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57K views 65 replies 28 participants last post by  AlBundy 
#1 ·
When I owned my '95 ETC, the dealer told me to hit it hard once a week. I was reluctant, but did so once every two weeks. They told me it was very important for the Northstar engine. Not only does it clear out carbon - but it does something else..

Does anyone know what this 'something else' is? I trusted my dealer so I did it and had no problem doing it. But, I can understand why one may believe that the dealer just wants you to beat on your car to break it..

Any thoughts?
 
#5 ·
Chuck C said:
besides, dealers have a tendency to talk of the top of their heads :rolleyes:
Well that's the nice way to put it ;)

Personally I believe it's a load of bull. I cannot fathom how "hitting it hard" could be of any benefit. Now "back in the day", when say your cad was carburated, and was only used for idling around town that has more of a basis in reality, but considering the tight nature of the PCM controlling all aspects of the engine I find it almost absurd that the engine would *need* any kind of driver influence to remedy any aspect of it's operation. As long as any EFI engine reaches operating temperature during operation then that's really all that it needs. If you need to run it *longer* in order to reach operating temp then that I could understand, but running it *harder* isn't exactly beneficial.

I'd love to know the reasoning behind the dealers statment.....I've been proven wrong more than once (a day), but I suspicion that the dealer is essentially full of it.
Jay
 
#6 ·
Sure, idling the car around all day and pampering it is a sure way to keep your suspension and paint like new, but your engine hates idling. It'll do it forever, but after a while, the carbon deposits will build up on the pistons and eventually cause problems.

Benefits I can see from winding the car every once in a while:

1) Blow out all the carbon deposits.
2) Really heat up the converter and clean it out.
3) Clear the mufflers out of any interior rust/scale.

You'll notice, I'm sure, that if you only kick it every once and again, you'll get some smoke out the tailpipes. This is normal with every car and is indicative of the carbon and the rust blowing out. If you do this more often (like many times each day), you won't see this smoke anymore.

The transmission is strong (4T80-E) and can handle the power. If it couldn't, Caddy would have put it behind the Northstar. It's the strongest TFWD transmission GM Hydramatic makes. WOT upshifts won't hurt the tranny at all (unless something else is wrong, like you're low on fluid or something).
 
#7 ·
The higher velocity of the airflow during full-throttle runs can help clear deposits that have accumulated in the combustion chambers, and exhaust system. That, combined with the sudden expansion of several items along the way due to the excess heat brought on by the full-throttle run helps loosen deposits too.
So bottom line, the heat loosens the deposits, and the increased airflow helps blow it out.
Hopefully this explains it a little better.
 

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#8 ·
I'll have to stick by my assertion from before, I'm just not seeing any carbon buildup, nor any other deposits accumulating on any EFI engines to the degree seen on older carburated engines. As long as the engine is operated for a long enough time for the engine to reach operating temp and actually driven at anything approaching a normal RPM range then you shouldn't have any problems with any foreign buildup, either in the combustion chamber or in the catalytic convertor (exhaust).

If there is actually a buildup of either carbon or other particulate in the engine, or exhaust then I'd suspect that it's not actually a problem with how it was driven, but more likely a problem with maintenence, ie. oil change intervals, leaking injectors, etc.

Of course, *if* the engine is literally only run for a few minutes at a time, or continually short tripped, then you will encounter problems, mainly due to the buildup of condensation internally which will destroy the oil in short order. But again, that's more of a temperature, or maintenence issue than it is a rpm issue, and no ammount of full throttle blasts will cure that.

I would have to wonder though, that if you're seeing smoke exiting the exhaust during full throttle blasts, that perhaps what you're seeing is actually excess fuel, or more likely burned oil, than carbon and rust deposits. Carbon and rust deposits really aren't smoke, nor to they resemble smoke upon exit.

End result, as long as the engine is kept in top shape, and driven normally, there shouldn't be any buildup of either carbon or rust to a degree that would hinder engine performance/mileage.
Jay
 
#9 · (Edited)
It's true that newer MPFI engines will get "less" dirty inside, but the fact is, a byproduct of combustion is carbon and the engine WILL get dirty inside. In fact, a de-carboning procedure is a VERY common procedure for a dealership to perform on a Northstar. In fact, there's even a TSB out about carbon deposits doing so much as to unseat the rings during "normal driving":

http://www.nhtsa.gov/TSBScans/sb631313.pdf

You are correct -- much of the smoke at WOT is excess fuel, since the engine runs rich at WOT to protect the pistons and engine from detonation. But this will appear as a brown "smoke". Oil burning is usually a bluish smoke, pretty distinguishable from excess fuel in the exhaust. And when I say "smoke", I don't mean a plume...I mean a light dusting. Pretty much every car I've seen on the road will "dust" a little bit at WOT.

