In response to your call for more reader-submitted queries, I realized I’ve had one right in front of me and have never thought to ask my fellow TTAC commenters. I have a 2006 Toyota 4runner with the amazing 4.7L 2UZFE V8 engine, currently with 90,000 miles. I purchased the truck with 55,000 miles. However, this motor seems to have a fairly common weakness.
The thin-wall exhaust manifolds are prone to cracking at the flange where it bolts up to the head. This engine was used in a variety of Toyota
trucks, but in the 4runner, being the smallest truck of that group, this presents a particular problem. There is absolutely zero clearance between the frame and the manifold. On the bigger trucks, there are aftermarket headers available, and most will replace with those parts when/if they experience this issue.
Some owners have had success in having the dealer replace the manifolds under a TSB related to an issue with smelly exhaust, with the catalytic converters being the source of the smell. On some years of this motor, the first set of cats is the same piece as the exhaust manifold itself and gets replaced as a whole part. And there is a factory emissions warranty running 7 years/100,000 miles. So that’s usually enough to get the work done by the dealer without much complaint, as long as the symptoms can be replicated.
The noise on my truck has been there since I rolled off the lot with it. I’m not sure how much attention I paid to it at first, but it was there. The noise is far more prevalent when the engine and ambient temps are warm, and when the engine is under load. so fast/slow acceleration from start in the lower gears tends to consistently produce it. Which, truthfully, makes somewhat less sense as any crack would close as the metal expands with heat. But as with most car owners with an internet connection, I informed myself about my vehicle. And yes, I have wondered if I’m just reading about something on the internet and then self-diagnosing. But I’ve been racking up the miles, and i did purchase an extended Toyotacare warranty, so I feel like I should do my best to keep the truck properly maintained while the work is covered.
So, after living with the truck for a year and recognizing that it wasn’t just my internet-colored imagination, I took the truck in. They did actually recognize the exhaust smell, but only replaced ONE of the 4 catalytic converters. and it was not one of the ‘pre-cats’ directly off the manifolds. As for my noise complaint, they determined that they were hearing something, and that it was caused by the exhaust system, which had been installed at some point by a previous owner. it consisted of some cheap piping and a Flowmaster muffler (which, let me tell you, sounded AWESOME with the V8, heh), and looked to have been done on the cheap by a muffler shop. They found some leaking at the seams, and would not attempt to further diagnose the noise issue without a full OEM replacement. a $1,000 assembly of parts not covered because it is considered a ‘wear item’. they sort of relented and agreed to install an aftermarket bolt-in part at a quarter of the cost. after all that was done, they determined the noise was ‘normal’ and sent me on my way. and it still sounds exactly the same. that was at about 80,000 miles, about 6 months ago (haha I drive a lot).
With my driving habits, and edging closer to the warranty expiration, I took it back in yesterday. Though it was a cold day, they were able to hear the noise, again. and again they stated that it was ‘normal for this engine’. The reason I am leaning towards the manifold and not a ‘tappet’, or ‘valvetrain’ noise as the service manager claimed, is just the nature of the sound. were it a top-end noise, the amplitude would be higher. same with a downstream exhaust leak. what i hear is a ‘tick’ with what sounds like every pulse from ONE cylinder. meaning at around 1500rpm under load, it will repeat itself approximately once per half-second (i’m guessing, but that seems close). and i would describe valvetrain noise as more of a constant clatter anyways, prevalent under any operating condition.
So what should I do? Take it to another dealer? Take it to an independent guy for at least a casual diagnosis? Is there another cause for this issue? I’d love to say this is just a normal noise, but I know it isn’t. Having done my research, the only way to actually SEE a crack in the common location is removal of the manifold. not a job I am equipped to handle. I truthfully don’t mind the noise so much, but I love this truck and because it’s a Toyota
truck, I plan to put at the very least another 100,000 miles on it. and so I don’t want the problem to further degrade and fail over time, given the expense and difficulty of replacing this particular part.
I love how you “love this truck and because its a Toyota I plan to put at the very least another 100,000 miles on it.“ Not because I’m a hater, because I plan on doing the same thing with my orphan Lincoln-Mercury vehicles. We all have our quirks, some of us are just crazier than others: and both of us should just give up and find something else to drive.
Or not. Because odds are the replacement manifold is an improved design, if this is any indication.
Having personally dealt with bad exhaust manifold gaskets, leaky headers and the like, it does sound like your diagnosis is on the money. But who cares?
Replace it when it gets worse. I’d recommend cutting off the replacement mufflers you put on after the dealership demanded it, replacing with some mild flowbastards (get it?) or Magnaflows, or whatever floats your boat. I like the mufflers from the 2005-present Mustang GT: you can get them for free at some exhaust shops when your average stangbanger demands a more obnoxious sound…but they are actually the best balance of rumble and sophistication on the market!
Those of us who like to wrench around on older vehicles simply gotta love free shit. Especially when it masks the impending failure of your cracked manifold. Let the problem get worse, obviously worse, then let an independent mechanic fix it.
Bonus! A Piston Slap Nugget of Wisdom:
As you modify a vehicle after the warranty expires, avoid the dealership’s service department. It’s in both parties’ best interest to keep it like that: less BS for the owner and less risk of giving bad service (at a lower profit compared to other tasks) with the repercussions that come with.
Take it from the guy farting around with a restomod Mercury Cougar for the past 13 years. Time to cut the cord.
EDIT: I forgot that there was still an extended warranty on the vehicle, that changes everything. Going to another dealership and asking them to scope it out (literally) for a crack is a good idea.
Send your queries to sajeev@thetruthaboutcars.