1991 Toyota Supra Reviews - Page 4 of 5

Good to see another happy Supra owner (although this thread is over a year old, I'll bet he's still happy! lol).

The MK III Supra was known to have a BHG (blown head gasket) problem. Factory specification under-torquing of the cylinder head bolts led to failure of the seal, usually before before 100,000km of driving time had elapsed. Aware owners could avoid this by having the head re-torqued to a higher setting. I have done this on three of the five Supra's in the family stable and not had a problem :-)

My belief is that this problem was aggravated by the hot-spot between number 3 and 4 cylinders.

Actually, I believe the aggravated Hot spot is around the #6 cylinder, at the rear of the block. There are a few reasons for this:

1. Heater core hose location

2. EGR cooler plate

3. #1 Pre-catalytic converter location.

All these items retain excessive heat and can keep the rear of the motor hot, even hours after shut down. During these times, the rear of the motor is still hot and the rest of the motor has cooled down. This affects the expansion and contraction rate of the metals. This can lead to a warped head, since they are cooling at different rates.

The other reason is that Toyota Service Repair Manual states that the head bolts should be torqued down to 54 ft/lbs, which is entirely too low of a value to provide sufficient clamping load. The bolts should be broken loose and re-torqued to 75 ft/lbs. Beyond that, the bolts exceed their plastic region and can no longer hold a good clamp. When you stretch something too far, like an over-torqued head bolt, it can no longer return to its original shape. 75 ft/lbs has been determined to be the plastic limit of the stock head bolts through standard ANSI methods (I think that's the standard test procedure.

Hope that helps.

It is a very poor reflection on Toyota that the head gaskets are constantly blowing on these cars.