Disappearing Coolant + White Smoke = Head Gasket Replacement
 

Like many of you, I've also read the multitude of threads regarding "disappearing coolant" and "white smoke" coming from the tail pipe. In my case, I only noticed this after 20,000km and specifically only after high rpm performance sessions, such as after autocross events. What was causing the problem?

I took it to my dealership and they agreed to look into the issue more carefully.

Our initial hypothesis was that during sustained high RPMs the high pressure and heat were creating a "pinhole" type of leak in the head gasket allowing coolant to flow into the exhaust and vice-versa.

Step one was to perform both compression and leak-down tests while the engine was hot. These turned out to be normal. The dealership agreed this was possibly due to the difficulty in performing the tests while the engine was at peak temperature -- the engine was cooling down enough to "reseal" the leak.

Step two was to perform a hydrocarbon coolant test to determine if there was any exhaust in the coolant. It turned out there were hydrocarbons present in the coolant.

Step three was to remove the heads and inspect the gaskets. After removing the engine and the heads, no physical damage to the gaskets was found. However, we did see a very clear white stain pattern on the inside face of both gaskets indicating that coolant had hardened and accumulated in these areas. (See photo below.)

http://i61.tinypic.com/svnh9g.jpg

We looked closely at the open-deck design, and specifically at the gap in between the two cylinders, at their tops. (See photo below.) We suspected that during sustained high RPMs, while coolant flowed normally across this channel to the other side of the block, there was also sufficient pressure to force coolant to flow under the gasket and into the combustion chamber.

http://i58.tinypic.com/2dilrbb.jpg

Step 4 was to send out the heads to a machine shop for testing. The heads pressure tested fine and the decks were also found to be true.

Step 5 The dealership is replacing both head gaskets with OEM gaskets while I wait and continue to enjoy my loaner Yaris.

Final conclusions

Though I never noticed a decrease in performance, I'm glad to have diagnosed the issue early so that warranty service could be done. If more of us encounter the same issue, perhaps Toyota/Subaru will issue a TSB.

Either the stock gasket was not manufactured with enough tolerance or who knows, maybe the cylinder head bolts were not torqued down enough at the factory?

Since I'm already at 45,000km I may just be able to squeeze in one more head gasket replacement under warranty.

What is the point of replacing the HG if the design of it is already defective. Lets start writing letter to Subaru of America/Canada so maybe they will investigate the issue further.

With one instance (that ive seen) of this being documented, theres no way to tell if this is just an isolated case or not. More than likely, it is, as many cars have surpassed 20k km and continued on clicking on just fine. If i see a running list on this board ill become concerned.

At the same time, many have noticed some loss of coolant. Myself included, though it seemed to go away after I refilled once.

OP, I wonder if you had some loose bolts. Also, GrimmSpeed has some extra trick gaskets you might be interested in.

I asked my dealership if they would install an after market gasket. They said they would but that they couldn't honour the warranty for any future issues with the heads or gaskets.

Those white stains do not show up on the area where the cylinder walls seal against the gasget. Doesn't look like it was leaking into the cylinders...

I understand how the stain pattern could be interpreted that way. The results of Step 2 above and white smoke from the tail pipe when hot indicated otherwise.

I don't know enough about fluid dynamics or material science to make a sound theory. Based on the symptoms witnessed, it appears that leakage into and out of the cylinders only occurred during very specific time periods, namely under very high pressure conditions. I'm guessing the gasket was continually under the most strain in the stained region, thus accumulating residue, and then high pressure would cause the gasket to cross its strength threshold and then cross contamination would occur.

Typically when coolant is getting into the cylinder that particular piston will be much cleaner than the others thanks to being "steam cleaned" by the vaporizing coolant.

It appears the coolant is slowly evaporating. I noticed there is is super tiny hole on the top of the coolant reservoir, right behind the refill cap. Not sure what purpose this tiny hole serves....

That's just to protect the reservoir against people who don't know what a "full" line means.

Coolant is lost 3 ways: liquid leakage, out the tailpipe, or most commonly, evaporation.

Evap at normal temp is a symptom of failure to maintain pressure. The coolant literally simmers off over time like steam out the top of a pressure cooker.

99% of the time it's just a shitty radiator cap. Get a new one before considering anything more exotic.

My car with 29k miles started to do this a few weeks ago. I converted it back to stock, and sold it.


I wasn't going to deal with the dealer doing it under warranty and putting the same part in that failed back in for round 2 with the chance they mess something else up while in there or the second choice of pulling the engine on it and going through the trouble of building it myself.


There is a serious problem with these engines under stress, I know of many others that have had problems and there's several thread about it, which is why I didn't make a new one. Good luck to anyone tracking these cars, hopefully a solution is found but I wasn't going to be the guinea pig.

Seeing all these threads like this is really starting to make me regret purchasing this car.


I specifically bought the car to use as a DD and occasional auto-x and HPDE work.

Mine was all highway miles to and from events, about 2k miles of track use and a couple hundred autocross runs. I was really disappointed when I started having the same issue as others.

Guess I'll just have to be a hard parker with this car.


That sucks.