Have you verified that it doesn’t have the tow prep package by entering your vin into the vehicle specifications page on the Toyota owner’s site? I thought the vast majority of the V6 2007’s had the tow prep package. The tow prep package does not include the trailer hitch nor the final wires but does include the heavy duty cooling system and transmission cooler and trailer prep wiring, so you could have it and not know it.
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There is a short answer and a long answer. The short answer is that the combined vehicle weight limit is in the owner’s manual, available online on the Toyota Owners' site. For my 2005 V6 Limited AWD 7 seat with tow prep package it is 8860 lbs with a 3935 lb curb weight, which by definition includes a full tank of gas (see the owner's manual glossary of tire terminology though the definition varies by the source) but not the hitch weight. Most (sane) experienced tow drivers will tell you to keep the vehicle gross weight including tongue weight, the trailer gross weight, each axle weight, and the gross combination weight all less than 80% of the rated capacity.
For the long answer a little more information is helpful.
How many miles on the car? How is it running and shifting? Is the check engine light on? 5 passenger or 7 passenger? Does it have original equipment rear struts? Does it have original equipment brakes? How old are your tires and what are the tire maximum load ratings? How far are you going? Any mountain passes or major altitude changes? What will the temperature be like? Any plans for a roof rack mounted carrier? Do you need to travel at night, especially on two-lane highway?

 

Thanks C R - went to the Toyota Owners site and saw no mention of tow or tow prep packages, only cold weather and "VP Value" packages. So I'll assume no such HD cooling/Trans coolers are included. If there's a handy way to check physically I can hop under the car but I'm comfortable in thinking I don't have it. Now, to address your Q's:

How many miles on the car? About 82K
How is it running and shifting? Really great, we owned since 79K, been service by Toyota it's entire life.
Is the check engine light on? No
5 passenger or 7 passenger? 5
Does it have original equipment rear struts? Yes, nearly certain it does
Does it have original equipment brakes? Pads/rotors have been replaced (stock replacements)
How old are your tires and what are the tire maximum load ratings? Brand new, TBD on load rating
How far are you going? NYC to Houston, so ~1,700 miles
Any mountain passes or major altitude changes? Don't think anything major (not crossing the Rockies/Poconos/Catskills for ex.)
What will the temperature be like? July trip headed south, let's assume very hot
Any plans for a roof rack mounted carrier? No
Do you need to travel at night, especially on two-lane highway? Only as necessary or if really delayed. Planning on 3 day trip, 8-10 hrs a day

 

So did some homework bouncing around the Toyota Owner's site and weighing some things and people.

• Trailer will be filled with about 600lbs (585 calc'd), plus the trailer weight of 850 gets me to 1,450lbs (1,435 as calc'd). This is less than the 2,000lbs limit set on the owner's manual for my model/options.
• Car will carry three people (530lbs), some luggage (190lbs = 90lbs weighed+100lbs allowance), and a hitch setup conservatively estimated at 75lbs which gets us to a tick under 800lbs in the car (795lbs as calc'd). This is within the vehicle capacity limit of 860lbs as laid out in the owners manual.
• I believe curb weight is 3,880lbs (which includes full tank of gas confirmed in owners manual). So, Curb + Vehicle Capacity + Estimated tongue Load (9-11% based on owner's manual) = 3,880lbs + 795lbs + 144lbs = 4,819lbs. This is about 90% of the GVWR of 5,360lbs.

Am I thinking of this the right way? I'm half thinking of one-way renting an SUV (~$1,500) instead of towing (~$550 for trailer+$300 hitch and accessories) to avoid unecessary wear on our car too.

 

I think the 90% of GVWR is OK. If you add the individual axle ratings (at least on mine), they exceed the total rating. A 1500 lb trailer should not be a problem. You are well below your gross combined weight limit of 7360 lbs.
Of course, almost any towing puts a strain on the vehicle. But you bought it to use it.
What I would do:

