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Exhaust Smoke Blowout At High Engine Rpm

LS 0181158

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Lately, I've noticed my '98 LS 400 blows out a substantial amount of blue/brown smoke on the infrequent occasions when the engine is revved to redline. Understand that I don't drive like a maniac, and even brisk acceleration for my style (due to the torque of the engine) means gear changes near only about 3000 rpm. And in 5th gear highway driving, 3000 rpm = 96 mph, so the engine is RARELY run faster than that. Most of my shifts in daily driving occur around 2000 rpm.

Also, about 10K miles ago I asked my mechanic to complete a fuel injector cleaning service (along with timing belt/water pump change and a bunch of other maintenance work). The LS has about 178K on the odometer now and runs fantastic. Fuel filter replaced this past Spring, plus K&N air filter (which does need to be cleaned soon). I've always run 93 octane fuel and performed oil changes every 3K or less.

As I indicated, under unusual circumstances (when passing on two-lane roads, for instance), it becomes necessary or desirable to floor the accelerator. You all know what happens next--as the gas is pressed, the transmission immediately downshifts out of fifth (the car starts to accelerate smoothly) and then--after a pause, and with the pedal floored--grabs second. Instant rocket-ship acceleration, and in mere seconds, the car has traded 55 mph for 80 plus. In the past three months, I've called for this maybe four or five times. Today, it was an indecisive 3-Series BMW I was attempting to let merge; after I had slowed to nearly a walking pace and he still didn't come over, I began to gently accelerate past him. Naturally, the driver chose to accept my earlier invitation at precisely that instant, necessitating the 5th-2nd (or possibly 4th to 1st) downshift to scoot out of his way!

A quick glance in the rearview mirror revealed literally a CLOUD of dirty-looking smoke hanging in the air It was clear this got kicked out the tailpipes through the 4000-6000 rpm sweep (lasting only a second or two), and my car stopped generating the smoke at the next upshift.

Now, I remember reading on a Cadillac forum that Northstar engines last longer and tend to stay cleaner when run hard. The poster (I seem to recall he was a mechanic) had taken apart/rebuilt numerous such engines, and commented that those that had been "babied" were usually the most gummed up. The same person recommended a regular procedure for engines that usually waffled around town at low rpm: drive at a steady 55 mph with the transmission in 3rd. Accelerate to raise the rpm near redline, and then let off the gas, allowing engine braking to slow the car. Repeat several times.

Perhaps the 1UZ-FE V-8 is a completely different animal--I wouldn't know--but might the same tendencies apply? Despite my fuel injection cleaning last fall, do I not "blow the carbon out of the engine" enough? Like I said, really hard acceleration near redline is the only time I notice smoke. Today there was a lot of it, which prompted the post.

Any suggestions for how to keep my engine clean and generally healthier would be very welcome!

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You've already got it figured out I think. When you drive gently the exhaust system gets deposits in it, as well as the converter. When you suddenly use full throttle the extra exhaust gases tend to scour the system and you see the accumulations get blown out as brown/black smoke. At full throttle most systems, and I'm sure Lexus is one of them, go to a rich condition to protect the engine, which bypasses the normal emissions standards. That produces the black/grey smoke you see. It's all quite normal. The rich condition also overheats the converters, which cleans them further.

The engine isn't dirty, just the exhaust.

As for fuel injection cleaners, they are mostly a waste of time and money. Just use full throttle every now and then, and the extra duty cycle that the injector sees, and the increased fuel flow, will clean things up just fine. Every engine needs to "take a deep breath" every now and then. Doesn't hurt a thing.

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I know this is an issue with VW.

At VW they recommend owners to use the whole range of Rpm from 2000 to 6000.

Maybe it's true with Lexus also they say luxury engines are delicate engines tht requires a lot of babying but I don't know I think they don't know much about Luxury cars.

But Lexus engines DO handle high rpms really well so maybe it's a good idea to step on the gas a little more.

I don't drive hard but I step on the gas a lot more in my Lexus the I did in all my other cars that I previously owned and the Lexus is still in the best condition when compared to my other cars.

At 141k still on the oem Tranny and engine and it's driving like new and still got A LOT OF POWER

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The Lexus V-8 - and all Toyota engines for that matter - are among the LEAST delicate engines ever built. The V-8 has six bolts at each main bearing! Balanced to a fraction of a gram. A valve train that is silent and capable of least 1 or 2 grand past normal redline.

You want to hear about delicate? Try a Chevy LT-1 in the fourth gen Camaros. They are pieces of junk. I had one. The Ford 5.0 HO with forged factory pistons? That one is as tough as an anvil, but still no match for Lexus.

You won't hurt that engine clearing it out every now and then.....

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Thanks all!

Great comments, and just what I wanted to hear, too. IMHO I am more concerned about the effect of full-throttle acceleration on the transmission than the engine--although Lexus (and for that matter Toyota) transmissions I KNOW to be extremely robust. But I've changed my transmission fluid three times in just over 60K miles of ownership, and now, at 178K, the thing still shifts smoothly and crisply. In my experience, Honda products are fantastic vehicles too, but the automatic transmissions are not quite as durable. I drove a kind of ragged-looking 1990 LS 400 with 210K for a bit--no problems at all--and heard of other LS 400's continuing to 700K on the OEM engine and transmission--but we don't need to start on that subject, do we?

When I DO accelerate hard, I try to keep a steady foot on the gas, and I'm always conscious of what the transmission is doing so my right foot can modulate the stress at shift points to the greatest extent possible. With that said, an occasional standing-start run to redline through a few gears in "PWR" mode should be good for the engine, exhaust and cats. Of course, extra-legal speeds are reached in no time flat under those circumstances!

SRK, I did not know that under full throttle the engine goes to "a rich condition to protect the engine." Good information, and makes sense to explain the smoke to some degree.

Dannymcenrow, 141K is NOTHING on these cars! With good care, I fully expect my car (and any other LS) to last to at least 300K, or more. Just look on Autotrader--many, many LS 400's (the majority of older ones by this point) have more than 200K, and a good number look new yet have 230K, 260K or 280K. There's one on there now with 342K! And the miles don't even seem to affect asking prices that much. Show me an American car (or even a BMW or Mercedes model) achieving that kind of longevity on such a regular basis. I think it's true luxury car engines are reputed to be SOPHISTICATED, but not necessarily "delicate"--especially in the case of Lexus engines (as SRK pointed out), and in older BMW [the 1985-1993 M30 inline-6, for instance] and Mercedes [1980's 3.0-liter inline-6 and 5.6-liter V-8] cars. These motors, among others, seem as bulletproof as anything Detroit may have built back in the day.

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