Hyundai 2.5 Smartstream Engine Problems – Top 5 Problems!

Hyundai 2.5 Smartstream Engine Problems – Top 5 Problems!

January 19, 2024 0 By CarGuy

Are you looking to learn more about the Hyundai Smartstream engine problems? If that’s the case, look no further because, in this article, there will be a lot to discuss on the Hyundai 2.5 Smartstream engine problems.

Doing your own research before you decide to purchase a used car should be one of your top concerns because this decision can be a good thing and also a very bad thing. A car with an unreliable engine can quickly drain your wallet and your nerves. That’s why we are here to help you out.

So, what are we going to cover? First, we shall discuss the specs and the applications of the 2.5 Smartstream engine. Then, we will cover the Hyundai 2.5 Smartstream engine problems and also the reliability of this engine. So, let’s get started!

Hyundai 2.5 Smartstream Engine Specs

The Hyundai 2.5 Smartstream engine is an engine that falls under the Smartstream family of engines. This engine family replaces some of the previous engines used by Hyundai and Kia.

What is interesting about the Smartstream family is that this engine family incorporates engines from 1.0L up to 3.6L and comes in a variety of configurations.

For this article, we are primarily interested in the 2.5L engine. This 2.5L engine is an inline-4 that implements the latest technologies. Such as turbocharging, variable valve timing, and direct injection.

But there are also versions with regular port injection. Which is a big pro since not everyone loves the GDI engine. The GDI has some issues that we will discuss later.

Now let’s list the specs of the 2.5 Smartstream engine.

  • Configuration: Inline-4
  • Displacement: 2.5L
  • Bore: 85.5 mm
  • Stroke: 101.5 mm
  • Block & Head Material: Aluminum
  • Head Design: DOHC, 4 Valves per cylinder
  • Compression Ratio: 10.5:1 naturally aspirated, 10.0:1 turbo versions
  • Aspiration: Naturally aspirated or turbocharged
  • Fuel Injection: Port or Direct Injection
  • Horsepower: 177 – 290 hp
  • Torque: 171 – 311 lb-ft (232 – 422 N-m)

Hyundai 2.5 Smartstream Applications

Now let’s take a look a the applications. We shall cover both the standard naturally aspirated one and the turbocharged version of the engine.

Smartstream G2.5 G4KM Naturally aspirated MPI engine

  • 2020 – Present Hyundai Santa Fe
  • 2019 – Present Hyundai Sonata
  • 2020 – Present Kia Sorento

Smartstream G2.5 G4KN Naturally aspirated GDI engine

  • 2019 – Present Hyundai Sonata
  • 2020 – Present Hyundai Tucson
  • 2023 – Present Hyundai Santa Fe
  • 2021 – Present Hyundai Santa Cruz
  • 2019 – Present Hyundai Grandeur/Azera
  • 2019 – Present Kia K5
  • 2021 – Present Kia K8
  • 2020 – Present Kia Sorento

Smartstream G2.5T G4KP Turbo GDI engine

  • 2021 – Present Hyundai Santa Cruz
  • 2020 – Present Hyundai Santa Fe
  • 2020 – Present Hyundai Sonata
  • 2020 – Present Kia K5
  • 2020 – Present Kia Sorento

Smartstream FR G2.5T G4KP Turbo GDI engine for RWD cars

  • 2023 – Present Genesis G70
  • 2020 – Present Genesis G80
  • 2020 – Present Genesis GV70
  • 2020 – Present Genesis GV80
  • 2020 – 2023 Kia Stinger

Hyundai 2.5 Smartstream Engine Problems

Now let’s list the common Hyundai 2.5 Smartstream engine problems.

  1. Carbon Buildup On Valves
  2. Oil Consumption
  3. Carbon Buildup On Pistons
  4. Piston Slap
  5. Failed Injectors

Now that we learned which are the common problems with the 2.5 Smartstream engine, we can move on and further elaborate on these problems.

This is crucial in order for you to further understand these issues and how serious these issues are. So, without further ado, let’s discuss them.

1. Carbon Buildup On Valves

The first problem on our list of 2.5 Smartstream engine problems is the carbon buildup on the intake valves.

This engine uses both MPI and GDI injection. The engines with MPI do not have this problem with carbon buildup.

Carbon buildup on the intake valves is only common on versions that use direct injection (GDI). These include the 2.5 naturally aspirated GDI and the 2.5 turbo GDI.

So, why is this a problem? Well, MPI uses a method of injecting fuel through the intake ports. This way of injecting fuel washes the intake valves and keeps them nice and clean.

