Compression release?

[MVaden]

Since the day I bought my truck it has made a loud sound and hard shake when I turn the engine off. A service guy at the dealer where I bought it told me it was normal for the Cummins and that it was just releasing compression.



I've been noticing people spinning around and looking at the truck when I turn it off in a parking lot. It is very loud, it snorts and shakes the truck really hard, but I kept thinking it was normal.



A buddy picked up his new 600 today and wanted me to go for a ride with him to check out the new truck. The truck is the identical setup as mine except it is Atlantic Blue. It rides and runs just like mine but when he turns it off it does not snort and kick. We drove around for half the day and made several stops (local truck accessory shops) and it did not do it once.



Also when I put my truck in gear or change from Reverse to Drive or Drive to Reverse it hits hard like when a u-joint goes out. I had questioned the service guy about this also and he said it was normal because of the tourqe of the Cummins and not to worry about it. Well my friends new truck did not do this either.



Here's what I'm wondering, is there that much difference from truck to truck and are these are normal things, or should I take it in and get it checked out at another dealership.



Thanks

 

[rbattelle]

The dealer is right and wrong about this. What I would call a "violent" shutdown is normal, to an extent. See, the compression ratio on these is 17:1, and when you shut off the fuel they stop VERY suddenly. This causes a very rough shaking as the engine comes to a full stop in just a couple rotations. The effect is much more pronounced (from what I hear) in automatic trucks, due to the additional mass of the torque convertor. In fact, I've heard that the engine in automatics stops so fast that the alternator/water pump/PS/AC accessories can't stop as fast as the engine and the fan belt actually emits a loud "SQUEEK"! This is all completely normal.



Having said that, if your truck sounds REALLY BAD, like much much worse than your friend's, there might be a problem. I've never had my truck spook anyone anywhere when I shut it down.



So, what might cause an extra-violent shutdown? Hard to say. Could be a transmission that's binding somehow, causing the engine to stop even faster than normal. Could be a fan clutch that's engaged, again causing a faster stop.



I would suspect either an engine accessory problem, or a transmission/driveline problem, rather than an engine problem. I recommend either forcing the dealer to listen to another truck on the lot shutdown, or taking it to another dealer for 2nd opinion.

 

[Pawpaw]

Originally posted by rbattelle

In fact, I've heard that the engine in automatics stops so fast that the alternator/water pump/PS/AC accessories can't stop as fast as the engine and the fan belt actually emits a loud "SQUEEK"! This is all completely normal.

I didn't know automatics were worse, but mine shakes and squeeks every time. It seems like at least once a week someone asks me what's wrong with my truck!



It's done it from day one.

 

[amsoilman]

I go along with rbattelle on this one! Most all these engines will do this at some time, especially the automatics.

 

[nickleinonen]

my engine shuts down kinda roughly but i never have gotten belt chrip

 

[Jengle]

I get the shake too, and quick stop, but no squeak, but I got the standard. The autos I test drove all squeaked. But they were all about the same. None were noticably louder than any other, of the same model.

 

[BCrane]

I get the squeak as well. . Sometimes it does it, other times not... . It seems that if the truck has been running for a while it won't do it. Only the shorter runs...

 

[thames1948]

Mine always squeeks on every shut down.

 

[FlyFisha']

Yep, they all shake and some squeak. My 04 manual has no squeak but my dad's '96 12 valve shakes and occasionaly will give a good squeak of the belt.



It's normal, infact my '94 Ford idi does it as well. It's a very high compression engine -- 20:1.



Jeff

 

[LEPage]

Better check your u-joints. All 3 of mine in the rear shaft were junk at 40,000mi. I didn't have time to put new ones in myself, so I opted for the $100 deductable. I have very little doubt I could have gone to NAPA and purchase better joints W/ grease fittings for less.

 

[Vaughn MacKenzie]

Originally posted by rbattelle

The effect is much more pronounced (from what I hear) in automatic trucks, due to the additional mass of the torque convertor.

Actually the rotational mass of the Auto trucks is less because the flywheel on manual transmission trucks is a lot heavier. They don't shake as bad because the engine spins over longer after shutdown and doesn't stop with a sudden jerk. I would say after turning off the key my engine spins for about another 6 compressions. On an Auto it's about half that, resulting in the abrupt jerk. Personally I kinda like it, lets me know there's a real engine under the hood



Vaughn

 

[jaynes]

I will second this (or, what number are we on now?). Being a '91 model (does that make much difference?), mine is an auto, and let me tell you. It gives a pretty good shake, and the squeek is loud! It doesn't squeek when it's cool, but once the belt gets warmed up and expands alittle, it really chirps, i think partly because my idler pulley is getting weak after 217,000 miles. The belts do expand just a hair, don't they?



Josh

 

[rbattelle]

Originally posted by Vaughn MacKenzie

Actually the rotational mass of the Auto trucks is less because the flywheel on manual transmission trucks is a lot heavier. They don't shake as bad because the engine spins over longer after shutdown and doesn't stop with a sudden jerk. I would say after turning off the key my engine spins for about another 6 compressions. On an Auto it's about half that, resulting in the abrupt jerk. Personally I kinda like it, lets me know there's a real engine under the hood



Vaughn

Vaughn's right (as usual). I had the right idea, but wrong about the rotating mass auto vs. manual.