1997 2.5L TJ Wrangler HOT exhaust.

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When I say HOT I mean it. I've always been aware that my girlfriends TJ exhaust system gets hotter than I'm used to. I didn't think much of it because I've seen other Jeep owners gripe about this with seemingly no root cause. The engine is in good tune (plugs look good, exhaust has no smell). It has no vacuum leaks, I've replaced the intake/exhaust manifold gaskets in the past, no codes, MPG is where it should be. I note from the carfax that the original cat and exhaust were replaced at a Jeep dealer in 2001 around 38,000 miles. That cat is still there, but the system was replaced again around 2007 with 60,000 miles by my girlfriends father. And then by me in 2011 with 80,000 miles. Currently at 92,000. Does extreme heat increase the oxidation rate of the metal? In 2011 I had the exhaust on my Accord and the Jeep replaced at the same time by a shop I like that bends their own. After 4 years the Accord's is nice and grey (despite being my winter beater) and Jeep (which is kind of pampered and sees little to no salt and limited mileage) started to look rough after only a couple years. It sounded bad too, the insulation in the muffler couldn't take the heat. I painted the whole system with Eastwood Rust Encapsulator when I did the frame over in Spring 2014. It all burned off on the first trip, even the end of the tail pipe, it has a max temp of 400 degrees. Right before the last state inspection the muffler developed a hole on top. I started it up cold to feel around for the location of it. This is when I noticed just how hot the exhaust gets, it was scalding hot in about a minute. After it cooled I put JB Weld on the hole,(max temp 600). The next day I went for a short drive and the JB Weld disintegrated into this charred brittle mass. I wish I had a heat gun to know exactly what the temps are. The Jeep is a short vehicle so the cat and muffler are close to each other. That plays a role, but the end of the tail pipe shouldn't melt your skin. I think it more complex, perhaps a tuning issue. Jeep may have used some lazy timing figures. I've hooked my scanner up to live stream data and make sure my IAT sensor is reading correct temperatures. (if they read falsely high it will force the computer to retard timing). There is no way to adjust timing on this Jeep. The only trick I know of to advance it would be wire in a resistor on the IAT sensor so it reads the coldest temperature possible at all times. I ordered this Dynomax replacement system tonight, I'm curious to see how it handles the heat. http://www.amazon.com/gp/product/B000CIXO3U?refRID=PYHFTMV8HJA99PG3TJYC&ref_=pd_ybh_a_1
 
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Your cat is clogged/and or your engine is dumping fuel into the cat. That's why your cats keep getting replaced. Heat is not killing the cat, the heat is just a byproduct. You've either got a dead cylinder, stuck open injector, or injector driver, or something. You need to look at the fuel trims and 02 wave forms. Don't play part swap. If you don't have the diag tools bring it to a mechanic.
 

Gasbuggy

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Originally Posted By: KingCake
Your cat is clogged/and or your engine is dumping fuel into the cat. That's why your cats keep getting replaced. Heat is not killing the cat, the heat is just a byproduct. You've either got a dead cylinder, stuck open injector, or injector driver, or something. You need to look at the fuel trims and 02 wave forms. Don't play part swap. If you don't have the diag tools bring it to a mechanic.
The cat was replaced in 2001 and not again, I stated in the post that it was still on there. Jeep replaced many catalytic converters on the 97 model under a recall, this Jeep just missed that window with it's early 1996 build date but perhaps still received a faulty part. I can't say for sure why it was replaced in 2001. If the cat was clogged I would have power loss. Same with dead cylinder, stuck injector, or a fuel issue all together. There would be many other symptoms and OBD II should throw codes. There are not enough symptoms to support it being a fuel issue, that is why I thought timing.
 
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Do you have a knock sensor? If you rap on the motor when it's idling does it retard further? Is a 4 cyl jeep so doggy it's always driven pedal to the metal?
 
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To answer your question in short; Yes, heat increases oxidation rate of anything, including metal. But, this is a 1995 Jeep thats been living in PA. I think you got your money's worth out the factory exhaust.
 
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Pipes and mufflers rust out rapidly when used on short trips where they don't get hot ENOUGH. This lets condensate (water) stay around and corrode them from the inside. Any car will have the tail pipe get hot enough to burn you. Too hot would be parts glowing red, especially the cat.
 
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Shouldn't have a knock sensor - only ones that had a knock sensor were the Renix MPFI that came on both the 2.5 and 4.0L at some point or another. It has an automatic, right? The 4.0L and 2.5L engines were designed to run "hot" - 210 degrees is the sweet spot. Combine that with an automatic transmission and things are going to get toasty under there. As long as it's not getting single digit gas mileage and runs smoothly - and the trans is not slipping - I'd consider it normal. Jeeps of that era are known for everything rusting out; still are. I'd say 20 years on the factory exhaust is fine.
 