In summary, the amount of deposits in your engine is certainly related to the state of tune your engine is in. Having said that, it's never a bad idea to go ahead a wind out your engine every now and again. The Northstar engine has a very aggressive hatch pattern on the cylinder walls to retain oil for good lubrication during high-RPM operation. This is there as a design feature and has the unfortunate downside of increased oil consumption and combustion chamber depositing. The upside is the rings and cylinder walls are lubricated VERY well and engine wear is brought to an absolute minumum. The Northstar isn't your average small block Chevy. ;)
 
#10 ·
As an aside, someone could convince me that WOT blasts can help dry out the exhaust. Normal exhaust temperatures are in the 600-800 degree range. Way back at the muffler, this may or may not be enough to keep away the condensation. At WOT, exhaust temperatures can sky-rocket -- to upwards of 1500 degrees. This will certainly burn away/blast away any stray molecule of H2O in the exhaust system somewhere. :)
 

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#11 ·
I will have to semi- agree on both points. There are tons of old people that never push their cadillacs, and they run just fine. Also, there are people that drive their cadillacs really hard, and still run fine. I suppose pushing it once in a while cant really hurt it, i dont really see the need to do it a lot. I can see the benefit of that extra pressure to blow all the crap out of the exaust. Personally, i dont think that doing this will make your car run longer and make it more reliable, although i do think it helps more than it hurts.
 

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#12 ·
This is a little off topic, But, I've got this engine in my shop today, the guy didn't want to ruin YES I said RUIN it with unleaded gas so he pulled it in the garage and parked it in 1988! NOW, He wants to drive it. Needless to say He did more damage to the engine by leaving it idle than he EVER would have driving it! The engine is totally shot,seals,rings everything. He left the gas in it for 14 years! ( You shoulda smelled THAT! ) OK, Back on topic....I like to run my engine kinda hard because I like the feel of the thing working hard. On the newer engines with all the computer controls you don't need to "BLOW THEM OUT" Bear in mind that no matter how good an engine is....Pushing it to its limit is ALWAYS a risk. It's a machine and when you use it hard it can and eventually will break! Your dealer knows that and is in fact talking out of his head as you say. The problem is...His head is firmly stuck in his ass! That's my opinion and is not intended to be construed as the opinion of Cadillac Forums.
 
#13 ·
in a way its a warranty litigation in the making
 
#15 ·
kcnewell said:
On the newer engines with all the computer controls you don't need to "BLOW THEM OUT" Bear in mind that no matter how good an engine is....Pushing it to its limit is ALWAYS a risk.
This is true. The "limit" is not necessarily the "redline" of the engine, though. The engine can and will run at redline all day long. You'd be surprised at the testing and validation procedures that the Northstar engine went through. Here's one, for example, to validate the head gaskets' strength and durability:

A cooler chills a batch of engine coolant to very cold temperatures (I forgot the exact temperature, well below zero) and this coolant is pumped into the engine. The physical engine gets so cold, frost forms on the outside of the block. The engine is then started and immediately brought to WOT and run at 6000 rpm ("redline") until the coolant is near boiling (about 250 degrees). It's then immediately shut off and that coolant is cycled out and a new batch of subzero coolant is pumped in and the engine is shocked with this vast change in temperature. This is one cycle, and THREE HUNDRED CYCLES were performed consecutively and the engine was then disassembled for analysis. No head gasket failures. No mechanical failures. The thing performed exactly as designed.

When I heard of the many rigorous tests the Northstar went through to validate its design, I was utterly amazed. The worst thing you can do to a high-speed high-performance engine like the Northstar is to granny it around, never opening it up. Back in the days of pushrod V8s with 5000 rpm redlines, constant high speed was riskier because of the design and construction of components (cast iron cranks for instance). The Northstar is designed and built as a world-class engine, with an array of forged and cast alloys in use where appropriate. It is built to run and run hard! :)
 
#17 ·
I drive it pretty easy usually around town. Afterall, your mileage DOES go into the crapper when you hot-foot it around all the time. :) But on almost every freeway entrance (if there's not a slow Honda or Acura in front of me), I'll let that Northstar run, baby! I grew up on iron-block pushrod engines, so I was never used to the DOHC nature, but the sound of four camshafts singing in harmony is just unmatched! :thumbsup: Did you know that a full 250 lb*ft of torque is available at JUST 1000 rpm??!! That's big-time! The Northstar is incredibly flexible for a DOHC design. You can lope around at just above idle if you want, but it'll open up and run if you let it!

Remember, when you floor it, you're not "pushing it hard", you're really letting it run at its potential. Marine and aircraft engines run at WOT all the time. Northstars make great marine and light aircraft engines.
 
#18 ·
I have to agree with pushing the northstar. If the results of those cycles are true, then what could a little redlining possibly do to it, if it can survive all that. They are really designed to last, if you take care of them.

I was realizing the importance of WOT-ing and engine, or at least really pushing. My fleetwood never gets pushed, it only gets driven once a week, and about 1 a month on the highway. I pulled it out of the garage, and revved it a couple of time. Nice little puffs of smoke. Next time i have it out i am going to really slam it down.
 
