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oil weight for turbo'd car

4947 Views 17 Replies 11 Participants Last post by  DieToRemain
So i know this doesnt have to do with tacomas but it might still be relevant to someone on here. Anyways my buddy has an sr20det fully built pushing around 370rwhp. (hasnt upgraded the fuel system or turbo yet, motor is built for 700ish) The car is always ragged on and we were having a discussion on what oil he should be running. he currently runs conventional 5w30 every 1500 miles. I suggested switching to something like the valvoline 5w40 diesel oil (engine only has about 20k miles on it) for more protection when driving hard but still nice and thin upon start up. Plus the diesel additives would help keep the engine much cleaner. Any thoughts?
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I run Redline 5w30 in my truck, but I know a couple guys up here that run a Rotella diesel oil for break ins only for the higher zinc content.

I wouldn't run anything heavier than 30 even to break it in but that's just me. if you're having issues with it burning oil or something then your oil weight isn't the problem heavier oil would just mask an underlying problem in the motor. :waytogo:
I've been wanting to know, older school guys argue that with aftermarket F/I, the increased BTUs when romping on it make the conventional oil's viscosity go too low so they use much thicker oil.

But in the more modern age of synthetics that resist viscosity change much better in extreme temperatures, is this old method outdated?
*All info cross referenced from*

This info greatly helped me decide which oil to use in my turbo car...maybe it will benefit some of you guys as well.

What is a UOA?
Used Oil Analysis, or UOA's, tell how well your motor oil has functioned in your vehicle. By analyzing which particles of metal are in your oil, a UOA can reveal developing engine problems and provide clues into which parts of your engine are wearing.

How do I get one?
If you would like to have a UOA done on your oil, visit and order the free test kit. Blackstone Labs charges $20 for the analysis and an extra $10 if you would like a TBN (Total Base Number), which essentially tells you how much life was left in your oil.

How do I read a UOA?
A UOA shows the elements in your oil in parts-per-million (PPM). Blackstone Labs provides this list of common elements:
Aluminum: Pistons, bearings, cases (heads & blocks).
Chromium: Rings, a trace element in steel.
Iron: Cylinders, rotating shafts, the valve train, and any steel part sharing the oil.
Copper: Brass or bronze parts, copper bushings, bearings, oil coolers, also an additive in some gasoline engine oils.
Lead: Bearings.
Tin: Bearings, bronze parts, piston coatings.
Molybdenum: Anti-wear additive, coating on some new rings (washes off as break-in occurs).
Nickel: Trace element in steel.
Manganese: Trace element, additive in gasoline.
Silver: Trace element.
Titanium: Trace element.
Potassium: Antifreeze inhibitor, additive in some oil types.
Boron: Detergent/dispersant additive, antifreeze inhibitors.
Silicon: Airborne dirt, sealers, gaskets, antifreeze inhibitors.
Sodium: Antifreeze inhibitors, additive in some gasoline engine oils.
Calcium: Detergent/dispersant additive.
Magnesium: Detergent/dispersant additive.
Phosphorus: Anti-wear additive.
Zinc: Anti-wear additive.
Barium: Detergent/dispersant additive.
In addition, Blackstone Labs provides this diagram of reading an actual report:

The UOA will also detail the physical properties of the oil, the descriptions of which are provided in the sythetic/dino comparison below.

Understanding the Differences Between Synthetic and Dino Oil:

Synthetic oil has no peer when it comes to predictable and consistent lubrication. Even if the basic lubrication qualities were the same, the characteristics of synthetic oil that insure reliable performance cannot be denied. Let's compare:
Molecular consistency:
Organic: Multiple molecular lengths
Synthetic: Molecular configuration uniform.
Why important: Lighter organic molecules tend to evaporate in the heat of the engine environment, eventually losing up to 25% of the volume. The loss of the shorter (and more volatile) length chains alters the original composition of the oil, affects its flow qualities and temperature rating. Synthetic oils are "designer molecules". There are no smaller chains with no tendancy to evaporate under heat (see flash point below).

Flash point:
Synthetic oil burns at almost twice the Ferenheit temperature as traditional oil. It remains consistent under extreme conditions with no degradation, thinning, boiling or evacation from bearing surfaces due to vaporization. Temperatures that would severely degrade traditional oil does not affect the lubrication qualities of synthetic. Jet aircraft engines will not run on standard oil. Synthetic is required. Race cars and other high performance engines used to use caster bean oil for its superior qualities. Synthetic has replace caster bean for high stress environments.

Traditional oils are poly-unsaturated while synthetic oils are fully saturated. Traditional oils will combine with crankcase polutants to form new and unpredictable molecular compounds, severely compromising the viscosity rating of the oil. Synthetic oil, being fully saturated (no open chain molecular sites able to bind with other organic compounds) and are not affected by the presense of pollutants, bypass gasses, fuel dilution, or water.

Traditional oils are treated with viscosity modifiers to produce the traditional variable viscosity ratings (example: 10W40). Synthetic oil is designed to be a particular rating by virtue of its molecular configuration. Usage does not modify its performance whereas traditional oil gradually loses their additives. 10W40 becomes 10W30 over time, for example. Changing the oil every 3000 miles is a must to maintain consistency when using traditional oil. The extended changes recommended, mostly marketing in my opinion, are too long to insure that the oil is maintaining its designed qualities, let alone guarantee the filter is not bypassing. Wait that long and change your oil. Notice how much smoother the engine becomes after the change. Not a good sign.

