Any Mk-III Supra owner should know about Cylinder Head Gaskets. These model Supras with 7MGE and 7MGTE engines are notorious for blowing head gaskets. Blowing a head gasket is an engine crippling event, and can cost a lot of money to repair. It is, within reason, a preventable accident, but only if caught within time.
What is a head gasket?
A cylinder head gasket is a wafer of fibrous material that is sandwiched between the two halves of your engine - the head (at the top) and the block (bottom). The block is the largest single component of the engine, and forms the cylinders. As part of its manufacture it also has water and oil channels which carry coolant and lubricant around it and into the head. The head sits on top of the block and contains the valves, cams, spark plugs, and forms the roof of the cylinders. The gaskets function is to seal the gap between the two halves, and prevent oil water and combustion gasses from escaping from their designed areas.
Click HERE for a view of a new head gasket
Click HERE for a view of a cylinder head (top view)
Click HERE for a view of a cylinder head (bottom view)
Click HERE for a view of a cylinder block
What is a blown head gasket?
A Blown Head Gasket (BHG) is where the gasket fails, and stops sealing. There are many reasons for this, and many effects of it failing. In simple terms the gasket breaks down, and allows the combustion gases to leak through into the cooling system and/or the lubrication channels. A BHG may also allow oil and/or water to be sucked into the cylinders during the period in which the cylinder is in vacuum.
Click HERE for a view of a blown gasket (wide shot, one cylinder)
Click HERE for a view of a blown gasket (close up, same cylinder)
Are all Mark-III Supras vulnerable to BHG?
All cars are vulnerable to BHGs due to various factors - a head gasket is a fallible component like any other part of your engine. The 7MGE & 7MGTE engines in the 3 litre Mk-III Supras are VERY prone to blowing gaskets. The primary cause of this is due to incorrect assembly during manufacture - the specification for the torque applied to the head bolts in the factory was approximately 20-30 lbs-ft too low, meaning normal running of the engine will eventually cause the gasket to fail. Toyota have never admitted this to be a problem, but did retrospectively change the torque specifications after the fault became known.
What can I do to prevent a BHG?
If the gasket in your engine is still in good condition, a BHG can be near permanently prevented by re-torquing the head. The procedure for doing this can be found HERE.
This is not a guaranteed fix for the problem, particularly if your engine has been driven for some years without this being done. It will generally prevent the problem from occurring for a lot longer, and in some cases will help extend the running life of the existing gasket if it has already begun to fail.
How do I know if Ive blown a gasket?
The most usual means of detecting a BHG is by noticing your temperature gauge skyrocketing. A BHG does not directly cause the engine to run hotter - the break in the gasket allows combustion gasses to leak into the cooling system, forcing radiator water out into the overflow bottle. Eventually too much water gets forced out and the engine cannot keep itself cool. The result is an overheating engine. In this case your overflow bottle will most likely be full to overflowing, and the auxiliary electric cooling fans on the radiator will be going full blast.
The symptoms of a BHG can many and varied. Other possible indicators are:
BHGs can sometimes be hard to prove. There are many factors which may cause an engine to exhibit BHG-like symptoms, and you dont want to have to be pulling your engine apart should it be simply a case of a dead radiator cap. Some of the ways to test for BHGs are as follows:
Whats it going to cost me to fix?
That all depends on whether you get the job done professionally, or whether you do it yourself. Typically a garage will end up charging between $1500 and $2500 for the whole job, parts included. This is a fairly variable figure, as a lot of the cost will depend on what work needs doing to the engine once it is apart.
The major costs of doing the job yourself are as follows:
What can I do to prevent another BHG?
If the BHG repair is done correctly the first time, you should never have further problems with it. An engine that BHGs once is not any more likely to BHG in the future unless it has been damaged in some way (eg warped head or block). Continue BHGs are a sign of other significant problems with the engine.
Once the BHG repair is complete, there are a couple of good rules to follow to ensure that the gasket seals correctly:
For the first 1000Kms after the repair:
And if you're really in love with your engine: