Our Community is 940,000 Strong. Join Us.

temperature of catalytic converter

07-12-2017, 01:07 PM
I have a 2001 Buick Lesabre Ltd and I have replaced the fuel filter, front oxygen sensor, MAP sensor, mass air flow sensor twice and still can't get my "check engine" light to go out. The car misses under a load, like going up a hill, and also runs very rough until it warms up, just setting still. Someone said it could be the catalytic converter so I went and purchased a temperature gun, drove it until it reached operating temp and the front of the cat measured 330 degrees and the rear 403 degrees. Is that sufficient evidence that the converter need replacing?

07-15-2017, 10:11 AM
I sure would like to thank everyone for all your great replies, but I can't. That's because I got none. Every request has received at least one reply but mine. I'm really a nice guy, I really am. I guess I'll just change out a few more parts and maybe I'll get lucky.

Blue Bowtie
07-15-2017, 11:44 AM
The normal internal temperature of a converter can exceed 1,500F. Reading less than 500 on the exterior is not alarming. That may seem hot, but that is why there are heat shields surrounding the converter and warnings in the owner's manual about parking on unpaved surfaces and over vegetation.

The fact that the outlet temperature is higher indicates the cat is functioning.

Regarding the operational problem, it would be very helpful to know what DTCs (codes) are causing the warning lamp. Instead of replacing parts on a guess, gather the data and perform some diagnosis.

It will also be very helpful to know the standing and running fuel pressures.

Tech II
07-16-2017, 09:57 AM
Agree with Blue that the cat is functioning based on temp.....and if there was a cat problem it would set an efficiency code.....

Rough idle on a cold start that clears up as the engine gets warm?

Last time the vehicle had a complete tuneup, plugs and wires, PCV, air filter?

Misfire under a load?

Have you been adding coolant? if not, check coolant on a COLD engine.....check reservoir level compared to the "cold mark"....remove radiator cap and make sure the coolant is to the top of the radiator, before starting the car....

Why did you replace all those parts? If because of a code, that is shot gunning.....Just because a code is set, you don't replace the part the code is named after.....that code means there is something wrong in the Whole circuit the part is in, or, the code is set because something affects the running of that part...... Let's say for example, an O2 sensor code is set....do you replace the O2 sensor? No, first you check to see if the O2 sensor is working.....a code can be set, not because the O2 sensor is bad, but because it is reading something that is skewed by something else in the vehicle, like a vacuum leak.....

As Blue said, we will need a list of the Powertrain codes, to give us a starting point.........

As for nobody answering, there are a lot of people on vacation, this time of year.....hang in there....

07-16-2017, 11:54 AM
Thank you both for answering my post. Sorry to be a little cranky, but at 75 years old, I guess I feel I have earned the right to be a little cranky.
I have been replacing the parts because of the codes ( at the present I can't even remember what they were) but that what I have been doing. I spent 25 years in the auto parts business but retired before the electronics and computers came into play real heavy.
You know, I do believe that the coolant level has been being low every time that I checked it. What does that actually mean?
The car actually only has 86K miles on it and it is a spare vehicle for our family. The plugs, wires, pvc valve and air filter all were changed out at about 50k.
I was going to check a couple of the plugs, just the other day, but with an arthritic elbow, I didn't have the strength to pull the darn plug wire off of the plug.
Anyway, thank you both again for the replies.

Blue Bowtie
07-16-2017, 12:47 PM
That's O.K. You're entitled to be a little cranky. It keeps the rest of us on our toes.

If the coolant level is constantly decreasing, that could be an indication of an intake gasket leak - Either upper or lower. Even at under 100K miles, the age and thermal cycling will take its toll and cause the gaskets to creep, and eventually leak.

The same thing can occur if the original plastic coolant bypass elbows develop leaks. They usually do, and replacement with metal elbows is the normal solution. One is at the right (front) end of the intake base the other is beneath the belt tensioner assembly, joining that to the front case.

I just did the intake gasket replacement about three weeks ago on my daughter's 2001 Impala (same Buick 231 V-6) at 140K easy miles. You may be in for this soon:


Dorman offers and improved plastic upper intake kit with several advantages and improvements over the original design. FelPro has an updated gasket kit for the lower intake which includes a metal-framed gasket with silicone seals instead of the original fiber cores. Neither of the sets are prohibitively expensive. However, there will be a lot of bending and wrenching to perform the replacement, so it may be a good thing that the vehicle is a "spare" that you can work on in short sessions, resting your back and joints in between.

That engine, with the minor problems like this resolved, is almost bullet-proof. It's certainly worth the expense of repairing it.

Tech II
07-16-2017, 05:36 PM
If coolant is low, that would cause an initial rough idle on startup, if coolant is pooling into cylinders overnight(possible upper plenum problem at EGR opening in upper plenum)......

50K last tuneup? That could mean you need another one......take the wires off the coil terminals, one at a time, and look for arcing/corrosion on the coil terminals....that will cause a misfire.....carbon tracking on the insulators of plugs is common....if that is the problem, wires AND plugs should be replaced.....

