300K Miles Club

[Bru]

Its finally happened. In January 2021 my speedometer turned over 300K miles. When I bought the Supra in 1995, it had 110K miles. It took until year 2000 to make it to 200K miles. It took an additional 20 years to add the next 100K miles. I rebuilt the entire drive train in 2014, but I only drive about 4K miles a year now. At that rate, its going to take me another 25 years to get to 400,000. The car could outlive me.

Bru

07/20/2024 update 309K miles
About a month ago, the temperature gauge started acting funny creeping up above where it normally sits in the middle. At the same time I was having random pressure leaks around hoses that were spring clamped. Turns out the composite head gasket was going after 10 years. I took the head off and noticed that several of the coolant passage copper grommets on the exhaust side were distorted allowing combustion gases to leak into the coolant jacket. It never overflowed the overflow tank after stopping, which is typical behavior for a head gasket leaking into the coolant jacket. Right now I'm in the middle of a replacement and this time I'm going with a Cometic metal head gasket with a thickness to be determined when I get the head back from the machine shop. The roughness average of the block and head need to be around 40. Since I used a 20 thousandths shim gasket under a composite gasket last time, the block is still smooth. Cometic makes a wide range of thicknesses. I would've gone with an HKS, but their bore diameter is 86 mm and I want something closer to the 83.5 mm that is stock. The Cometic bore diameter I'm choosing is 84 mm. Since I'm doing this refresh, I hand lapped the exhaust valves and replaced every hose that needed it. Now I get to play with adjustment shims to get the valve lash in spec.

11/03/24 update
The Cometic head gasket I ended up getting was 0.098" thick with a bore of 84 mm. 0.020" total had been removed from the block over the years and 0.029" from the head. Add that to the 0.054" standard head gasket thickness and it ends up being 0.103 needed to return to factory specs. The closest I could find that Cometic made was 0.098", which is within the 0.010" deviation from new Toyota allows. I torqued the head ARP stud nuts down to 72 foot-pounds. I had no issues for 2 months, and then noticed oozing coolant leaks on the exhaust side. There was no liquid inside the cylinders. I re-torqued the head stud nuts by loosening them 1/2 a turn at a time and then going up to the maximum ARP allows of 90 foot-pounds. The compression check was the same as the original build up, 160 psi with a difference of 3 psi across all 6 cylinders. Toyota allows 14 psi difference. After a week no leaks, but I'm keeping an eye on it.