Broad brush, compliments of Walker Exhaust.
500-800°F
Normal operating temperatures of a converter are 500-800°F, and up to 1200°F when the vehicle is under heavy load. To melt the catalytic converter's substrate, the temperature inside the converter would have to exceed 2000°F.

 

There is no precise temperature reading, they depend very much on the amount of exhaust going through the pipe when check. What you should be more concern with is the differences between the inlet and outlet, which tells you whether the cat is working or not. In general, the outlet should be considerably higher when the cat is working.

 

There is no precise temperature reading, they depend very much on the amount of exhaust going through the pipe when check. What you should be more concern with is the differences between the inlet and outlet, which tells you whether the cat is working or lot. In general, the outlet should be considerably higher when the cat is working.

Inlets 840 outet 425 at idle

 

Possible restricted cat!
What is your reason for checking the cat temps? Check engine light?

 

Got a light on for EVAP it's all new went away for 6months then came back on. Been on for 3 months again and just started taking longer to start then Usual. Everything looks good on scanner but those cat temps seemed off to me.the car has 256,000 dropped 5 mpgs in the last year

 

With so many miles on the car, might have to think about doing some testing to determine the health and condition of the engine and parts. And whether it is worth while putting money into it.
A restricted cat can cause high back pressure in the exhaust system, including hard starting, not to mention poorer fuel mileage.
Does the engine use oil? Unburn fuel, oil, etc going into the exhaust system can do some damage to the cat.

 

Burns no had BG moa added every oil change. Haven't had to do anything to the engine so far. Only seems to really hard start after sitting awhile

 

If you got a code for an EVAP problem why are you worried about the cat? The first thing to check and the easiest is the gas cap for that code. Also riding around with a check engine light on for months can cause a small problem to turn into a large problem.

 

Caps new everything is new on the EVAP system had it on a real scan tool today and only thing that looked off to me was cat temp

 

Pull your o2 sensor to see if it’s reading 600 degrees and watch how quick it drops temp. The o2 might be slow to respond.

 

When you fill up the car, do you stop at the first click or try to top it off beyond that?
250K miles is a long way for O2 sensors to go. Same with vacuum lines - but you say those were all changed?

 

I wouldn’t rush to over complicate the temps. Converters are a bit weird at times. If you’re not getting a catcode then don’t worry. If it’s getting stopped up then replace it but it should give you a light. Evap can get flooded if you over fill your tank because it’s made for fumes, not liquid. Usually if evep catches a big dose of liquid the valves need to be replaced. It mostly emissions related, not usually performance. Ceramic in a cat can collapse but still not impede flow. My truck did that pretty bad before it would throw a rear o2 light.

 

Not enough exhaust flow when starting for any exhaust blockage to matter. If it's that clogged, you probably couldn't drive it.

 

Give my suggestion a try, see if that makes any difference; turning the key on without running the pump will prime the system, a 2nd key cycle will help build up pressure. If for nothing, you can at least cross it off as a possibility.
Nevertheless, checking the fuel pressure with an external gauge wouldn't be a bad idea, you will know whether your fuel system is getting good pressure or not. With the mileage on the vehicle, any thing can happen.
If it runs worst when it is down to a 1/4 tank, might consider looking inside the tank to see if the lower part of the tank is water or not. Again, back to the mileage of the vehicle, it had been through many tanks or gas, and not all stations' fuel are as good as they should be.
Or find some additives to add to the gas, maybe that will help without doing much work.

 

Test for water in the gas.

 

Test for alcohol/ethanol in the gas.

How to test the alcohol content of gasoline | Delphi Auto Parts

Here’s a safe, fast and easy way to check the alcohol content of gasoline using a graduated cylinder.

www.delphiautoparts.com

.

 

I've seen a clogged cat cause a no start condition on a freshly rebuilt engine. This engine builder I knew asked me to come and look at an engine he had just built and he couldn't get it to start. My observation when he tried to start was that there was no airflow. It had the cat right on the exhaust manifold so we dropped it and you could see the cat entrance was glassed over. It started and ran great once we cleaned the glass off. I've been told the rule of thumb is the exit should be 200F hotter than the inlet. It sounds to me that you have a clogged cat, good luck.

 

That's on the meh side of normal, although at idle I might expect 150-200 deg difference. What are you trying to check? The two things that kill a cat. is severe misfire or head gasket leak. Up to about 2008 the rule of thumb is outlet should always be hotter than inlet. After that I saw the temps to be pretty close or even outlet cooler by 200. If you had a clogged cat with that much temperature drop you would have the pedal to the floor to get to 60. Downstream O2 sensor and fuel trims tells the story, car warmed up it should be steady at 450-650 F. Clogged cat at speed fuel trims go full lean ( negative ), other wise fuel trims at a steady speed +/- 8%. If the MAF wire is clean.

 

So, what do you think about OP's cat temp readings? And what could be the cause? What steps should he take to find out what is wrong with his car?

 

The downstream O2 shoul be steady around .550mv give or take. If it is switching up and down the low temp out is a failing cat. If it is steady close to 1 volt it is a clogged cat.

 

You should test the o2 sensor and ensure it’s measuring high temps. Solely to exclude it from the issue.

Ambient temps will heat it more. In arizona, we see 100F and higher during the summer. Add the heat of the road and the ambient temps, these contribute to higher temps on the cat.

Hit the bottom of the cat to listen for loose material moving around inside. The substrate will breakdown over time. I’m surprised you’re not seeing a P0420.

 

Found the problem. Started to get a misfire on cylinder 2 changed all the plugs and coils. Still misfiring cylinder 2 plug was soaked. Injector was sticking open. Couldn't get any locally anytime soon so added Lucas fuel treatment. Been running good since and the lights off, no evap code either Cat temps down 100 degrees . Usually do fuel treatment every 25,000 but forgot to do it at 250,000 .