A secondary misfire can usually be found by this......drive the vehicle on a highway at 55-60 mph....should be no misfire while cruising.....now find an area where this is a slight upgrade, and lightly accelerate(don't want to accel hard and make it downshift......we want to stay in fourth and keep that TCC engaged)....if it starts to buck, that is usually a sign of secondary misfire, usually wires, plugs, coils, or some combination of all three....

07-16-2017, 11:40 PM
I did have to replace those elbows a few years back and I did use the metal Dorman ones. I will have to keep a closer eye on that coolant level but I sure do hope I don't have to do the intake job. I don't think I would be up for that at my age.

I do have three new coils coming, ( ordered before my post), so maybe, just maybe I'll get lucky. If not thanks to you nice people, I have other avenues to explore.

Blue Bowtie
07-17-2017, 07:55 AM
I did have to replace those elbows a few years back and I did use the metal Dorman ones. I will have to keep a closer eye on that coolant level but I sure do hope I don't have to do the intake job. I don't think I would be up for that at my age.

I do have three new coils coming, ( ordered before my post), so maybe, just maybe I'll get lucky. If not thanks to you nice people, I have other avenues to explore.

Good job on replacing the elbows with metal.

With only 86,000 on the clock I would expect the coils to be intact, but testing is the only way to verify that.

Without being negative, I can say that I did the same kind of thing for over six months. I kept monitoring my daughter's '01 and topping off coolant routinely. It finally reached the point where it was inevitable and I didn't want to wipe out the crank bearings with coolant in the oil. I took my time and milked the project into a two day job over a weekend, cleaning, sealing, and preparing everything - I didn't make flat rate.

Since then it hasn't lost a drop of coolant, the random EGR error codes have not reappeared, and P0420 converter efficiency code has gone away. I think I was lucky in that the coolant was going through the air side and out the exhaust and not getting into the oil pan, but affecting the converter operation.

If you're not cozy with all the reaching and bending, it may be worth paying a trusted mechanic to replace the gaskets and upper intake.

07-18-2017, 11:06 AM
Thanks Blue,

Just to make it a little more simple as to where this old foggy mind of mine can understand what do I need to do to stop the coolant leakage?
Step by step please. Tell me what I need to clean and what do I need to seal?
I will very grateful, because that sounds like that has been my problem all along.

I am tired of chasing rabbits.


Blue Bowtie
07-18-2017, 10:21 PM
The first problem is that the plastic upper plenum can suffer damage from hot EGR gasses being routed too closely to the internal mounting boos/bulkhead for the throttle body. The resultant warpage can allow coolant to seep into the intake with no external leakage. The aftermarket has recognized this and offers a replacement plastic upper manifold as a kit. The kit is very complete, including the manifold, thermostat seal, throttle body seal, all intermediate gasket/seal assemblies, new injector O-rings, new coolant elbow O-rings, two new properly sized EGR tubes, a new plastic vacuum "T" header, and several other bits and pieces I'm forgetting. The kit I used is a Dorman 615-180. If you search online the complete description is available. Mine set me back over $100 but the gasket set alone without the new plenum was over $60.

While the upper plenum is off it only makes sense to do what you will be doing in another year anyway, and pull the last ten bolts to replace the lower intake gaskets.

The plug wires need to be moved out of the way for the rear bank. Relieve fuel pressure and the remove the lines. Unplug the electrical connectors for the MAF, TPS, IAC, and CTS. Unplug the connectors from the injectors and move the harness out of the way. Remove the injector rail assembly with the injectors. Remove the throttle body (it can be left in place and removed later, but some of the hoses and wire harness will have to be held back while removing the plenum). Drain the coolant to a point below the lowest coolant elbow. Remove the coolant overflow reservoir. Remove the accessory belt, alternator, alternator mounting bracket, and brace. Remove the EVAP purge lines and electrical connectors. Then remove the ten or so bolts holding the plenum to the lower intake.

There are tutorial videos on YouTube showing the procedure in total, like this:


When reassembling, apply Permatex/Loctite 565 thread sealant to the lower intake bolt threads. The thread into the water jacket and NEED this sealant. Everything else can get antiseize compound to permit easier servicing next time someone goes in. Clean every surface on the heads and lower intake flange so that no gasket material or sealant residue remains. Follow the bolt tightening sequence and torque specifications for the lower intake and the plenum. Torques are surprisingly low, but the entire assembly will seal very well at the specified torques.

07-19-2017, 03:54 PM
WOW! At this stage in my life, would anyone like to buy a 2001 Buick Lesabre LTD with low mileage and several new parts replaced?
The car drives like a dream, but I can't do that kind of work anymore and I don't think it would be feasible to pay to have it done either.

Blue Bowtie
07-19-2017, 09:53 PM
A LeSabre is easily a 300,000 mile vehicle. In Alabama, it might be even longer. Here along the Wisconsin border the salt usually gets to them after about 20 years, or about three times as long as a Honda. I recently retired my '95 LeSabre with only 230-ish thousand on it. It ran great, and is still running (for someone else). After replacing the fuel tank, all the brake lines, fuel lines, and several other items that were rusted away, it was time for me to move on.

There is certainly some value in it, and for the right person a couple hundred in repair parts would make it an excellent purchase. Then again, for the right shop, it might not be that expensive to complete the repairs. It wouldn't hurt to ask around.

07-20-2017, 12:41 PM
I will ask.

Thanks again

Add your comment to this topic!