Any connection between overheat and cats?

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Sep 6, 2006
Cincinnati, OH
I just took a 500mi trip and at the end of my trip I found my vehicle starting to overheat (NO temp mod) maybe 3/4 of the way up the scale. AC on (but cutting off), maybe about 80 degree weather, a little hilly.

I've noticed that the passenger floor (seems more like just before the cats) has started to get hot. Could my potentially clogged cats contribute to my overheating?

Also I changed the fluid not more than 20k ago, and there is a seemingly unreasonable amt of sediment floating around in the radiator. Where is this coming from?

Right now I'm going to give the radiator a quick flush, I'm at a friends and I didn't bring my toolbox that I usually keep in my car for situations like this, go figure. I'm hoping to make it home without doing any damage. Any other quick things I should do?
Yes, plugged cats could cause your engine to overheat. Be sure to check all your fluids and other "obvious" things though. A trip to an exhaust shop could tell you pretty quickly if you have plugged cats.

The question is why did the cats plug, if indeed they are?

What oil did you change? Engine oil or fan clutch oil? Need more info. How many miles, service history etc. Have you changed the o2 sensors? Have you done an overflow bubble test?

What fluid did you use back when you changed it 20k ago? Did you change fluid color (red to Green)? There is usually crap floating around in the cooling system and may be "normal" wear. I am not talking about chunks or sludge. I'm talking about a film of black stuff which will float on the top of the fluid which you can see when the fluid is drained into a 5 gallon bucket. Are you pulling the block plug on the driver's side when you flush it? Taking the thermostat out and flushing the block will also get a bunch of fluid out that is on the passenger side of the engine.

Must be summer time .....
Sorry about the ambiguity. I changed the coolant, did a full flush about 20k ago and changed the fluid from red to green. I have not changed the o2 sensors and have 185k on it.

If it helps at the car was loaded with 7 people, luggage, aftermarket bumper, AC when it worked, and I got 15.26 miles per gallon over the coarse of the whole trip. I don't know if good gas mileage means that my cats are not clogged.
Are you running the blue hub fan clutch or the original?

Higher temps will make the floor board feel warmer but doesn't meen the cats are clogged.

Original. I tried to spin the fan while the engine was cold to make sure the clutch didn't spin too freely. Spinning as hard as I can the fan rotates maybe once.
Do you mean that while you were traveling that the A/C would get hot and cold over many cycles? At the same time you were seeing the temp gauge move? If this is the case, I would bet your radiator is mucked up from the change in anti-freeze along with the many miles on it. Fan clutch is most likely weak also. Clutch/ Fan should roar for 15 or more seconds at start up in the morning. Flushing will not fix a seriously mucked up radiator.
When I had the AC on, it would be cold and then the engine would start to overheat. When the temp gauge went to 3/4 the AC would shut off and the engine would go back to normal. Also what do you mean "mucked up from the change?"
Original. I tried to spin the fan while the engine was cold to make sure the clutch didn't spin too freely. Spinning as hard as I can the fan rotates maybe once.

This needs to be done when the engine is hot.

I would be willing to bet that the fluid in the clutch needs replacing or just drop in a new blue clutch. The other suspects could be the thermostat, dirty fins on the radiator or clogged up radiator. Clean the fins with simple green and see if that helps, easy and cheap stuff first. Then try the clutch. Then t-stat. My thermostat has 4 years and about 50k miles on it and it is not working properly. With the RT temp guage mod, I have been watching the engine temps creep up over time, not badly but warmer than with a new tstat.

You do realize that you have a somewhat severe overheating problem and should be taken care of before Houston summer goes into full swing.

Hope this helps,


PS Take a look at the new club in town T4x4T - Toyota 4x4 of Texas
From other posts on this web site, when a person mixes toyota red and green antifreeze, nasty clobs of crap form because the colors are of different base chemicals. Many people argue that the green anti-freeze bottle may say it is compatable with other types, but there are many threads that say this simply is not true. I figure that the truck came with Toyota red from the factory, so I base lined my cooling system with Toyota red when I bought my cruiser used. Search antifreeze.

My truck did the same thing that yours did on my first trip. A/C cut on and off (like it is suppose to do when it begans to overheat) and the temp gauge would be moving in the upper area. I replaced the radiator, fan clutch and did the temp gauge mod. The antifreeze that I replaced was not green, but it was DARK - red. For 35000 miles I have had zero cooling problems. The PO did not maintain it like he should have.

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