Porsche Enthusiasts Club Forum

Is this normal? My nearside exhaust seems to get a lot hotter than the off side?

I assume they should be the same temp?

My exhaust does rattle when I start up and it is cold so is this a sign of impending box failure? Or something worse?
thanks

I guess the obvious question is are you experiencing any difference in performance? If not I suggest you take it out for an almighty thrashing and check it again.

no noticable performance issues, plugs and coil packs are 6 months old. Not tried a 0-60 run though to see how close the car is to book. I had just driven the car in low gears high revs on a 'slow lap' of a race track (hitting 5-6000 rpm in 2nd I guess at times so it was getting a mild thrashing, it was after this that I noticed the temp difference (and the hot smell from that side)

Possibly a heat shield missing? I'm sure that if there's a temp difference across the two sides of the exhaust it throws up a code and puts it in limp home mode, running without a map? Do you have a thermometer to see if it is actually greater on one side?

it defo feels hotter on that side - so after letting car cool the offside silencer box I could touch, whereas the nearside was pushing the heat out and I values my hand so did not touch it. I am thinking that hot is normal and maybe the baffles are gone in the offside box so it is not retaining as much exhaust gas therefore heat? As when eth car starts up there is a rattle from the exhaust which seems to be offside but hard to tell.

Rattle + heat is more than likely to be a melted cat. They melt into small balls that cause the startup rattle & then they clog the outlet of the cat meaning there is a heat buildup. Better be sitting down when Porsche tell you how much they want for one

I agree that a rattle can be a symptom of an impending CAT failure but you would normally also experience a significant drop in performance with a melted CAT. As Lee suggested get the temps checked either side before you go any further and if you can do a diagnostic check to see if anything shows up.
It could be as you said that the baffles have moved on one side causing that rattle and heat build up, I had this same issue on my 964 and was suspicious that the CAT had failed. I proved otherwise by starting the car up from cold listening to the rattle putting by hand over the tail pipe until the engine is near stall condition then letting go. If the rattle disappears give the engine a blip of the throttle, if the rattle returns it points to your baffles.
To the best of my knowledge the only way you can check out your CAT is to remove it and look inside.

This may be of interest to you it's off eBay

"A catalytic converter should never fail!
If it does, then there is a problem will not be fixed by simply replacing the converter. The fact that it failed is the result of a less apparent problem under the hood. If your catalytic converter needs replacing, then one of the problems listed below most likely contributed to its failure.
Here is an example of catalyst in different stages of damage (or lack of).

Engine Tune-up
A number of problems could occur to the catalytic converter as a result of an engine that is out of tune. Any time that an engine is operating outside of proper specifications; your converter suffers unnecessary wear and damage, as well as your engine. The damage is often the result of an incorrect fuel/air mixture, incorrect timing, or misfiring plugs. Any of these conditions could lead to catalytic converter failure or worse.

Excess Fuel Entering Exhaust
The fuel that powers your vehicle is meant to burn IN THE COMBUSTION CHAMBER ONLY. Any fuel that leaves the combustion chamber unburned will enter the exhaust system and “light off” when it reaches the converter. This can “superheat” the converter to temperatures far above normal operating conditions and cause a CONVERTER MELTDOWN.
This is an example of a converter meltdown. The converter was super-heated due to a raw fuel condition in the exhaust flow. The excess unburned fuel ignited when it struck the hot ceramic catalyst and drove the temperature far above the normal operating condition of the converter. The ceramic catalyst is unable to withstand the extremely high temperature and begins to melt. The ceramic collapses and the converter is destroyed. The melted ceramic may block the exhaust flow and cause additional damage to the engine. A converter glowing red-hot or evidence of heat discoloration confirms this situation. The too-rich condition that led to this converter melt down could be the result of a number of malfunctions including faulty oxygen sensor, an incorrect fuel mixture, worn spark plugs or plug wires, a faulty check valve, incorrect ignition timing, sticking float, faulty fuel injectors or other ignition malfunctions.

Oil or Antifreeze Entering Exhaust.
Oil or Antifreeze entering the exhaust system can block the air passages by creating heavy carbon soot that coats the ceramic catalyst. These heavy Carbon Deposits create two problems. First, the carbon deposits prevent the catalytic converter from reducing harmful emission in the exhaust flow. And second, the carbon deposits clog the pores in the ceramic catalyst and block exhaust flow, increasing backpressure and causing heat and exhaust to back up into the engine compartment. Your engine may actually draw burnt exhaust gasses back into the combustion chamber and dilute the efficiency of the next burn cycle. The result is a loss of power and overheated engine components. Possible causes are worn piston rings, faulty valve seals, failed gaskets or warped engine components.

Deteriorated Spark Plug & Spark Plug Wires.
Spark plugs that don't fire or misfire cause unburned fuel to enter the exhaust system. The unburned fuel ignites inside the converter and could result in a partial or complete melt down of the ceramic catalyst. Spark plugs and spark plug wires should be checked regularly and replaced if damaged or if wires are worn or cracked.

Oxygen Sensor Not Functioning Properly.
An oxygen sensor failure can lead to incorrect readings of exhaust gasses. The faulty sensor can cause a too rich or too lean condition. Too rich and the catalyst can melt down. Too lean and the converter is unable to convert the hydrocarbons into safe elements and may not pass a state inspection.

Road Damage or Broken Hangers.
The ceramic catalyst inside a catalytic converter is made from a lightweight, thin-walled, fragile material. It is protected by a dense, insulating mat. This mat holds the catalyst in place and provides moderate protection against damage. However, rock or road debris striking the converter or improper or broken exhaust system support can cause a Catalyst Fracture. Once the ceramic catalyst is fractured, the broken pieces become loose and rattle around and break up into smaller pieces. Flow is interrupted and backpressure in the exhaust system increases; this leads to heat build up and loss of power. Possible causes of a catalyst fracture are road debris striking the converter, loose or broken hangers, potholes or off-road driving.


After You Install A New Catalytic Converter, if your car caused the OEM catalytic converter to fail, it could cause The New Converter To Fail as well. And the warranty that comes with a new replacement catalytic converter does not cover the type of damage listed above."

I think you really should get the car connected into a diagnostics tester if there is a significant temperature differential across each exhaust bank.

After visiting Bristol OPC they found that the rattle was caused by the rear pipe knocking against the expansion joint on the exhaust system, as the car gets hot, system expands and stops the rattle. Not getting it fixed as joints are corroded so I can live with a rattle.

Heat issue - well got a temp gauge laser pointer thing (they probably have a correct name) and to be honest it has not happened again. so not sure if it was a one off with the car getting some mild track exercise or heat soak from disc or cooling header tank (as it was on that side)? her way no loss of power, no observations from OPC when it went in. I will keep an eye on it but all seems ok? I will keep you all posted!