PROBLEMS with My New 2.7L (Auto)

Ok, well it's not new. New to me though. Just bought it 2 weeks ago sight unseen. Took a couple Megabus's and an Uber ride to get to it and drove it 500 miles home (drove great - although I babied it, the whole way).
Most everything checked out when buying it, except a couple symptoms which seemed like no big deal AT ALL, but the mechanic I paid to look at it mis-diagnosed multiple things (and completely overlooked another). Now, I'm a bit out of my element trying to identify/diagnose and fix these few issues. And with the recent purchase/loan I don't have unlimited funds to keep throwing at mechanics who don't take the time to diagnose accurately. So any help here would be GREATLY appreciated. FWIW, I understand mechanical and electrical concepts just fine, I just don't have a lot of hands-on experience with vehicles.

Specs: 2003 Extended Cab, 2.7L 3rz-fe, auto trans., Prerunner, SR5, 265,000 miles
1 owner - serviced obsessively at Toyota dealership where it was purchased (55 Maint. records on Carfax report)

Problem #1: Rattle inside rear catalytic converter. Mis-diagnosed by "sight-unseen mechanic" as rattling heat shield. Heat shield has been removed, but rattle remains. It is DEFINITELY INSIDE the rear converter, and sounds like towards the very front of cat (incoming side). Loudest when idling. It passed emissions, and no CEL, just annoying as hell.

Question: Can I just unbolt the whole 3 foot piece, see if the broken honeycomb falls out and put it back on? Am I asking for more problems by doing this? Will I need to replace the 2 gaskets if I remove and reattach?

Problem #2: Squealing Belts. Mis-diagnosed by "sight-unseen mechanic" as "probably just a worn belt". In actuality, the belts themselves look fine. The compressor belt is too tight (probably purposefully covering up a bad tensioner pulley). ALSO, one of my local mechanics says that the harmonic balancer is worn and needs replaced because the 3 crankshaft pulleys shift out away from the motor when starting and when revving.

Question: Is this sound logic? Does this sound like the best/only diagnosis of this pulley shifting?

Plan: I have parts coming from RockAuto:

Harmonic Balancer (Dayco Premium PowerBond OEM PB1256N)
Crankshaft Seal - front (National 710644)
A/C Tensioner Pulley (Dayco 89038)
3 Drive Belts (Continental Poly-V Belts)​

Question: Am I missing anything? Is there anything else I should do/replace while in there?

Problem #3: Disappearing Coolant. Overlooked by "sight-unseen mechanic". When I picked up the truck, the first thing I noticed was a half inch of coolant in the reservoir. It wasn't running hot though. Filled up coolant before driving 500 miles. Did not lose an ounce during the trip home. 5 days later (and a bunch of shorter trips, 1-5 miles), the coolant is back down to half inch in reservoir. There is NO COOLANT ON FLOOR of my garage.

Process of elimination:
Reservoir is NOT cracked.
Removed Skid plates - only residue is oil just below oil filter (sloppy oil changes)
Leaking into Cylinders?....Engine Oil looks perfectly normal, not milky. Exhaust smells normal, not sweet. No white colored exhaust.
Leaking into Transmission?....Transmission Fluid looks normal, not milky. But, the trans fluid level is high, very high.​

Question: Is it possible that coolant is leaking into transmission fluid, but NOT showing the telltale milkshake color? At least not yet? Only other thing I can think is that it's leaking from the radiator, but only under certain driving conditions. Does this make sense? Or, where else could it be going?

Obviously, the coolant issue is my biggest concern, and also the most baffling to me. Any suggestions?

 

As far as the catalytic converter, you can try to get those bolts off, but you would be way better off to just cut them. New bolts are cheap. Yes, you will need the exhaust gaskets, but they are also cheap.

You should just replace that cat while you have it out, I used an aftermarket one. It cost around $120 I think, it's been a while. Been working fine, no rattles, no CEL.

I would try a new radiator cap.

 

I agree with ajm on just replacing the cat.

What do you mean by shifts away from the engine? There are thrust bearings inside the motor (around the middle of the crankshaft) that control the amount of movement the crankshaft experiences. It could be that they are out of spec, but a crankshaft should have some movement fore and aft. I would be very suspicious of a harmonic balancer failure unless you were having to constantly adjust the belts. Timing isn't controlled by the harmonic balancer like other vehicles.. I have only heard of a harmonic balancer failure on the 2.7 one time (at over 300k miles). I heard that the crankshaft sleeve over the woodruff key separated from the physical pulley and caused some damage to the front seal/timing cover. If you choose to replace it, use the motor to break the bolt loose. I had to use my 1500 ftlb pneumatic impact wrench to break mine free (never been done since the motor left the factory), which I only need to bring out of the toolbox when working on my farm equipment. Also, there are 2 (TWO) accessory pulleys bolted to the harmonic balancer. one runs the AC and the other runs PS.

As far as the other issues, it could be a number of things, but if you drove it 500 miles without overheating i'd bet it is a small issue with regards to the motor itself. Is it low in the reservoir tank or the radiator itself? ajm is right, change the radiator cap and see if that was your problem before going into other items. Since you checked for cracked reservoir tank and i'm sure looked at your freeze plugs/water pump to see if they are weeping it may be a leak inside the radiator allowing coolant into the ATF fluid (I have no experience with AT tacomas, so i am not sure if the radiator is a dual chamber one like other vehicles). If that is the case, you have a lot on your hands. Obviously you will be replacing the radiator. you may be able to salvage the tranny. Try changing the transmission fluid and let the ATF sit in the drain pan (clean before use) to see if coolant separates from the ATF.