ukrkoz

Yeah, except one of the rear bolts going loose, I believe, resulting in less torque on head gasket.
Coolant leaks are tricky. It is common for them not to show under the vehicle, if fluid is blown off the engine onto under carriage or evaporates. If leak is under pressure only. Then engine cools down and leak stops. That's why dye test shows it well. Hair cracks may take HOT engine to show, so just a pressure test may not reveal it.
I re read OP coolant post. Unfortunately, without hands on, it is hard to judge. "half cup" is by far not enough to refill from "almost invisible" to Low mark. "all sucked in" can also be interpreted various ways. If there was no coolant left at all in canister, then there was air gap in radiator and it created vacuum and sucked coolant back in - but that's not another "half cup" to refill.
That's how goes it with online diagnostics.They are only as good as problem description. But, as the result, I went and checked on wife's RX coolant level. dead smack on sharpie mark.

ukrkoz

Ad hoc. Camry Hybrid was plagued with bad pumps and coolant leaks. They changed design in 2011 to upgraded one that fixed the problem. But that's on 4 cyl hybrid engines. I do not recall any major concerns with bad pumps at Highlander Hybrid forum, that being same power train as RX.

paperthin

Post #14 states 50-60,00miles but we got just over 143,00miles. Not sure if that is a separate conversation.

There is no white smoke, there is no contamination in the radiator or under the radiator cap, but i recognize that doesn't mean there could be a micro crack somewhere.

Anyway I heard the noise again today, but from a different standpoint. I was standing in front of the car today the street, sound much different from that standpoint. It definitely sounds more like a rattle dead centre up high in the front. It was dark out so I couldn't go look down below what it could be. It sounds like something is loose. Normally I am at the passenger front door area when my wife starts up because there is no room up front. Ukrokz is right hard to try to communicate the problem online. Thanks for trying guys...

update: If i had just did a search instead of relying on this forum i would have seen that the noise is extremely common. prefectly illustrates this. Sounds like it is a low oil noise issue.

Droid13

This is the same sound my RX made when the engine light came on - with a low VVTi oil pressure code. The difference, when code was thrown the noise lasted about 10 seconds, not the brief moment in the video. Fortunately, it hasn't returned in a long time.

paperthin

Interesting. Never a code for me, and it seems that it is about half a second now after oil change. I have only had it once or twice since the my oil change whereas last Aprilish it was more often and closer to two seconds.

tharper51

I have a 2010 RX450h with 66K miles on the clock. Lately it has developed a noise from the engine on initial startup. It sometimes sounds like a knocking/tapping noise and other times sounds like a chain grinding noise. I dont think its missfiring but does feel a little lumpy when driving off for the first 10 to 30 seconds. No faults have come up on the dash.
Can i have advise on how i can check it? What can i check to see if its a VVT-i issue? Is it something i can fix myself as i am a mechanic but i have no experience of these V6 engines.

Droid13

Some similar discussions on this topic for you.

https://www.clublexus.com/forums/hyb...n-startup.html

tharper51

Yes i have been through most of them, however most of them are rubbish.