Overheating and head gasket repair


New Member
I have a 1995 Lexus SC400. I rescued the car from an owner that could not find the problem to engine overheating. I checked all the usual suspects including hoses, surge tank, air pockets and bleeding the coolant system, thermostat , housing, and o-rings.(etc) I was thorough. The engine would not get hot, but would pressurize and release coolant in the overflow tube. If the car would sit for any length of time after running 30 min, it was gonna overheat. Very frustrating. I decided that cylinder pressure was leaking past the head gasket and pressurizing the coolant system. I felt if I could get the TWC (catalytic conv) off I would replace the head gaskets. I was able to remove the cats after heating the nuts/studs, removing two frame braces on each side, was able to get a box end wrench on the bolts from the front and broke them loose that way.........I removed all the stuff on top and front of engine. I removed the cams, and was surprised that the exhaust cam has two gears side by side and one is spring loaded, wow, would never have thought of that. Next I removed the head bolts and they were really tight. Used the proper sequence per lexus manual to un-torque the bolts. The middle bolt on the bottom was loose. I mean no torque at all. That would explain some issues I was having. I haven't checked the bolts with mag particle inspect, but suspect the Torque To Yield (TTY) nature of the bolt failed or cracked or something. Every other bolt was very tight including all cam journal bolts. Lexus says I need to replace all head bolts when I put it back together, and I will, probably cam bolts to................. Has anyone had a similar issue or repair like this? byw, this engine ran great in this condition.


Well-Known Member
Yep. Every now and again I've removed torqued to yeild bolts and one or two are loose. Often they are stretched outside spec. I nearly always replace.


Super Moderator
Staff member
I assume you are based in Sydney from the Karl Knudsen reference.

I have used and have great faith in Thornleigh Cylinder Heads (also trades as NAS Automotive).

They may not be the fastest turnaround but they are honest and reasonable.