA to see if the product is causing increased wear, as many do.
If you feel that you have to buy a can of additive get one from a major engine or hydraulic fluid company, as they have the facilities to test it fully and are far less likely to be selling a potentially damaging product.
Most folks that use additives would be far better off using a better quality or different viscosity range oil or an oil designed for their specific needs, like an HM oil, classic car or race oil.
Never forget, if in doubt, read the instructions not the advertising and that means the maintenance and users manuals in combination with any additional approvals.