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      04-28-2011, 09:30 PM   #1
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Possible 6MT mechanical overrev mistake!!

Been driving MT for over 10 years now, but might have pulled a potentially serious fail out of clear oversight.

So I'll cut right to the chase here. I was traveling approximately 70 MPH (no more than 75 but can't be 100%) downhill on the freeway as I'm getting ready to exit (was in 3rd engine braking down from high revs). The ramp is goes off the right and up hill. It is nicely banked to the right - so it's one of my favorites to hold tight in.

Anyway, I entered the ramp at more or less the speed stated above and as i begin to go up the hill I downshifted into second. It was a good downshift, but I was not cognizant of my speed. I would have slowed down more before shifting if I knew it was that high. It had to have still been around 70 to 75 but i'm hoping it was less. I sort of failed to measure the speed at which the hill was slowing me down and assumed I was going slow enough before i shifted (as is typically always the case - third gear and up hill!).

Car revved all the way up to into yellow - not sure exactly where - might have been just in or not even. I was terrified and couldn't tell. It kept me from enjoying what might have been the most amazing sound and behavior I have noticed from this engine to date. the needle really slowed as it approached the red and nothing came on the dash or iDrive.

My question is - did I dodge a bullet or could the car still have overreved without the tach indicating the same? Presumably, if I mechanically overreved the car beyond 8400, the needle would have been pretty far into the red right??

Alternatively, does the rev indicated on the tach match what is actually occurring in the engine in the case of a mechanical overrev?

I hope I'm just being paranoid but I found this, which doesn't help my concern.

I'm hoping the omnicient Bimmerpost members can let me know instead of having to ask the dealer...

Thanks!
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      04-28-2011, 09:43 PM   #2
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Quote:
Originally Posted by E=mc2 View Post
Did you hear any clicking sounds? Did you check the engine/under the car for oil? The clicking sounds is almost the most common symptom of a problem, the oil under the car is more of a catasrophic failure indication. The next 100 miles is very critical. Watch out for these symptoms, but you'll never be 100% sure. Something might show up in 2000 miles too.
Did not notice clicking and really don't think it got that high on the tach. Certainly no higher than i've hit while accelerating.

I am about to go turn it on again and see if anything seems unusual. After this event occurred, I still reached upwards of 7000 on my way home (but only during acceleration). I probably should have taken it easy - but i really was in denial at that point. I kept telling myself "there's no way you got that high, it would have showed lights and warning all over." It wasn't until i got home that i started to freak out again and write my OP.
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      04-28-2011, 10:06 PM   #3
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Originally Posted by E=mc2 View Post
All the overrevs I read, and I am very paranoid myself being a 6MT driver in my 335 - so I read a lot of them, indicated sudden symptoms. Blowing a gasket is the most common (and the most expensive) one which always resulted in clicking sounds. The oil leaking is basically another one, but that I think pretty much involves destroying the pistons and the engine (i.e. if you were to money shift from 3 to 1 doing 75 mph). I think you are fine, I'm pretty sure these engines can easily take up to 8600 rpm. The problem is, if you did overrev and by chance you have any engine related issues in the near future (maybe the next 6 months), they might find out about this and use it against you. But this is highly unlikely (your engine failing suddenly). So don't worry about it. Like I said, if nothing happens in the next 100 miles, most likely it will never happen again.

I hate to say this and I don't mean to start a flame war, but this is one of the biggest reasons I got a DCT for my M3. I cannot even begin to think what would happen if by chance I made a mistake like this (not just money shift, but a small overrev like this) and screw the engine in a lease car. It's just not worth the headache.

I have been driving manuals for 10 years myself, so before anyone says I don't know what I'm talking about, please take it easy

OP, don't worry, I'm sure it's fine.
Yeah. I just went out and checked it out and I did not hear clicking or see oil. I will post a video for additional opinions. I proceeded to take it out and it still drives like a young stallion. I think i'm ok but hoping the S65 gearheads can confirm.
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      04-28-2011, 10:07 PM   #4
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That's the money shift. The rev limiter doesn't protect you when you redline it on a down shift. Impossible to tell how high it was for how long without a digital readout. (I believe the dealer can scan you for overrevs). Hopefully not an issue. I think I saw the 2nd gear redline is about 70, but I'm not positive. If you hit 9k, it probably isn't the end of the world. I'm not sure when this motor goes into valve float (chance that valves hit the pistons) - that is the death result of the money shift. This is typically a 5th to 2nd instead of 4th shift. At this point, no reason not to just drive it, not much you can do about it. Ultimately have the dealer scan it next time you bring it in.
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      04-28-2011, 10:16 PM   #5
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Hmm. I'm still pretty worried now.

