Can I Put 10W40 Instead of 5W30? What Will Happen?

You can reduce the chances of a ceased engine by 32%, only if you chose the correct engine oil and change it after regular intervals. Out of many engine oil types available in the market, 10W40 and 5W30 are the most common ones.

Car users often pose this question on car forums that can I put 10w40 instead of 5w30 and vice versa. In this article, we will conclude this discussion once and for all.

Can I Put 10W40 Instead of 5W30?

No, you cannot put 10w40 instead of 5w30 under normal conditions. The highly viscous nature of 10w40 will not allow the engine parts to move freely. It offers higher friction and instead of reducing the wear and tear of moving parts, it enhances it.

For each engine, there is one manufacturer’s suggested configuration of engine oil. If the manufacturer recommends using 5w30, then it would be foolish to use any other oil.

Configuration of engine oil should match the design parameters of the engine. Some engines might pose problems like overheating, excessive wear and tear, and poor performance if thicker engine oil is used.

Before making this big change, you must consult a professional mechanic. Or at least read this article till the end, I will guide you that under what circumstances you can use 10w40 instead of 5w30.

Also read: Does Engine Oil Brand Matter? Can You Buy a Random Brand?

What’s the Difference Between 10W40 and 5W30?

The only difference between 10w40 and 5w30 is their viscosity. The former engine oil is thicker and clings on to the engine parts more. In comparison, 5w30 is slightly thinner and does not cling to the components.

If you go deeper into the names of these engine oils, then you would know that the first number in their code represents the cold viscosity and the second number represents their hot viscosity.

However, the main difference is only between their viscosity.

What Bad Will Happen if You Put 10W40 Instead of 5W30?

Following bad things can happen if you put 10w40 instead of 5w30:

  1. The Engine Won’t Start

If you use 10w40 instead of 5w30 in a car that is not used to thick engine oil, then chances are that it won’t start at all.

The process of starting in an internal combustion engine is such that the current produced in the ignition coil is passed on to the spark plugs, which gives an initial push to the pistons. Or, in the case of diesel engines, the piston is compressed up to the point of self-ignition.

Now, if you use heavier engine oil, it will make it extremely hard for pistons to move initially. Thus, the delay in starting the vehicle.

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  1. Poor Engine Performance in Winters

If you use 10w40 in an engine for which 5w30 is recommended, then you will get poor engine performance in winter. In winter, you already need a thin oil. Which offers low friction and does not freeze in cold temperatures.

Thin oil will heat quickly and reach the optimum working temperature. With thicker oil, the lead time of engine warm-up is increased. Hence, you will feel a lag in performance.

  1. Wear and Tear of Core Engine Parts

Core components of the engine are used to a certain limit of friction. If high friction is offered between the surface of mating components, then chances of wear and tear are increased.

High friction would also mean shorter life of the engine. An engine is nothing but a combination of components like rings, pistons, and cylinders. If they wear out quickly, so will the engine.

  1. Lower Fuel Efficiency

If you use 10w40 instead of 5w30, then you will experience a lower fuel efficiency. The high viscosity of the oil will mean that more work will be lost in overcoming the friction offered by the oil.

When more power is consumed to keep the pistons moving, then a low amount of power is available at the output shaft. Low power output per unit fuel consumption means low fuel mileage. Hence, using thicker oil will go heavier on your pocket as well.

  1. Variable Engine Parameters

Critical engine parameters like spark timing, valve timing, and timing chain adjustment will be disturbed if you use 10w40 instead of 5w30.

For an engine in which 5w30 is recommended engine oil, its parameter are set as such to match the speed of pistons moving in limited friction. If the amount of friction is increased, which is the case when 10w40 is used, a delay could occur in the timing of critical parameters.

A microsecond delay in ignition or spark timing could affect the performance of the entire engine.

  1. Engine Overheating

There is a high chance that your engine will overheat if you use 10w40 instead of 5w30.

The reason why your engine might overheat is simply due to the increased amount of friction offered by mating parts to each other. When components of the engine have to rotate in a dense environment, then more power will be lost.

As a result of this tussle, the local temperature of the engine might increase as well.

Also read: 4 Bad Things that Will Happen if You Don’t Change Motor Oil

Are There Any Situations When You Can Put 10W40 Instead of 5W30?

Using 10w40 instead of 5w30 is not always a bad decision. At times, mechanics suggest you to use a thicker engine. But that is only under specific kinds of circumstances. Let us see that what are those:

  1. Car is Too Old

If your car is way too old, by this I mean at least 15-20 years old, then you can use 10w40 instead of 5w30. But strictly during the summers only. Old engines tend to heat up very quickly. It is due to the deposits on their insider surface.

Thick oil has excellent performance at high temperatures. It will maintain its film strength, and it will also keep the engine oil pressure under check.

  1. Harsh Weather is not an Issue

If you live in a somewhat moderate temperature zone where you don’t have to face harsh temperatures, then you can use 10w40 instead of 5w30. That’s because the temperature is not a variable factor, 90% of the bad things caused by thick oil are eliminated.

But you will get most of the benefits of using thick oil. Hence, this tradeoff will be beneficial for your car.

  1. Car has a Powerful Engine

If the car has a very powerful engine, then you can try your luck with 10w40 instead of 5w30. In heavy vehicles, 10w40 is already the recommended engine oil.

With a powerful engine, you can take a chance. Since you would not have to worry about engine performance and fuel mileage. But you could reap the benefits of using a thick engine oil nonetheless.