Shamefully, I am only getting around to doing this mod now after purchasing the resistors - what seemed like a year ago. Completed it this weekend actually without a hitch.
First off I want to give a BIG THANKS to Raven Tai for doing all the work on this mod. I remember when he was doing the testing and reading his every post, as his progress developed - most of it electrical mumbo jumbo, at least to me anyway. His instructions were great and saved me much time, effort, and most likely a broken dash if I had to figure out how to dissamble the thing myself.
I have not driven my rig much after the install, but I have noticed that the gauge is MUCH more responsive. With the AC on and driving agressively, the temp gauge reached the 3/4 mark - something I have neve seen before in my years of driving. Actually it was quite disappointing to see how easily I could make this engine "hot" with little more than the AC on and some agressive driving on a cool spring day in May. I am afraid to see what will happen in August. No wonder Toyota installed the "zener diode". Probably cheaper than installing a larger radiator.
The 80 series engine has an iron block and an aluminum head. These metals expand and contract at different temperatures and the head gasket has to work especially hard to try and seal together two surfaces that are expanding and contracting at different rates. In my opinion, this is why these engines are prone to head gasket failure. Having a properly working temp gauge is a MUST to monitor temperatures and adjust your driving BEFORE temperatures reach their maximum and the head gasket has blown.
Raven Tai we all owe you BIG TIME for this. If you are ever in Philadelphia, look me up - dinner and drinks are on me.
Cheers!