I guess the key question is this: If it never entered the Red (which I am sure of), have I avoided harming my engine?
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      04-28-2011, 10:30 PM   #6
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your fine. with an 8200 rpm redline, you really have to do something stupid to money shift and do damage. This car likes to be in the yellow, you should drive it there more often
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      04-28-2011, 10:33 PM   #7
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Originally Posted by E=mc2 View Post
I don't understand what you are concerned with. If you are absolutely sure it never entered the red, you are fine. The yellow goes all the way up to and including 8300 rpm. That's okay (even DCT will rev the same). You need to exceed 8300 and go well beyond 8600 rpm to do any damage.

This is one of those things that you will never know. I am telling you right now up front. If it's going to keep bothering you, go to a dealership and have them scan the logs. But that might backfire as well, if you did do a minor overrev, its still an overrev for them.
My concern stems almost entirely from the issue of whether or not the tach is accurate as to actual engine speed. I recall a thread stating, on acceleration to redline in any gear, the tach "lags" behind the engine's actual revs. Although I did not enter red, and I am 99% sure, if there is a lag in the readings than I still could be screwed, no?
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      04-28-2011, 10:35 PM   #8
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Even if it was 75mph you were only about 4% over the maximum 2nd gear speed of 72 mph (http://www.m3post.com/forums/showthread.php?t=292787). So that would be about 8700 RPM. It is probably fine. And if you are positive it was not even in the red then you probably were only going 70 mph and are definitely totally fine.
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      04-28-2011, 10:42 PM   #9
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Originally Posted by dizzyj View Post
your fine. with an 8200 rpm redline, you really have to do something stupid to money shift and do damage. This car likes to be in the yellow, you should drive it there more often
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Originally Posted by mkoesel View Post
Even if it was 75mph you were only about 4% over the maximum 2nd gear speed of 72 mph (http://www.m3post.com/forums/showthread.php?t=292787). So that would be about 8700 RPM. It is probably fine. And if you are positive it was not even in the red then you probably were only going 70 mph and are definitely totally fine.
I'm guessing I got lucky and dodged a bullet. I appreciate posts like this.

What about the variable tach in this situation. Would it have immediately dropped the red to 6000 or 6500 RPMs? I have seen that happen when I hit the rev limiter on acceleration. Anyone else seen that before? I've had it happen about 3 or 4 times in my 5 months with the car.
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      04-28-2011, 10:51 PM   #10
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Quote:
Originally Posted by Seattle S65B40 View Post
I'm guessing I got lucky and dodged a bullet. I appreciate posts like this.
Yeah I think you are fine. BTW, this is another reason (as if we needed one, but anyway) why you should never shift a car without rev-matching. If you rev match, you are always conscious of your speed because you need to know that to know what RPM to target for the downshift.

Quote:
What about the variable tach in this situation. Would it have immediately dropped the red to 6000 or 6500 RPMs?
Not to my knowledge, no.

Quote:
I have seen that happen when I hit the rev limiter on acceleration. Anyone else seen that before? I've had it happen about 3 or 4 times in my 5 months with the car.
I've never experienced anything like that. Though I have DCT. Still that sounds really bizarre and I question why it would ever need to do that.
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      04-28-2011, 11:04 PM   #11
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Originally Posted by mkoesel View Post
Yeah I think you are fine. BTW, this is another reason (as if we needed one, but anyway) why you should never shift a car without rev-matching. If you rev match, you are always conscious of your speed because you need to know that to know what RPM to target for the downshift.



Not to my knowledge, no.



I've never experienced anything like that. Though I have DCT. Still that sounds really bizarre and I question why it would ever need to do that.
I gave it plenty of gas and came close to matching the rev, but I was a bit under throttle for sure. It might have been a good thing, because that close to redline and any more throttle might have screwed me.

As to the tach, I'm getting worried now about it varying quickly like that. Need 6MT guys to speak up to confirm, but I think that's normal. I think it only happens when you hit the rev limiter so that you can give the engine a second to compose itself before you beat it up some more. It rises back up to normal within seconds (1-4 seconds or so). I would think guys who track their car have seen this, but if not, then I better get my car in for service.
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      04-28-2011, 11:09 PM   #12
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Did you feel the car accelerate when you downshifted? If yes, you were NOT into the red zone. If engine didn't have any power after the downshift (with gas pedal depressed, of course), that's a sign you overrevved the engine. But at 75, you were barely there. Pay attention next time .
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      04-28-2011, 11:14 PM   #13
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Quote:
Originally Posted by Seattle S65B40 View Post
I gave it plenty of gas and came close to matching the rev, but I was a bit under throttle for sure.
Ok well I guess my point is that at 75mph it is impossible to match revs properly for 2nd. So, now that you are aware that 72mph is the max speed for that gear you know to never attempt to go to second above that speed.