#55 ·
Unfortunately,
Many (if not all) the tests that engineers run on test engines are NOT directly applicable to production engines run on the street.
As for engines run at WOT, Many aircraft engines are run at a NEAR full-throttle for the following reasons:
1. Better fuel efficiency
2. Less wear on the engine
3. More effective use of the engine's power
Aircraft engines that are run this way are are usually in the more expensive aircraft because in order to do it, you must have a variable-pitch prop.
Marine engines are NOT run at WOT. They ARE generally run at a relatively high throttle angle due to the constant load produced by the water. True, once you get the craft on plane, it is easier to maintain speed but overall there is a large load placed on the engine constantly. Oh, and the different materials used in the engines (brass, bronze, etc.) are used because they are non-sparking, and less likely to corrode, not because they are more durable.
I have to bring this one out of the archives just to add my $.02 with regards to aircraft engines.
I'll keep it very simple. A safe takeoff requires that the aircraft achieve as much altitude and airspeed in the shortest amount of time possible. Basically you want to attain enough altitude and airspeed that if you experience a loss of power you would be able to turn back and glide to the airfield that you just departed. With that concept in mind it's easy to understand why aircraft engines are run at 100% power on each and every take-off. This is the safest way to operate and therefore it is also the manufacturers recommendation.

If you look at a typical Cessna 172 used for flight training at any relatively busy trainig facility you could expect to see a airplane that endures upwards of 30 practice takeoffs and landings on any given day. A typical climbout in a 172 would be about 4-6 minutes before the throttle is cut to a 65-80% power, cruise setting. Using those figures you'd be looking at a plane that runs 3 full hours per day at 100% power....when was the last time you did that in your Caddy??

In actuality, it's an apples to oranges comparison because aircraft engines are subject to MANDATORY maintainence on a routine basis as well as scheduled overhauls (rebuilds) each 2000 hours or so. This sort of maintainence is a good idea when your wheels are frequently 5000 ft off the ground and you spend 3hrs a day at max power.
 
#21 ·
It seems that some ricers have to be at WOT to stay at highway speeds :-D .

In response, i would have to agree that most aircraft engines run at high RPMs, but i dont think they run at WOT. IMO, i dont think there are any engines that run at WOT constantly. My relatives own a marina, and most of the engines that are in there are simply small block chevys, chryslers, and fords with marine conversions (such as wet manifolds, brass water pump, and other things i cant think of). Sure, some can endure more WOT than others, but there is no engine (that i know of) that is specifically designed to be at WOT all the time. End of story.
 
#22 ·
While most engines are not designed for full-throttle use, the Northstar IS designed for this. Read below, from a statement by a friend of mine, a GM Powertrain engineer who worked on the Northstar project back in the late 1980s and early 1990s:

=====
The 300-hour test I referenced is run at full throttle, maximum power, maximum RPM. On a Northstar we don't usually bother with the LD8; we run everything at 6000 RPM, 300 HP continuous, for 300 hours. That is like driving 150 MPH for 300 hours, or about 45,000 miles actually. If you can drive the equivalent of twice around the world at 150 mph, you are not the average customer. Besides, that test is just used to rapidly accumulate high load cycles on things like pistons, bearings, cranks, and block bulkheads.

There are many other dyno schedules we use to validate the engine for strength, longevity and gasket endurance. The gasket endurance test is particularly interesting because the engine is in a dyno cell and it is hooked to a large industrial chiller on one cooling system and a short-circuited radiator/hot water tank on the other. The schedule is run at WOT and about 4400 RPM (peak torque). The engine cooling system is short-circuited and the coolant gets to about 260 F. The engine goes to idle and is shut down. The cooling system is automatically switched and the engine is flooded with coolant from the chiller at -20 F. Frost literally forms on the block as the temperature drops. When the core of the block gets to -20 F the engine is started and immediately goes to WOT at 4400. It climbs back to 260 F from -20 F in about 6 minutes. Now for the killer: that is one cycle. A full test is 1200 cycles. Routinely run 1600 cycles to establish statistical significance of the data. If you know a customer that can mistreat an engine worse than that I would like to know how they are doing it.
=====

That coolant cycle test is the one I mentioned. I got my facts wrong, though. I said they do it 300 times, they really do it 1200-1600 times. My bad. :p

The Northstar is a high-speed, high-performance engine. It LIKES to live in the upper ranges of the tachometer. This ain't no small block Chevy! :thumbsup:
 
#23 ·
Those really are tremendous results.
 
#25 ·
Unfortunately,
Many (if not all) the tests that engineers run on test engines are NOT directly applicable to production engines run on the street.
As for engines run at WOT, Many aircraft engines are run at a NEAR full-throttle for the following reasons:
1. Better fuel efficiency
2. Less wear on the engine
3. More effective use of the engine's power
Aircraft engines that are run this way are are usually in the more expensive aircraft because in order to do it, you must have a variable-pitch prop.
Marine engines are NOT run at WOT. They ARE generally run at a relatively high throttle angle due to the constant load produced by the water. True, once you get the craft on plane, it is easier to maintain speed but overall there is a large load placed on the engine constantly. Oh, and the different materials used in the engines (brass, bronze, etc.) are used because they are non-sparking, and less likely to corrode, not because they are more durable.
 
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