Diesel Engines Large Oil Volumes - Why?

[BrianGlenn]

Diesel engines have large volumes of oil contained within the engine components and oil pan. Why are the volumes so large? Just conversation, any engine design experts out there?

My diesel Light Duty Truck, 6.4L displacement had 15 quarts (14 litres) and my Medium Duty 400ISL, 8.9L displacement holds 28 quarts. This is compared to my gasser Jeep Hemi, 5.7L displacement holding 7 quarts (6.6 litres), or my Subaru STi, 2.5L displacement holding about 5 quarts (4.7 litres).

My common sense thinks oil volumes are higher for diesels due to:

• relative volume of oil holdup in engine vs pan,
• large volume to prevent oil temp spikes due to short term spikes/change in engine load,
• large volume to allow slight contamination (particulate, diesel) between changes and not exceed contaminant specs,
• large volume to accommodate more volume of additives that help engine but are consumable (i.e. corrosion inhibitors, etc that are part of the OEM oil spec?)

Others?

EDIT: Do diesel engines circulate oil significantly faster (oil lubricating rate)? Would this require more oil volume to protect oil pump?

Curious...
Brian

[schrederman]

Locomotive engines carry about 100 gallons (or more) of oil. It's never changed. The filters get changed and new oil gets added... but unless contaminated by an engine or filter failure, the oil is never actually changed. My 6.7 Cummins holds 12 quarts... and your question is interesting. Maybe someone that knows will satisfy our curiosity.

[Slolane]

In addition to lubricating the engine, oil carries heat away from engine components - bearings, pistons, etc.

These large diesels generate a tremendous amount of heat. The large capacity oil pans give the oil time to cool off before it gets circulated again.

[loisjop]

The 600hp isx holds 56 qts. Mostly for cooling I'm sure.

[dennis45]

In simple terms,

The larger the displacement, the more lube oil capacity required.
Oil drain intervals are based on the amount of miles, or hours, it takes to saturate the oil with the by products of combustion to a point where it can no longer provide adequate lubrication. If there were no combustion taking place in the engine, the lube oil would last infinitely longer.

But, Compare the amount of fuel consumed and heat generated between your 4 cylinder, 2 liter engine and the 8.5 liter plus diesel and you can see why the larger engine needs more oil capacity.

Imagine if you will, a highway truck with a large Diesel engine with the same oil capacity as your hemi. It would require an oil change every couple of days to ensure proper lubrication. Not very practical.

Some applications actually have additional oil reservoirs added to increase capacity and allow for extended oil drains.

[BrianGlenn]

Thanks for the replies; not disputing anything said, however I am looking for some clarification on a few posts:

Originally Posted by Slolane

In addition to lubricating the engine, oil carries heat away from engine components - bearings, pistons, etc.

These large diesels generate a tremendous amount of heat. The large capacity oil pans give the oil time to cool off before it gets circulated again.

Agreed to take heat away from contact points (lubricating film area) However I don't believe the pan size (pan oil volume) is calculated to support cooling of the oil; my ISL has a oil cooler integrated into the block which exchanges heat between oil and coolant - this is the primary source of oil cooling, IMHO. Comments?

Originally Posted by dennis45

But, Compare the amount of fuel consumed and heat generated between your 4 cylinder, 2 liter engine and the 8.5 liter plus diesel and you can see why the larger engine needs more oil capacity.

Not sure I subscribe to this belief - the coolant system is the primary system to remove the heat generated. Combustion temperatures are lower in my diesel vs gasser (800F vs 1,400F average, 1,200 vs 1,500 max).

Thanks again - good points and very interesting for me.

Brian

[rollondown]

Add the sheer size of the engine. The oil passages in your 6.4 hold XXX amount. Well when you double your engine size, your fluids have to increase as well. I'm sure there is a formula for diameter and length of passages, pressure needed to maintain flow, volume of fluid needed to remain at XXX temp, etc.
Our Cummins M-11 holds between 34-38 Liters of oil depending on filters.

