Three problems related to manifold/header/muffler/tail pipe have been reported for the 2003 Toyota Highlander. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2003 Toyota Highlander based on all problems reported for the 2003 Highlander.
Head gasket bolts stripped out causing coolant to leak and loss of cylinder compression. This occurred on a Toyota 2. 4 liter engine. This is a common failure mode on these engines due to a design defect. The thread fatigues at the intake side of the engine because the manifold is plastic and there is a rubber insulator between the manifold and block which traps the heat in that part of the block and fatigues the aluminium threads on the head bolts. This happens on many models from 2001-2006 that utilize the Toyota 2. 4 liter aluminum engine. This is a $2,500-$5,000 repair. Toyota has issued a service bulletin on this. I believe they should have some responsibility in fixing this design problem. Engines shouldn't fail at 100,000 miles without cause such as overloading or abuse. I don't have a tow package and have garaged this vehicle. There was no cause and effect. This failure I've come to learn is common for this engine.
Leak at rear of engine, under intake manifold. Head gasket, or warped head. Cylinder head bolt threads damaged . Toyota said some vehicles equipped with the 2az-fe engine may exhibit damaged cylinder head bolts.
The incident occurred on a family road trip from chicago, IL to hamilton, on, canada. After driving about 7 hours into the 8. 5 hour trip, I noticed the check engine light appear and the temperature gauge rise to the very top. I immediately pulled over and assumed that there was not enough coolant to keep the engine cool, as it was a hot day. After several minutes, I restarted the car and noticed the temperature gauge had returned to its normal position. I re-entered the highway and was only able to drive for about 10 minutes before I noticed the temperature gauge begin to rise once again. I exited the highway and found a canadian tire store in london, on, canada where a mechanic looked at the vehicle and concluded that there was some sort of leak in the engine. I was told that it could be one of two very uncommon problems that would both cost a great amount of money to fix and would most likely extend my family's stay in canada. We were told that we could stay in london and have a mechanic begin working on the vehicle the next day or continue on to hamilton by stopping every few miles to refill the coolant, as we were only about an hour away. We decided to continue on to hamilton and stopped around 5 times to refill the coolant level. Upon reaching hamilton, on, canada we found a local mechanic who took a closer look at the vehicle and its engine. We took the vehicle to him on Friday, July 6, 2012 and he told us that it looked like an intake manifold gasket leak. On Saturday, July 7, 2012 the mechanic informed us that the leak was in fact coming from one of the 4 cylinder heads as the bolts on the engine were stripped. Our only option was to completely replace the engine. The mechanic was able to find a matching engine nearby and completed the replacement by Tuesday, July 10, 2012. We returned home to chicago the very same day without any problems along the way.