I just had my water pump replaced and thought I would share what I learned in my particular situation in my 2008 ISF
It may also help other identify a leaky pump in advance of the dealer and or purchasing a used F.
I had been losing coolant very slowly, and had been monitoring my reservoir level over a 3 month period. I knew that the cooling system is a closed system, and if my reservoir is low - it must be going somewhere. I had no signs of external leaks, on the ground or visible to me inside of the engine. My oil level was stable, so I was sure it was not leaking inside of the motor.
I took a small flash light and shone it on the serpentine tensioner, and found a massive leak and build up of pink coolant, that must have been happening over time. I did not take a picture before, just after the repair was done. The tensioner is below the water pump (pulley with exposed bolt heads)
You can actually see the area from both sides of the reservoir - it was easier to get my camera in from the passenger side
Here is a zoomed in shot - I have circled the area where pink coolant will be evident.
Lexus describes this in the there technical data, that if any coolant is leaking from the air or drain hole - replace the water pump. This is where mine was leaking from (lower drain hole).
(a) Visually check the air hole and drain hole for coolant leakage.
If leakage is found, replace the water pump.
(b) Turn the pulley and check that the water pump bearing moves smoothly and quietly.
If necessary, replace the water pump.
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2008 IS F Series 2/ Mercury Metallic 1F2/ Joe Z/ aFe/ Garax 6K/ Volk VR G2 19"/ F-Sport Rear Sway/ ISS Forged DES/ BCR/ Beatsonic/Sprint Booster/ Wald Rear Diffuser/ Wald Spoiler
2012 Lexus CT200h Fire Agate Pearl
2001 Lexus IS300 Solar Yellow- Sold
2001 Lexus IS300 Ltuned Stage 2 (Stolted) - sold
After reading this thread I went and checked my water pump, and this is what I found out:
Guess I need a new water pump
__________________ 2008 StarFire Pearl Lexus IS-F: JoeZ Exhaust, AutoCouture Front Lip, Lexon Rear Deck Spoiler, Custom Front Grill, FSport Rear Sway Bar, Tom's GT Shifter, HOEN 3000K Fogs, MTEC 4750K DRL's, Polarg Wedge LED's, Tanabe Front Under Brace, 19" WedsSport SA-67R Wheels, Michelin Pilot Super Sport Tires, HKS GT4 Coilovers. 1997 Custom Pearl Supra TT: Too many mods to list !