Cooling off the turbos?

I recently found myself the happy owner of a Mazdaspeed 3. I’ve had a car with cojones before (a 1969 Olds Cutlass with the Rocket 350 V8), but I’ve never had a car with turbo before. While I was perusing the quick start guide, I found a warning that, if I’d been driving at highway speeds or going up a long hill, I should wait 30 seconds before turning off the engine to allow the turbos to cool down, lest I hurt the turbos.

So, my question is: (1) Is this a thing? Like I said, I’ve never had the turbo before. I do love how it makes the car go “zoom-zoom”, though, so I want to make sure it keeps doing that for many miles to come. (2) Assuming it is a thing, what are the “rules”? By which I mean: Let’s say I drive home from work on the highway. I then have three minutes drive on surface roads with speed limits ranging from 35-50 mph. Do I still need to sit around in the driveway for 30 seconds before I turn it off?

Thanks all. :slight_smile:

On aircraft, it is wise to take care of your turbos. $$$$$

Usually, very low power movement on the ground takes care of the cooling.

Car turbos are somewhat more robust & you cas also pullover if you kill one. In aircraft, not so much. An engine will usually work with the turbo inoperative but if it also esplodies, it becomes more of a problem.

Do it.

Try this: run the car really hard at night, say up the mountain to Big Bear Lake while trying to keep pace with a fast air-cooled 911, then open the hood to see the turbocharger glowing orange. When I did this, my turbocharger got so hot it was putting out light in the visible spectrum. The turbo, not the exhaust manifold. I was shocked when I saw it.

Normal driving is like any other car. Heed the warning if you do drive it hard. 30 seconds is not enough time, however. Do a cool down drive.

Use synthetic oil for the higher temperature rating.

In my turbo Volkswagen, the turbo is cooled by the oil. When the engine is turned off, the oil pump is not running, so the turbo isn’t being cooled. I don’t know if your Mazda uses a similar arrangement. I’ve never really worried about, because I don’t tend to do high speed driving immediately before stopping. The few times this has happened, exiting a highway into a rest area, for example, haven’t been enough to cook it yet.

  1. yes, if your car’s turbocharger is not water cooled. the turbine section gets very hot when you’re dipping into boost, and if you run it hard and don’t let it cool before shut down, the residual heat can “cook” the oil in the bearings.

  2. I would still give it at least 15 sec. at idle; oil isn’t a particularly effective coolant so even puttering around on surface streets is keeping the turbo hot.

that said, I’ve never done this on my SRT-4 but Chrysler has pretty religiously used water-jacketed turbos since the '80s so I don’t have to worry about it.

You really don’t need to do it if you drove on city streets for the last part of your drive…if it makes you feel better, you can do it, but I’d only do it if I knew the car really got a workout.

A lot of guys that modify their cars install “turbo timers” – these allow you to turn the key off and exit the car as usual, but the car continues to run for a preset amount of time, allowing the turbo to be cooled properly. I used to have one on a pretty heavily modified AWD turbocharged Talon that I drove. You get a lot of people saying “hey, you left your car on!” with one.

Now I drive an AWD turbocharged WRX, and I don’t worry too much about it because the car is stock. If I was driving in the mountains and working the car hard and pulled off for gas, I’d probably let it idle for awhile before shutting down. But on my daily commute? I don’t really think about it.

Welcome to the Mazdaspeed 3 club, that torque really pushes you back in your seat and puts a smile on your face. Just keep a firm grip on the wheel!

IIRC the Mazdaspeed 3 turbo is cooled by engine oil, so what I do is drive a few miles gently before turning the car off. Luckily my road is a couple miles long and I don’t like to annoy my neighbors by flying down the road so the problem pretty much solves itself.

Yeah, I’ve had a few hair-raising moments with the torque steer, like when I stomped the pedal a bit too hard making a left turn around a median in first and just about wound up doing an unintentional U-Turn. :smiley:

So huh, this is a thing. Does it even count if you’re not hitting the boost? Most of my highway driving just involves getting it into sixth, setting the cruise and making sure I don’t fall off the road, with RPMs somewhere between 2500 and 3000, depending on speed. Usually the boost gauge doesn’t even register, though I guess sometimes it blips up into the -6 PSI to 0 PSI area. (And what does that mean, by the way? Are the turbos sucking air out of my engine?)

I have a Mazdaspeed 3 too, love it to death! There are a lot of easy aftermarket mods for it, let me know if you’re interested and I can tell you what all I did.

As you have surmised, if you’re not really on it, the turbo isn’t working that hard, hence isn’t getting that hot. To need more than 30 seconds to cool down, you’d have to be doing something like track driving HARD. Normal freeway driving isn’t really going to heat it up to need more than just a few minutes of surface street driving. I think that back in the 80’s/90’s, letting a turbo cool down was much more important. No one has said it yet, but waiting for the engine to warm up first before really getting on the gas is also advised, for similar reasons, just in reverse. I think this is just as (or more) important than the cool-down rule.

If you keep your foot out of it, you can also get great mileage out of it, since you’re not dipping into the turbo. I just drove from Austin to Dallas yesterday, with A/C on, and I got 31 MPG, a personal best. If I remember correctly, the highway EPA MPG is only 25, so go figure. The only significant engine mod I’ve done was a corksport cold air intake.

Your boost gauge is simply a measure of the air pressure inside the intake, generally at or near the manifold. When the turbo is not boosting, the engine is sucking air in faster than the turbo is moving it, so your boost gauge reads in the negative.

Ahh, got it. And yes, jmwatts, the fuel economy has been a pleasant surprise. While cruising on the highway, the “instant” MPG per the display on the dash is usually in the 30-34 range. My trip from Columbus to Cedar Point to Cincinnati came out with an average of about 31, I believe (I didn’t take the highway, but the “back roads” were mostly with speed limits of 55). The EPA mileage is 18/25, IIRC.

Do tell about the mods. Not sure if I’ll do anything to it, but that doesn’t mean it’s not interesting.

Most modern turbos used on cars have both oil and coolant plumbed into the housing. The oil keeps the bearings happy and the coolant keeps the oil from being cooked when you shut it down. If you have been doing some “spirited” driving with significant boost, you might give it a minute to cool before shutting it off. If it’s just normal city driving, don’t worry about it.

I did Corksport’s short ram intake:
This was a pretty easy install, mainly just unhooking the existing plumbing and hooking this up instead. You will want a 10mm deep socket (trust me). It’s a modest gain in power, probably slightly better MPG since the car breathes easier. You can really hear the turbo sucking in air when you’re on it hard, but in relaxed driving there is no sound difference that I could tell.

The only other item I got was shifter bushing set
which gives shifting a more precise feel, and helps when shifting into 3rd gear quickly. This was an issue on the first generation of MS3’s, not sure if that carried over to the current generation.