Can you still drive with a cat that rattles??

[a6jus]

Need a set of cats, as has been posted before, two Mercedes garages have told me they need to be replaced asap!!!

I was told that they could break up and get sucked into the engine causing massive damage & expense!!!

Malcolm (TV) stated this was rubbish could not happen, but why are they both saying the same thing???

Would like to replace CATS but at over £1300 to replace + anything else they find wrong eg(O2 sensors at £110 each and I have 4) I need to save up, but need the car to run around in.

Any help/advice???

 

[Parrot of Doom]

They're both telling you the same thing because they both want you to spend money with them.

Theres no chance of anything getting back into the engine from the exhaust, its just silly.

The quote you have seems very high.

 

[psmart]

Can't say about the petrol models, but the diesel pre-cats have a wire mesh at the engine junction, so even if they did break up and some back current were setup, they would stop at the mesh.

If your short on cash, find a local welder, get him to split the cats open, remove the core, and re-weld. Someone did something similar as I recall, it is technically illegal, because your supposed to be keeping the high and mighty green party happy, so if you go this route, dont tell anyone! BUT save up the cash before your MOT, as they will spot it!

Another solution, have you no handy (mechanic) mates, because replacing the exhaust is straight forward, which would save you quite a few quid.

 

[television]

It is not possible to stop them from the rattling, I know and tried , I would have a word with a firm who make up special exhaust , its only going to be the one, they cut them off with an angle grinder and weld a new one in.

Malcolm

Forgot, no harm in driving around with the noise

 

[Tony]

There was a thread a few months ago about the possible damage to the engine and someone posted an explanation of how it can happen. You wouldn't think debris could be sucked into the engine but it is possible - it's not only the dealers that say this. It depends on where the broken cat is. My car has 2 cats on each bank - the first is near the engine and the second is at the back. As it happens the ones that break up on my car are the rear ones, so there is no danger to the engine - I've driven for months with rattling cats and have had no problem. It may be the same on yours.

 

[Tony]

There was a post by davidsl500:

"Modern Exhaust systems are suprisingly complex for a bit of pipe. To get maximum benefit the exhaust length/bore is critical and designers use "pulse tuning" to drag out the gasses. If you have a constriction in the pipe then the exhaust gasses will flow over the blockage and as a result will be travelling at a higher velocity which would cause a partial vacuum to be formed upwind of the blockage - the debris can thus be dragged back up the exhaust into the engine."

 

[panason1c]

A long shot but worth a try..............Drill a few holes (1/8th 'ish) and screw a few long self tapping stainless steel screws into the 'cat box.....that should stop the blighters rattling for a while untill you can afford to renew them.


ps.......It will also lessen the chance of them breaking up if they cant rattle.......

 

[television]

A long shot but worth a try..............Drill a few holes (1/8th 'ish) and screw a few long self tapping stainless steel screws into the 'cat box.....that should stop the blighters rattling for a while untill you can afford to renew them.


ps.......It will also lessen the chance of them breaking up if they cant rattle.......

Sadly I tried with mine and it does not work, it just crumbles away like a stale sponge.

Malcolm

 

[panason1c]

Sadly I tried with mine and it does not work, it just crumbles away like a stale sponge.

Malcolm

...Back to the drawing board then................:-D ..New idea!!.......How about drilling a hole big enough to insert the nozzle of a cartridge gun and squeeze in a small amount of 'firegum' or 'sealer/cement that is used on stoves/woodburners....would this 'glue' the ceramic core to the case?

 

[big x]

...Back to the drawing board then................:-D ..New idea!!.......How about drilling a hole big enough to insert the nozzle of a cartridge gun and squeeze in a small amount of 'firegum' or 'sealer/cement that is used on stoves/woodburners....would this 'glue' the ceramic core to the case?

If you do that you stand a good chance of wearing the bores on a V6 due to pulse resonance drawing small bits back.It's true cats have a wire mesh on the front end to stop larger chunks but it's quite course and will let sand size pieces through.
You could gut the cat which will work fine until MOT time.Details plus pics here:
http://www.mbclub.co.uk/forums/showthread.php?p=262368#post262368
I've been running a gutted cat for 2 years on my C180.

adam

 

[big x]

They're both telling you the same thing because they both want you to spend money with them.

Theres no chance of anything getting back into the engine from the exhaust, its just silly.

No, your wrong.

adam

 

[television]

Some things here do not add up, if the exhaust is blocked the engine will stop, try shoving an apple up some ones tait pipe, and it will stop.

If a CAT breaks up, why should it block the system, after all its only a honey comb of holes, sinse its all holes where is it going to block, and with what.

The CAT material is just like dried powder, you can rub it all away with your fingers, what harm can that do,
sorry don't believe it.

malcolm

 

[psmart]

and then theres diesel...

No, your wrong.

adam

I doubt very much that an exhaust box is resonance tuned for Diesels equipped with Turbo Chargers! Back-pressure is extreme between turbine and exhaust ports, and pulse formation from turbine to outlet depends on the amount of gasses flying over the turbine compared to those flying through the wastegate (or those directed onto the vanes in a variable nozzle arrangement)!

But, where talking about petrol!

 

[big x]

Some things here do not add up, if the exhaust is blocked the engine will stop, try shoving an apple up some ones tait pipe, and it will stop.

If a CAT breaks up, why should it block the system, after all its only a honey comb of holes, sinse its all holes where is it going to block, and with what.

