PeachParts Mercedes-Benz Forum - 300TD Hot Idle Shaking

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Quote:

Originally Posted by surfblau (Post 251624)

300TD - om617 Hot Idle Shaking - apparently solved

Symptoms:
Shakes (sways in the engine compartment, harmonically, side to side, wide osscilation) at hot idle in park or in neutral at 600 rpm.
Completely smooth in any gear at 900 rpm.
Runs smooth at cold idle at any rpm.
Always starts easily.
Never smokes.
Always idles smoothly (rpm wise), never hiccups, stalls, misses, etc.

In short, everything was perfect except the sometimes violent shaking that at times seemed to be lifting the wheels off the ground.

So I changed both engine shocks, but not the shock mounts or external rubber pieces.

And the shaking is gone, though there is still some vibration, but it seems fairly normal.

Both old shocks had only resistance to finger pressure, and had a grinding sound on compression or extension.

My guess is that at cold idle, the shocks still provided some resistance, but after 20 minutes of driving, the heat thrown off by the engine reduced their shock absorbing ability and the engine ran with it. Wide ossications were the result. ( it could still be a compression problem, or the IP could be crudded up, maybe someday when I have a garage I will get around to tinkering with it more.)

In summary, ENGINE SHOCKS MATTER.

I hope this helps someone like me in the future....

I've got the same symptoms. My indy tells me changing engine shocks won't help. However, your reasoning makes sense and I'm going to give it a try. Question: Why did you only do the shocks and not the mounts?

Quote:

Originally Posted by rcounts (Post 1883580)

What if you only have a mild case of the "hot idle shakes" sometimes?

Sometimes after a run on the highway, the first time or two that I stop, it will shake a bit, but after a couple of stops it pretty much quits doing it.

Now what the heck could cause it to come and go like that?

That is what mine was doing. Except it would shake heavily after coming off the freeway and more on hot days. I turned my rack damper bolt out about 1 turn and it helped a great deal. The shakes are very mild and not unbearable at all now. The engine does not shake as much at startup any more either. Just a little stutter or two then its smooth. I turned in 1/2 turn today and it lopes a bit less and still no major shakes. Maybe new shocks will take care of what little is left.

Quote:

Originally Posted by biopete (Post 1888940)

Good to know that my problem isn't unique and that here is a simple solution. Do you have (or can you take) a picture of the rack damper bolt you speak of? Sorry for such a newb question, but I haven't done much with (or learned much about) most of the IP adjustments yet...

300SD shakes when hot. Tried a rack dampner bolt from a low mileage car that does not shake. No improvement. New injectior nozzles. No improvement. I have reason to believe it has excellent compression because it has hardly any blow by and can cold start at 50F in about 5 cranks with no glow plugs and the car does not smoke at all at any time and has excellent power. It does not have any engine shocks as I haven't been able to afford them after the engine swap because their 70$ a side.

I was curious a month back and decided to unbolt the engine shocks from the low mileage 300D (pristine idle). No difference AT ALL. Engine idles fine even at full temp. It just shuts down harder. So I don't think its engine shocks. I'm getting to the end of the road in terms of options and am either going to buy those shocks and pray they fix the problem or swap in another injection pumpe

Quote:

Originally Posted by rcounts (Post 1889052)

No pic but if you look at ip from drivers side quarter panel, it is a bolt on the right back side of the IP -- the side facing the rear of the car -- about in the lower middle . It is has a 14 mm lock nut and the bolt takes a 12mm. Get a couple longhandled ones and put em on and loosen the locknut then you can loosen the bolt a half turn and tighten the lock nut.

I'm going to check my timing chain for stretch too. I think I have a little of that. It idles much better now though.

I believe the hot idle shake is related to fuel lubricity. When diesel gets hot, the lubricity goes down so that would explain why it only happens when hot. But why would less lubricating fuel cause the engine to shake? I suppose another factor is fuel energy.

In my case I've noticed that when running WVO, the shakes go completely away. B100 , hardly any shakes, B20 mild only after long interstate drive. ULSD -- shakes pretty good after car gets hot. So try some b100 and see if your hot shakes go away or some fuel lubricity additive and see if that helps.

My 1982 300SD has the vibration problem and no matter cold or hot but only in idle.
It is extremely noticeable specially at the air cleaner housing that shakes a lot side to side. I had couple times the air cleaner mounts, those three rubber support, replaced due the vibration transmitted from engine to air cleaner housing.
Temporarily I am using a piece of rubber squeezed between valve cover and air filter housing to minimize that vibration but I want to see that issue solved.
I read completely your thread and found it very helpful and let me say that your persistence was fantastic.