IS250 clogged cat??

[Bergsy]

Hi all,

 

Picked up an 07 IS250 a little while ago and recently there's been excessive heat coming from underneath and occasionally an eggy smell.   Am I right in thinking clogged/knackered cat?

[LenT]

11 hours ago, Bergsy said:

Hi all,

 

Picked up an 07 IS250 a little while ago and recently there's been excessive heat coming from underneath and occasionally an eggy smell.   Am I right in thinking clogged/knackered cat?

Hello Nick,   I noticed that you’ve not had an answer yet from an expert, so I thought I might offer some suggestions until one comes along.

And my answer is: possibly….

If by an occasional eggy smell you actually mean the stink of rotten eggs (or stink bombs, as we used to call them) then you may well have a problem.  That will be hydrogen sulphide, which means that the catalytic metals are no longer able to convert the sulphates in the fuel to sulphur dioxide, which only faintly smells of eggs.  So it depends on how sensitive your nose is!

However, the fact that you’re detecting excessive heat is a more positive sign, because the process involved is vigorously exothermic and when a cat is doing its business it can work up to 1000C degrees.

Fortunately a failing cat does offer other clues.  For example, you may hear rattling noises from it as the internal ceramic structure degrades and bits fall off. In fact the internal structure can be quite fragile - especially when it’s hot.  So if the exhaust system has had a bang that could cause internal damage.  Starting and fuel consumption will both deteriorate and the exhaust smoke will darken in colour.

The problem is caused because the car has mainly done only short journeys and the cat hasn’t got hot enough to kickstart the reaction needed to remove the combustion products that have collected in it.  So one possible cure is to take it for a long journey, keeping the engine revs at least above 3000 I would suggest.  Easy enough if it’s a manual but you may have to use the gear select option if it’s an auto - I don’t know your model.

Once the catalytic reaction starts you will notice a burning smell and the heat from it if you stop.  Do that a few times and it may improve the situation.  But if the cat has suffered permanent internal damage then, unfortunately, replacement is probably the only cure.

One final thought: I don’t know your model but my IS250 actually has three catalytic converters of two types - one up by the exhaust manifold and two under the car.

I hope this helps.

[steve2006]

A very nice and comprehensive reply Len. 😀

As mentioned it does sound like a duff cat and when you do get the bad egg smell it usually means there is no cure apart from replacement (there are various potions like Cataclean which claim to clean the cat but never used them personally).

Taking the car for a good high speed run holding low gears for higher RPM can burn out the contaminants but be aware it generates a lot of heat ( they have been known to glow red) so take care where you park afterwards and be aware of any fire risks.

You mentioned you only purchased the car recently was this privately or from a motor trader? If the latter you do have statutory consumer rights should the car develop faults in the first 6 months.

[ColinBarber]

How hot does the engine get? Is the temp gauge a fraction below the mid point or higher? It's possible that a lean running engine will overheat the cats.

[LenT]

1 hour ago, steve2006 said:

but be aware it generates a lot of heat ( they have been known to glow red) so take care where you park afterwards and be aware of any fire risks.

A very good point, Steve.  There have been some devastating fires - and fatalities - that have been tracked down to a hot catalytic converter and a car badly parked on dry vegetation.  More common in, say, California than here in the UK, which is why it can be so easily overlooked.

[Bergsy]

Thanks for the replies everyone. Some things to try then before going straight down the new cat route, Cheers.

[Bergsy]

9 hours ago, ColinBarber said:

How hot does the engine get? Is the temp gauge a fraction below the mid point or higher? It's possible that a lean running engine will overheat the cats.

It sits a fraction below the mid point. Haven't seen it move any higher.

[LenT]

On 5/31/2021 at 8:25 PM, Bergsy said:

It sits a fraction below the mid point. Haven't seen it move any higher.

As I understand it, it's the temperature of the exhaust gases that will be the more crucial factor.  The cat has to get to between  200C - 300C in order to initiate the chemical reaction.  That's why it takes a few minutes of reasonably high revs to reach it.  No doubt that will be influenced by the fuel/air mixture, the general operating efficiency of the engine, how much unburnt fuel/oil is passing through the cat and the internal state of the cat itself.

As the performance of the cat deteriorates, so the internal temperature rises.  So while they may normally operate between 650C - 850C, a failing or clogged cat can go up to 1000C.  So it seems that one clue as to what's going on internally is the state of the exterior. If the metal is clearly discoloured by high temperatures then that may well indicate a catalytic converter in distress!