Towing Basics

Ok, I just bought a TM 3124 and towed it from Casper Wyoming to Denver. It towed like it wasn't even there with my V6 4runner, with it's 6000lb towing capacity. I have towed a lot over the years so I know that once I head UP I will see more issues but I plan to take it easy.

My questions are:

1. When is the transmission most stressed, at a constant 3000 RMP and constant speed, or a lower RPM and shifting around. (Auto Transmission)

2. Is it my transmission that is stressed in carrying a big load, or is it more my engine?

3. I am never in a hurry while towing, and am happy behind the slow semi's, so what is the rule of thumb to tow big loads, while trying to be as gentle on the TV as possible?

Thank you,
Jason

[Wavery]

Your engine and transmission are always under more stress when towing or even if you just have a heavy load in the vehicle. More weight causes harder work which produces heat. Heat is your enemy.

Now, more specifically to your question. It is better to have the engine running at a constant RPM that is about 2/3-3/4 of the engines maximum RPM level rather than to have the trans hunting for gears. Some people are afraid that engine uses more fuel at higher RPMs. That isn't necessarily true. If the engine is lugging and hunting for gears, it is probably using more fuel than if you leave it in a lower gear and run the engine at a constant RPM while pulling up a grade (even a small grade).

The higher the RPM the more HP the engine develops and the engine has to work less when it is at a higher RPM (as long as you aren't pedal to the metal) and it produces less heat.

When the trans is "Hunting" for gears, that puts a lot of stress on the (transmission) torque converter and develops a lot of heat. Most of that heat is dumped into the vehicles radiator which in turn will make the engine run hotter. So the answer is....Heat is hard on both engine and trans. They are both connected by the same cooling system and a hot trans = a hot engine and visa versa. That's why it is very important to have the largest auxiliary trans cooler that you can fit in the vehicle.

The other killer is pulling a hill at low speeds (under 35) or sitting in traffic. There is not enough airflow through the cooling system to remove the heat fast enough. That is why I always recommend a trans cooler with a fan.

Here's an example of the fan assisted trans cooler on my Silverado V8. I have the fan wired to the engine cooling fan with a relay so that every time that the radiator fan comes on, the trans cooler fan comes on at the same time.

Another tip on "Keeping Cool" is to use synthetic fluids. Synthetic fluids have far better cooling properties than petroleum based fluids. They also have a higher maximum operating temperature....it's all a win-win. Synthetics are more expensive but it has to be changed far less frequently which makes the fluid changes cost no more but the product is far superior.

Excellent information...thank you!

I don't mean to sound picky here, but my 2005 V6 4Runner has a tow rating of 5000 lbs.

Besides synthetic oil, what other "synthetic" fluids are there to consider in the heat equation?

Phil

I also run synthetic fluid in my transmission and in the differentials. Be sure to check the owners manuals as some differentials require the addition of a small amount of limited slip additive available at most automotive stores. You mention going up and have considered many of the concerns there, but don't forget the coming down part. Most of the energy used in going up needs to be handled when you come down. Be sure to check the braking system and possibly swap out the brake pads for High temp/ heavy duty ones.

Originally Posted by P and B

Besides synthetic oil, what other "synthetic" fluids are there to consider in the heat equation?

Phil

Someone correct me if I am wrong, but lubricating fluids are only 3 places: engine, transmission, differential(s).

I still run Dino oil in my engines. I have been getting 185k to 220k+ so far with that strategy.

My GM trucks have a factory spec of synthetic for the front and rear differentials.

Transmission is ATF. I really don't know what that is.

There is also power steering fluid, but I just don't see towing as impacting that.

Brake fluid should not be impacted by towing, as long as you downshift when going down long steep roads.

[Wavery]

Originally Posted by P and B

Besides synthetic oil, what other "synthetic" fluids are there to consider in the heat equation?

Phil

Synthetic engine oil is good but (for the cooling aspect) synthetic trans fluid is essential IMO, for dissipating heat build-up through an auxiliary trans cooler.

Few chemicals will dissipate heat better than water. It is important for your trans fluid to pass through your radiator to remove as much heat as possible (unless you have a very big external trans cooler or multiple trans coolers). The addition of an auxiliary trans cooler will assist in removing that heat and keeping from having some of that heat from being dumped into the radiator. However, when using synthetic trans fluid with an auxiliary cooler, it makes the auxiliary cooler 100% more effective because synthetic fluids release heat at a far faster rate then petroleum fluids.

You can also get synthetic power steering fluid. When towing (or carrying any heavy load), there is more stress on your power steering also. I also switched to Synth P/S fluid.

Originally Posted by harveyrv

You can also get synthetic power steering fluid. When towing, there is more stress on your power steering also. I also switched to Synth P/S fluid.

Not that I don't believe you, but I don't see the connection as to why towing would increase the temperature of power steering fluid. I would have thought that the power steering fluid temperature was more related to air temperature and frequency of turning the steering wheel.

For someone towing without WD bars when they should have them, resulting in weight reduction on the font axle, I would have expected that to lower the power steering fluid temperature.

[Bill]

My primary concern has always been the transmission, since its operation is more or less invisible, and less understood than the engine. Somewhat to my surprise, slowing down to "take things easy" is not the best answer. I base this on actual observation of the aftermarket transmission temperature gauge that I added to my Explorer (mine is a Aeroforce Interceptor, but the Scan Gauge is also good). When travelling more slowly, the transmission gets hotter. If you are going to tow in the mountains, you might consider getting one. Installation is simple, by the way - it simply plugs into the OBD port under the dashboard in your vehicle.

I agree with most of what Wayne says. Slower means hotter at least partly because of the reduced flow of cooling air. Slower may also means hotter because slower may imply that the engine RPMs are lower, which forces the transmission to work harder as it hunts for the proper gear. To my surprise, I learned that a transmission has several intermediate gears between each real gear. Between 3rd and 4th, for example, there may be several intermediate gears, which are really differing degrees of slip in the torque converter. The drivetrain computer controls the amount of slip, but as Wayne points out, ANY slip generates heat, and lots of it.

From Payson to Heber-Overgaard, Arizona, the road is good but climbs very steeply. My wife and I climb this road at least once every year, with a heavily loaded TM. Using our gauge, we have intentionally adopted several different driving strategies, to try to find the best one. Staying slow - like 30 mph - and leaving the transmission to find its own gear, is the worst method. The temperature of the transmission rises rapidly. We have learned that staying fast - like 50 mph - and manually downshifting to 3rd (in our 6-speed transmission) gear, is much better. At the higher speed, airflow is better, of course, but I believe that with the higher engine RPM and lower gear, the transmission is able to lock up the torque converter.

As an aside, if your vehicle came with a temperature gauge in the dash, you can be pretty sure that it is not a real temperature gauge, but is really an "idiot light" with a fancy face. (There is a lot of discussion on the Internet about this.) If you have noticed, like so many drivers, that "I've climbed steep hills and the temperature gauge never budged!", then your gauge is a fake. There are a few exceptions - vehicles with real gauges - but for most, an aftermarket gauge like a ScanGauge is the right answer.

Just my experience, but perhaps it is helpful.

Bill