Quote:
It might have been a good thing, because that close to redline and any more throttle might have screwed me.
Actually I don't think it matters one way or the other because if you are going too fast you are going to force the overrev regardless of how high you revv'd prior when trying to match.

I think your car is safe. I'd like to know more about this business about the sliding limiter dropping to 6k tho. That's really strange if that's how it is supposed to work for 6MT cars.
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      04-28-2011, 11:34 PM   #14
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Originally Posted by elp_jc View Post
Did you feel the car accelerate when you downshifted? If yes, you were NOT into the red zone. If engine didn't have any power after the downshift (with gas pedal depressed, of course), that's a sign you overrevved the engine. But at 75, you were barely there. Pay attention next time .
Honestly, it happened so fast, but I think i just took both feet of all pedals and just let the car slowdown for a sec and proceeded driving. In retrospect, i should have popped the clutch back in and gone back into third.
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      04-28-2011, 11:39 PM   #15
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Originally Posted by Seattle S65B40 View Post
I gave it plenty of gas and came close to matching the rev, but I was a bit under throttle for sure. It might have been a good thing, because that close to redline and any more throttle might have screwed me.

As to the tach, I'm getting worried now about it varying quickly like that. Need 6MT guys to speak up to confirm, but I think that's normal. I think it only happens when you hit the rev limiter so that you can give the engine a second to compose itself before you beat it up some more. It rises back up to normal within seconds (1-4 seconds or so). I would think guys who track their car have seen this, but if not, then I better get my car in for service.
Still need someone to address this please. I get the feeling no one else has seen it before??
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      04-28-2011, 11:54 PM   #16
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I'll comment on the tach needle being slow and I do not intend to get into DCT stuff.
In DCT when I'm on 7th for example driving 70mph and I want to go to third quickly. Instead of 4 clicks I put the pedal to the metal and down shift. That takes the car to the third around 6K. I keep my hand ready to quickly upshift cause in 2 seconds the shiftlights become red yet the needle is still in the 7K range. That happens so often and gets worse if you go 5th to 2nd for example while on 55mph. I think the needle is unreliable when it gets to high rpm downshifts. Saying that I think your car is fine. If being in yellow is bad my car would have been gone long ago.
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      04-29-2011, 12:43 AM   #17
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Quote:
Originally Posted by Seattle S65B40 View Post
Honestly, it happened so fast, but I think i just took both feet of all pedals and just let the car slowdown for a sec and proceeded driving. In retrospect, i should have popped the clutch back in and gone back into third.
At 70mph you would have still been in the power band in 3rd gear and had plenty of engine brake,no reason to try to blip and go down to second.Use the brakes to slow down the car,unnecessary stress on the drivetrain is never a good thing.Car should be fine tho,I don't think you over revved the engine.Drive on
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      04-29-2011, 12:44 AM   #18
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Still need someone to address this please. I get the feeling no one else has seen it before??
I have not seen that before..
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      04-29-2011, 12:49 AM   #19
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Quote:
Originally Posted by Seattle S65B40 View Post
I'm guessing I got lucky and dodged a bullet. I appreciate posts like this.

What about the variable tach in this situation. Would it have immediately dropped the red to 6000 or 6500 RPMs? I have seen that happen when I hit the rev limiter on acceleration. Anyone else seen that before? I've had it happen about 3 or 4 times in my 5 months with the car.
Never had it happen/seen that happen on my '08 6MT M3. I lived in yellow/red zone w/ that car (didn't use 5th or 6th gear much, loved the money 3rd gear, 4th gear was my cruising gear ).

Anyhow, I'm sure your car's alright.
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      04-29-2011, 01:02 AM   #20
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After working with many different types of cars for many years, this what i have learned. Now this is not a fact for all engines but something i have learned from old school techs.

When a car maker makes an engine and sets the red line at lets say at 6,000rpm, the engine can actually go safely to 6,500rpm with out being damaged. In other words, the car maker tests the engine to its full limit on the dyno, then they subtract 10% or so and set the red line.

The % or rpm they subtract varies on the engine design.

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      04-29-2011, 01:07 AM   #21
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Never had it happen/seen that happen on my '08 6MT M3. I lived in yellow/red zone w/ that car (didn't use 5th or 6th gear much, loved the money 3rd gear, 4th gear was my cruising gear ).

Anyhow, I'm sure your car's alright.
+1 on this.

I would just observe the car over the next few days and see if there are any noises, leaks, etc. Once the data is gathered, you can go and take appropriate action.
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      04-29-2011, 01:10 AM   #22
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sudden lowering of redline with variable tach

That's interesting. I can't believe no one so far has seen that. I may have to start a whole nother thread on that to get more peoples eyes on this question and see what I can come up with. It's bizarre and has rarely happened, but the fact that no one else has seen it is concerning. I guess I'm not too worried, as the car has driven just fine after each time it happened. But what does it mean??
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