Longevity of replacement cats? - Waino
In May 2005 at 110,000 miles, the internals of the original cat on my Mondeo estate broke up and a replacement was needed. This was duly discussed with my regular independant repair man and we concluded that, as the car was a little long in the tooth, we'd go for a cheap 'pattern' replacement. The replacement cost was £109 plus a portion of the total service bill to fit it. I believe a 'genuine' replacement would have been nearer £300.

After 2 months, the internals failed and the new cat became noisy so a replacement was fitted FOC; then, at 11 months, a leak developed in the flexi bit at the front and again it was replaced FOC. We've now gone over the 12 months guarantee (?) period so now I'm wondering how long this one will last and questioning the wisdom of using a cheap cat on a car (1997) that I'd like to keep going for a few more years yet.

I'd be interested to hear the views and experiences of other Backroomers after replacing cats - particularly in respect of 'pattern' vs original manufacturer.
Longevity of replacement cats? - Roger Jones
My mechanic has extensive experience with German cars (that's all he works on) and has yet to have to replace a cat. In the light of that I began to think that cats are designed as life-of-car components and that perhaps, for once, the manufacturers were to be congratulated, given the expense of the things.

I don't suggest that the cats on Deutschemobiles are particularly durable, but I wonder if there has been anything about the performance or use of the Mondeo that has weakened the cat. Perhaps it's a weak feature of Fords -- I don't know.

For example:

"A catalytic converter relies on receiving the proper mix of exhaust gases at the proper temperature. Some engine oil additives or engine problems that cause the mixture or the temperature of the exhaust gases to change reduce the effectiveness and life of the catalytic converter. Leaded gasoline and the over-use of fuel additives can shorten the life of a catalytic converter considerably. Even some gasket sealers and cements can poison a converter.
A catalytic converter can also fail because of certain other factors. A number of problems could occur to the catalytic converter as the result of an engine that is out of tune. Any time an engine is operating outside proper specifications, unnecessary wear and damage may be caused to the catalytic converter as well as the engine itself. The damage is often the result of an incorrect air/fuel mixture, incorrect timing, or misfiring spark plugs. Any of these conditions could lead to a catalytic converter failure or worse."

And see:


where they say "If your catalytic converter fails, there is probably some problem with your vehicle. Replacing the catalytic converter will not solve the problem."

And for general interest, the following can be found at:


"Caring for the CAT

There are several things you can do to ensure your CAT has a long and healthy life:

1. When fitting the catalytic converter don?t use exhaust paste in front of the cat. When the exhaust paste hardens it can break off in chunks and destroy the monolith.

2. Always use the correct fuel for your car.

3. Never use a fuel additive without first reading the instructions to find out if it is suitable for use with a catalytic converter. If in doubt, consult the manufacturer of the additive.

4. Never attempt to bump or tow start your car. This causes unburned fuel to be injected into the cat, which makes the monolith overheat and melt.

5. Never tow anything that is too heavy for your vehicle to cope with. For example, an overloaded caravan will actually push a car along when it travels downhill. This sends unburned fuel into the exhaust system and can cause the monolith to melt down.

6. Have your car regularly serviced to your car manufacturers specifications. In particular make sure the engine is running properly. A poorly tuned engine can cause the monolith to break down or become covered in soot, which stops it working correctly.

7. Take care when driving through deep puddles, fords, or parking when there has been heavy snow. The cat operates at an extremely high temperature, and when it comes into contact with water or snow it cools down rapidly. The steel shell cools more rapidly than the monolith, and in extreme circumstances the monolith can be crushed as the steel shell contracts.

8. Don?t park your car over long grass or anything similar. As the cat operates at such a high temperature it can actually set the grass on fire!

9. Drive slowly over speed bumps or very bumpy roads to reduce the chance of the exhaust system being grounded. This could cause impact damage to the cat."
Longevity of replacement cats? - Cliff Pope
Volvo cats never wear out. Mine's 13 years old and just passed its emissions test easily. 342,000 miles.
Longevity of replacement cats? - P 2501
Yes they do - my neighbour has needed two on his 5 year old volvo.
Longevity of replacement cats? - henry k
In May 2005 at 110,000 miles, the internals of the original cat on my Mondeo estate broke up and a replacement was needed.

The replacement cost was £109 plus a portion of the total service bill to fit it.
I believe a 'genuine' replacement would have been nearer £300.

Last year the cat on my 88 saloon, although it was OK for the MoT, became so rattly that SWMBO demanded a replacement.
Ir was done by a Ford main dealer as part of other work/service and I must presume be a pukka Ford job.
IIRC it was about £200 plus £15 for a couple of exhaust gaskets plus I guess VAT.
I was pleasantly surprised cos I expected up to double that.
Longevity of replacement cats? - Roberson
The cat on my '93 Polo 'failed' almost a year ago to the day (or 6000 miles ago) at 106000 miles. The internal monolith had broken up, and on acceleration, it would produce an annoyingly loud clanking. However, it had been like this for some time, and IIRC it passed an emissions test in this condition too. It should have lasted a lot longer, but there had been ongoing problems with the distributor which was wreaking havoc with engine management, giving all sorts of running and starting issues. I have a feeling that it was this what finished it off.

It cost £199.25 including VAT and labour for an OEM Ernst part. The price for my particular cat have dropped dramatically from £145 ex vat to £89 ex vat....typical.

I've also had an Ernst back box and centre section fitted too, and the quality is second to none, lasts an age. However, the only problem with the cat is the flange for the joint to the manifold is allowing a slight leak which I can't seem to fix.

As far as 'pattern' cats go, it'll be the same as the rest of the 'pattern' exhaust system. I've had non OEM exhaust parts before and the quality of both manufacture and material is very poor, and they never seem to last.
Longevity of replacement cats? - Adam {P}
I remember when my Fiesta's cat broke up and then the car caught fire because of it.

60 quid later, second hand cat - job was a goodun'.
Longevity of replacement cats? - trigger_mike
I used to sell the pattern part cats made by fuel parts at a motor factors i used to work, never really had many problems, some wern't a great fit, but for the price of them you could'nt complain.

Ask Honest John

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