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thanks... thats what i did... its badly discolored and im sure its really dirty....im looking on internet and it seems the electrical sensor is discontinued and so is the cap... would a new tank accomodate the old sensor and cap?
The original overflow tank was prone to leaking and/or cracking and was discontinued. Lexus redesigned the tank as a fix. I don't know the part number off hand but it is very expensive (around $200). The new overflow tank also requires a pressurized cap (about 13 psi) similar to the one found on your radiator and a redesigned level sensor (around $60). The level sensor is the thing that lets you know when your coolant level is low. If your tank is leaking try replacing the gaskets first. Keep in mind if you can't stand the sight of the old tank and decide to buy a new one...the new one will get stained just like the old one did if you mix tap water with your coolant. Use distilled water. If its coming from the tap be sure you have a reverse osmosis system like the one under your kitchen sink. The stains are either mildew from bacteria growth or a result of hard water. Good luck.
If you are having trouble with the tank either cracking, leaking or an inability to bleed your cooling system to help deal with heat being available in your car consistently then a change over to the re-designed parts may be a required consideration for future expenses.
I wound up having to replace the works, cap, tank, and sensor just last week and found upon inspection of my old tank that the intake nipple (pointing directly at engine) was plugged with hard water crap that was limiting if not completely restricting expansion of fluid back to the tank.
When I finally installed all new parts, bleeding was a snap and everything went along as it should. Now when I rev car to 2-3k I can clearly see the fuild circulating back into the tank with great vigour where as before it did not do that at all, in fact there was no fluid going back to the tank.
Interior heat functions perfectly now with no drop in temp at lower rpms just as it should and no more gurgling sound when starting up the car in the morning which is likely due to a large airpocket.
Cool thing about the new tank was the instructions on bleeding the system sticker is in tact and new. Anyone need to confirm the process, let me know.
Hope this helps a few out.
ps - tank for me in canada was $180, Cap $30, Sensor $90. Install took about 20 minutes total and is very easy. At this point, this 91 has a completely new cooling system, right from the radiator, pump, thermo, tank and all associated components. A testament to the design is through all the issues I had with the cooling system it never overheated in any conditions, it would ride just above the normal mid point and now that it's overhauled it rides right on the centre point when warm.
to keep this from happing again try changing your antifreeze using Toyota red antifreeze and distilled water my 1991 lexus has 239,000 miles has same radiator and hoses and only 1 tank changed at 100,000 miles I DRAIN THE BLOCK THEN THE RADIATOR AND DON'T FLUSH THE SYSTEM I JUST REPLACE THE ANTIFREEZE AND SO FAR NO PROBLEMS FOR A 18 YEAR CAR LS400