Engine Cleanliness:
Traditional oil will form compounds with crankcase polution and recipitate deposits to the case of the engine. Synthetic oils cannot combine with crankcase chemistry and thus will not form sludge or other undesirable compounds to clog oil passages or retain dirt inside the engine. Because synthetic oils will suspend dirt and other chemisty, those particles have a greater chance of being removed by the filter.

Cold Weather performance:
Synthetic oil will flow at -60º F. where traditional oil is wax. Starting a synthetic oil equiped engine when it is 0º F. is like starting traditional oil when it is 40º. The engine runs effortlessly verses exhibiting the typical stress when using traditional oil at low temperatures. Cold weather operation before warm up is not nice on engine bearings and cylinder walls when the oil viscosity approaches jello.

Use a 1 micron aircraft quality oil filter and you might never have to change synthetic oil as it doesn't degrade. Traditional oil would stay just as clean, but would be compromised over time by chemical bonding altering its structure (see saturation above).

Expensive car manufacturers are not stupid:
BMW and other premium cars insist that their engines be lubricated with sythetic oil. BMW warns owners to change oil ASAP if anything else is used. Using synthetic oil with regular changes provides the level of protection to the engine that maximizes its life. Certainly, it is more expensive up front, but the benefits will be realized in smoother performance, higher gas mileage, lower oil temperatures, greater resistance to damage if a coolant system failure raises the engine temperature, and ultimately a lower cost of operation. We spend $20,000+ for a car and complain about spending an additional $10 every three months to protect this expensive investment. It doesn't make sense. Quality maintenance is part of the expensive of a car.
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List of Subaru EJ25 (STI engine) UOA's:
Please note that these aren't all directly comparable to one another as different individuals drive their vehicles much harder than others. Lots of short trips in stop-and-go traffic on cold days can be brutal on an engine without the owner ever driving aggressively. In addition, things like oil and air filters make a difference; for example the cotton filter supplied with cold air intakes often do not filter as well as OE paper filters, and contaminants can show up in the UOA. The impact of a poor oil filter should be more obvious. I will also warn that oils showing great results on other (non-Subaru) engines will not necessarily perform well on the EJ25 engines. Of course, this all makes for great debate and discussion, and these analyses are here so that you may draw your own conclusions.

Have a thirst for knowledge?
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i use 10W40 regular. For some reason, when i used synthetic, blue smoke comes out of the exhaust.
i use 15w-40 just because of how hot it gets here:shrug:

I've used 5w-30 and 0w-30. (edit: when I lived in Washington state) Synthetic is always the answer for me. Depending on what climate you're in, should also dictate what weight/viscosity you use.

I do like Tacoholic's idea, seems pretty trick.
i use 10W40 regular. For some reason, when i used synthetic, blue smoke comes out of the exhaust.
Some have argued that the molecules in synthetic are "smaller" and in older vehicles used to mineral oil it seeps past seals and the synthetic oil gets burned.
this is all very interesting, for all of you that suggested 5w30 still, does anyone know why valvolines racing oil is all heavy weight conventional oils like sae30, and 20w50s? I cant help but imagine there must be something in these that gives a better protection, or at least better bearing tolerances.
Racing engines are run much hotter than street motors and are pushed to the limits. For instance in extremely high horsepower 4 cylinder drag racing motors they fill the blocks with concrete and run extremely high boost levels. The motor has no cooling system to it other than the oil and they run things like aluminum rods which expand and change much more with heat than forged steel or chromoly. I still don't see any reason personally that you should have to run heavy oil on a street motor if it is truly built for the best compromise between high performance and reliability. I would definitely go with synthetic on a turbo motor though just for the fact that the oil is what is cooling the turbo and you don't want it to break down due to the heat from the turbo. I would also run an oil cooler as well. Some may say a cooler isn't necessary I just feel like it's an easy way to prevent bigger issues and help keep your motor safe. Just my .02 :shrug:
i use 10W40 regular. For some reason, when i used synthetic, blue smoke comes out of the exhaust.
then your motor has a bad seal(s) somewhere, generally either piston rings or valve seals. Synthetic will expose any leakage issues you may not know you have.

As far as oils to use, I would say to use the new Rotella synthetic diesel oil, not sure of weight, I think it is 15-40, I know the non synth is 15-40.
In all the brainwashing I've had from google and other car boards, its a re-accurent theme that increase power/BTUs, go up in weight. I bought some 0w40 Mobil one in anticipation of the IS300's next oil change.

But there is so much conflicting information out there. In this post that info posted mentioned synthetic keeping it's viscosity in control, but I've read on that same forum (bob the oil guy) that synthetics of course still need to use additives to provide the duality in viscosity (cold and hot), and that those additives burn off and all synthetics over their use begin to become one type of viscosity.

I run an oil cooler, but its response time is lagged (thermostat) and the cooler itself is small. I'm at a loss at what to put in, but I'm gravitating towards staying with what the engine is built for, 5w30.
I run 10w30 in pretty much everything unless its a high mileage/problem motor that I'm trying to limp along for the time being or whatever.
just to follow up, he decided to try 10w-40 in it, car runs like a brand new car, smooth power band and all together just seems to run smoother, sacrifices a little bit of power at the low end, but wide open up near 8k rpm he said it pulls smoother and harder than ever before...just gotta let it warm up a little longer now wiht the 10w instead of the 5w.
i use 15w-40 just because of how hot it gets here:shrug:
diesel oil!
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