• Make sure the maintenance is up to date. Since you are new to the forum and the vehicle seems to be new to you, I will give some maintenance recommendations in a separate post.
• Have the rear subframe and rails inspected to make sure they are structurally sound before installing a hitch.
• Do not use overdrive. The 4th gear clutch is significantly stronger than the OD clutch. This is the reason why there is a switch to turn off OD. You can still do 70 mph at just 3000 RPM. I do not use OD if my passenger weight + cargo + loaded trailer weight exceeds 1200 pounds.
• The major limitation without the tow package is engine and transmission cooling. I would use a bluetooth scanner which can read transmission temperature and monitor it closely on my phone. I like to keep my transmission temperature below 205 degrees F, and I would pull over and let it cool down if it gets to 225 degrees F. Only a few scanners can read the Toyota specific modules to read transmission temperature. I like the OBDLink MX+.
  I would change transmission fluid immediately after the trip for regular maintenance, and I would probably try to change it during the trip if I saw it go over 235.
• Also monitor engine coolant temperature. I don't think I have seen mine go over 205 degrees. At 208, the high speed fan turns on. I have not seen a definite upper limit for temperature on the 3MZ-FE, but I probably would not want it to get over 210. The FSM identifies 203 F as the upper limit of normal range. The thermostat in the 3.3 is set to begin to open between 176 to 183 degrees, and be fully open at 203 degrees. The maximum the gauge will read is listed in the FSM as 284F.
  You will see higher temperatures discussed on forums. There are some newer aluminum engines that regularly operate at 220 degrees or even hotter, but the head gaskets, head bolts, valve seats, and structure are designed for it.
• Use premium fuel when towing. The 3.3 is designed for 91 octane (reference Section 2 of the owner's manual, fuel type), though it will run on 87. If the ECM detects knock, it will retard the timing, which will tend to cause exhaust valves and exhaust system, including the cats, to run hotter. In your case, the vehicle has very low miles, which might mean it had a lot of short trips resulting in heavy deposits in the combustion chambers, which tend to result in knock, so I would keep the octane up.
• A limitation of all Highlanders is the lack of a means to level the suspension when towing. It will affect handling, and your headlights will point up, potentially blinding oncoming drivers. I try to avoid driving at night especially on 2-lane roads and I stay well-back from other cars when towing. And I don't use the fog lamps.
  If you get the Curt hitch, it is rated as a weight distribution hitch, and having an equalizer will help a lot to level the car, but the equalizer is pricey.
• Make sure that the draw bar (ball mount) has enough lift to provide clearance for the trailer tongue skid going up ramps a curb cuts.
• You will notice much longer stopping distances.
• Use the transmission for descent assist to avoid warping the brake rotors. As TheLowlander points out, the brakes on these 1st gen HL's are just adequate. I had to replace my rotors after loaning my car to a relative who took it to the mountains. The ECM does have descent assist capability, but sometimes it needs help. I use 3rd gear a lot when descending. However - remember to put it back into Drive when no longer descending. Leaving it locked in a different gear can cause excessive stress on the transmission. I am pretty sure that is why Toyota went to the expense to put the additional selector indicator on the dashboard.
• Once I have decided to use a trailer, I try to put weight in the trailer rather than in the car.
• I don't think the lower rated alternator will be a problem, but you might ask for a trailer with LED lights.
• I run my tire pressures at about 36 PSI on tires with a rated maximum of 44 PSI.

 

I will update my recommendations above later today.

The quick way to inspect for the tow prep package is to look for the external transmission cooler under the battery.
I also included a thread discussing the tow package and one discussing hitches and weight distribution equalizers.
External transmission cooler

Towing package V6

I recently bought a 2007 V6 with the towing package what does the package include?

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Equalizer

towing with 2004 highlander

Hi fellow highlander's. My wife and I have fallen in love with a 19' Escape travel trailer. We have the V6 AWD with tow package, It's rated at 3500 lbs. tow capacity. Trailer is 2510 lbs. dry with 256 lbs. tongue weight. Was wondering what have other people towed with their 1st generation...

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One thing to think about that might influence your decision: Will you get any more use out of that trailer hitch, or is this just a one time thing? I use a hitch mounted bike rack from time to time and also have a hitch mounted cargo hauler, which I like way better than putting stuff on the roof.

