Catalytic converter temperature
04-07-2011, 02:56 PM
#1
Catalytic converter temperature
Hello folks,
I did some reading about catalytic converters and learned that a good catalytic converter will usually run slightly hotter on the outlet than on the inlet @ 2500 rpm. Some websites say it should be 100 degrees hotter on the outlet, others say it should be about 40 or 50 degrees.
Tonight, I checked the temperature of the main cat converter on my max with an infrared heat gun, and here is what I found out:
@ 750rpm : inlet temperature = 180 degrees, outlet temperature = 180 degrees
@ 2500rpm : inlet temperature = 245 degrees, outlet temperature = 195 degrees
Now based on what I read, the outlet should be hotter, however it is the opposite on my car. Does that mean my main cat is shot/partially clogged? What is going on?
Also, after 15/20 minutes of driving, my car feels really slow, like i'm hauling a 4000lb trailer or something. The power feels down at every rpm range.
I did some reading about catalytic converters and learned that a good catalytic converter will usually run slightly hotter on the outlet than on the inlet @ 2500 rpm. Some websites say it should be 100 degrees hotter on the outlet, others say it should be about 40 or 50 degrees.
Tonight, I checked the temperature of the main cat converter on my max with an infrared heat gun, and here is what I found out:
@ 750rpm : inlet temperature = 180 degrees, outlet temperature = 180 degrees
@ 2500rpm : inlet temperature = 245 degrees, outlet temperature = 195 degrees
Now based on what I read, the outlet should be hotter, however it is the opposite on my car. Does that mean my main cat is shot/partially clogged? What is going on?
Also, after 15/20 minutes of driving, my car feels really slow, like i'm hauling a 4000lb trailer or something. The power feels down at every rpm range.
Last edited by Gizm0; 04-07-2011 at 04:10 PM.
04-07-2011, 05:13 PM
#2
Not sure on input/output temperatures, but out cats (especially the precats) have a tendency to slowly disintegrate and increase back-pressure. When I swapped mine out with a pair of low mileage used ones on my other 5.5 gen, my 45-85 time dropped by nearly 3 seconds.
04-07-2011, 08:36 PM
#3
Hello folks,
I did some reading about catalytic converters and learned that a good catalytic converter will usually run slightly hotter on the outlet than on the inlet @ 2500 rpm. Some websites say it should be 100 degrees hotter on the outlet, others say it should be about 40 or 50 degrees.
Tonight, I checked the temperature of the main cat converter on my max with an infrared heat gun, and here is what I found out:
@ 750rpm : inlet temperature = 180 degrees, outlet temperature = 180 degrees
@ 2500rpm : inlet temperature = 245 degrees, outlet temperature = 195 degrees
Now based on what I read, the outlet should be hotter, however it is the opposite on my car. Does that mean my main cat is shot/partially clogged? What is going on?
Also, after 15/20 minutes of driving, my car feels really slow, like i'm hauling a 4000lb trailer or something. The power feels down at every rpm range.
I did some reading about catalytic converters and learned that a good catalytic converter will usually run slightly hotter on the outlet than on the inlet @ 2500 rpm. Some websites say it should be 100 degrees hotter on the outlet, others say it should be about 40 or 50 degrees.
Tonight, I checked the temperature of the main cat converter on my max with an infrared heat gun, and here is what I found out:
@ 750rpm : inlet temperature = 180 degrees, outlet temperature = 180 degrees
@ 2500rpm : inlet temperature = 245 degrees, outlet temperature = 195 degrees
Now based on what I read, the outlet should be hotter, however it is the opposite on my car. Does that mean my main cat is shot/partially clogged? What is going on?
Also, after 15/20 minutes of driving, my car feels really slow, like i'm hauling a 4000lb trailer or something. The power feels down at every rpm range.
Glad to see someone find this info on their own, and even took the initiative to test it
04-08-2011, 06:17 AM
#4
^^ Yes the car was at operating temperature.
I think the signs of power loss slowly started when my rear precat went bad and probably sent small debris down the exhaust and partially clogged the main cat... weird thing though is that I have no CEL?
