5VZ-FE slow coolant loss

it could be seeping from here also.

 

I'm EXTREMELY late to this post, its probably dead by now, but oh well.

I had a similar issue, not losing quite as much as you are / were and had zero evidence of where it could be going. I accidentally located a leak at my bypass tube under the lower plenum. the seal blew on it and filled my valley with coolant. Found it while doing my fuel injectors......glad I dropped something in cylinder 5 injector port resulting in me having to remove my lower plenum to fish the item out.

Long story short......its a shitty job in a way but if you still haven't found the leak yet then it may be worth your time to check it out. if you can check the rear of your engine block for evidence prior to investigating.

 

If coolant enters the combustion chamber you will usually have a slight miss on startup, usually goes away within 1 sec or so. Mine did this for weeks until finally I saw white smoke from the exhaust.

Check for a milky residue on the oil filler cap to rule out water in oil.

 

Chasing a mysterious coolant leak until you are stumped because you can't find it; and it's on a 5VZ. This sounds familiar.... get a block tester. There's a decent chance you have a cracked head. The 5VZs and 3RZs are both plagued with it.

 

I have an experience with chasing a mystery leak.......
happens once in a while......before thermostat opens....I get a leak back side thermostat gasket...

The mechs that put my motor together used a little rtv on that gasket......found out why....
switched out stat to put real toyota one after first one.....
Only leaks once in a blue moon........cold mornings before stat opens....