Thick oil vs. thin oil, and cleaning..pls. discuss

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addyguy

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I'm just wondering if the viscosity of an oil affects it's 'cleaning' ability.

Forget the actual add-pack of the oil, JUST focus on the viscosity and it's relative cleaning ability.

Lets say you have an engine with a light to moderate amount of sludge and deposits in it, and you want to clean it up. If you use a thick oil in it, when you start up the engine and run it, the oil presuure will be higher. Therefore, b/c the oil will be under higher pressure, it will theoretically 'push' against the surfaces of the engine harder as it flows through, so it 'should' flush deposits out more effectively - like if you spray a strong jet of water at dirt.

However, if you use a thinner oil, it will have less pressure, BUT it will flow better inside the engine, and will get into 'nooks and crannies' of the engine slightly better, so it will flush junk from smaller orifices better than a thick oil. I know the actual differences between the two will be minimal, but they will be there.

So, what say you?

This has been 'bugging' me for a while, so I'd love to hear lots of opinions on this!
 
There will never be any sludge in the areas of the engine where oil pressure "pushes" (ie, in bearings, in lifters, inside oil galleys.) Sludge accumulates only in places where the oil sits more-or-less stagnant and under zero pressure- under valve covers, in the lifter valley, etc.

Intuition says that a thin oil might dissolve deposits better, but hard cold science says that its really the additive package and chemical composition of the base oil (ester vs. PAO vs. GrpIII) that makes a bigger difference than thickness.
 
There are no nooks and crannies in an engine . The only areas that see oil pressure are the bearings and depending upon design the valvetrain and they usually aren't a problem . Except hydraulic lifters which are the most precise machined and clearanced item in an gasoline engine. Oil flow well in an engine no matter the visc when at operating temps.
 
viscosity has no relation to oil's cleaning ability, IMHO.

It's the add pack that matters, given that the base oil are essentially the same (using VI improver to modify it's viscosity).
 
Originally Posted By: 440Magnum
There will never be any sludge in the areas of the engine where oil pressure "pushes" (ie, in bearings, in lifters, inside oil galleys.) Sludge accumulates only in places where the oil sits more-or-less stagnant and under zero pressure- under valve covers, in the lifter valley, etc.

Intuition says that a thin oil might dissolve deposits better, but hard cold science says that its really the additive package and chemical composition of the base oil (ester vs. PAO vs. GrpIII) that makes a bigger difference than thickness.



I agree completely, that the sludge occurs where oil pools. That being said a thinner oil will have a higher volume of flow for a given pressure and perhaps in theory be less likely to form deposits. But like 440 points out, other factors are far more important than viscosity.
 
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I think its all unrelated.
Cleaning ability is additive package and optimum conditions (working cooling system for example)

As the others have said, sludge will not form where there is oil pressure.
 
Originally Posted By: 440Magnum

I think magnum summed it up well. Dont confuse the fact that bc petroleum solvents tend to be of low viscosity therefore a paraffinic base of low viscosity would clean better. You DO want an oil at near operating viscosity for the largest % of your daily trip. A five mile oneway in the dead of winter (0-15deg F)just never works unless you have a remote heated oil tank with windage control low capacity sump ala NASCAR spec. Running too light a viscosity would help a Winter short tripper, but would not protect the engine on sustained high speed/high stress loads.
 
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Engines are designed to drain oil back to the oil pan to be recirculated by the pump. Yes there are oil traps in just about all engines I have seen. Viscosity is a variable as to how quickly the oil can slosh out of a trap. The add pack with detergent combats this issue and has a greater effect than viscosity alone. The answer is many things factor towards elimanting sludge & varnish. I only use synthetic oils whether group 3 for my daily work car, or group 4 for my 35VQDE. Some engines also are better designed and do quite well with a good group 2 like the GM Ecotecs. Variables my friend is your answer.
 
Even if a thin oil did have some advantageous cleaning ability over a thicker oil it's really an academic question.

Unless you want to potentially damage your engine one would never use a lighter oil than what provides the minimum oil pressure as specified by the engine manufacturer. Of course to do that you will need an accurate OP gauge, which most BITOG'er don't have.

But you do have an OP gauge and did determine how light an oil you can run in your own application you've just optimized your viscosity selection and there would be no reason to go back to a thicker oil.
 
Originally Posted By: addyguy
I'm just wondering if the viscosity of an oil affects it's 'cleaning' ability.

Forget the actual add-pack of the oil, JUST focus on the viscosity and it's relative cleaning ability

As I understand the question, if both have the same additives then which is better at cleaning the engine ?

I don't have proof/data but believe that the thinner oil is better of cleaning because it goes to places that thicker oil hardly go to, and it drains to the sump from those places faster/easier.
 
No, a thinner oil doesn't go to places a thicker oil can't, it just gets there faster.

I thick 440Magnum described the situation well.

I would add that the solvency nature of an oil is more related to it's chemistry not it's viscosity. Furthermore the difference in viscosity between a 20wt 8cSt oil and 40wt 13cSt oil at 100C is insignificant and to the naked eye will both will appear to have the consistency of kerosene.
 
with only thick vs. thin, I would think the thinner oil would clean better. it flows thru the passages faster. faster = more friction right? O wait, we are talking lubrication. Now I just confused my own thoughts on the subject
 
Originally Posted By: SL8R
This is the most useless thread I've come across in a while. I'm not sure that's an accomplishment, but it is notable.



way to contribute
banana2.gif
 
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