I'll replace it anyhow, I'm hesitating b/w spending $30 to replace it with a pipe, or spend $180 to replace with a brand new cat...
I think the signs of power loss slowly started when my rear precat went bad and probably sent small debris down the exhaust and partially clogged the main cat... weird thing though is that I have no CEL?
I'll replace it anyhow, I'm hesitating b/w spending $30 to replace it with a pipe, or spend $180 to replace with a brand new cat...
04-08-2011, 06:55 AM
#5
If the problem is the main cat, you can replace it with a test pipe and not have to worry about an SES light since it isn't monitored by the computer. The precats will still keep the exhaust clean if that is a concern.
04-08-2011, 07:07 AM
#6
OK so that would explain why I would have no CEL even though the cat is bad. So there is no O2 sensor downstream of the main cat?
04-08-2011, 10:12 AM
#7
...but if you replace it with a test pipe, you'll have to deal with all the problems that come from having no catalytic converter. Search on here to learn more, but "smelling like a gas station" is a common complaint. Personally, I do NOT want to smell my exhaust when I'm idling at a light.
Pro-tip: Modern three-way catalytic converters, like the ones in our cars, do not significantly hinder performance like the original cats from the 70s or the first three-ways from the mid 80s.
Pro-tip: Modern three-way catalytic converters, like the ones in our cars, do not significantly hinder performance like the original cats from the 70s or the first three-ways from the mid 80s.
04-08-2011, 10:37 AM
#9
Also, gizm0, from more research of my own as you piqued my interest:
Under normal operating conditions, the converter should not have to work very hard to accomplish its job. If an engine has good compression, is not sucking oil down the valve guides, and the fuel, ignition and engine management system are all working properly, there should be relatively little HC and CO in the exhaust for the converter to burn (a few tenths of a percent CO and less than 150 ppm of HC when the engine is warm). In many late-model engines with multipoint fuel injection, combustion is so clean that the converter has little to do and the difference between the inlet and outlet temperature may only be 30 degrees F at 2,500 rpm--which is a lot less than the old rule of thumb that says a good converter should show at least a 100 degree F difference fore and aft at cruise. At idle, the converter in many late-model vehicles may cool off so much that there's almost no measurable difference in fore and aft temperatures. So checking exhaust temperatures fore and aft of the converter at idle and 2,500 rpm may not be the most accurate way to determine if the converter is working or not.
and
To clean the exhaust, the catalyst inside the converter must be exposed to the hot exhaust gases. Lead, phosphorous and silicone can contaminate the catalyst and prevent it from working its magic. Lead used to be the most common contaminant, but is no more since it was eliminated from gasoline. Phosphorus is still a threat, and comes from motor oil. So if an engine is burning oil because of worn valve guides or rings, phosphorus will shorten the life of the converter. Blue smoke in the exhaust and an emissions failure are pretty good clues that the converter has been fouled with phosphorus.The new "SJ" rated motor oils contain less phosphorus than earlier SH rated oils. The difference isn't much (about 20% less compared to SH oils), but over time the lower level of phosphorus reduces contamination to extend the life of the converter. Silicone can find its way into the exhaust if the engine develops an internal coolant leak through a crack in a combustion chamber or a head gasket. Silicone will ruin the oxygen sensor as well as the catalytic converter, so chances are if the converter has been fouled the O2 sensor will also need to be replaced. White smoke in the exhaust is a clue that there's an internal coolant leak.
---
Buuuuut, if there is such a huge difference in temperatures like yours, I think it's safe to say some problem exists.
