Hi. I have a 2008 Lexus GS350 AWD. Had it for about 3 years now. Great car. I'm having issues with coolant staying in the reservoir though. I had someone tell me I don't need coolant there bur pretty sure I do. Even when the engine is cold, hasn't been driven in days... there's 0 coolant in reservoir. If I put a little or put alot, it just goes away. Not sure what's going on. It never overheats but don't mess my baby up. I don't see any obvious holes in hose or reservoir.

ETA - The coolant doesnt leak when the car is sitting and hasnt been drove for days. Its comes out when im driving it hard

 

How many miles? Is your radiator leaking? First thing I would do is replace the coolant cap with OEM.

 

Have you ever replaced your water pump? If not I would replace it just incase, because it is a fail item on our cars that can potentially overheat the engine. Once you overheat these engines the cylinder heads warp. Usually coolant leaks behind the waterpump pulley, it builds up pink slime on the backside of the pulley.

Like Lex2k suggested the radiator cap I would replace aswell. I would also clean the area around the inside of the cap. Aswell as the thermostat, no need to go oem for all these parts. You can go on rockauto purchase (Aisin water pump under $100, denso thermostat, oem radiator cap, idler pulley, dayco serpentine belt)

Im not the type of person to say replace many parts that are still good, but in this case with cooling its better insurance and peace of mind just to knock it out and get over it. If you look recently a member blew up their engine due to over heat.

 

So what you're saying is, you fill it up, you don't drive it and it just "goes away"? If so - replace reservoir.

 

pull the reservoir, fill it with water, and let it sit for a few hours and see if is leaking. could have a crack along the seam or something that isn't obvious upon inspection.

 

No, it’s not so simple with these particular engines in this year range. There is a known water pump defect that has destroyed multiple engines. Aisin is a capable company, but not infallible as is widely assumed. He has to find the leak source (if it’s not being combusted) before making an assumption like that.

The first responses get to the major issues here. A bad rad cap or failing water pump are the top of the differential diagnosis list for early 2GR-FSE engines. One is irritating, the other can be catastrophic. Any cooling anomaly with them is a major red flag to take very seriously.

 

but will any of those issues drain the reservoir even if the engine hasn't been run?

 

Yes.

And the OPs post is not 100% clear on that point.

 

interesting!

 

Uhh... Are you sure that a bad water pump will drain the reservoir if it's been filled up after it was already empty, without said water pump ever spilling? If that's the case, then I've been bleeding coolant loops the wrong way for a long, long time.

I do agree that both of those things should be checked, and they should both be pretty obvious if they're bad (the rad cap will most likely disintegrate if bad and the water pump should have obvious pools/trails of pink crust), but OP's post heavily implies that this isn't such a case. Not that replacing the water pump and especially the radiator cap (new original parts please, especially the cap) is ever generally a bad idea.

 

There are some very specific design and build failure issue here with this engine and years. I am guessing you are unaware of them - but it’s a little more sensitive than a normal situation.

 

Meant to write "without said water pump ever running", sorry.

What design failures were there? The faulty water pumps have been well documented, but those were units.

 

The manufacturing/qc failure was with the bearing assembly. The design problem was with the Young modulus of the casting; it’s length and flexibility were not able to match the block over time and after enough heat cycling. A different gasket design to compensate for this was also part of the water pump revision on later models and replacement pumps.

In then end - yeah, it could be a reservoir leak. But on this engine in the early years (I think this was mainly 2006 to 2010 - I think 2011 was the revision year but not 100% on that), it has to be checked really carefully. The only effective engine heat warning is the wetted coolant temp sensor. When the coolant goes, it’s no longer wetted and there’s no heat warning mechanism. The engine can seize or warp the heads.