2010 460L with 99k miles. No sign of coolant leak in garage, driveway or anywhere the car is ever parked.

This is also posted in Car Chat but want input from broader audience.

- Took LS into Lexus for interior parts replacement 4 weeks ago and they noticed low coolant. Used a boroscope to supposedly identify a leak - they took a pic of something resembling a brain which they said was the red/pink coolant. They gave me a quote for 8 hours labor at a grand total of $1,400 to "re-seal engine block coolant valley". Don't have good experience with Lexus so told them I wanted a 2nd opinion before authorizing work.

- Took it to my Toyota dealership - they supposedly used a boroscope to also identify the area. They were less confident in their ability to do the work due to it being a Lexus V8 engine and suggested I take it back to Lexus to be safe. No charge for assessment.

- Due to my apprehension to my local Lexus dealer, decided to take it to a high end import mechanic who has been in the same location 35 years - used to take my Audi to him and very reputable shop. It is only him and another ASE certified tech and they do tons of work on BMW, MB, Range Rover, Audi, Rolls, etc. He had the car for 2 hours today and said he doesn't see a leak anywhere. He mentioned that coolant leaks leave a chalky white residue and he saw no evidence of that. He also saw no other parts that were wet or had the residue - said he checked all belts, hoses, and water pump as well. He said I could drive the car with confidence that there is no leak. He said the LS460 is a relatively basic engine compared to some of the more complex cars they service and was confident in his diagnosis. I showed him the pic that the Lexus tech sent and he just smiled and said "Not sure what they're doing, but I'm confident you don't have a leak." No charge. *Note - the car had been sitting for 7 days without being driven - I had the car running for a total of an hour and drove it about 6 miles today to get it to the mechanic. Not sure if that impacts if/how coolant would flow - the car was running for a solid hour though.

I don't want to pay for un-needed service (why I ditched my Lexus dealer 10 years ago), but I also feel apprehensive about 2 places telling me they see something and the indy saying he sees nothing. Need some advice.. I'm not a DIY type so please keep that in mind.

Thanks!

 

My LS460's coolant reservoir also needs to be filled half quart per 5 month or 7k miles of driving.
This losing coolant might be due to slow leaking of radiator.

 

For my 2008, I drive 5K a year but I drive very aggressively. I've only need to do a small top off once a year. I have a new radiator and unsure if the water pump was replaced. It's normal for some evaporation to occur especially since you are in a very warm climate and if you are not checking coolant levels regularly, it may seem like a large coolant loss.
You are nearing the 10 yr mark where the small tube on top of the radiator gets brittle and will easily break off with a slight bit of pressure. Had it not been for this design flaw, the radiator would last longer.

What ever you do, don't add any coolant leaking seal products you'd buy for automotive stores.

 

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If you are losing coolant and don't see anything on the ground, it's very likely a coolant valley leaking problem, as your Lexus dealer said. It is a unique Toyota/Lexus design problem with LS460 engine (1UR-FSE). See here for more info: https://www.clublexus.com/forums/ls-...96k-miles.html. My 2008 LS460 had this problem at 81k miles and Lexus dealer fixed it (replaced the valley seal) free of charge as part of warranty service.
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I agree - I read that thread from Fatherto1 a while back and just re-read it this morning. What exactly is the definition of the "coolant valley" or "valley plate"? Concerned my local indy shop didn't see anything because I checked my coolant level this morning and it's below the "low" line. Not sure what I would dread more.... paying Lexus $1,400 to fix it or rolling the dice and paying my indy whatever he would charge when he couldn't spot the leak..?!

 

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If your coolant stays just below the LOW line and doesn't drop further, it is fine. Mine always stays below the LOW line. In the beginning, I always added coolant and brought it above the LOW line. However, after a few days, the coolant level would drop back to just slightly below the LOW line. Then, I stopped adding coolant and wanted to see if it would drop further. My coolant stayed at slight below the LOW line for months and months. I realized that somehow my coolant would be purged out when it was above the LOW line. As a result, I stopped attempting to add coolant and bring the coolant to above the LOW line. I essentially accepted it that the "correct" coolant level for my car is slightly below LOW line.
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Read the ISF forums on ‘coolant valley plate’. Seems to be somewhat common...

 

Interesting, thank you.