The CAT material is just like dried powder, you can rub it all away with your fingers, what harm can that do,
sorry don't believe it.

malcolm

It can restrict flow if a large chunck is pushed side on,the holes run front to back only.When I was removing my honeycombe that is exactly what had happened.Remember if the fibreglass padding which holds it in position is blown out the substrate has room to move.If you break the honeycombe up it makes a nice grinding paste in the engine.This is all very well known,I know for a fact MB US have replaced V6's because of this.IL 4's tend just to blow the stuff out through the silencer.

adam

 

[AdrianDW]

MOT without CATS?

As a diversion to this one, anyone put their beastie through an MOT, but sans cats?
I ask as I have a V6 W210; these have two cat elements per pipe (4 in all - presumably to pass US emissions regs which would fail a mouse fart!), and both of the rear elements have gone in the last few months, so I've had them whipped out and a length of suitable stainless pipe welded in place.
Now, my friendly Merc technician suggests that the car could well pass its MOT with just the front two in place (suggested a dose of injector cleaner, a couple of tanks of super and a good "Italian Tune" would help too, plus a nice warm engine when she goes in). He suggested the front two cats get, and stay warmer, and (unsurprisingly considering their location) are less prone to the rapid cooling issues that often afflict the lower elements; consequently they rarely go, and he assures me has seen cars similarly treated fly through the MOT.
Anyone with any similar experiences, or technical thoughts on the likelihood of this scenario?

 

[psmart]

I doubt very much that an exhaust box is resonance tuned for Diesels equipped with Turbo Chargers! Back-pressure is extreme between turbine and exhaust ports, and pulse formation from turbine to outlet depends on the amount of gasses flying over the turbine compared to those flying through the wastegate (or those directed onto the vanes in a variable nozzle arrangement)!

But, where talking about petrol!

(Sorry Adrian, just sidestepping for a sec)...
Another possibility to consider, is your car a Kompressor? If so, then I doubt the tuned exhaust creating vacuum, and suck back would occur. The basic idea of a tuned exhaust is to get the pulses to line up as they exit the cylinder chamber, such that the high pressure at the head of the pulse pushes forward, creating a vacuum which helps to pull the next pulse out of the engine. All tuned circuits are at a given rev range though!

BUT, a compressor will be pushing the exhaust pulse out, due to it high pressure into the inlet port and valve overlap, disrupting any pulse trains, and thus vacuum pockets! ie. no vacuum should = no cat suck back.

 

[big x]

As a diversion to this one, anyone put their beastie through an MOT, but sans cats?
I ask as I have a V6 W210; these have two cat elements per pipe (4 in all - presumably to pass US emissions regs which would fail a mouse fart!), and both of the rear elements have gone in the last few months, so I've had them whipped out and a length of suitable stainless pipe welded in place.
Now, my friendly Merc technician suggests that the car could well pass its MOT with just the front two in place (suggested a dose of injector cleaner, a couple of tanks of super and a good "Italian Tune" would help too, plus a nice warm engine when she goes in). He suggested the front two cats get, and stay warmer, and (unsurprisingly considering their location) are less prone to the rapid cooling issues that often afflict the lower elements; consequently they rarely go, and he assures me has seen cars similarly treated fly through the MOT.
Anyone with any similar experiences, or technical thoughts on the likelihood of this scenario?

I hear bigger engined stuff can get through without the pre-cats,not sure about the other way round.Surely worth trying though.
My own 1997 C180 running Shell Optimax and no cat only just failed. On smaller engines these days it really is a very marginal benefit having a cat.
I made the mistake of buying a cheap aftermarket cat and on the 4 cylinder cars they sound so tinny and loud I only fit it for the MOT.
My smooth running 1994 E320 is still on the original cat (they are date stamped).It's difficult to understand why the later V6's seem to knock them out quicker.They are the same make Eberspaecher.It might be the exhaust pulses are smoother on the IL 6 than the V6 and IL 4.
BTW BMW E38 V12's can also suffer cat material getting into the bores although it's very rare.My Hitler cat avatar agrees.

adam

adam

 

[television]

It's difficult to understand why the later V6's seem to knock them out quicker.They are the same make Eberspaecher.It might be the exhaust pulses are smoother on the IL 6 than the V6 and IL 4.



adam

On the 129's it is only the V6 that has cat problems not the V8, interesting

malcolm

 

[Tony]

As a diversion to this one, anyone put their beastie through an MOT, but sans cats?
I ask as I have a V6 W210; these have two cat elements per pipe (4 in all - presumably to pass US emissions regs which would fail a mouse fart!), and both of the rear elements have gone in the last few months, so I've had them whipped out and a length of suitable stainless pipe welded in place.

That's also something I've been considering. I've blown 3 cats so far (in 5 years) and on each occasion it's the rear cats that go on the V6. (Mercedes refuse to recognise that there's a problem). The front cats are fine, and it's interesting that the after-market companies only make the nearside cat for the V6 - this is the one that has one front cat and both of the rear cats. They don't make the offside part which has just the precat, for the obvious reason that no one would buy it. My own opinion is that the rear cats get broken by rapid cooling when water splashes on them, but I may be wrong. It may just be a bad design, who knows.

My guess is also that the car would get through the MOT without the rear cats. As you say, this is something they do in the US when the rear cats break. The other alternative is to get an after-market metal cat and throw away the front cat (which is not to Merc spec and throws an engine code) and weld the Merc front cat onto it. The metal cats are very unlikely to break up.