Toyota 2AZ-FE Stripped Block Threads (AKA Stripped Headbolts)

3 block threads known to fail

The 02-04 Toyota 2AZ-FE I4 short blocks have a vulnerability in the design where under the right conditions three block threads can suddenly strip causing catastrophic loss of coolant, overheat and breakdown. Caught early, the failure is recoverable and repair is relatively inexpensive. Ignored or driven in this condition the engine will likely need replacement.

Wrongly described and diagnosed all over the internet... The steel head bolts don't strip, the threads in the aluminum short block the steel head bolts screw into strip (see red box in picture). The three threads that fail are located at the thinnest part of the block, thin to accommodate the curvature of plastic intake and a layer of insulating foam. The foam insulates the plastic intake from the heat of the block, but it also traps heat, creating a hotspot. Unlike the other threads there really isn't much aluminum to insulate/dissipate heat because of the coolant channels. So in these years maintaining the coolant is critical.

Dual Layer

HG failure

The Head Gasket on the 2AZ-FE is dual layer steel, thicker at the edges to "give" a little during expansion and contraction.  Toyota changed the HG design in 07, adding more metal to the HG (in the area the finger above is pointing to). Exactly where the HG failed in that pic. More metal means less chance of a failed HG, less pressure on the threads during expansion and contraction.

There is no definitive trigger, but based on above one can assume that the trigger is low/poorly maintained coolant or a blown HG which leads to an overheat. depending on how bad the engine was allowed to overheat, the aluminum gets very hot, expands, the block threads cant hold and strip

Diagnosis:
If you've caught it early, haven't overheated, its possible that you've only suffered a bad HG and the threads themselves are fine. A gurgling sound from the dashboard, gradual loss of coolant, running hot, and fouled oil are signs of a failed HG. The symptoms of stripped block threads are more dramatic. A rapid, sudden coolant loss and overheat, strong smell of coolant, wet intake manifold insulating foam. The key is inspecting the foam. There are several sites where you can add your VIN to verify short block part number Your looking for PN 410-09050 which is the problem block. Used on some models until 06.

Repair:
Toyota states TSB EG015-07 for updated short block. Thats extremely costly, basically replacing and rebuilding the engine for thousands of dollars. What needs to be done is drill and tap the holes and install a threaded steel sleeve for the head bolts to screw in to. Just like new, even stronger! Its a forever fix. There are different types, I would stay away from the helicoils only go with a known as a timesert or even better, the Huhn kit specifically designed for the 2AZ-FE. This kit can be purchased on eBay. NS300L 2AZ-FE HEAD BOLT THREAD REPAIR KIT Also recommend purchasing the modified HG for 07+ if you can get it.

Prevention:
Drain and filling the coolant every 40k. 4qt drain gets 90% of capacity (6.5qts). Don't mix. Use the factory Toyota Long Life Coolant (Red). Its concentrated, so once its diluted 50/50 with distilled water, its relatively inexpensive. DO NOT head down to Walmart for some cheap-ass coolant, its a big mistake! Zerex Asian Formula is another option. Replacing the thermostat and pressure cap every at 80k is a good idea. maintain the same temp thermostat, lowering thermostat temperature is undesirable in a modern Toyota engine. Many engine operating characteristics including VVT-i are set via engine temps. And if it starts to overheat don't keep driving. Don't ignore it, or it can cost you big. You can't blame Toyota for that.

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Cleaning your VVT with Kreen

Variable Valve Timing (VVT) has become a staple of most modern engine designs. VVT operation depends on hydraulic oil pressure from a long winding path of tiny oil passages known as "vanes". Oil for the VVT system is filtered through a tiny screen, then passed to the Oil Control Valve (OCV). The OCV allows oil to pass on to the to the VVT controller/actuator. The oil pressure turns the controller which advances or retards the intake and exhaust cams. The ECU decides how much to open or close the OCV based on engine revolutions, throttle position, engine coolant temperature and intake air volume. Oil pressure is regulated, which turns the actuator to different positions.

Vulnerable deposits, a dirty VVT system can impact engine performance, gas mileage and give you annoying ticks. This is especially noticeable at startup. Changing the oil on time and the use of premium synthetic oils go a long way to keeping the system clean. But there are times where manual intervention is necessary. Before you start tearing the VVT system apart, try an oil additive called Kreen from Kano Labs. Its an industrial cleaner not sold retail, as it can be hazardous if not handled properly. Kreen is very effective at reducing hardened carbon deposits and varnish. Not a fast flush, Kreen can be added to the oil and driven while the cleaning process takes place.

The way I use Kreen is adding 3oz per qt of oil for 1,000 miles, change the oil. So for example if you change your oil every 5,000 miles you would add Kreen at 4,000. I also suggest use outside or in a well ventilated area, and transfer Kreen from its aluminum container to a glass bottle.

Kreen can also be used as a piston soak and in the gas as a fuel system cleaner. Using this product every 30,000 miles will give you a trouble free quiet VVT system. 

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Thick oil and the VVT-i startup tick

If you own a late model Toyota you may have noticed a 1-2 second ticking noise at startup. While there could be other mechanical problems, most of the time the culprit is a stuck/locked VVT-i controller. What can I do to resolve this? In some cases its an actual controller failure. But for most its oil selection.

Its called Variable Valve Timing because its always running. From the second the engine starts, VVT is attempting to adjust to conditions. When it can't, gets stuck, it will tick for 1-2 seconds. Unlike Honda's VTEC that uses two sets of cam shaft profiles – one for low and mid range rpm and another for high rpm operation, VVT camshaft timing is varied using oil pressure according to engine revolutions, throttle position, engine coolant temperature and intake air volume.

VVT operation depends on hydraulic oil pressure that arrives through a long winding path of tiny oil passages. So tiny they are known as "vanes". Its critical the system stays clean. Its critical the system maintains proper oil flow and pressure as fast as possible to prevent that annoying startup tick.

Proper lubrication comes from a combination of oil pressure, flow, and film strength between moving parts. Oil pressure by itself is no indication of proper engine lubrication. Oil pressure is managed by the oil pump and relief valve. Thick oil will have higher pressure because there is more resistance to flow. Too high and it will flow out the oil pump relief valve back to the sump, lubricating nothing including the VVT system.

As stated above, thick oil will have higher pressure because there is more resistance to flow. Add that to the tiny "vanes" of the VVT system and you have a oil flow lag as compared to the rest of the engine. By as much as 1-2 seconds. No coincidence that's the duration of the noise.

Modern thin oils have better flow, better viscosity modifiers to manage film strength. That means better lubrication and cooling, keeping pressure within spec. Tthin as possible is a good thing, especially for the VVT-i system.. "Thin as possible" meaning some older engines have mechanical issues like wear/higher tolerances, valve seals, rings, etc. causing oil consumption that may prevent its use.

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