 

Maintenance recommendations if a low-mileage ‘07 V6 AWD was new to me:

• Safety inspections. I have a trusted shop and I have them look it over about once a year, just to put it up on a rack and have another set of eyes on it. This should include inspecting tires and setting pressures, including the spare.
• Watch the Toyota DIY maintenance videos by The Care Care Nut on YouTube.
• Use a scanner to check for pending codes, I/M monitors complete, fuel trims, misfire counters. If fuel trims are off by more than 10% I would clean the MAF and throttle body.
• I usually like to allow at least 2 weeks between any maintenance or repair and a long trip just to try to be sure there were no mistakes.
• Change air filter, PCV valve. Make certain that the air filter housing clips are in place, and the cover hinges are good. Clips are only available as used parts from a U-pull yard, but seem to be the same for all 1MZ, 2AZ, and 3 MZ engines, easy to find. I usually change the cabin air filter too.
• Change the oil and filter if it was last done more than 2000 miles ago. I always replace the crush washer and put a very thin coat of high temperature grease on both sides to help keep the blue film from sticking. (You can find my rant about oil changes, flat tappets, new oils, and ZDDP in other threads).
• Change coolant (only Toyota Super Long Life), power steering fluid, and full brake fluid flush with ABS valve actuation if not done in the past 3 years. Flushing the cooling system is usually not warranted on these as long as the Toyota coolant was used, just do coolant replacement to replenish the additive package.
• Make sure the AC is working well
• Check and preferably change differential and transfer fluids if not done in the past 30K miles. They get surprisingly hot, especially the transfer. I would recommend taking it to a shop, as the vehicle needs to be level, you need a 6 point socket and long extensions. Much easier on a rack. The owner’s manual says straight 90 weight oil, but that has become hard to find in name-brands. I know Toyota is using 85W-90 synthetic, and last time I used Valvoline 80W-90 hypoid synthetic. I always replace the crush washers. They each only hold about a quart, so any external seepage is a concern over time.
• Inspect the transmission, transfer and differential vents to make sure they are open. Clogged vents can result in excessive internal pressure and leaks - which can be permanent once started. Easier on a rack.
• New Denso or Motorad radiator cap.
• Fuel injector or system cleaner such as Techron in the fuel tank.
• Transmission fluid: This is probably the area of most disagreement on the forum.
  Some options are listed below. Recommendation from The Car Care Nut on Youtube is 30,000 mile changes.
  I think any of the first 3 are reasonable. I would probably choose the first if the transmission is shifting well without harshness or flare:
  1. Check the level. If the transmission fluid looks good and does not smell burnt, don't change it until after the trip. Leave well-enough alone for now.
  2. Do one drain and fill, which will get out a little under half of the transmission fluid, and let you inspect for any issues. It will also allow you to add some Lubegard to the transmission, which is endorsed by many members.
     Whenever you drain these transmissions, I think it is always a good idea to measure how much you took out so you can compare with how much needs to go back in. It can be difficult to read the dipstick correctly with these modern thin fluids. I always replace the crush washers.
  3. Do 3 drain and fills with at least 25 miles in between. This will get out most of the old fluid, moisture, and replenish the detergent, anti-varnish, anti-sludge additives.
  4. Drop the pan, replace the screen - probably overkill at this mileage.
  5. Do a transmission flush - I would not do this on a transmission that was shifting well.
  6. If the transmission fluid smells burnt, there is a problem. Take it to a transmission shop for diagnosis.

Transmission fluid - the greatest controversy among the regulars on the forum. Since your vehicle is a 2007, make certain which fluid it calls for T-IV or WS. If WS, you can skip this paragraph and just use the Toyota WS (my recommendation). I believe all first generation Highlanders still use T-IV but double check.
For most of the first generation transmissions, there are three primary choices that come up on the forum:

1. The OEM recommended Toyota T-IV (tee-4) ATF meeting the JWS 3309 specification. Most aftermarket fluids state they are compatible with T-IV, but that is an assertion by the manufacturer and they are not qualified to JWS 3309. The AISIN and Idemitsu fluids may be an exception, and there may be one or two more exceptions from Japan.
   The downside is that it is not a synthetic, and is expensive in some markets.
2. The Valvoline MAXLIFE synthetic fluid that states it is suitable for T-IV applications. Good anecdotal experiences with it on the forum. I have not used it because it says it is suitable for both WS and T-IV applications, and the starting viscosities of the two are different, so seems like a compromise.
3. Valvoline Import Multi-vehicle synthetic (blue bottle). States it is suitable for T-IV applications and there are good anecdotal experiences on the forum.
4. There is a fourth: fluid additive- Lubegard Red Many on the forum and a few pro’s I know swear by it. I haven’t tried it yet. Some say it is great and some say it is just another way to extract money from consumers.

