Oil dilution not functioning

[captain_kaoss]

Depressing the oil dilution button does not decrease engine oil pressure as expected

[jackill]

I checked, and it could be - I set cold start at 5*C and after startup set 1400 RPM for 5 minutes. Test 1 - without dilution, test 2 - holding oil dilution.

Rate of pressure drop was the same, and after 5 minutes in both cases engine parameters were the same:

 

PS. I checked on Reflected's tutorial movie and there pressure drop is quite noticeable and happens quite fast after starting diluting.

Edited June 25, 2023 by jackill

[Art-J]

Was Reflected's vid recorded before recent cooling system revisions in all V-12 warbirds? Maybe they broke all oil diluters - will have to check the Mustang as well.

[Screamadelica]

Reflected's video was before the revised cooling systems were in place for the Spitfire.

I've noticed that no matter how long you hold the oil dilution button down there is never any dramatic drop in oil pressure like it previously was.

Not sure what you should see in real life..?

Edited June 27, 2023 by Screamadelica

[Dragon1-1]

AFAIK, IRL it's used before stopping the engine, to make it easier to warm up during the next start. I don't think it's used during warmup.

[jackill]

I will check later, but I believe that after a minute @1400RPM, holding the button, pressure still was staying at around 150.

[jackill]

I made a different test: 10*C, started the engine, put it to idle and immediately started dilution. Oil pressure was staying at 90 lb/sq inch when oil temp rose to 10*C. Touching the throttle resulted in bumping pressure to 120 lb/sq inch.

 

PS. Manual for warming-up is stating:

• Ensure that the oil pressure is within 60-120ft/in 2.
• Set the throttle to the position corresponding to 1000-1200 RPM according to the tachometer.

• Continue to warm the engine at an RPM of 1000-1200 until the oil temperature reaches 20°C and the coolant fluid temperature reaches 60°C (shown by the left and right instruments respectively)

Nothing specific regarding dilution button either. Logic suggest that adding fuel should reduce viscosity thus lover the pressure, allowing for more RPM = faster warming up.

Edited June 28, 2023 by jackill

[slickdevel]

Oil dilution, this a process where gasoline is added to the oil prior to the aircraft being shut down. There was no 10w-50 oil as we have today and simply adding a few squirts of gas prior to starting is not  going to dilute 21 gal or more of 50 weight oil enough for a cold weather start. To be realistic you would have the ground crew start the engine long before the mission. If you wanted to do it correctly?

Researching this for the P-51 last year I found this under ""landing": 

Page 27 of  Army Manual AN 01-60JE-1 for the P-51D-5, stopping engine: "(2) If a cold weather start is anticipated, hold oil dilution switch, on pilot's switch panel, "ON" (2 minutes maximum)."

[Art-J]

^ Yes, most DCS players with sufficient tech knowledge understand and know it very well. It's also mentioned in DCS manual for the Mustang If I recall correctly.

That being said, for years a simplified / compromise solution has been implemented in Mustang and Spit - diluting cold oil before startup would actually work in DCS. Obviously not a realistic behaviour, but a necessary "lesser evil" in a situation when the sim doesn't model persistent airframe and engine status from previous missions like civilian sims do, and it doesn't feature a "pre-warmed" engine option like Il-2GB series does. Thus it's been the only way available for us in DCS to keep the oil pressure within limits at very cold starts.

So the question is:

a) do the symptoms described above mean the devs decided to go for full realism during recent grand modelling overhaul and it's intended behaviour now, or;

b) is the realism compromise still supposed to be in, but there's a bug which just makes oil dilution inop at any condition?

It's never worked in Thunderbolt module, now we know it stopped working in the Spitfire, maybe I'll find some spare time to load the sim and check the Mustang today.

Edited June 29, 2023 by Art-J

[jackill]

After reading this, I am also leaning towards an option that it was a bug, fixed by new cooling model. From said Pilot's notes (https://stephentaylorhistorian.files.wordpress.com/2020/04/spitfire-ix-xi-xvi.pdf) :

 

Also interesting material: 

 

Edited June 29, 2023 by jackill

[Art-J]

A bug or a necessary gameplay compromise, depending on one's point of view ;). In either case, tried the Mustang and it seems to behave like the Spit now as well, so It might have been intended for all we know. Revised oil system and all.

[NineLine]

I tested, diluting before and not diluting before start-up at about -5 OAT and saw a decent difference in how the engine started and the pressure shown after start-up. 

[grafspee]

Compromise should be done that way that plane should spawn with proper diluted oil depending on OAT or previously pre warmed by crew. Probably both ways up to mission designer to choose. And this should be end of story.

Edited February 16 by grafspee