Two problems related to engine head gasket failure have been reported for the 2004 Toyota 4Runner. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2004 Toyota 4Runner based on all problems reported for the 2004 4Runner.
This 2004 Toyota 4runner had 145000 miles on it when the check engine light came on, along with vsc and vsc trac lights. Engine ran rough/rumbled for few seconds after each start, then the rumbling would stop. At autozone they diagnosed a p0306 error code. Took it to the dealer who scanned code # 0306 #6 cylinder misfire. Further testing showed coolant seeping under headgasket, and dealer recommended replacing cylinder headgasket. Researching the issue, it looks like it's not an uncommon problem with this particular car at this mileage. What made me file this complaint is that each single one of the owners who posted online mentioned this particular diagnosis code of cylinder #6 mifire. I found itinteresting that everybody has the same exact problem, and not even once it was any other cylinder misfire but # 6. I had the dealer replace the headgasket, which took care of the problem, but since it's a recurring problem, I think Toyota should take of this issue.
Cylinder 6 misfires caused by oil leaking into cylinder 6 combustion chamber around spark plug. The issue is traced back to a head gasket failure on the 2004 4runner v6 engine. Cylinder 6 is the weak point where such failures occur especially at start up and when the engine is cold. There is clearly a design flaw in the 2004 v6 4runner's head gasket which requires many hours of labor to repair and should be covered by Toyota.