Turbo Lubrication: Observations and Analysis

Hello everyone,

A digital LDA (Latent Dirichlet Allocation) can indeed provide interesting insights.

After a cold start, my boost pressure is at -10 mBar at idle. This means the engine is creating a vacuum in the intake manifold, and the (weak) exhaust gas flow is not strong enough to drive the cold turbo sufficiently to provide as much air as it would normally draw in.

When the engine is warm, the oil pressure is exactly 0 bar, which means the lubrication provided by the warm/hot oil is even better, allowing the relatively weak exhaust flow to drive the turbo "strongly."

A difference of 10 mBar isn't much, but on the other hand, the boost pressure when driving comfortably in the city is also not much higher than 50...100 mBar, so the difference in lubrication of the turbocharger isn't that small.

Consider these thoughts as a measurable addition to the reasons why a TDI engine absolutely needs to be warmed up before being driven hard.

Best regards,

Jan.

VW had already pointed out a long time ago that the loader was a bit of a grumpy old man .

It is also found in every good engine manual .

CU Gremlin.

IMHO, the exhaust gases from a cold engine cool down significantly as they come into contact with the cylinder walls and the exhaust passages leading to the turbocharger, thereby losing even more energy.
This is also why cold-starting can be particularly difficult for turbocharged diesel engines.

Hi Gremlin,

I didn't want to present this as a new discovery, but rather as a reasonable piece of evidence, because unfortunately, there are still some people who incorrectly claim that TDIs can be cold-started.

I consider the initial hesitation to be a form of "self-defense" on the part of the control unit .

Best regards,

Jan.

Hello,

I've already mentioned elsewhere that it starts much better with thinner oil, especially when starting from cold.

Since the turbocharger bearings essentially float on the oil stream, I imagine that the turbocharger itself wouldn't be affected by the oil temperature, as long as there's oil pressure. Cold oil is just thicker, so it requires more power to drive the turbocharger.

I also always wait after a cold start until the turbocharger is clearly audible running in idle, which can take up to 5 seconds. Only then, in my opinion, does it have enough oil to start, and the automatic transmission and the rest of the engine should also be adequately lubricated. This time can be used to activate other functions like lights, heating, seat adjustment, mirrors, etc.

And regarding high-speed cold starts - to my knowledge, this is primarily harmful to the cylinders.

Anything that runs on oil pressure can handle that.

Can you hear your turbo when the car is idling?

Best regards, WarLord.

Sure, no problem.

Take a look at my footer!

VW has already pointed out that the grumpy loader has been a problem for a long time.


Yep, I can understand that. Even though, in my opinion, older TDIs always had the best pulling power...
But it probably depends on the oil. The new 0W-30 oils are really like lubricating water, so thin. A 5W-40 is already a much thicker fluid...

Hi Jan6k,

Unfortunately, I am more familiar with the electrical side than the mechanical side. But I wonder why you see this as proof that the charger should not be operated with cold oil. It is clear that the charger requires more effort to turn when the oil is cold. This would cause it to rotate slower, and therefore deliver less pressure , as your measurement also demonstrates.

My question is: Why is it not allowed to crank the engine when it's cold? The starter motor spins even slower with cold oil, which theoretically should actually be even better.


Just to get something out of the way: I know that you shouldn't crank a cold engine, and I don't do that either. I just don't understand the reasoning behind it in this particular case.

Regards,
Private.

Hi Private,

The reasoning was something like this: Cold oil causes sluggishness, and if you force the part to spin quickly, it puts more stress on the bearings than if it were warm, and it also increases the risk of the oil film breaking down.

However, it's true that one crucial factor is missing from the chain, namely oil pressure.

Overall, it wasn't really intended as an argument, but rather as a single point.

Best regards,

Jan.