Why HTHS is important for an engine oil
Choosing an oil for their car, many drivers are used to being guided by the SAE viscosity index. But lately on websites which are devoted to lubricating fluids more often one can find mentioning of HTHS index, which is often called “viscosity index”. Allegedly, this parameter should also be a defining criterion when choosing a lubricant. In this article, we are going to find out what HTHS really is and what its peculiarities are.
HTHS of oil: what is it?
The viscosity of a machine oil is affected by a number of parameters, such as temperature, pressure and the amount of additives in the product itself. One of these key parameters is the HTHS. HTHS is an abbreviation for High Temperature High Shear, which stands for High Temperature Viscosity at High Shear Rate.
To measure HTHS, a rotary viscometer is used, in which oil is tested according to ASTM D4683 method. The lubricant is placed between the stator and the rotor of the device, and then heated to 150 °C. The rotor rotates and torque is transmitted through the oil to the stator. The viscometer measures the speed of the transmitted rotation and the level of torque response.
The resulting number determines the viscosity of the oil. A lower number means a thinner oil film. A higher number means thicker oil and a thicker film. HTHS viscosity is measured in mPa*s – millipascals per second.
HTHS groups of oils
All lubricants can be divided into oils with high and low HTHS. According to the ACEA classification, HTHS values correspond to the following categories:
- More than 3.5 mPa-s – A3/B4, C3, C4, E4, E6, E7, E9;
- 2.9-3.5 mPas-s – A5/B5 and A1/B1 and viscosities 5W-30 and 0W-30 as well as C1 and C2;
- 2.6-2.9 mPas – ACEA A1/B1 and viscosities 0W-20 and 5W-20.
There are also oils with HTHS 2.4-2.6 mPas-s and viscosity 0W-16/5W-16. These fluids are classified not by ACEA, but by API – SN and higher.
You can learn more about the classification of motor oils in this article.
Technically, higher viscosity oils protect the engine better than low viscosity oils due to a thicker oil film. Recently, however, engine manufacturers have been targeting oils with low HTHS. Why is this so?
In modern units due to the high accuracy of assembling the minimum clearances between rubbing parts are provided. These engines are specifically designed for low viscosity oils which can easily seep between the rubbing surfaces, form a thin oil film and seal the gaps. Friction losses in the engine are reduced, resulting in lower fuel consumption and emissions. This, in turn, enables compliance with stringent environmental requirements.
However, low HTHS has a couple of significant drawbacks to consider when choosing an oil:
- When operating at high speeds for a long time, low viscosity oil forms too thin a protective film and can burn out quickly. However, this disadvantage is solved in modern oils by using special additives like titanium oxides, which make the thin oil film more durable.
- At low temperatures, the air-fuel mixture can ignite with a delay. The fuel gets into the oil and liquefies it. If you use low viscosity oil in your engine, it will degrade its properties. The problem is solved by using special additives which keep the oil at its optimal viscosity.
What HTHS should I put in my engine?
Each engine has a definite parameter HTHS of engine oils. There are engines designed for low viscosity oils. There are engines designed for a thicker oil film.
If the engine is designed for heavy loads, pouring in a low viscosity oil will simply damage it. The film will be too thin and will not provide proper wear protection and tightness between the cylinder and piston. Conversely, if an engine is designed for low viscosity oil and you pour in a lubricant with a high HTHS, it simply will not be able to penetrate the narrow gaps between the friction pairs. This will lead to rapid engine wear.
So, when choosing an oil, it’s important to pay attention to the manufacturer’s prescriptions and tolerances. For example, if your engine is prescribed a C2 approval, you can change it to C3. But if C3 is prescribed, it definitely cannot be changed to C2 due to the lower HTHS. Otherwise, the engine protection would be reduced. Likewise, if your engine is prescribed a A5/B5 approval, you may change to A3/B4. But not the other way around.
In the ADDINOL catalog, you can find high-quality, low-viscosity oils that meet the most stringent standards for engine protection. These include:
- ADDINOL Giga Light 5W-30 is a C3 approved oil that can be poured into engines rated for C2 approval.
- ADDINOL Super Light 5W-40 is a full-ash oil that protects engines against fuel wastage as effectively as possible.
- ADDINOL Economiс is a super low viscosity oil with a fuel-saving effect.
You can use the oil selection service on our web-site: specify car brand, model and equipment to make sure the oil is suitable for your car.
What are the dangers of 0W 5W in summer. High-temperature viscosity HTHS. Viscosity modifier (= base thickener).
Учитывая опыт знакомых и вопросы в личку, до сих пор не могу понять увлечение большинством в летний период, в жару >35C, in climatic conditions where there is no winter in principle (south of Russia and Europe), to fill up “zero” and “five”, having read various loch oilyl-clubs or even worse – to ask for advice on forums. With this in mind, let’s finally put an end to this question.
