This just sounds so strange.

Never worked on a Lexus engine, but I know in the cars I've worked on in the past, there was a "full" line on the plastic coolant container for when the engine is cold and another for when it is hot. Any coolant added above the cold line would get blown out when the engine was hot.

I would have thought that the traditional way to check for a coolant leak is to pressurize the system and see if it holds that pressure indefinitely. If the engine coolant system holds pressure, could it be as simple as a crack in the plastic tank that allows coolant to leak out as you're driving and the tank is shaking around a bit in its mounts? In my experience it takes time and repeated hot/cold cycles for the cooling system to top itself off from the tank, not something that would happen in 8 miles.

Finally, I would not trust an independent mechanic diagnosis over a Lexus diagnosis if there is serious money involved. I would seek out a second Lexus dealer opinion without mentioning the first Lexus opinion to them.

 

If you over fill the reservoir the excess will get pushed out it is impossible to maintain a level higher than the HOT marker with the engine at operating temperature. You said the level stayed the same for two weeks if so you don't have a leak of if there is one it's very small.

 

I was supposed to drop the car off at Lexus this weekend but I showed up and they were out of loaner cars... so, given my level of frustration with them I'm not sure what I will do. The next-closest Lexus dealership to me is just over an hour away so it will be an inconvenience taking it there. I drove the car about 250 miles this weekend and coolant level remains at the "Low" level. I read the owner manual last night and it says the fluid level should be somewhere between "Low" and "Full" when the engine is cold. So the thing I continue to not understand is why the coolant level only drops when I fill the reservoir somewhere between "low" and "full". When it's at the "low" level, it never moves - even after a 100 mile one way trip in 95 degree outside temp like this weekend. My engine temp gauge stays pinned right in the middle, so I literally have no symptoms of anything wrong other than the level remaining at low. Thoroughly confused.

 

something tells me the independent garage opinion was the right one.

 

You may be right, Jill. My current thoughts are:
1) Lexus and Toyota both used a bore-scope to see coolant in the valley plate. Lexus was quick to call this a "leak" - but provided no documentation of how they determined that (long duration pressure test to identify source of leak, etc). They quoted me 8 hours of labor to fix it, but again didn't tell me exactly what they would fix (exact source of leak). So, I'm not denying that coolant may be at the valley plate (will buy my own scope to verify) but I don't have enough info yet to know that it's there due to a leak.
2) I have owned this car 2 1/2 years and never even looked at the coolant level until Lexus told me about this roughly 2 months ago. So there's a chance I've been driving around with it at the "low" level the entire time I've owned it. I know my Toyota dealer would get it to "full" during each oil change as part of their overall inspection process, but given my recent experiment where I personally topped it off and it went right back to "low" within 10 miles, the reservoir may be at the "low" level within 10 minutes of my oil change.
3) One of my buddies suggested I ask Toyota to put my oil in a clear container at next oil change and see if there is any hint of coolant in the old oil. He said that would be a bad sign and would signal to identify and fix the leak quickly.
4) I'm going to buy the bore-scope and have a look for myself and then take a ride up to Toyota to talk to the master mechanic there and tell him everything that's happening to get his thoughts.
5) I'm going to fill the reservoir again and start the car and watch to see what happens. I don't see any signs of residue of coolant anywhere on the engine, so I don't think it's overflowing out of the reservoir, but I'm at least going to see if I can witness anything happening.

I need to have confidence to drive the LS as I use it for work and occasionally take 500+ mile round-trip excursions in it. Even with no symptoms, I'm a bit apprehensive of doing one of those long trips at the moment. Appreciate any thoughts an the above.

 

OK- another update. At the advice of a member in the IS-F forum yesterday, I let the car sit overnight, opened reservoir cap this morning, started engine (cold), and began pouring coolant into the reservoir while engine was running (cold start). Previously I had always filled the reservoir first, replaced cap, and then started the engine. This time, immediately after starting the car I walk back to the engine and notice the coolant dripping out of a small black hose that is connected to the reservoir... Called one of my mechanically inclined buddies after sending him the below pic showing the hose, and he says that's the overflow hose doing it's job. So.... now I'm thinking I don't have a leak at all. My reservoir just pushes out excess coolant any time the reservoir is above the "low" level (I don't know why). I poured probably 2 ounces of coolant in and it started dripping out. So, each time I get my oil changed and they top off my coolant, upon first start of the engine I'd imagine somewhere between 10-15 ounces (difference of "low" line where mine stays to "full" line) is getting pushed out of this hose, and likely collecting down at the very bottom of the engine (valley plate).

Anyone have thoughts? I'm wondering if this mystery is solved. Lexus saw coolant at the valley plate and immediately gave me a $1,500 proposal to fix a "leak"... yet they never told me where the leak was. In the pic below, the hose where the coolant was coming out is the small black hose directly behind the reservoir cap (hose is not connected to anything other than reservoir). If there is no leak, my indy mechanic was correct.

 

I said the same thing in post 32.

 

Yes, you did... my confusion in your post was around the fact my reservoir does not have a "cold" and "hot" level - it only has a "low" and "full" marking. The manual says to fill the reservoir between "low" and "full" while the engine is cold. In trying to do that multiple times, the second I would start the car it would immediately drop back down to "low." Having the engine running cold and then filling the reservoir offered the first chance for me to see the dripping of the coolant out of the overflow hose.

Based on what I've reported, would you be comfortable there's no leak if this was your car? My only lingering thought is wondering why my reservoir can't be filled past the "low" setting without the excess immediately being pushed out.

 

That's how the system works based on air/liquid volume ratio in the reservoir and coolant expansion, all regulated by the coolant cap. On my Lexus the same thing will happen if I fill it more than the first line with a cold engine the excess will be pushed out.

tldr; if the coolant level is always at the low line on a cold engine you have no leaks. FYI it can vary slightly depending on outside temperature and how long the car has been sitting.

 

I am pretty confident you very likely do not have a leak.

 

Interesting, thank you. Are you saying that changing the coolant cap could potentially result in a different amount of coolant being held in the reservoir without being pushed out? Essentially, if I tried a new cap, is it possible that would allow me to have the coolant level remain at "full" instead of at "low"? Thank you again.

 

I hope you're right! I'm glad I have taken my time in not paying Lexus $1,500 to fix a problem that may not exist. If I have some way of proving to myself that there is no leak, I may write an email to the service manager asking them to explain exactly how they came up with a diagnosis of a leak just based on seeing coolant in the bottom of the engine. Not to mention this was "found" as my car was there for replacement of "sticky" interior parts - I guess it was part of an inspection process, but I've had bad luck with this dealer in the past trying to charge me for things I didn't need, so I'm always skeptical with them.

 

Think about it! You posted the original thread in Aug, it is now three months later. You would know if you had a leak by this point. I

 

No, if the cap is working correctly on a cold engine the level will be at the low line. That's how the system is designed forget being OCD about it lol.

 

Fair point!