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Not daft, possible.

Also there are a couple of places where it can leak and immediately evaporate off so you'd never see a puddle on the ground. A garage should be able to check for these.

I would first have the car inspected to check for potential leaks or the coolant going somewhere else (eg head gasket, although if that were the case you'd likely have other symptoms). My local garage didn't charge me when they couldn't find anything wrong. It would be silly to spend £28 on a radiator cap when the issue might be elsewhere, in my case I did that as a last resort after a suggestion from a mechanic I know. Apparently when they pressure test cooling systems they often remove the cap in order to conduct the test and then neglect to test the cap itself. I don't know if this is what actually happened with mine, all I know is that the garage couldn't find any issue at all, I replaced the radiator cap and have driven over 1500 miles since without losing any coolant.

Yeah my apparently defective cap also looked absolutely fine to the eye. New OEM cap was £27.70 from Toyota.

I recently had unexplained coolant loss on my RX, garage couldn't find any leaks but it had lost a fair bit. I replaced the radiator cap and it hasn't leaked since. I would definitely get it checked because as others have said the coolant has to be going somewhere.

Over 1500 miles since I replaced the radiator cap and not a drop of coolant loss 🙂

Nope but it's a Harrier rather than a regular RX, so 4 cylinder 2.4L 2AZ-FE engine. Pretty gutless for the size of the car at only 160hp so constantly revving high especially up steep hills, but returns pretty decent economy. Up in scotland where I'm averaging 50mph a lot of the time even with the hills and mountain passes I'm doing better than 30mpg, haven't measured actual mpg but after about 1500 miles the range computer is showing about 40 miles more range than it does when I'm in London.

Also, regardless of what you think an issue might be, it's never a good idea to go to a garage and ask for a specific thing to be done unless you are absolutely 100% sure of the diagnosis. Garages will often do exactly as you ask and give you the car back with the same problem, and in all fairness it's likely a problem you never even told them about. A great garage will start by asking you what problem you're trying to fix by doing this and then advise you that regassing the aircon isn't going to fix it, but there are plenty who will just take the money. If you go to them and just describe the problem you're having then if whatever they do to fix it doesn't work then it's their problem not yours. I agree with @PCM that this should be resolved with the dealer, depending on where the vent is and how it's accessed it could potentially be a big job if lots of the dash has to come out to get to it.

To explain the vent door issue a bit more - the AC system doesn’t actually cool, it removes heat which has the effect of cooling. This is done centrally and then the cold air is re-heated through the vent system according to the temperature setting of the climate control. The same cold air from the heat exchange goes to all vents, so if one is cold and another is warm then the AC heat exchange is working (ie not a refrigerant issue) but one of the vent doors is in the wrong position causing warm air to re-heat cold air on one side (assuming of course this isn’t set as different via dual-zone etc).

Ah i see, makes sense

No disrespect intended David but that would be a waste of money if the system is blowing cold enough through one side of the vents. This fact proves it is not a refrigerant issue because there's only one heat exchange process taking place and if there's cold air blowing anywhere then that part of the system is working. If it was low on refrigerant or leaking it would be blowing warm everywhere. Assuming of course that the cold air is as cold as it should be, but it sounds like that is the case here.

https://www.pistonheads.com/buy/listing/12091970 Looks so nice. Cooled seats I bet are amazing on a hot day. Pretty much the same fuel economy as my RX but probably 10x the driving fun.

Slightly off-topic but I'm musing over what car I'll likely buy next, assuming that the world hasn't gone fully electric by the time my RX dies. I'd like to stick with Lexus but would also consider Toyotas, maybe even a Honda Accord. I'm not really a fan of the SUV body style, it's a big lumbering inefficient thing and the only benefit you get for all that burnt fuel is lots of boot space and slightly more comfort getting in and out. So my next car I want to be a car-shaped car (i.e. saloon), decent power but not over the top (LS would be lovely but I can't afford all that fuel). So I'm thinking GS or IS, GS is probably comfier right? But also more thirsty and no manual option. Not sure if I want a manual or not really, I'm lazy and drive in traffic a lot, but manuals are fun too. GS looks like it might have slightly more boot space than an IS but probably not by a lot. It's rather depressing when I consider that my RX returns around 30mpg with a gutless 160hp engine tugging a massive SUV around, and a 3L GS 300 making 245hp would be really zippy and return very similar fuel economy. Boot space is still a consideration but only for holidays so I'm thinking roof rails and a big roof box and I can take it off when not holidaying. I don't tend to spend more than about 7k on a car so would be looking at 2005-2010 year range which tbh I think is still the sweet spot for overall cost per mile anyway. Hybrids are an option for a bit more fuel economy but not really sure if it's a false economy at that kind of age because a single battery incident would more than wipe out any fuel savings on the difference between 30 and 35mpg.

If it blows ice cold one side but not the other then the refrigerant level is fine, as @Herbie says it'll likely be one of the doors malfunctioning and not directing the cool air where it's supposed to go. Assuming of course you haven't got the manual vent door control halfway shut xD I think there is a relearn procedure for those on many cars, they have to learn where the home position is after a battery disconnect. Not sure if it just happens by itself or whether you can trigger it somehow but might be worth a shot? @Herbie are you sure its normal for the AC to be warmer at idle? I always thought that was indicative of a weak or failed fan, but I guess if it's a very hot day then the system only has so much cooling capacity even with the fans on.

You can just lean the lever towards the gear position from neutral and when the revs line up with the syncromesh it’ll pop in. Wouldn’t recommend making a habit of it though.

2nd seems to work fine for steep descents, just wasn’t brave enough to try 1st.

Assuming a 4-speed slushbox, which is better for descending a steep hill: 2nd and intermittently braking, or 1st and braking a bit less? 1st gives more engine braking obviously but also makes the engine rev up to 4-5000rpm, not sure that's healthy for it to have all that torque coming from the wheels..

Yeah I quite like having a car where I don't really care about the paintwork at all as long as it isn't rusting. Whenever there's a scratch I just blob a bit of paint on it and leave it to dry, don't care what it looks like. I can't imagine driving a brand new car, would be so stressful worrying about it all the time.

Well I wouldn't buy a brand new car anyway but this doesn't seem like a great deal. One way or another for a 6000-mile limit over 3 years you're paying £12,800 which is 45% of the retail price of the car and at the end of that 3 years you own 0% of it. £355/month seems like a lot of money just to drive a car. Presumably they ding you if you exceed the mileage allowance too.

Isn't PCP basically a scam? Pay a ton of money to not own a car, why would you do that?

How much do you save over 3 years by buying it from somewhere other than Lexus? I would suggest this is a false economy and to just buy it from there, then at least you know it's the right fluid and won't cause problems down the line. A leaking steering rack is going to cost a hell of a lot more than some fluid.

Curious why you need a specialist? Most Toyota/Lexus specialists should be able to handle AC work competently, do you have a specific problem that has eluded other garages?

I got a small chuck of our hotel back from travel insurance. All in all not a terrible result.

Similar question on mine - I have a simple non-hybrid with a 4-speed transmission. Lots of steep hills in Scotland. I've been using 2nd to descend where there are corners (except for the long straight going south on Lecht road - that one I just let it roll and pretend it's a rollercoaster for cars). 1st would give more engine braking but it makes me a little nervous given that it revs up to nearly 5000rpm, not sure if that's good for the engine. Also remember to use the brakes intermittently, if you keep them on all the way down a long steep hill you can overheat them and cause damage.

Also I'm not sure I'd be willing to cheap out on something like a brake hose. That much of a price difference is probably for a reason!