To begin with let’s understand the difference in composition of 0W/5W/10W/15W oils, etc. All oils are made up of a blend of base oils + an additive package, which includes a thickener (VM). The less viscous the base oils in the composition – the lower(!) the cost and worse the wear protection. Remember this thesis. But by making nulls on the basis of cheap base oils you can get more profit. Especially with hydrocracking. Yes, yes, don’t be surprised a good 0W30 is cheaper to make than a good 10W30 if you make them on the same base and tweak it to current tolerances. That’s the kind of marketing brain wrenching. But due to the small production volumes of 0W oils, they do come out more expensive at retail … and that’s why most oils like 5W20 10W30 10W40 15W40 20W50 are mineral . Making them even on a hydrocracking basis is expensive.
Based on these tables and some other data, the minimum amount of thickener: 0W20 5W20 5W30 10W30 15W40 20W50. Remember these viscosities. Viscosities are sometimes adjusted by adding high viscosity bases to the formulation (usually hydrocracking).
Oils that can be made without thickener at all: 10W20 20W20 15W30 20W40 25W40 and monograde SAE20 SAE30 SAE40 SAE50 .
The maximum amount of thickener respectively in oils of the type, the content reaches 16%: 0W30 0W40 5W40 10W40 . Imagine that up to 1/6 of the oil volume is a polymer, which does not lubricate anything at all:
Over time, it will precipitate on the pistons and stick together with the combustion products in the oil…
If you have a usual atmospheric engine, not squeezed to the limit (up to 80hp liter), most likely, if you change oil often and not bring it to oil, you can avoid trouble, because the thickener will not have time to polymerize into asphalt (together with hydrocracking, which is now in 99% of oils in the amount from 10% to 90%) and the amount of dirt in the oil will be insignificant. Pistons temperature there is usually up to 300C, rings up to 400C. Which agrees perfectly with my test. But if you have a turbo engine (and if you have also over 100hp with 1L), and if your oil in the crankcase warms up to 120-150C, the picture above will be at any oils with a lot of thickener, with any tolerances, if it is for example 0W40 with 13-16% thickener. As pistons are heated above 400C, and rings up to 500C. Unfortunately it is difficult to find information on the oil composition. Producers do not flaunt it.
Because of the high viscosity base oils with viscosity 6cSt and 8cSt (10-12cSt and higher is the price in space), and the desire to make multigrade 5W and 0W oils, oils based on PAO, esters, hydrocracking are often made based on oils with viscosity 4cSt, as the cheapest base. In our country such a base costs only 40-50r per liter. Compare that to the cost of gasoline… That means the thickener is dosed there as much as possible, because the base has to be thickened 3-4 times. Especially in W40 oils, and even in “pseudo race” oils W50 and W60… Therefore, switching to fully synthetic oils 4g and 5g, even with the space price is not a panacea…
But that’s not all. There is also such an interesting parameter as HTHS. High-temperature viscosity at 150C and high shear rate. And here everything is even more complicated and interesting.
Note that the less thickener in the composition, the more viscous the base oils, the higher the HTHS. Contrary to the opinion that the higher the TI, the higher the high temperature viscosity, this is not true even according to the SAE chart. Already at 150C you can see the difference between, say 15W30 10W30 5W30 0W30, the former may have a higher HTHS than the 0W40! Viscosity modifier at high temperatures works worse and worse. And above 150C it practically does not work any more, the oil turns into “water” that does not lubricate any more. I.e. the viscosity modifier can work effectively in the range from 40C to 150C, to draw you a beautiful 0W40, IV under 200C, as you like it, but to the work of the oil in the engine in operating mode, where temperatures are much higher than 150C it will have no relation… as a result of the polymer thickener working in time, its viscosity to 150C may not change. Above that, it can break down… some people, especially lucky ones, pile on 0W40 oil in summer (or, even worse, 0W30 A5/B5 and 0W20 A1/B1!)… the liners turn to foil, camshafts to dust, or even piston skirts get scraped… and then they cry about “engine shit, manufacturer is a jerk, materials are bad… things used to be better… there were no such marketing oils before, this is what they used to be without…
All in all, a few viscosity recommendations can be made based on this data.
If you don’t live in the far north, there is no sense to use 0W oil, even in winter. If you want “zero”, I feel like laughing, then pour 0W40 instead of 0W30, because it has higher HTHS. Pour oil in accordance with a season, taking into account minimal and maximal ambient temperatures. If you live in the south and have occasional snow in the winter, forget 0W and 5W oils. If you have a specific craving and don’t have 10W 15W oils…then you can go like this: pour 5W30 oil in the winter, pour 5W40 oil in the summer. It’s simple – HTHS is higher. There is no point in getting carried away with W20 type oils, without good reason. You should get addicted to W30 A5/B5 oils only in winter, but not in summer. You should not look for W30 A3/B4 specially, it’s easier to look for W40 leaner.
And one more thing, taking into account the strong dependence of temperature of oil in the crankcase on the environment… This table was not drawn by any idiot, as someone thinks, all that we assemble looks like this: