What I have learned from reading consistant questions/complaints why? May be related to the same culprit. Head gaskets weaken / blow for a reason; pressure! And its definably not compression, so what is it? Backpressure / Heat (combustion not coolant). If your one that has to deal with emission's or have a noticeable power loss, a clogged catalytic converter is generally the problem and when the average person buys a new one they buy the cheapest one they can find, which in turn is generally to small or poorly designed for the application, yes performance increases and you pass emissions but one never seems to get the feeling its all there. Thus ignoring the Cat. which if designed bad enough for what you've put it on will cause your engine to perform poorly and eventually blow another head gasket and all the while your mind is over the Cat. because you replaced it. Most exhaust systems start from the Cat. back and also ignore it and yes it sounds more powerful, but.
For those of us fortunate enough to still be able to remove the cat and get away from it and get exhaust moving again, we ignore the o2 sensor(s) which should be replaced with quality, not price, battery disconnected overnight and let the ECM relearn the new fuel conditions upon startup. So unless someone else has another spin on my thoughts, that's my story and I'm sticking to it.
I am currently working on an ACS that if I can get it figured out, would be the answer to actual performance. which is why I ask about failed sensors that do not throw codes.

 

I had two 22RE trucks that I bought new that ran over 450xxx miles with the stock converter.

Both had head gasket failures because my wife continued to drive the truck after seeing the temp get hot. I'm in AZ. Both happened at over 300xxx miles.

Both were because I never had the radiator serviced. I always flushed my system and changed coolant like I was supposed to, used distilled water or pre mix coolant and the radiator LOOKED clean.

I have since learned that the rad HAS to be serviced or replaced every few years or it will slowly plug up internally. Even though it looks clean.

I had one aftermarket converter fail because the media broke loose inside the shell. I've never had a converter plug up.

As far as the head gasket failing again.......hasn't happened to me after rebuild. I HAVE seen plenty of guys do a quickie head gasket fix that doesn't last.

If you don't deck the block and timing cover, get the head redone properly, clean the head bolt holes and use new head bolts and fix your cooling system, it WON'T last.

I agree as heat being the culprit. I never had the converter cause it though.

 

Head gasket failure is 99.5% not the result of a bad Cat Converter. Toyota uses good converters and as long as you don't let unburnt gas (running rich) go down the exhaust...they will be good for 500,000+ miles.

It's the cooling system that makes head gaskets fail. If you don't change your coolant every few years, it turns acidic. Also just poor maintenance in the cooling system also contributes to the problem. This causes a reaction in the motor because of different metals (aluminum and steel) and it's called electrolysis. It will eat away at the aluminum quicker than the steel, but even the steel will develop pits after awhile.

I take it you've never looked at a head after a gasket has blown. There are pits and deformities everywhere. This is because the coolant has never been changed and it ate away the head and the sealing surface. Once there is a pit under the head gasket...it fails.

Sorry, but I am not buying for failed cat converter theory....

 

I don't dig the cat theory either... my head gasket blew because of heat. I upgraded to the multi-layer metal gasket, had to get a new head, my valve passages where toast from a misguided "machine shop" previous owner did home "repairs" for a different type of engine thinking all engines are the same and it worked on his domestic engine so it'll totally work on an import...

as for the cat, I have a fairly new one, the rest of my exhaust system is toast. and my o2 sensor needs wire repair... but I've never heard of a cat going bad and causing the engine to blow a HG... unless it was fully clogged long enough to go through all the other gaskets and the significant oil loss caused a lot of metal to metal contact making the coolant an inadequate cooler and the engine over heats... but that's kinda extreme.

 

So if the Cat theory is correct(not)

A 22rec without a cat should under normal conditions never have a head gasket failure

Since most of these vehicles i work on have well over 150,000 miles.

They all get a new radiator after a real good cooling system flush.

Most often the same time as the timing chain and all new goodies.

 

I think he's implying more along the lines of the CAT getting plugged up, thus allowing a build up of heat and pressure on the head. But...

1. CAT's very seldom plug up.

2. IF the CAT was to fail, there would be noticeable difference in engine performance...thus allowing it to be fixed before a larger problem occurs.

An engine with no cat at all will not plug up...it's free flowing. I just doubt there will be enough back pressure to fully allow the valves to close...thus other issues.

 

If you put a new cat on your truck make sure its spayed and neutered lol

 

Unless your blowing huge chunks down the exhaust to plug it up most CATS fail from material contamination.

I have 2 CATs that are bad but have the same flow as if they were just bought.
The first is a OEM Toy CAT of my old 92 4R with 305K mi that has never had any problem other then the knock sensor pigtail going bad.
The CAT is just weak but fails smog.
The second one just doesn't work at all due to 2 blown HG, Antifreeze coats destroys the active properties of a CAT, The honeycomb is all there and has full flow, It just does not heat anymore.

 

There you go, pick'n on the big dog, while I'm trying to sleep on the porch. This was meant for info in the newbie's section. I probably shouldn't of rambled on like I did so let me attempt clarity for the pro's (big tires and stereos).
For starters a little research on converter's regardless of make, model or color. May give some insight as to what they do and how easily they can be damaged and 500k is nonsense. Yes electrolysis is a reality but for newbies there is more to it than distilled water and anti freeze (I've tasted the water in Phoenix and now understand why there babies are born naked). But electrical grounds to and from the engine, body and chassis can cause electrolysis (hence electr...) regardless of moisture content. the only way you can test a cat is to know the engine manufacture's backpressure specs and install a pressure gauge at the upstream o2 sensor and compare. Blowing through it like an duck call don't work or looking at it with your spotlight don't work. Some other statements are answered by the end of the statement. What my original post is meant to say is get the correct cat not the cheapest universal and if your going to spay and neuter, and want actual performance, replace your o2 sensor and disconnect the battery preferably overnight so it starts cold and relearns the fuel system and modifications. Or not!

