Name some causes of thinning please

[TomJones76]

I've got some UOAs with a worrying amount of thinning.
Is there a good site with a list of reasons for oil thinning? I know that energy-conserving 5W30s have a tendency to thin to high 20-weights, perhaps by design.
Any other suggestions?
Is there a page with some causes listed?

 

[Ray H]

1: Fuel dilution (common during cold weather with insufficient warmup while the motor runs richer)
2: VII polymer shearback
3: Base oil shearback
(not unusual during highspeed and/or hot weather operation)
4: Formation of aromatic solvents from oxidation
(This list should not be considered exhaustive.)

 

[Pablo]

heat

 

[Titan]

It's the way the testosterone molecule interacts with the hair follicle. See Male Pattern Baldness for more info.

Oh, at LEAST Viscosity Index Improver breakdown...

 

[Mitch Alsup]

Accumulation of microscopic particles in the oil contributes to viscosity lowering.

 

[moribundman]

middle age

 

[GoldenRod]

Ray H wrote:

"Fuel dilution (common during cold weather with insufficient warmup while the motor runs richer)"

I thought you guys were saying last winter that a long warmup was the cause of fuel dilution.

 

[Bill in Utah]

Toyota Timing chains...

At least in my engine.

Bill

 

[Palut]

quote:

---

Originally posted by GoldenRod:
Ray H wrote:

"Fuel dilution (common during cold weather with insufficient warmup while the motor runs richer)"

I thought you guys were saying last winter that a long warmup was the cause of fuel dilution.

---

Yep, because fuel dilution is higher at idle when combustion is less efficient. So more fuel is put into the oil during the long warmup. The oil then runs colder because of the cold weather, and is less able to burn that fuel off.

 

[427Z06]

Good question, TomJones76.