Head bolt failure and Coolant Loss on 2002-2006 Toyota 2.4L engines

Some owners would notice coolant loss and leaks on the back side of the 2.4L engines, resulting in $4000+ of repairs, because head bolts simply come loose by themselves. I suspect 2007+ engines will suffer the same fate down the road.

"3/6/2008

Coolant Loss on 2002-2006 Toyota 2.4L, 2AZFE engines

The following information concerns the loss of coolant on some

2002-2006 Toyota 2.4L, 2AZFE engines. The location of this condition has been noted at the rear of the engine where the cylinder head bolts to the cylinder block. It has been reported that stripped head bolt threads have been found on some of these engines during tear down. When the two rear head bolts lose their clamping ability they allow coolant to seep out at the rear of the cylinder head.

To repair this condition, engine builders report using thread repair tooling used for various GM engines. Specifically, Cadillac 4.6L engines use the same threaded head bolts (Figure 1). The head bolts for this Toyota engine may be reused if they are not damaged and meet the following length specification.

Using a vernier caliper, measure the length of the head bolts from the seat to the end.

Specified bolt length: 6.350? to 6.465? (161.3 mm to 164.2 mm). If the length is greater than the maximum, replace the bolt.

This information was provided by the Engine Builders Association (AERA)."

a_24l_2azfe_engines.aspx

According to what I can gather, the threading didn't go all the way to the top, and if the bolt starts to loosen at all it pulls out of the head when it gets to the position where there aren't any threads to hold it in.

How did that happen, it seems they were over torqued when being made?

This is something like I would think GM would have done, we has a 82? caddy with the 4.1, everytime we went to the dealer there were 5-6 motors on the floor for the week they replaced under warranty, even my dealer said the 4.1 was probably the worst motor gm ever made. Well maybe the Olds deisel conversion and the Vega were worse but the caddy would blow head gaskets starting at 40000 onward, several I saw on the highway in meltdown mode, black and white smoke out the exhaust. Toy has noted alot of issues with their "becoming #1 in sales but after this much time selling a defect like this it is disturbing.

Not to be too obvious, but head bolts aren't supposed to just loosen up in the first place. I'm guessing they skipped a step in assembly, or had materials problems.

Actually, I was thinking about this.

At 40,000 miles my hachiroku needed a pre-emptive HG replacement. Interesting because the 86.5-91 or 92 Supras had the same basic engine design, and they also needed to have the HGs replaced. Of course, this is a Yamaha engine...

Knowing then what I know now, I would have told them to pay for the HG on the '86', since it is now apparent it was a congenital problem. Hey, it was only $400 1988 dollars...

According to what I saw, the threads aren't robust enough. The fix appears to be Heli-coils. They sure as hell won't pull out!

When Toyota actually produces bad designs like that, you know they've finally replaced GM. ;-(

Poor engine design/metallurgy is one reason. Or overheating in that area of the engine another (that isn't anything new after Toyota engines sludging for all those years). Overheating makes aluminum alloy brittle and helps to make engine sludge.

Most head bolt threads don't go all the way to the top. Some are deep inside the block. There are premium ARP 1/2" diameter studs that people have used with good results in hot rod applications. In those high performance applications cylinder head were held by nuts to the head studs, not using head bolts.

Actually the stronger, solid insert called Time-sert should be used. Helicoil is great for many other applications, but for head bolts and spark plug holes I would Time-sert.

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I'd like to point out that we still don't know what model years are involved, despite the title of this thread.

Some 2004's do seem to be involved. But even with the

2004's we don't know what the failure rate is: 1 in a thousand? 1 in ten thousand? However, if it is 1 in 500, that would definitely not be good.

Also, we don't know for sure if the head bolt problem described by posters at CamryForums.com is related to a partial threading issue. The partial threading theory was brought up here; it was not brought up by the posters at CamryForums.com , where it was suggested that the loosened bolts could possibly be related to an excessive heat spot near the head bolts caused by use of a plastic intake manifold with a piece of foam rubber insulation.

It's possible that the partial threading found in * some * engines and the plastic intake manifold found in all engines are 2 totally different issues and may not be related to the same problem. They may be different problems. Or it's possible that both conditions must be present for the loosened head bolts failure to materialize. We just don't have enough info yet to know. Maybe the suits at Toyota know by now, but we are just speculating as to: (1) the model years involved and (2) the cause. I guess we also don't know how extensive the loosened bolts issue is: 1 in 1,000? 1 in 500? 1 in 200?

Or one in five thousand? John G Dole, you put down Toyota's coolant in the thread titled "Coolant and ATF fluid changes on Toyota" without mentioning that the coolant performed poorly only because the test used old-fashioned, cheap brass copper radiators with high-lead solder. Not revealing that fact about copper brass radiators made me think you were trying to do a hatchet job on Toyota ;-) [wink]

For other laymen like myself: copper brass radiators are a relic from the past with no relation to today's aluminum radiators :-)

John Dole, you're obviously a smart guy who knows a lot about cars, but you seem biased against Toyota :-)