Time to operating temp - High VI vs Low VI

[TrevorS]

Will a higher VI eg 5w40 oil get to operating temp faster than a low VI eg 15w40 oil?

Or is it just a case of it being thinner during the warm up period?

Part of the reason for asking is that I've seen two engines that saw cheaper mineral oil on annual oil changes (as per manufacturer) but with low mileage that got varnish and light sludge.

I'm wondering if operating at temps lower than required may have contributed and whether higher VI oils can mitigate such problems.

 

[dparm]

This Eneos video demonstrates the VI versus temperature relationship very well.

 

[Shannow]

The work that an engine does shearing the oil in the bearing will be higher in the higher viscosity oil...i.e. more viscosity, more temperature rise across the bearing (and relief valve), the quicker the thicker oil will warm...

To an almost minute degree...

 

[Quattro Pete]

If anything, I'd expect the 15w40 to get up to temp faster, simply because it's thicker at startup and thus generates more heat due to higher internal friction.

But a 5w-40 should flow better at very low starting temps where most of the wear occurs, so it should be better from that standpoint.

Not really sure if either of this would be responsible for sludge. I suspect something else entirely is to blame.

 

[Donald]

In theory there might be an unmeasurable difference, but the temp of the block is going to control the temp of the oil.

Any recommended oil is going to move through the bearings and oil galleys just fine picking up heat.

The block for my Cummins diesel is 1000 lbs. I drive about 35 minutes to work, some two lane roads, some highways, no city traffic. In the winter its just gotten warm when I get to work.

 

[Shannow]

Donald,
the majority of the oil temperature rise is the work that the engine does to the oil...motor an engine without fuel or spark, and the oil gets nearly as hot.

 

[TrevorS]

So this is more to do with short trips and / or the oil quality not being up to 1 year intervals than the grade used.

Thanks!

 

[Doug Hillary]

Hi,
TrevorS - I have done a lot of testing on this subject - on Porsche, Benz and Heavy Diesel engines. A lot depends on the engine's design and the "layout" of the cooling and lubrication systems

As Shannow has alluded to, warm-up time also depends much on the load/work/application of/on the engine

Generally about 15 minutes may be required before some coolant/lubricant equilibrium is reached. This is why using the lowest viscosity lubricant permitted/approved is wise.

Having an oil filter with excellent flow characteristics is a plus (especially with large lubricant/coolant capacities) and if a non-thermostatically controlled oil cooler is fitted this will likely delay reaching the equilibrium point too - especially in a cold ambient temp.

Lubricant intercoolers are probably the best but again much depends on the "layout" of the engine as mentioned earlier

I hope this helps a bit

 

[Shannow]

Doug, I was more referring to the fact that the shaft spinning in the bearings will heat the oil...but your point is well taken. Driving off sensibly is way better warm up than sitting idling.