Why does my auto gearbox take time before revving higher?

Our tech guru has the answers to your car questions
by Ferman Lao | Jul 24, 2013

Hi, sir Ferman! I'm a fan of your column. You explain complicated things in a more understandable way.

I'm writing to you because I have questions on the Mazda 3 and the Mazda 6. The Mazda 3's automatic gearbox annoys me. It stays at 2,000rpm for more than 10 seconds before revving higher. It's very frustrating since I tend to depress the accelerator even more just to get up to speed. Using the manual mode doesn't help, either.

My mom, with whom I share the car, also noticed this despite knowing less about cars. I can't drive efficiently, which is bad for me since I'm just a college student. I think it's not normal because we didn't experience this back in 2010. Can you tell what the problem might be?

My other question is on the Mazda 6, which I've been reading about in the magazine and on the website. The Skyactiv tech is all so amazing, especially the 14:1 compression ratio without the possibility of pre-ignition. But I'm struggling to understand why they get such few horses from that.

For instance, I know that race cars have very high compression ratios and get a large amount of power. Considering that it's a 2.5-liter with direct injection and 14:1 compression ratio, I think 185hp at the crank is a bit measly compared to the boxer in the 86/BRZ that has a lower displacement and lower compression ratio. Is there something I'm missing here?

Thanks a lot!

James Perez

 

Hi, James. Thanks for the kind words. That's what I'm here for.

Continue reading below ↓

Most automatics usually behave in a similar fashion because of how they transfer power from the engine to the transmission. Unlike a manual transmission that uses a clutch to transfer the power, a typical automatic transmission uses a torque converter. It's essentially a fluid coupling that needs time to engage fully to transfer power from the engine to the transmission. This bit of time needed is what most of us feel whenever we step on the accelerator and feel like there is nothing happening.

I don't quite understand what's happening when you say that it stays at 2,000rpm for 10 seconds before the engine rpm goes up, or how hard you are stepping on the accelerator when you encounter this situation. However, even when the torque converter isn't fully engaged yet, power transfer does occur and the vehicle does move forward. If the situation you're encountering doesn't allow the car to move forward or increase vehicle speed, then it is possible that you are either low on automatic-transmission fluid or having a blockage somewhere in the system, preventing correct operation--and thus, power transfer is not as efficient as it should be.

All these assume that the engine is operating properly and there's nothing wrong. It is also possible that the engine is not putting out the correct amount of power in that particular rpm and throttle opening range where you are encountering the problem. The effect feels like the transmission is not responding correctly.

I don't have a lot of information on the Skyactiv engine on the Mazda 6, but you'll have to keep in mind that how much power engines make will all be subject to what the design objective was when they were first commissioned. In the case of the Skyactiv engine in the Mazda 6, engineers were after a lightweight large-displacement four-cylinder engine that had low emissions meant to go into a passenger car and not a high-performance sports car. That would mean the tuning and design of the engine would've revolved around that premise. The camshafts, the intake and exhaust manifolds, and other aspects of the engine would've been optimized for low-rpm torque versus high-rpm horsepower, and the tuning would have also been spec'd around that premise.

Continue reading below ↓

If I look at the power and torque graphs of both vehicles, I wouldn't belittle the Skyactiv engine. It make 45Nm more torque at a much lower rpm than the FA20, and only 15hp less at 1,000+rpm less. Who's to say that if it had been tuned differently with different cams and other related components, it wouldn't significantly do more? On a side note, a 2.5-liter engine as found on the previous-generation US-market non-turbo Subaru Legacy makes about 175 or so horsepower.

 

Hi. I have noticed that each time I turn off the engine of my Subaru Forester, water would drip from below the hood. This would happen every day and even when I first used it. I have consulted the Subaru people and even the mechanics when I had my 10,000km change-oil/checkup. I was told that the dripping comes from the air-conditioning and that it's absolutely normal. Is this really the case or should I consult someone else regarding this? I have owned another vehicle before and I have not had this kind of drip. I hope you can answer my question. Thanks!

Raychelle Tan


Hi, Raychelle. It is normal. Different cars will have different designs as far as the drain for the cooling coil is concerned, and yours just happens to be like that. Most modern cars will also exhibit the same characteristics as your Subaru Forester in that aspect.

The water you see should be colorless and odorless--that's just condensation forming on the cooling coil's surface, and slowly being collected and drained out of the car. It's very much the same process you see happening on your household room air-conditioning unit. There's no need to be alarmed as this dripping can usually be taken as a sign that your A/C system is very efficient in cooling your Forester's interior.

Continue reading below ↓

If by chance you observe water or liquid that is not colorless or odorless forming under your car, that's the time you should be concerned. Seek the attention of a qualified service center or mechanic when that happens.

I hope this puts your mind at ease, and thanks for writing.

 

Best regards,

Ferman Lao
Technical Editor

Do car problems keep you awake at night? Send questions to topgear@summitmedia.com.ph.

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