©DenLorsTools.com Summary: Toyota engines are known for their great gas mileage, being very dependable and lasting for well over 100,000 miles. One thing Toyota engines don’t handle very well is being overheated. Toyotas are susceptible to the common causes and failures that affect other vehicles as well as new common failure. In this article we’ll do a quick rundown of common causes of overheating in any type of car. Also an additional failure that is causing blown head gaskets even on cars that have not been overheated.

In my experience, Toyota drivers are some of the most brand loyal car owners there are, second only to Honda. My neighbor’s daughter just recently had a series of overheats in her little Toyota Corolla. First was the radiator, then a small coolant hose and then the blown head gasket came near the Skyway bridge! Luckily she got off the bridge and was able to call for help. Unfortunately, the engine had a badly blown head gasket. When trying to fill the the cooling system, water came gushing quickly into the exhaust manifold. With around 200,000 miles on the engine they decided to replace the motor with a good used one rather than trying to repair it. Probably cheaper in the long run in this case.

Common Causes of an Engine Overheating

1. Water Pump – The water pump can leak on any car, usually from the bottom weep hole. There are typically two weep holes in a water pump. The top one acts as a vent that allows any moisture to evaporate rather than trapping it and causing bearing corrosion and then failure. It is normal for a very small amount of coolant to seep past the shaft seal and out the bottom weep hole. This lubricates the seal prolonging its life. If the seepage turns into a drip the water pump needs to be replaced. I’ve actually seen a water pump that someone had placed a small wooden dowel inside to stop the leak. Another customer once said “Those darn water pump manufacturers put those holes in there on purpose.” Thinking that they were designed to fail, which is simply not the case. If the hole is plugged, the bearing will soon fail due to water causing it to rust. Water pumps can corrode from within for other reasons as well. The impeller can rust to a point where it can no longer pump coolant. This can be caused by poor maintenance and/or electrolysis eating away at the metal.

2. Coolant Leak – Obviously if a leak occurs the cooling system will not work as designed. The heat normally transfers from the engine to the coolant which is then pumped and cooled off in the radiator. Then the cycle repeats itself. If the coolant is not full, there will not be enough cooling capacity to keep the engine from overheating. Leaks can occur anywhere coolant circulates. The radiator, water pump, hoses, heater core, engine block, head or multiple gaskets in between. Pressure testing the entire cooling system is the best place to start if a leak is not obvious but is suspected. Coolant or radiator caps shouldn’t be forgotten, since they are usually off when pressurizing the system. And block testing for carbon in the cooling system is a good way to check for internal leaks; Which may indicate a blown head gasket, or extreme cases a cracked head or block.

3. Thermostat – A thermostat that sticks in the closed position can cause an extremely fast overheat condition. This stops coolant from circulating so it’s just as bad as having no coolant in the system at all. The spring is designed to open the thermostat when it reaches a certain temperature. When I worked at CarMax, we would routinely have to show extended warranty inspectors that a thermostat had failed by heating them up in a large coffee cup using a heating element. With a thermometer in the cup, the thermostat can be tested to see if it will open at the correct temperature. The spring’s temperament can be altered if a car is severely overheated. That’s why it’s often recommended to replace the thermostat if an overheat of any kind occurs in addition to whatever else had failed.

4. Radiator – Radiators can not only just leak, but they can also get plugged up (or obstructed). In the 80’s we used to remove the radiators and have them “rodded”. Sort of angioplasty for the tubes that make up the radiator. This cleared the passages to restore circulation and cooling capacity. Nowadays, the supply of low cost radiators made in China has put most radiator shops out of business.

Other Cause of Head Gasket Failure

As mentioned briefly before, head gaskets can fail usually when another component has first went bad. Like a water pump or some other cause of overheat has occurred. And then the driver ignores the signs of overheat and continues to drive the vehicle… sometimes repeatedly until the car comes to a stop and cannot be driven any further. Now there’s a new twist to head gasket failure. With aluminum blocks that are prevalent in most cars today, there’s a new problem car owners are facing. And this problem is causing head gasket failure before the car overheats. This is opposite of what commonly has happened in the past. Now, a head gasket can fail without the car overheating. Sure, if it is driven after the head gasket fails, then it can overheat and potentially cause other issues. This fairly new cause is the failure of threads for the head bolts in the aluminum engine block. The threads can just fail on many Toyotas and some other models too, like Honda and the Cadillac Northstar. The problem can occur due to the extreme torque of the steel head bolts into the much softer aluminum blocks of these cars. Aluminum blocks are used to decrease overall vehicle weight, but at the sacrifice of strength of the threads for the head bolts. Some repair shops will suggest a new block or replacing the entire engine with a rebuilt or good used one. One of the best solutions and one that is recommended by Toyota and other car manufacturers like Cadillac is to use a Time Sert Kit and installing steel threaded inserts into the existing block. This is not to be confused with Helicoils. Heli Coils are a certain brand of thread repair, but is not nearly as strong as the solid threaded bushing type inserts produced by the Time Fastener Company.

Toyota Vehicles with M11x1.5mm Head Bolts

• Scion tC with 2.4 L 2362 CC L4 DOHC 16 Valve 2005 – 2005
• Scion tC 2006 – 2007
• Toyota Camry 2.4 L 2362 CC L4 DOHC 16 Valve 2002, 2003, 2004, 2005 – 2006
• Toyota Highlander 2.4 L 2362 CC L4 DOHC 16 Valve 2001 – 2007
• Toyota Rav4 2.0 L 1998 CC L4 1AZFE DOHC 2001 – 2003
• Toyota Rav4 2.4 L 2362 CC L4 2AZFE 2004 – 2005
• Toyota Rav4 2.4 L 2362 CC L4 DOHC 16 Valve 2005
• Toyota Solara 2.4 L 2362 CC L4 DOHC 16 Valve 2002 – 2007

Related Articles & Products

Time Sert Kits

Time Sert Articles

TIME-SERT 2200 at Wise Auto Tools (our sister site). More information on this Head Bolt thread repair kit on this product listing.