What makes one engine prone to sludge vs another?

[kartracer55]

So I was curious, what makes a particular engine more prone to sludge? For example, why is VW 1.8T such a sludge prone engine? Let us please assume frequent 3k/3month oil changes with quality oil. Please dont turn this into a "synthetic does have that problem thread," I would really like to know the technical reasons which make one engine design more sludge prone than another.

Thanks
Jim

 

[c3po]

I will take a shot at this, not changing your PCV, short trips, too heavy of a viscosity oil like when your owner's manual calls for 5w30 and you put in 10W-40, also on some of the engines that were sludge prone they had very small return holes in the cylinder heads, also if you put in a lower temp thermostat, remember you want your engine to run as hot as it can to burn off combustion byproducts, but I think that the number 1 issue is the small return holes in the cylinder heads that get clogged up, every engine that has had this sludge problem the manufacturer of that engine has went too bigger return holes, if you want to prevent sludge use a maintenance dose of Auto-Rx.

 

[dwendt44]

Some head designs have places for oil to puddle, so it sits and cooks the lighter elements off and the thick parts stay.
Some engines also flow less oil to and through the heads. Still enough for lubrication, mind you, but less than others.
High oil flow would wash hot oil out of head faster.
My 2¢

 

[Merkava_4]

I think the way blood flows in the human body is similar to how oil flows in an engine. What happens when your blood flow gets restricted and starts pooling in one area? You get blood clots.

 

[mechtech2]

Bad PCV systems, for the most part. Possible a hot running head.

 

[bar1]

The 1,8T isn't known as a sludge prone engine in Europe. The problem in US was AOA/VWOA recommended the wrong oil to it's customers (a mineral oil). VAG never approved anything other than VW502.00, VW504.00, etc. to this engine.

 

[bar1]

Originally Posted By: kartracer55
For example, why is VW 1.8T such a sludge prone engine? Let us please assume frequent 3k/3month oil changes with quality oil.

If you use VW/Audi (VAG) approved oil in the VW 1.8T engine it will NEVER sludge with OCI of 3,000 miles.
In Europe OCI is 18,000 miles (30,000 kms) with the approved long-life oil (depending on OLM). Severe service is almost 10,000 miles (15,0000 kms) with VW502.00 approved oil.

 

[Max_Wander]

Excessively uneven heat distribution (hot spots) among internal engine surfaces combined with poor flow and poor crankcase ventilation. Short trips, long OCIs and VII laden oil exacerbates this, IMO.

 

[BrianWC]

High heat, low sump volume, and PCV seem to be the main issues.


Heat increases oxidative stress on the oil. Poor crankcase ventilation means acids and fuel attach the oil, depleting additives then attacking the base oil. The 4 liter oil volumes spec'd for some of these smaller, hotter engines combines with the previous factors to make an engine environment very conducive to sludge and varnish formation.

 

[ChiTDI]

Heat, PCV design, pooling of oil in the heads, different owners (use and maintenance).

 

[lovcom]

...yea, and I read someplace that sunspots contribute as well...lol

 

[cmhj]

Cheap booze?