What gets damaged when the engine is over-revved?

You keep saying "reasonable RPM." WTF does that mean to you? The only QUANTIFIABLE "reasonable RPM" I can think of is defined as "below the rated redline of the engine." Yes I know that redlines are somewhat arbitrary- but guess what else- they're USUALLY rather conservative, meaning you can probably go somewhat beyond them without causing damage.

You keep implying that this happens frequently. I don't think it does. And I've owned some *very* high-mileage and heavily worn engines in my day, but I never hesitated to put the pedal down when it came time to merge onto the freeway. Guess what- I've never had an engine failure in a bit over 1 million miles logged. Never. No spun bearings, no rod knocks, no blown head gaskets. I finally retired one engine when it got to be "fill the oil and check the gas," but it would still run right up to its usual WOT shift point if I asked it to. Since its still sitting in my garage 6 years later, I'll bet you I could bolt it back in the car and it would *still* do that. Of course it was a Chrysler 383, so the cards are stacked heavily in my favor....

Well you just explained in full the limits of your thought process. But here's the deal-> The owner of the car asked the guy to shift. It would be folly to attempt to explain "reasonable" to someone who thinks an appropriate response to that request is for him to accelerate to much higher RPM. It also is not possible to explain reasonable to someone who thinks that increasing the stress on engine components doesn't increase the chance of failure. You can't explain reasonable to people who buy lottery tickets because they think it's a good investment. Some people just don't get what is possible or probable.

As I said some people know what is reasonable for a particular engine. Others have no clue. It is my belief that in the hands of the owner his engine would last a good long while - maybe another 100k or until the body rusted out. In the hands of that other driver it would probably not last 1000 miles. Does that "quantify" anything for you? Probably not.

That is all really beside the point, everybody agrees damage is not impossible when revving to 5000 rpm. How likely it is will depend on the particular engine, but that also is not really the point. The point I dispute is the contention that if it fails it would have failed anyway. That simply is not true. That was the question that was originally asked and the answer that "whatever happens would happen anyway" is just not accurate. If you believe that running that engine up to 5000k (as opposed to never driving over 3000 rpm) doesn't increase the likelihood of premature failure then there is little hope of discussing what is "resonable"

No it doesn't. That's because most people who have cars at 150K don't wind it up to 5000 rpm on every shift. They simply have the brains not to. If you think driving like that doesn't increase the probability that something will go wrong (that would not otherwise happen) then you are not as smart as the average driver.

I know a guy 40 years ago who put a brick on the throttle of a '49 chevy with 200K to see if he could blow the engine up at WOT. It went thru a whole tank of gas without blowing up. So from that we can conclude that would be a reasonable thing for you to do to your car, Right?

-jim

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Reasonable= Within acceptable limits.

I agree that the car owner has every right to tell the mechanic what to do and not to do with his car. If the mechanic doesn't listen, the owner has every right to complain.

I disagree that the mechanic drove unreasonably just because the owner says so. If you drive outside of the parameters set by the manufacturer, THEN you are driving unreasonably.

It's also possible at 3000 rpm, or even 500rpm.

...and every time the owner starts the car it could fail. Failure can happen any time. The only way the mechanic can be responsible for the failure is by treating the car unreasonably. That means doing something it was not designed to do, NOT something that the owner doesn't like.

...and a mechanic, trying to troubleshoot an issue, might just drive in a manner that would help identify any issues. It doesn't automatically make him responsible for anything that happens.

Let's see... Show me where GM says that it's within specifications to run an engine at WOT for a full tank of gas, with no load.

You can string meaningless words together it doesn't really say anything. What's an "acceptable limit" for a 10 year old car with

150k. You are not going get Ford to make any claims at all about how high you can safely rev an engine like that. As far as they are concerned, it has already exceeded its useful life expectancy.

As far as I know Ford does not warrant any of it's engines to run to within new car specs for 150,000 miles. The parameters you are clinging to are a fiction.

That statement is intended to avoid the real question. The OP wants to know - Is damage more likely if you shift at the manufacturers recommended shift points or if you wind it up to 5000k? I think he understands perfectly well that no one can say for absolute sure how his engine got to be as it is now.

Your preoccupation with assigning blame is telling. And it wasn't a mechanic it was one of the service writers that drove the car and it wouldn't surprise me if he knows less about engines than the car's owner.

You must have a guilty conscience. There was no mechanic, and no one but you has said anything about assigning blame. If you think the OP was asking can he collect a new engine from this guy then you are a few cards short of a full deck.

The general question is at 150K can winding the engine to 5k in second gear cause damage that would otherwise not occur if you always drove it below 3k. And the answer is yes it can. That is a simple yes or no question. It is more likely for damage to occur at 5000 rpm. And that is true whether the car is new or old. But the probability of damage increases as it gets older. But, No he can't prove there was damage. At this point that would be like trying to sue if you didn't win the lottery. Just because you can't prove cause and affect doesn't mean you have to be ignorant of the probabilities.

GM or Ford do not claim an engine at 150K performs to new car specifications. Where did you get that idea? They make no claims of any specifications at all.

-jim

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jim wrote:

I'll ignore the insults and try to explain in rational engineering terms why I have been saying what I have.

