Currently, Toyota only offers the 4Runner with a V6. But the 4th-gen 2003-2009 Toyota 4Runner also offered a V8. The 4th-gen Toyota 4Runner has had some notable issues, rusting frames being particularly egregious, but the later 2007-2009 models are just as off-road-capable as new 4Runners. YouTube team Throttle House called the 4th-gen 4Runner’s V8 one of Toyota’s most reliable engines—but is it really?
Why the 2003-2009 Toyota 4Runner V8 can be problematic
The 4th-gen 4Runner’s 4.7-liter V8 wasn’t a model-exclusive engine. According to Canadian Gearhead, the engine was also used in the Tundra, Land Cruiser, and Sequoia. And while it does a fairly sterling reputation, its one fault, as some Expedition Portal forum users put it, is cracking its exhaust manifold.
The issue, according to Canadian Gearhead and CarSpec, is with the 4.7-liter V8’s catalytic converters. Catalytic converters need to be warmed up properly in order to lower emissions. So, as Toyota 4Runner owner forum users explain, to help the V8 comply with emissions standards during cold starts, Toyota incorporated a secondary converter into the exhaust manifold.
However, according to Tundra World and Expedition Portal forum users, this design forced engineers to make the metal there thin. Thus, as the metal heats and cools, it expands and shrinks, eventually cracking. This causes a leak and catalytic converter failure, causing, as many forum users and CarComplaints reports have cited, a horrible sulfur smell.
How often does this happen?
Although this doesn’t happen to every single Toyota 4Runner with a V8, Consumer Reports claimed this was a fairly common problem. Canadian Gearhead even said that there are “two different types of Toyota 4.7s: the ones that already have cracked manifolds, and the ones that are about to have cracked manifolds.” One owner reporting to CR even went so far as to call it a defect.
CarComplaints notes that the issue was enough of a problem for Toyota to issue an official technical service bulletin. The Toyota 4Runner’s V8 was enough of a hassle that the automaker stopped offering it in the 5th-gen SUV. And none of the other trucks or SUVs that had the 4.7-liter V8 offer it in the US today.
Can the Toyota 4Runner’s V8 problems be fixed?
Part of the Toyota TSBs appears to have been, according to Toyota 4Runner owner forum users, simply replacing the cracked manifolds with OEM ones. However, while the parts did fit, they had the same design flaw. Eventually, they’d crack again. This is also the most expensive solution, as many Toyota 4Runners with V8s are out of warranty.
It is possible for a skilled mechanic to simply weld the crack shut. However, it appears that this is, at best, a temporary fix. The weld fixes the crack, but it doesn’t fix the problem with the metal itself.
There is another solution, though. It is possible to fit aftermarket exhaust manifolds/headers to the 4.7-liter V8. Commonly-recommended brands are Doug Thorley, Pacesetter, and Dorman. Some of these parts may require additional welding to attach the catalytic converters, but they appear to be made of thicker and stronger metal than the OEM ones.
However, these parts are not 50-state emissions-legal. Especially if you live in California, this solution may not be feasible. That being said, it does appear that Dorman, at least, offers CARB-compliant aftermarket Toyota 4Runner V8 exhaust manifolds.
One additional caveat about aftermarket exhaust manifolds: according to Expedition Portal owner forum users, Toyota modified the manifold design for the 2005 and 2006 model years. Make sure, if you’re going to install an aftermarket unit, that it will fit your engine.
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