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86-95 Trucks & 4Runners 2nd/3rd gen pickups, and 1st/2nd gen 4Runners with IFS

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Old 02-22-2007, 07:04 PM   #1
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Clogged cat cause of blown headgaskets?

I was talking to a guy named John at Oregon Engine Rebuilders. He said that it was known among engine rebuilders that clogged catalytic converters are the primary cause of headgasket failure among the 3vze.

He remanufactures 3vze's and said that only 1 has come back with a headgasket failure as he requires everyone to conduct a backpressure test at a muffler shop (usually free) prior to installing one of his remanufactured 3vze's. The muffler shop makes a hole before the catalytic converter, installs a pressure sensor and then starts the car. 4 psi is considered high and he has seen cars with pressures as high as 10 or more. He says this puts a high stress on the headgasket which is then likely to fail. Most muffler shops will do it for free as they then have a chance to sell you a newly installed catalytic converter.

The cause of clogged cat is usually oil in the exhaust. I think most 3vze's leak a little oil. Mine typically burns/leaks a quart every 3000 miles. I think a lot of this is due to ring leak-by which could, in turn, clog up your cat resulting in high backpressure which then causes a HG failure.

Oregon engine rebuilders link is here:
http://cgi.ebay.com/ebaymotors/Toyot...82717708QQrdZ1
The discussion came up because I asked how he could warranty the 3vze for life with the HG problem. This was his answer and I would think he must be correct as he has a lot of money now riding on all the 3vze's that he has sold.

I've done a lot of research on this and have never heard of this before... Can anyone else confirm or deny this?
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Old 02-22-2007, 07:33 PM   #2
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wow?? i would just think it would stall the motor due to not being able to complete cycles
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Old 02-23-2007, 12:15 AM   #3
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Sounds a lot like snake oil. Probably the biggest difference you could make in guaranteeing a HG job for life is to mill the head. I'd venture a guess that almost everyone who replaces a HG does NOT check the head for level, resulting in (eventually) another blown HG...

my $.02
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Old 02-23-2007, 05:51 AM   #4
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Clogged cat cause of blown headgaskets?

I agree with TNrabbit it could be just talk.
I would think a somewhat plugged Cat Conv would raise more heck with the exhaust valves then causing premature headgasket failure.
I believe there are alot of 3VZE's that don't get the proper attention to the head surface when performing a headgasket. Or other engines for that matter.
I'm not yank'in my own chain but I have done quite a bit of work on foreign engines especially headgaskets. Generally they tend to allow 3 to 6 thousands of warpage across the head. Back in the 80's when I was working on hondas at a dealer,... if I found even .002 warp on a head, I sent it out. It's just not worth doing twice. And for saving what $38.00 for a resurface? This cut back on repeats, redo's, rework, or comebacks on headgaskets almost altogether.
It makes you wonder how many people actually do check head warpage "correctly" with an accurate straight edge like a Bluepoint or Starrett.

Their just not that expensive either, I think I gave $60.00 for 18" one which covers most head sizes back in the early 80's.
http://buy1.snapon.com/catalog/item....re&dir=catalog
I have seen so called mechanics trying to use a carpenders square, and even a long 3/8" extention!
Makes me shake my head even now.
I know if i'm that far into any headgasket job it's worth taking the time and doing it right.
They aren't that fun to do, I don't care what engine it is.
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Old 02-23-2007, 07:03 AM   #5
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That's an interesting theory, I don't know if there's any physics to back it up or not. Certainly running with a clogged cat isn't good for anything. I guess it could make a good excuse to get out of the warranty claim
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Old 02-24-2007, 08:07 PM   #6
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The other thing he did mention is that they don't use Felpro headgaskets. They go with rock something or other.
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Old 02-25-2007, 02:23 PM   #7
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Quote:
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The other thing he did mention is that they don't use Felpro headgaskets. They go with rock something or other.
Well, if these are good gaskets, if you get your parts from EngineBuilder, you'll be in good hands. That's what my rebuild kit came with.
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Old 02-25-2007, 05:08 PM   #8
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I also feel that it is improper steps taken when doing the head gasket. We all know that most 3vze have HG problems. So when you do it do it right have the machine shop look at it. The head is aluminum and warps very easy compared to iron. I don't think that a blown HG has anything to do with a clogged cat. If that were true you would see it on alot more motors. But i do have to say the cat is a part of the vehicle that most people forget about until it rots off. They can become clogged and cause poor performance.
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Old 02-25-2007, 05:14 PM   #9
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I have heard, and dont know for sure but once the head is torqued you should retorque it after about 200-500 miles to make sure its not loose.
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Old 02-26-2007, 02:23 PM   #10
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I have heard, and dont know for sure but once the head is torqued you should retorque it after about 200-500 miles to make sure its not loose.
That is a step used on some engines. I'm not sure if Toyota uses this method without looking. Honestly, it's pointless. I might get flamed for that comment but I'll explain. Torque To Yield (TTY) bolts are exactly what the name implys. How they work is that you torque them to their yield. Then you tighten an additional amount, i.e. 90 degrees. This additional tightening stretches the bolt past it's yeild point. With that explained, the bolts are already tightened past their maximum strength.

I'm not saying that it isn't recommended by some manufacturers, but it's just stupid when using modern head gaskets.
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Old 02-26-2007, 03:31 PM   #11
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If you re-torque torque-to-yield bolts, you'll break them off inside the block.
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Old 02-26-2007, 03:31 PM
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