But with GDI engines, this method is not used. Instead, you have an injector that sits on top of the cylinder.

This method of injecting fuel is more efficient but also more problematic since the valves are not washed.

Carbon deposits start to accumulate on the valves and create problems. They can even stop the valves from operating properly.

So, the only way to prevent this is to do a method known as walnut blasting every 60,000 miles or so to clean the valves of your engine.

This method can cost some money but it is the best proven method for removing the carbon from the valves.

2. Oil Consumption

Oil consumption is a very common problem with the 2.5 Smartstream engine. These engines start to consume serious amounts of oil when they are relatively low miles.

This is due to the fact that the cylinders expand under heat cycles and this allows oil to pass through the oil rings and end up in the combustion engine.

And oil consumption is not something new when it comes to Hyundai engines. The Theta engine also has this problem.

But when it comes to the Smartstream, this engine has cylinder expansion and this is what makes this problem unique to this engine.

Many owners advise that you replace the engine oil frequently on these engines and they also added bigger oil pans for the engine to run more oil in order to avoid these issues.

But overall, this engine has some kind of factory defect that can simply be described as a real deal breaker because this is another Hyundai engine with problems.

The solution to this issue is to flush the oil regularly and never leave your engine to run low on oil. Keep an eye on the oil level to avoid permanent engine damage because of oil starvation.

In the video, there is a Korean documentary on this problem where everything is explained.

3. Carbon Buildup On Pistons

Since a lot of oil passes through the piston rings, this oil ends up in the combustion chamber. It is burnt along with the gasoline and turned into carbon.

These carbon deposits start to accumulate on the crown of the piston. This isn’t a real problem since every engine does this.

But the different thing is that on this occasion, there are many of these deposits that can somewhat affect how the fuel is combusted.

Specifically on these oil-burning engines, the place around the edge of the piston is clean of deposits but the center of the piston is full of thick carbon.

On top of that these carbon deposits end up in the ring lands where the rings are seated into position. So, when this happens the rings become glued to the pistons thanks to these carbon deposits.

Overall, pretty bad situation that will definitely make you lose compression and performance from your engine.

4. Piston Slap

Piston slap is another problem that appears on the Hyundai 2.5 Smartstream engine. This piston slap is a problem that appears because of failed rings.

As we noted previously, the rings do not seal well and allow for oil to be burnt. This will allow larger tolerances between the piston and the cylinder wall.

If you have wide tolerances, there will be piston slap. This is a situation where the piston is banging against the cylinder walls.

Which is another clear sign of engine failure. This engine will not last for a really long time once it develops piston slap.

Now let’s move on to the next Hyundai 2.5 Smartstream engine problems.

5. Injector Failure

Another problem that might appear is having failed injectors on the GDI version. Some injector failures on these new engines were already reported on the Hyundai forums.

This was uncommon on previous Hyundai engines with direct injection. But on the Smartstream is becoming a more and more common thing.

These injectors fail internally and you have to replace them. What is bad is that this is not cheap to do.

Hyundai 2.5 Smartstream Reliability

The 2.5 Smartstream has poor reliability for such a new engine. These engines do not even have a lot of miles and major issues were reported on them.

However, they are somewhat avoidable if you do regular maintenance. Specifically, doing preventive maintenance and flushing the oil before time.

And also topping off the engine oil on a regular basis whenever the engine starts consuming oil.

This way you will be able to squeeze the max of this engine. Which is not much considering the problems and how early they develop.


In this article, we covered the 2.5 Smartstream by Hyundai. So, what did we learn? Well, we learned the specs and common applications in which you can find this engine.

In the second part, we discussed the common problems with the 2.5 Smartstream engine and we also gave a comment on the reliability up to date.

Overall, this engine isn’t an improvement over the notorious Theta but only the future will tell how serious these issues are.


What are the common Hyundai 2.5 Smartstream engine problems?

Common problems with this engine include carbon deposits on the direct injected versions of this engine, fuel injector failures, and oil consumption. Oil consumption can become serious and your engine could lose serious amounts of engine oil. This is the most threatening problem to this engine overall. It can lead to piston slap and the need for a new engine.

Is The 2.5 Smartstream reliable?

Well, it is difficult to tell. These engines have not been here for a really long time and their long-term reliability is unknown. But overall, it should be good for a maximum of 150,000 miles like other Hyundai engines around.

If you want to read more about Hyundai problems, you can check our articles on the 2.0 Theta engine and 2.4 Theta engine.