1) The manufacturer sets quantified, reasonable operating bounds for their engine. They set those bounds so that the engine should be able to operate ANYWHERE WITHIN THEM for its entire service life. They're sufficiently conservative so that an engine with a whole lot of wear, but no impending failure (there's a difference!) can operate safely anywhere in that range. 2) engine stresses increase non-linearly with RPM. The difference in stress between ANY TWO POINTS that lie WITHIN THE NORMAL FACTORY RPM RANGE for that engine is pretty negligible compared to the difference in stress that appear when you go significantly beyond the normal regime. When it comes to, for example, failing a connecting rod bolt in an engine with a 5500 RPM redline, the difference between 3000 RPM and 5000 RPM is tiny compared to the difference between 5000 RPM and 7000 RPM. This, by the way, is exactly why the "guy you knew of" who put a brick on the pedal of an old Chevy couldn't blow it up. Very low-performance engines like a Chevy stovebolt six don't have sufficient air movement ability ("breathing" in engine parlance) to free-rev far beyond their normal loaded operating rpm. Now if you tried that with my 300,000 mile 383, it definitely *could* free-rev to at least the point where stock valve springs would start letting the valves float (~6500 RPM or thereabout in its case) and probably past 7k. It would very much be in danger of snapping a rod bolt, even if it were brand new. But the danger of snapping a rod bolt at 5500 RPM is no GREATER with 300,000 miles on it than it was when new. I could go into a whole digression on WHY this is true for a number of components. In the case of rod bolts, they don't "age" because so long as you stay in the normal operating regime, the amount that they stretch is below the point where metal fatigue starts accumulating. If you exceed that point, they may not fail but the "clock is ticking" and sustained operation there will eventually cause failure. Aluminum behaves differently- it really doesn't have a fatigue threshold, so any flexing at all will ultimately lead to failure, but the amount of flexing speeds the progress toward ultimate failure. That's why airplanes, unlike cars, have a finite lifespan after which they CANNOT be operated safely, no matter how well-maintained. That's also why aluminum connecting rods, despite all their weight advantages, are not practical for street cars. 3) So the only remaining question is, "Is it possible for there to be a fault in the engine that won't fail if you "baby" it, but will fail if you ask for it to perform to its design specifications?" Obviously, there CAN be such oddities. However, my contention is that because of (2) above, if it can fail somewhere in the "normal" regime, you have INSUFFICIENT safety margin to assume that it can even continue to survive WITH babying. You're in the realm of "it might last 5 more minutes, or it might last another 10,000 miles." That's just not a satisfactory way to operate, period!

How do they "know" that? "Because I've never gotten it over 3200 RPM" isn't a valid source of that kind of "knowledge" about what is "reasonable." The factory specification that says "5000 RPM" for the life of the engine *IS* a quantifiable specification.

And you may be right. I don't think that this happens in more than .001% of engines on the road, but its theoretically possible. I just don't think its a practical concern.

I'm sorry, it just doesn't. It is at best a qualitative guess.

Yes true but, that's like saying the difference between a stick of dynamite and a 100 lb bomb is tiny compared to the difference between a 100 lb bomb and a nuclear device. Despite your best efforts to obscure, the difference between

3000 and 5000 is is quite big. Big enough that a huge number of bad things can happen that otherwise wouldn't.

But, this is avoiding the question.

He didn't ask about snapping a rod bolt. I agree it is unlikely that it would cause a rod to break out-right. but it might cause a rod to start knocking which will even with conservative driving over time only get progressively worse. And when it gets to the point 1000s of miles down the road where is really hammering then it will throw the rod. Your attitude is the owner has no business trying to avoid grief like that.

Remaining question? Is that supposed to fool someone into believing you have addressed any question that was asked up to this point.

Well at least you now are responding to the original question even if it back to your moralizing. What you call oddities are things that normally happen to engines as they advance in miles and age. And there could be several of these little oddities as you choose to call them.

What you are calling an oddity is more common than you think for engines at of that stage. The fact is that most people never tempt fate. They drive conservatively and thus they never find out what bad things are waiting to happen. Besides most cars have automatics so it is not as easy to achieve that kind of abuse.

If you go out and buy a hundred 10 year old pickups with 150K and manual trannies and start driving them like that, most of them will never make it to

200k. But if you drive in the way the OP does probably about 99 of them will make it. But you believe that people who have old cars like that have no right to find out for themselves what will happen.

Now you leap over that cliff called fantasy. The entire basis for this leap of fantasy is your moral belief that you are doing someone a big favor by driving at high rpms. It's a self serving argument. If you wreck the engine it would happen anyway. If you don't then the engine is good. If the engine is damaged the owner gets no opportunity to drive it without abuse themselves and find out so of course you can never be proven wrong.

The guy who posted the question now has a thumping in his engine when he starts it cold. So now he has an engine with an unknown life expectancy. Before that started I would say he had a good chance of making it another 100k driving the way he drives. Prior to the guy abusing the engine he didn't have that problem. Does that mean there is cause and affect? I would say there is a very good chance that it does. Originally you claimed that there is no probability that the problem originated with the abusive driving and apparently you now realize that claim was clearly preposterous. So now you claim there is a very slight chance it might have caused damage that would otherwise never happen, but that is still completely unrealistic.

-jim

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Wow... reading this thread in it's silly pointless entirety... Thats 11 minutes of my life I'll never get back. Hope this helps, Ben