 

jalopytech, we had no intentions of picking on you. but saying a bad cat causes bad HG is a little far fetched. theres lots of things that cause a cat to fail.

anyone logically knows that its better to get any part ment for your year/make/model than any universal fit.

especially for smog, its getting harder and harder to make it through smogs these days an old hose could fail you (working on getting my smog license currently)

also its not spay AND neuter.. it's spay OR neuter...

 

Good job clarifying...

 

The only other way that comes to mind as an experiment to prove my thoughts would be to go over to the neighbors house and pound a couple potato's in there tailpipe after they've received a new (quantity not quality) exhaust system on there 4 banger and see what blows up first.
I'll just lay here on the porch and watch.
OOPs I forgot! I ain't got no neighbors.

 

I've got to do both, my animals self multiply. How else could they end up with 14 toes and two heads? Similar too a twin overhead cam setup.

 

You do know that CAT's really don't "plug" up all that often and usually stop working due to oil or antifreeze contamination. So no need for your experiment.

However I want to hear more about how bad CAT's make head gaskets go bad...

 

Through the years I've cut open many plugged cat's and wondered why they were, the way they were, so I know they plug up. And not knowing there history other than complaints of no power, overly hot. Just crappy engine's because they ran bad, bad MPG, coolant system problems, head gasket failures, can't pass emissions, on-n-on.
I think that as a cat slowly becomes obstructed (not a windfall of debris from wherever). Its backpressure gradually and consistently generates enough heat back to the manifold(s) to heat the combustion chamber area(s) to cause whatever type problem you can diagnose as a top end failure, bottom end as far as that's concerned. The knock sensor will only retard ignition so far which is there original performance issue along with a need for constant valve adjustments which is also an indicator. Once upon a time, long, long ago big compression and low octane caused these similar problems.
Which brings me to yet another thought "Octane". The higher the octane the slower the combustion, slower burn, more power. So we are burning lower octane fuel these days and it burns faster-n-hotter. restrict the exhaust and whammo pre-ignition beyond the knock sensors capabilities.
Head gasket(s) usually the first to go, things come from together and usually there is all kinds of head work needed do to the wicked, twisting of heat, which in turn gets blamed on the head gasket.
My disclaimer: Some were I climbed out of the box.. And I only get off the porch when poked with a stick.

 

I know I only have experience on my old 85 and my current 93. On m 93 when I bought her the temp was running warm not hot but warmer than it should. I failed emissions in epic style for the title transfer. That was after Seafoam and good fuel with a lot of driving around to get it warm. I took it to my friend that has an exhaust shop and he listened to it and suspected my cat and muffler were toast. We talked and I went with a middle of the road cat and a flowmaster muffler sized at 2 1/4. Upon removing my old cat and muffler we discovered they were both plugged very very plugged. After installing my new un spayed or neutered cat my power went up temp went down and I passed emissions like a champ. I know this is a one time experience but a good exhaust lowered my temp issues. BUT FIRST and FOREMOST there is now substitute for proper service of you rig from brakes to motor to cooling and exhaust system. I do think we get a little lazy with our toys because they are so darn durable.

Now the big question is will she pass emissions with the egr unhooked. To be concluded by the end of the month.

 

As long as the EGR is sealing closed and operates correctly. You can plug the vacuum line(s) that controls the controls that control the EGR. with needle bearings bigger than the port they are connected to. And mark them so you know were they are the next time you need it. But beware of carbon buildup on the EGR tube before you take it to the sniff dogs the next time. Then just leave it to look like its working and an easy fix if you sell it.

 

darlin you need the egr to pass smog haha.

also cat's clog for various reasons, depending on the abuse you put your vehicles through it's good to service your exhaust system.

but like said before usually the back pressure is noticeable because of poor fuel/performance etc. or it doesn't pass smog.

I don't want a newbie reading this thinking that the head blew because of the cat, may have been a contributing problem, they cause heat which yota's are very sensitive to heat. but if they go out a buy a new cat AND that wasn't the problem (new cat on my truck and it blew the head) they'll be very upset with the loss of money.

 

I will let you know how it does. We do not have a visual inspection just sniff in Washington state. I doubt I will have to put my old stock exhaust manifold back on but I kept it just incase I needed it. I know there are many ways to temporally adjust the truck to burn cleaner. I will not go into details for the reason of someone who does not understand motors trying to do one of the ways and blowing up their truck.
And as I said in my previous post my was a one time deal. Best to stick to good plugs wires cap rotor and fuel. Then look at exhaust and intake. Aka just give it a good tune up with Toyota parts. And I seriously doubt there is a cat that lasts 400,000 +miles. Mine had to be replace just before 200k. And I have no idea what the PO'(s). Had put the truck through to "fix" it. So yes the cat could have begun to fail from fuel or antifreeze passing through. But mine was so plugged you couldn't see through it and it was a straight shot cat

 

10-4, I'll climb back in my box and stay on the porch.