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I would say lean condition. Could be a bad intake gasket. 1)read codes from OBD. 2)read your plugs. Other possibles a)lazy upstream 02 sensor b)clogged fuel filter c)exhaust restriction
 

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Originally Posted By: eljefino
Do you have a knock sensor? If you rap on the motor when it's idling does it retard further? Is a 4 cyl jeep so doggy it's always driven pedal to the metal?
No knock sensors on these Jeeps. I will check later with my scan tool if it retards on a rev. It's working but it doesn't need to be run hard to get around, no overdrive helps. I keep the weight down, soft top, half doors, aluminum wheels with 235/70/16 all season tires. People that go for big off road tires end up having to drive floored everywhere.
 

Gasbuggy

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Originally Posted By: Colt45ws
To answer your question in short; Yes, heat increases oxidation rate of anything, including metal. But, this is a 1995 Jeep thats been living in PA. I think you got your money's worth out the factory exhaust.
Originally Posted By: Miller88
Shouldn't have a knock sensor - only ones that had a knock sensor were the Renix MPFI that came on both the 2.5 and 4.0L at some point or another. It has an automatic, right? The 4.0L and 2.5L engines were designed to run "hot" - 210 degrees is the sweet spot. Combine that with an automatic transmission and things are going to get toasty under there. As long as it's not getting single digit gas mileage and runs smoothly - and the trans is not slipping - I'd consider it normal. Jeeps of that era are known for everything rusting out; still are. I'd say 20 years on the factory exhaust is fine.
The cat and exhaust were replaced in 2001, then exhaust was replaced in 2007, 2011, and I just ordered a new replacement. This will be the 5th one. Miller you are correct, they do run a hair under 210, and it is an automatic. Getting about 18-19mpg, which is great for a 3 speed Jeep.
 

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Originally Posted By: krismoriah72
I would say lean condition. Could be a bad intake gasket. 1)read codes from OBD. 2)read your plugs. Other possibles a)lazy upstream 02 sensor b)clogged fuel filter c)exhaust restriction
I replaced the intake/exhaust manifold gaskets about 4 years ago, also put a new upstream denso in at that time. I did a recent carb cleaner spray test around the engine to check for leaks. There is no traditional fuel filter on these Jeeps, it is "lifetime" part on the fuel pump assembly in the tank. I don't suspect a restriction, but I will know more when this replacement system comes and I can remove the old one.
 
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I seriously doubt that the exhaust is abnormally hot if you're getting decent mileage and performance. You would have to use an IR gun to compare the Jeep to something else, but all exhaust systems get well over the 600F that JB-weld is good for, at least when the engine is under load. I've had a scan-tool on my Ram and just cruising down the road the cat temps are around 800-1000F, spiking to 1400 under sustained load. The actual EGT before the cats is probably lower, but still over 600F I'm sure.
 

Gasbuggy

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Originally Posted By: 440Magnum
I seriously doubt that the exhaust is abnormally hot if you're getting decent mileage and performance. You would have to use an IR gun to compare the Jeep to something else, but all exhaust systems get well over the 600F that JB-weld is good for, at least when the engine is under load. I've had a scan-tool on my Ram and just cruising down the road the cat temps are around 800-1000F, spiking to 1400 under sustained load. The actual EGT before the cats is probably lower, but still over 600F I'm sure.
I think it runs hotter than most vehicles but that is normal for these Wranglers. I did some more searching and see a lot of people on the Jeep Forums who replaced mufflers with Flowmasters and other aftermarket mufflers that don't have a built in heat shield. They end up melting the carpet on the floor inside. One guy had a custom tail pipe bent up and it was close to the plastic gas tank. Melted a hole in the tank. Part of the problem may be that the exhaust is tucked up high, above the skid plate, and it's not getting hit with much air while driving.
 
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My ZJ exhaust has always been very hot as well. Various engine changes, tune adjustment, etc. have never changed that much. The bigger than stock exhaust on it now runs a little cooler than the stock setup did though. Other Jeeps of a similar vintage seem to behave similarly. Part of it is small pipe diameter, I think. Not really sure what other design factors would lead to it.
 

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I made a little video for you guys. I installed the new Dynomax catback tonight. I started it up to listen to it then I drove 4-5 minutes - 1.5 miles to the grocery store. Bought some groceries. Then drove back home, took a slightly longer way, say it was 1.9 miles. Afterwards I got out and grabbed a piece of snow to put on the tailpipe by the rear bumpers. Any of my other cars you could grab and hold no problem.
Also, the 4.5 year old muffler that I removed...
 
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