Under normal operating conditions, the converter should not have to work very hard to accomplish its job. If an engine has good compression, is not sucking oil down the valve guides, and the fuel, ignition and engine management system are all working properly, there should be relatively little HC and CO in the exhaust for the converter to burn (a few tenths of a percent CO and less than 150 ppm of HC when the engine is warm). In many late-model engines with multipoint fuel injection, combustion is so clean that the converter has little to do and the difference between the inlet and outlet temperature may only be 30 degrees F at 2,500 rpm--which is a lot less than the old rule of thumb that says a good converter should show at least a 100 degree F difference fore and aft at cruise. At idle, the converter in many late-model vehicles may cool off so much that there's almost no measurable difference in fore and aft temperatures. So checking exhaust temperatures fore and aft of the converter at idle and 2,500 rpm may not be the most accurate way to determine if the converter is working or not.
and
To clean the exhaust, the catalyst inside the converter must be exposed to the hot exhaust gases. Lead, phosphorous and silicone can contaminate the catalyst and prevent it from working its magic. Lead used to be the most common contaminant, but is no more since it was eliminated from gasoline. Phosphorus is still a threat, and comes from motor oil. So if an engine is burning oil because of worn valve guides or rings, phosphorus will shorten the life of the converter. Blue smoke in the exhaust and an emissions failure are pretty good clues that the converter has been fouled with phosphorus.The new "SJ" rated motor oils contain less phosphorus than earlier SH rated oils. The difference isn't much (about 20% less compared to SH oils), but over time the lower level of phosphorus reduces contamination to extend the life of the converter. Silicone can find its way into the exhaust if the engine develops an internal coolant leak through a crack in a combustion chamber or a head gasket. Silicone will ruin the oxygen sensor as well as the catalytic converter, so chances are if the converter has been fouled the O2 sensor will also need to be replaced. White smoke in the exhaust is a clue that there's an internal coolant leak.
---
Buuuuut, if there is such a huge difference in temperatures like yours, I think it's safe to say some problem exists.
Last edited by Eirik; 04-08-2011 at 10:40 AM.
04-08-2011, 10:44 AM
#10
^^ Yeah I read that one too, but its weird that the temperature is higher on the upstream side on my car... everything I read on the internet was talking about higher temperature downstream of the cat...
And yes, my car does burn some oil through the PCV. About 1 qt every 1500 miles or so.
And yes, my car does burn some oil through the PCV. About 1 qt every 1500 miles or so.
04-08-2011, 01:04 PM
#11
...but if you replace it with a test pipe, you'll have to deal with all the problems that come from having no catalytic converter. Search on here to learn more, but "smelling like a gas station" is a common complaint. Personally, I do NOT want to smell my exhaust when I'm idling at a light.
As you can hear, my car was still very quiet with a test pipe in an otherwise stock exhaust.
http://www.youtube.com/watch?v=OKR5QpYq_Yw
Pro-tip: Modern three-way catalytic converters, like the ones in our cars, do not significantly hinder performance like the original cats from the 70s or the first three-ways from the mid 80s.
04-08-2011, 01:33 PM
#12
Did not have anything like that when I removed my main cat and replaced it with a test pipe. If you smell your exhaust at a light it is because you have an exhaust leak and if that is the case, you didn't install the test pipe right.
As you can hear, my car was still very quiet with a test pipe in an otherwise stock exhaust.
http://www.youtube.com/watch?v=OKR5QpYq_Yw
That is true when the cars are new. Many of us have well over 100k miles on our cars now and a lot of them use oil. Cats do slowly clog over time and are often replaced because of that issue.
As you can hear, my car was still very quiet with a test pipe in an otherwise stock exhaust.
http://www.youtube.com/watch?v=OKR5QpYq_Yw
That is true when the cars are new. Many of us have well over 100k miles on our cars now and a lot of them use oil. Cats do slowly clog over time and are often replaced because of that issue.
04-08-2011, 03:25 PM
#13
Just a thought, but... If a cat was somewhat clogged and had all this hot gas comming at it, and could only let so much out; the hot gas fore of the cat would build pressure. Pressure + heat = more heat. Reduced pressure + less gas out aft cat = less heat.
04-08-2011, 05:48 PM
#14
I had to replace my precats as well, both were noticeably deteriorating.
04-08-2011, 09:06 PM
#16
Yet another reason you kind of eluded to without noticing, is pressure differential.
This difference causes a venturi effect on the Post side of the cat, which pulls in cool ambient air, and cools the Post side of the exhuast.
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