 

• Inspect the transmission, transfer and differential vents to make sure they are open. Clogged vents can result in excessive internal pressure and leaks - which can be permanent once started.

I have to ask... has anyone figured out how to inspect or replace the transfer case breather?

 

I posted the updates above

 

Good question, mine seems to be leaking from the front cover on the transfer case. I wonder if cleaning the breather might help.

 

Access is tough. I cleaned the outside on mine about 4 years ago, but Ralph's question made me look a little harder.
A good write-up from Blackness on the Camry forum. I found it using the part number Mylander said is the correct part in his thread a couple of years ago. Seems that it has been used for years in various applications, from 1991 to 2021 including all the Highlanders up to 2019.
But it makes me wonder if I did anything when I tried to clean it. I guess cleaning the outside is at least a first step.

Does the Manual Transmission on '95 Camry have a...

Does the Manual Transmission on '95 Camry have a breather/vent? Imma 'bout to replace both axle seals on a 1995 Camry that are leaking... 3 years ago I remember pressure hissing out of the fill plug when loosening it... so: does this manual tranny have a BREATHER/VENT to relieve built up...

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From Mylander:

Safe to change transfer case and diff fluid

My 2006 highlander is still running great but having some experience with cars now I would like to maintain this vehicle. Vehicle has been driven on mostly highways with little city for most of its life. Never towed anything with it. its a 3mzfe Sport with a 3rd seat. Did the timing belt and all...

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Transmission breather location and cleaning

These pictures should help you to find the location of the breather and replace it. Make sure you order a new o ring as well. I reused mine because I didnt have one atm. The breather connects to a hose and on the other end of the hose is another valve (attached to side of valve cover), which I...

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Diff and transfer fluid change + breather

Just doing a write up in case anyone tries this. I have a 2006 sport 3.3l 4wd. The diff fill and drain was a 10mm hex. So I removed the fill first then drain plugs. Put a whole quart of 80w 90 gl5 gear oil and torqued plugs to 36ft lbs. For the breather on top of the diff, to make it easier...

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Part Link from Toyota parts - don't know how long it will last

2020 Toyota RAV4 Breather plug; plug - 9093003133 - Genuine Toyota Part

Breather plug; plug. 2020 Toyota RAV4. Genuine Toyota Part - 9093003133 (90930-03133)

parts.toyota.com

 

Okay... so how did you get to the transfer case breather? Can't get to it from below (I've tried). Must be either with the intake plenum off or through the right side wheel well. Neither is going to be very darned convenient. I wish I'd thought to look last time I had the IP off.

If my rear diff is any indication, these things plug up inside the cap, so cleaning the outside isn't going to do the trick. When I removed the rear diff breather, it was so blocked up I just drilled a 1/16 hole through, re-installed and replaced with a new one a few days later.

Pressed in breather kinda suggests Toyota didn't think this one would need servicing... and maybe it doesn't. But if it plugs, there will be problems and the xfer case is one problem I do not want to have.

 

Okay... so how did you get to the transfer case breather? Can't get to it from below (I've tried). Must be either with the intake plenum off or through the right side wheel well. Neither is going to be very darned convenient. I wish I'd thought to look last time I had the IP off.

I can't remember how I got to it even to clean the outside. I had pulled the IP off to do the plugs, and may have had the wheel and fender liner off to check the power steering pump. I will try to get a look with a borescope camera over the weekend. I want to see if I can get a hose over the breather, remove the filler plug, and use a vacuum pump to suck out some of the crud. If I can hear air rushing in through the filler then it should be open enough.

OK I was able to get the borescope in from the bottom but need more light. I can see that it appears to still be clean, but can't know what that rubber flapper is doing. I did see that there is a third plug at the top - I guess for factory fill. I did not try to get a wrench on it. Looks like the filler plug. Just a thought- if there is a breather that fits that thread, it might be an alternative, but it will not have an oil baffle inside, so it might leak.
I was not able to get a tube over the breather from underneath. I will try next time I have the fender skirt off.