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First read 104:
http://www.lamborghini-talk.com/vbforum/showthread.php?p=6642&posted=1#post6642


Motor Oil 105
Part Five. Let’s use top gear:

Let’s go racing. I will discuss driving in traffic jams in the Florida summer as well as racing in Sebring though there is no commonality. People lump these two driving situations together but there is no overlap.

On the race track one usually uses all the BHP their engine can give them. You briefly step on the brakes for the corner then put the pedal to the metal the rest of the time. Your oil will get up to 302 F, but your cooling system is around 212 F. The engine produces tremendous heat but can only pass it off so fast to the cooling system. There is a lot of air moving past the cooling radiator so the antifreeze / coolant is able to get rid of the extra heat from this part of the system with relative ease.

The temperature of oil on your gauge is not as hot as it really gets. This temperature is an average with oil from different parts of the motor. Some parts are hotter than others. It is said that some of the oil gets as hot as 400 or 500 F in these racing situations.

In an earlier section I said that thicker oils are usually needed in racing situations but not necessarily. Remember that a major function of oil is to cool the inside of your engine. In ASTM D 4485 3.1.4: “Terminology: Engine oil- a liquid that reduces friction and wear between moving parts within an engine, and also serves as a coolant.” Since the oil with a viscosity of 10 cS at 212 F thins to a viscosity of 3 cS at 302 F we will get more flow. The pressure will go down some as well. This is OK as long as we have a minimum of pressure to move the oil.

This increased flow will result in increased cooling by the oil. This is a good thing. You would probably want more oil flow in these situations and you get it. The hotter oil thins and this increases flow. The higher flow works harder to separate the engine parts that are under very high stress. It all works out for the better. Higher revving engines need thinner oils. You do not necessarily need to go to a thicker oil while racing. Only experimentation will tell.

The best way to figure out what viscosity of oil you need is to drive the car in the conditions you will use. Then use the oil viscosity that gives you 10 PSI per 1,000 RPM under those circumstances. For some reason very few people are able to get this simple principal correct. I cannot explain further.

These same rules apply to engines of any age, loose or tight. Just because your engine is old does not mean it needs a thicker oil. It will need a thicker oil only if it is overly worn, whether new or old. Yet the same principals of 10 PSI per 1,000 RPM still apply. In all cases you need to try different weight oils and see what happens. Then choose the correct viscosity.

I am using 0W-20 in my Ferrari 575 Maranello right now. It has over 5,000 miles on the clock. There will be a day (my estimate is 50,000 miles) when I will have to go to a 0W-30. In the future I will have to increase the viscosity to a 0W-40, then a 0W-50, maybe. I will use whatever it takes to give me 75 PSI at 6,000 RPM during the lifetime of my engine. This formula works in all situations.

Some people have tried this and occasionally get a somewhat low oil pressure while at idle. This is fine. There is no stress on parts at idle, the smallest oil flow will do the trick. It is at higher RPM where more BHP is produced. This is where we need the flow. Remember that Ferrari uses 75 PSI at 6,000 RPM as the place to test your oil viscosity needs. If your oil gives this value under your driving conditions then your lubrication system has been maximized. Period.

Do not go 5,000 miles with the same oil if you are racing your car. You should change the oil every 1 or 2,000 miles. If you drive your car around town then you need to change the oil for that situation. Use racing oil on the track and urban oil around town. The best situation as described by Ferrari is to use the 0W-40 around town and the 10W-60 “racing oil” on the track. It has to be that “hot” track though. A compromise situation would be to use the 5W-40 for both but this may not be optimal. Certainly, if you are just an urban driver as me use the 0W-40 or even a thinner oil as I do in my Maranello. Again, I use the 0W-20.

FYI. The Formula 1 cars that run at 15,000 RPM and higher use straight 5 and 10 weight oils.

Now let me discuss what people think is a similar situation to racing. That is hot summer traffic jam driving. Your car should be able to handle this. If you have problems then you have a problem with your car, most likely in need of a cooling system overhaul.

continued:
 

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When you drive that car down the road mid-winter in upstate New York or mid-summer in Florida the engine and oil temperatures will be around 212 F. But your Florida vacation is suddenly altered by a hurricane. You have to get out of Tampa, but so do a million other people. It is now 95 F and you are in a snarl. Everyone thinks they need a thicker oil for this situation. This is false.

Your engine is not producing much heat at low RPM and low BHP output. The production of heat is relatively slow. It can easily be transmitted to your cooling system. The problem is that your cooling system has trouble getting rid of the heat. The oil and the coolant will slowly rise in temperature. They both rise together. The increase is no big deal for your oil. It goes to 220, then 230 F. The problem is that the cooling system can only handle heat up to 230 F. After that you overheat the cooling system and the car must be shut off. The oil never got that hot, It was just that the water got a little hotter than its system design.

You now see that overheating in traffic is a cooling system problem and not an oil system problem. Do not change to a thicker oil based on your traffic situation.

aehaas
 

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Dr Haas: Would this be a correct statement. Use the lowest (firsts number) viscosity available with the Manufacturers recomended (2nd number) viscosity. In other words if my manufacturer recommends a 10W30 Synthetic oil, it is better to use a 0W30 Synthetic (like Mobile 1 ) for all the reasons you gave in your articles.
 

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Dr Haas: You talk of not mixing oils. I have Agip 10w40 synthetic in my 99 Diablo. The factory is now recomending 5w40 synthetic. If I want to change to Mobile 1 0W40 can I just drain the oil tank or due I have to drain the oil lines also as you did in your Murcielago?? thanks.
 

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I dropped all the lines in the Maranello. I did not clear them in the Murcielago but they seemed smaller, thinner. Also, they are easy to get to in the Ferrari and much more difficult in the Lamborghini. I was not worried.

When I look at the blends from Castrol there are no differences from straight mineral oils by the numbers. They have the same relative startup viscosities, flash points and pour points. The Valvoline blends have slightly higher flash points otherwise no differences there either. I just do not see any advantages. I would just go for the pure mineral based or synthetic oils.

My guess is that it is just marketing to satisfy hte customer who wants a little of each thinking it is better than plain mineral oil and cheaper than the synthetic.

aehaas
 

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Dr Haas: I am not sure that I uderstood the answer to my question? I am reposting it here. Thanks.

Dr Haas: You talk of not mixing oils. I have Agip 10w40 synthetic in my 99 Diablo. The factory is now recomending 5w40 synthetic. If I want to change to Mobile 1 0W40 can I just drain the oil tank or due I have to drain the oil lines also as you did in your Murcielago?? thanks.
 

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Discussion Starter #9 (Edited)
No, you do not have to drain all the lines in the Diablo. However, it would be better to drain out as much as you can, all if possible. Do not do it if you are not skilled at changing lines. If it concerns you, change to the 0W-40 now and change it again in the springtime, 6 months from now.

I think all engine oils should be changed at least every spring.

One of the API / SAE rules is that oils should all be compatible. That is to say that mixing will not cause something to precipitate or solidify. There should be no adverse chemical reaction. However, if you mix 2 different oils/brands then each of the additives (assuming they are different ones) would be diluted 50 percent. You would start out with half the concentration of each additive.

All oils contain zinc at about the same concentration. This high pressure additive would be unaffected by mixing oils.

My Maranello has huge lines, possibly over an inch I.D. If you do not open the lines then you only change 80 percent of the oil. I guess that is OK as you are not asked to open the lines with regular oil changes.

aehaas
 
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