Jeep Wrangler engine explodes after 50,000 rpm

Image of article titled Best Of 2021: Jeep Wrangler's engine explodes after owner hauls the vehicle and spins it at 50,000 rpm

Screenshot: Toby Tuten (YouTube)

Has 2021 been a great year? Not exactly! But we did have a few posts that got good traffic. Take a trip down memory lane with us, looking back to 2021, a year that will look a lot better around that time in 2022.

To 2021 Jeep wranglerThe 3.6L 3.6L V6 apparently tried to rev up to eight times its red line after the owner left the vehicle’s transfer case low while towing flat , The reader reports. The resulting stresses tore the engine apart, giving a scene that appears to have been caused by a grenade.

The car’s website spoke with the foreman at a North Florida store to learn more about the crumbling white 2021 Jeep Wrangler Unlimited Rubicon that was towed flat behind an RV. From the player:

Tuten said The reader that when the technicians started to diagnose the vehicle, they noticed that it had been left in “4-Low”, which is what you would want when driving through rough terrain at low speed, or if it is stuck in a rut , but certainly not when being towed at highway speeds. For reference, the JL Wrangler manual explicitly states not to exceed 25 miles per hour with 4-Low engaged.

Video of the mechanical disaster that was once a dual overhead camshaft, naturally aspirated 3.6-liter V6, has been shown on TikTok and YouTube. Prepare your souls for destruction:

As you can see in the clip, the crankshaft is broken, the block and crankcase are in pieces, there is no flywheel or clutch kit to find, the catalytic converter is destroyed, the bell is Burned out, the manual transmission’s input shaft was sheared off, and – though it’s hard to tell – I’m pretty sure the upper control arm on the passenger side was bent by the flying debris. It’s just a huge mess.

But that’s what happens when you have a lot of alternate masses moving a lot faster than they were ever designed. The Pentastar upgrade was really only meant to run consistently around 6,600 rpm. With the Rubicon coming with a 4.10: 1 axle ratio and a 4: 1 transfer case low range ratio, and with the first gear at 5.13: 1, the vehicle’s crawl ratio is of 84.13: 1. This means that the engine spins 84.13 times faster than the rear wheels.

If we assume the RV was towing this Jeep at 60 mph (we don’t really know how fast it was going; the shop foreman The Drive spoke to guessed 55), we can use the fact that the Jeep stock 285 / 70R17 BF Goodrich KO2s are rated at 645 rpm to learn that at that speed, the vehicle’s tires were spinning at 645 rpm. Here are my calculations for that, in case you’re curious:

Image of article titled Best Of 2021: Jeep Wrangler's engine explodes after owner hauls the vehicle and spins it at 50,000 rpm

Photo: David tracy

The 84.13: 1 crawl ratio tells us that in first gear and in low range, the engine spins 84.13 times faster than the wheels. This means that with the RV towing the Jeep at 60 mph, the wheels of the Jeep were trying to force its engine to spin at 54,264 rpm. That’s 8.22 times the red line of the engine at 6,600 rpm. No wonder it exploded (if I had to guess, it happened way before 50,000 RPM).

Image of article titled Best Of 2021: Jeep Wrangler's engine explodes after owner hauls the vehicle and spins it at 50,000 rpm

Screenshot: Jeep

Towing a vehicle is a delicate process that requires careful reading of the owner’s manual. There are many factors that come into play, including making sure some components rotate and others not, and ensuring that what does rotate is properly lubricated.

Read it Jeep Wrangler JL Owner’s Manual, and you will see that it strongly denounces the towing of a four-wheel drive vehicle on a two-wheeled dolly, and that it sets out specific rules for flat towing (see above).

You will see that vehicles equipped with a manual transmission should be towed with the transfer case in neutral and the transmission in take. why is this the case? I reached out to two transmission engineers to find out, and the good news is, they both came to the same conclusion. Engineer 1:

The only thing that comes to mind is that parasitic drag inside the housing can still allow rotational transfer to the output shaft and thus continue to rotate the transmission. By turning it on, you avoid this.

I have no idea if this is really the case.

Engineer 2 talks about an automatic transmission that Jeep says should be put into “Park” during flat towing. But the same reasoning applies to the manual transmission:

My understanding is that with the transfer case in neutral, the wheels will still drive the driveshafts, but there will be no torque transfer to the transmission. Parking the transmission (I’m assuming you mean the Auto?) Would stop the internal components of the transmission from spinning. In my experience on other transmissions, often the neutral is not always a complete disconnect, as there is often a drag from the internals or an oil churn, which could transfer some torque into the transmission, and on a car that would mean it would run (albeit at low torque) with no engine lubrication off. Putting him in the park would prevent that from happening.

So the short answer is, putting the transfer case in neutral technically disconnects the wheels from the transmission, but the reality is that bearing drag and oil churning can still create torque on the drive shaft. transmission output. You don’t want the transmission output shaft to spin on its own for too long, because the input shaft has to turn to lubricate the gearbox properly.

By towing the Jeep in gear, you hook the input and output shafts together and couple them both to the engine – the inertia of these connected parts should easily be able to withstand the torque sent to the transmission output shaft. due to the mechanical drag transfer case. Ergo, by being in gear, you can avoid a scenario where only your output shaft rotates without the lubrication created by a rotating input shaft.

Tremec solves the lubrication problem on its Blog, where the transmission company actually recommends disconnecting the driveshaft leading to the manual transmission (note: this probably refers to two-wheel drive vehicles or those without a neutral option in the transfer case):

If you are going to flat tow a vehicle in which you have installed an aftermarket transmission such as the TREMEC TR-4050 5 speed Where Magnum 6 speed, you will need to disconnect or remove the driveshaft. Even with the transmission in neutral, if the propeller shaft is not disconnected or removed, the main transmission shaft will rotate with the rear wheels. However, the cluster will not rotate and lubrication will not be applied to critical transmission parts.

This will result in damaged needle bearings under the speed gears and / or the pocket bearing between the main shaft and the input shaft. This is why it is crucial to remove the propeller shaft if you need to tow your TREMEC equipped vehicle flat. If you cannot remove the driveshaft before flat towing, do not tow the vehicle flat.

Image of article titled Best Of 2021: Jeep Wrangler's engine explodes after owner hauls the vehicle and spins it at 50,000 rpm

Picture: Jeep

Although you might have first thought upon seeing the engine explode, “How the hell did an owner keep the Jeep at times in four-low and in a hurry? “ it should be clear by now that making such a mistake is really not that difficult to do. You are Assumed tow the vehicle in gear. The only mistake the owner made, as far as I know, was to keep the vehicle in the low position. But just look at the shift knob above and notice how the position of the four-speed shift lever is just below neutral. It is very possible that the driver simply pulled the lever too far and did not realize that the vehicle was not in neutral, but rather in low range.

If this is what happened, it was an extremely costly, yet seemingly easy mistake to make, and I feel for the owner.

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