[dennis45]

Originally Posted by BrianGlenn

Thanks for the replies; not disputing anything said, however I am looking for some clarification on a few posts:







Agreed to take heat away from contact points (lubricating film area) However I don't believe the pan size (pan oil volume) is calculated to support cooling of the oil; my ISL has a oil cooler integrated into the block which exchanges heat between oil and coolant - this is the primary source of oil cooling, IMHO. Comments?







Not sure I subscribe to this belief - the coolant system is the primary system to remove the heat generated. Combustion temperatures are lower in my diesel vs gasser (800F vs 1,400F average, 1,200 vs 1,500 max).



Thanks again - good points and very interesting for me.



Brian

Obviously my attempt at keeping it simple is not working. Here is an expanded version on oil cooling in internal combustion engines. Good bedtime reading......

https://en.m.wikipedia.org/wiki/Inte...engine_cooling

[twinboat]

Originally Posted by BrianGlenn

Thanks for the replies; not disputing anything said, however I am looking for some clarification on a few posts:



Agreed to take heat away from contact points (lubricating film area) However I don't believe the pan size (pan oil volume) is calculated to support cooling of the oil; my ISL has a oil cooler integrated into the block which exchanges heat between oil and coolant - this is the primary source of oil cooling, IMHO. Comments?



Not sure I subscribe to this belief - the coolant system is the primary system to remove the heat generated. Combustion temperatures are lower in my diesel vs gasser (800F vs 1,400F average, 1,200 vs 1,500 max).

Thanks again - good points and very interesting for me.

Brian

The lubricating system of many large engines also have piston cooler nozzles directed at the inside of the hollow piston. The oil absorbs the heat, where coolant can't go.

[BrianGlenn]

Originally Posted by twinboat

The lubricating system of many large engines also have piston cooler nozzles directed at the inside of the hollow piston. The oil absorbs the heat, where coolant can't go.

Thank you. Overlooked this before in my ISL400 Oil Flow Schematic. #4 in this schematic from Cummins Quickserve for my ESN. Good info; I wonder how much heat energy is dissipated from this oil spray.

Brian

[lynnmor]

A diesel engine has higher cylinder pressures at all times. The compression ratio is much higher. Even at idle, there is high pressure because the intake air is not throttled, (there is no throttle). What this means is that there is much more blow-by past the piston rings causing much more oil contamination. Just look at the color of the oil after operating for a short time.

[jimcumminsw]

Originally Posted by BrianGlenn

Diesel engines have large volumes of oil contained within the engine components and oil pan. Why are the volumes so large? Just conversation, any engine design experts out there?

My diesel Light Duty Truck, 6.4L displacement had 15 quarts (14 litres) and my Medium Duty 400ISL, 8.9L displacement holds 28 quarts. This is compared to my gasser Jeep Hemi, 5.7L displacement holding 7 quarts (6.6 litres), or my Subaru STi, 2.5L displacement holding about 5 quarts (4.7 litres).

My common sense thinks oil volumes are higher for diesels due to:

• relative volume of oil holdup in engine vs pan,
• large volume to prevent oil temp spikes due to short term spikes/change in engine load,
• large volume to allow slight contamination (particulate, diesel) between changes and not exceed contaminant specs,
• large volume to accommodate more volume of additives that help engine but are consumable (i.e. corrosion inhibitors, etc that are part of the OEM oil spec?)

Others?

EDIT: Do diesel engines circulate oil significantly faster (oil lubricating rate)? Would this require more oil volume to protect oil pump?

Curious...
Brian

Another point to make about oil capacity of a given engine size is to allow for so many exchanges of the oil in the tank per minute without foaming. The oil capacity is also calculated to allow so many PPM particles to be suspended in the oil until it is trapped by the filters. Most large engines have multiple oil filters on them thus the need for more oil too.