Excessive RPMs--bad day in the mountains

[MTSteve]

Have a new rig with an ISL9 (350 hp). On my first trip through the mountains--Spokane, WA, to Whitefish, MT, over Fourth of July Pass and Lookout Pass--I lost my concentration a bit and forgot a few basics (a hot, busy traffic day was probably not the best day for my first challenging drive). I'm concerned I might have exceeded the governed engine speed on a gentle climb and on a couple descents.

On the climb, the transmission was downshifting to 5, then quickly upshifting back to 6. I wanted to stay in 5, so when it was in 6 I reached down to go to 5. By the time I hit the button, the transmission was in 5, so I ended up downshifting to 4 and reving the engine--how high it got I'm not sure, but it took me a few seconds to see what happened and adjust.

Downhill, pure rookie mistakes I don't need to go into, just fix--I'm going out with a trusted old pro next week for hands-on instruction.

I certainly nevered exceeded 2400 RPMs, probably not 2300, on the descents.

So, the question is, what indications might I see that I damaged my engine?
And what kind of damage might these mistakes cause exactly? Any advice on how to go about assessing this? Or is that even possible at this point?

[mackwrench]

I take it still runs, if no new noise, ticking, knocking, or issue I'd say you dodged a bullet and can rock on.

Usually engine over speed can cause valve train failure, drop or bent valve and push tubes, strip/brake timing gears or pull connecting rod from piston and make big hole in block.

Engine over speed damage is generally something that pops up right away....

If you wanted to know what max rpm Engine turned, Cummins insite can read ECM and retrieve that info

[MoePo]

Highly doubt your engine was damaged. Your transmission will shift to the next gear before any damage occurs. In other words "over revv" the engine. When driving my coach with a ISC 350 down a grade using the exhaust my rpms climb to around 2400. No harm.

[Steve Ownby]

Originally Posted by MTSteve

Have a new rig with an ISL9 (350 hp). On my first trip through the mountains--Spokane, WA, to Whitefish, MT, over Fourth of July Pass and Lookout Pass--I lost my concentration a bit and forgot a few basics (a hot, busy traffic day was probably not the best day for my first challenging drive). I'm concerned I might have exceeded the governed engine speed on a gentle climb and on a couple descents.



On the climb, the transmission was downshifting to 5, then quickly upshifting back to 6. I wanted to stay in 5, so when it was in 6 I reached down to go to 5. By the time I hit the button, the transmission was in 5, so I ended up downshifting to 4 and reving the engine--how high it got I'm not sure, but it took me a few seconds to see what happened and adjust.



Downhill, pure rookie mistakes I don't need to go into, just fix--I'm going out with a trusted old pro next week for hands-on instruction.



I certainly nevered exceeded 2400 RPMs, probably not 2300, on the descents.



So, the question is, what indications might I see that I damaged my engine?

And what kind of damage might these mistakes cause exactly? Any advice on how to go about assessing this? Or is that even possible at this point?

I'm guessing that you are fine. The engine ecm protects from catastrophic over speed. On descents the ecm will up shift as necessary to protect the engine. In a closed throttle condition, the engine ecm allows higher rpm than when under power. My ISM will hold a gear until 2400 rpm when the Jake is operating.

[1bigmess]

New rig, electronic brains controlling everything? You should not have downshifted, even if you pushed the button to try to go all the way down to first gear, into a gear that would over-rev the engine as the ECM and all the other little brains and sensors should have known that was a no-no.

My dodge truck, which I know is a very different critter from yours, will not, I cannot, it won't let me, downshift into a gear that will take the engine RPMs over red line. The only way I can over-rev this engine is to already be in a lower gear, say second, and then go downhill to increase my road speed such that the engine RPMs go above red line.

It doesn't sound like you did that. It sounds like you were descending, punched the gear down button, and the transmission shifted down like you told it to, which I believe it would not have done if the lower gear would have over-revved the engine at the road speed you were moving at the time.

So, if you still feel bad, and you are anywhere needing to change the oil, get the oil changed, wash it, pat it on the back and say "I'm sorry", and enjoy the rig.

[Stiltner]

So I've got a dumb question.....somewhere in the past I was told that with modern day engines & transmissions that there is little you can do to damage them. Safety triggers are in place to prevent them from failure. 2400 RPM doesn't sound like it's to terrible of an issue. Additionally, 5 & 6th gear are overdrive gears for fuel efficiency.

