Bellow
Hardcore MB Enthusiast
NOTE to MODS.
I wanted to post this in Projects but I am denied access. Will you move to their please?
A poorly understood subject frequently over looked is grease compatibility – and with potentially very bad outcomes. The compatibility of one grease with another is by no means a given.
Firstly, a quick run down on what a grease actually is. It is oil. Look at the data sheet for any grease and you will find the base oil viscosity and despite what you may have expected, that viscosity may be lower (‘thinner’) than you expect. It will almost without exception be no thicker than oils you have poured. So why doesn’t grease pour? The reason is the second component of grease into which the base oil is incorporated, the thickener base. The analogy that best describes the two components is the bathroom sponge one where the sponge is the thickener base and the water the base oil. Saturated with water the sponge contains the water. Squeeze the sponge and out comes the water. Grease is a thickener base saturated with oil. Squeeze grease (bearing pressure) and out comes the oil (to do the lubricating). A property exhibited by some greases is reversibility. This is the ability of the thickener base to reabsorb the oil on release of load.
What anyone selecting greases needs to be aware of though is that not all thickener bases are the same and not all are compatible with each other if mixed. Greases that lack compatibility when mixed clash, dissolve each others thickener base leading to a fluid which is then free to run and escape. Thus, the bearing will be without lubrication and can be expected to fail. Why are there different types of thickener bases? Because each has its own unique properties better tailoring the grease to its intended application. However with each type their are trade offs. The most water resistant base is not the most temperature resistant base – for example. So there is obviously a requirement to identify the operating conditions the grease will see.
Thickener base types can be found within the technical data sheet for the product along with the NLGI #, and will often be referred to within its product name. A grease’s NLGI# is a function of its thickener base viscosity and will be typically a #1 or #2 (000, 00, and 0#s are semi fluid in nature and unlikely to have any automotive applications). An NLGI#2 grease is thicker than an NLGI#1 grease and can better withstand pounding forces without being displaced. An NLGI#1 is more fluid and is better suited when higher speeds are employed. Typically up to 3000rpm (on the bearing sizes we are likely to encounter on a car) an NLGI#2 is appropriate. For speeds between 3000 and 6000rpm an NLGi#1 would be used. They are the two NLGI#s you will likely encounter and in 99.9999% of cases the thickener base will be lithium.
Lithium and lithium complex based greases have a good range of all round properties, are compatible with each other and for most automotive applications are fine. There is one exception. Where high temperatures are involved an aluminium complex grease has slightly better high temperature capability in that it usually has a higher ‘drop point’ (the temp at which it starts to run) and better reversibility (see earlier). If, and only if, you expect a wheel bearing to be burdened with brake heat beyond what the manufacturer intended need it be considered. And, all other so called high temp greases are for kilns – not cars.
My advice therefor unless you have a quantifiable reason to deviate, stick to lithium and lithium complex based greases. This will eliminate the possibility of applying one grease on top of another with which it is incompatible, the whole lot running out and the bearing being run dry and failing.
I write all the above to clarify that in most instances greases fancier than lithium and lithium complex based greases are just not necessary and to warn you of the dangers of allowing them to mix.
I’ll attach a PDF showing a compatibility chart showing just what can and cannot be mixed should you absolutely be in the position of needing to know. Hopefully the above is of use to those of you involved in a rebuild project.
I wanted to post this in Projects but I am denied access. Will you move to their please?
A poorly understood subject frequently over looked is grease compatibility – and with potentially very bad outcomes. The compatibility of one grease with another is by no means a given.
Firstly, a quick run down on what a grease actually is. It is oil. Look at the data sheet for any grease and you will find the base oil viscosity and despite what you may have expected, that viscosity may be lower (‘thinner’) than you expect. It will almost without exception be no thicker than oils you have poured. So why doesn’t grease pour? The reason is the second component of grease into which the base oil is incorporated, the thickener base. The analogy that best describes the two components is the bathroom sponge one where the sponge is the thickener base and the water the base oil. Saturated with water the sponge contains the water. Squeeze the sponge and out comes the water. Grease is a thickener base saturated with oil. Squeeze grease (bearing pressure) and out comes the oil (to do the lubricating). A property exhibited by some greases is reversibility. This is the ability of the thickener base to reabsorb the oil on release of load.
What anyone selecting greases needs to be aware of though is that not all thickener bases are the same and not all are compatible with each other if mixed. Greases that lack compatibility when mixed clash, dissolve each others thickener base leading to a fluid which is then free to run and escape. Thus, the bearing will be without lubrication and can be expected to fail. Why are there different types of thickener bases? Because each has its own unique properties better tailoring the grease to its intended application. However with each type their are trade offs. The most water resistant base is not the most temperature resistant base – for example. So there is obviously a requirement to identify the operating conditions the grease will see.
Thickener base types can be found within the technical data sheet for the product along with the NLGI #, and will often be referred to within its product name. A grease’s NLGI# is a function of its thickener base viscosity and will be typically a #1 or #2 (000, 00, and 0#s are semi fluid in nature and unlikely to have any automotive applications). An NLGI#2 grease is thicker than an NLGI#1 grease and can better withstand pounding forces without being displaced. An NLGI#1 is more fluid and is better suited when higher speeds are employed. Typically up to 3000rpm (on the bearing sizes we are likely to encounter on a car) an NLGI#2 is appropriate. For speeds between 3000 and 6000rpm an NLGi#1 would be used. They are the two NLGI#s you will likely encounter and in 99.9999% of cases the thickener base will be lithium.
Lithium and lithium complex based greases have a good range of all round properties, are compatible with each other and for most automotive applications are fine. There is one exception. Where high temperatures are involved an aluminium complex grease has slightly better high temperature capability in that it usually has a higher ‘drop point’ (the temp at which it starts to run) and better reversibility (see earlier). If, and only if, you expect a wheel bearing to be burdened with brake heat beyond what the manufacturer intended need it be considered. And, all other so called high temp greases are for kilns – not cars.
My advice therefor unless you have a quantifiable reason to deviate, stick to lithium and lithium complex based greases. This will eliminate the possibility of applying one grease on top of another with which it is incompatible, the whole lot running out and the bearing being run dry and failing.
I write all the above to clarify that in most instances greases fancier than lithium and lithium complex based greases are just not necessary and to warn you of the dangers of allowing them to mix.
I’ll attach a PDF showing a compatibility chart showing just what can and cannot be mixed should you absolutely be in the position of needing to know. Hopefully the above is of use to those of you involved in a rebuild project.