In my case, I approach a down grade at 55 and once I hit the button to downshift, the transmission typically goes to 3rd or 4th gear and I coast down the grade using the exhaust brake and transmission. The transmission will not allow me to downshift if I'm not under 55.

[Harry B]

Your engine will not allow over revving it. Governors and ECM and TCM electronics will keep it all within limits. The thing you have to watch out for is excessive speed.
By not allowing it to over rev going down hill, may cause you to speed up excessively. It is than time to apply your service brake by stabbing it until you have a safe speed again and are within range of the engine and transmission control to kick in again. I doubt you did any harm to your engine or transmission.

[Piker]

Originally Posted by 1bigmess

The only way I can over-rev this engine is to already be in a lower gear, say second, and then go downhill to increase my road speed such that the engine RPMs go above red line.

Just wanted to make a note that on our old 1994 with Allison MD3060... If I stay in too low a gear on a descent, it actually WILL upshift if the engine reaches red line. Not sure if the OP's newer rig is like that or not.

I realize our old 5.9 is a little different... red line on a descent is somewhere around 3000 rpm. It is governed to not exceed 2500 rpm under power. That said, the principals of protecting the engine from over speed are probably the same, just at different rpms? I would think you're probably ok. Just my $.02.

-cheers

[mackwrench]

Just to clarify, you can in fact over speed a modern electrical controlled diesel engine.
The ECM will protect it from "on throttle" over speed, the transmission PCM will shift at specific rpm range,
But if road speed exceeds geared engine rpm it will over speed.
I recently seen a series 60 Detroit Diesel do just this. ECM recorded engine rpm at 4000 when it went to lunch...

[Skip426]

Originally Posted by Piker

Just wanted to make a note that on our old 1994 with Allison MD3060... If I stay in too low a gear on a descent, it actually WILL upshift if the engine reaches red line. Not sure if the OP's newer rig is like that or not.

I realize our old 5.9 is a little different... red line on a descent is somewhere around 3000 rpm. It is governed to not exceed 2500 rpm under power. That said, the principals of protecting the engine from over speed are probably the same, just at different rpms? I would think you're probably ok. Just my $.02.

-cheers

X2.

Different engines ,different red lines, under power and when exhaust or engine braking. SAME level of engine protection , Cummins, Cat and Allison programming , will not allow engine over revving , they WILL up shift ( my Cat at 2750 ) so I'm on the service brakes at 2500 RPM.

[Skip426]

Originally Posted by mackwrench

Just to clarify, you can in fact over speed a modern electrical controlled diesel engine.
The ECM will protect it from "on throttle" over speed, the transmission PCM will shift at specific rpm range,
But if road speed exceeds geared engine rpm it will over speed.
I recently seen a series 60 Detroit Diesel do just this. ECM recorded engine rpm at 4000 when it went to lunch...

I , assume , when you say " Road speed exceeds geared engine rpm it will over speed. " the driver in that case was rolling down hill in top gear at a very high rate of speed , with no attempt ( or unable due to loss of brakes) to slow the vehicle.
Rough calculation given my gearing and speed at 2000 RPM in sixth , would be 140 mph. I'd expect the Cat to crawl out of the engine compartment and attack my wallet at that speed , if I was able to stay on the road over 90.

[Mac99]

Previous posts have good advice, the tranny will not
allow a damaging shift to occur under throttle.
Downhill is another story, you should do everything
in your power to never go above 2600 rpm on an ISL.
From your descriptions, you are fine.

[MTSteve]

"Downhill is another story, you should do everything
in your power to never go above 2600 rpm on an ISL."

Governed speed for my engine is 2100/2200 rpm. So shouldn't I not exceed that, in all cases? (In the future I sure won't.) Or are you saying "in reality" I don't have to really worry about damage until 2600 or so?

Thanks to everyone for their responses. I really appreciate the help and the insight.

[Mac99]

Originally Posted by MTSteve

"Downhill is another story, you should do everything
in your power to never go above 2600 rpm on an ISL."

Governed speed for my engine is 2100/2200 rpm. So shouldn't I not exceed that, in all cases? (In the future I sure won't.) Or are you saying "in reality" I don't have to really worry about damage until 2600 or so?

Thanks to everyone for their responses. I really appreciate the help and the insight.

Under throttle you will not be able to exceed the governed
rpm setting of 2200. Going downhill you will see higher
rpms and you have to manage that issue, I believe the
max rpm on the ISC/ISL is 2600, and you must keep
below that by brake application when the descent is
steeper than the exhaust brake can manage for you.