How to Keeping your Tow Vehicle Cool?
Running ‘too hot’ can happen in cold weather but with summer upon us, the chances of overheating go up in high ambient temperatures.
Towing a van creates greater demands on your vehicle due to increased weight and wind resistance. This can cause various systems in your car to overheat.
In this article, with the help of some industry experts, we explore the various mechanical systems in your car that generate heat and how the heat is regulated. In addition, we cover the four Ms of cooling to protect your vehicle – managing your driving, monitoring your systems, maintenance, and modification.
Let’s start with the basics. Various systems in a motor vehicle generate heat under normal operating conditions. The engine, transmission, and brakes are all examples of parts of the car that get hot. All these systems have optimal operating temperatures and if exceeded, failure or premature wear can occur.
The engine
The engine generates heat through the process of internal combustion and the friction of moving parts. Engines dissipate heat in two ways:
- Liquid cooling regulates the temperature for fixed parts of the engine such as the block and head. Coolant is pumped through internal passages in the engine block and circulated through the radiator. The radiator has fins that enable air to pass through it dissipating heat to the atmosphere.
- Moving parts rely on the engine oil to distribute and dissipate heat.
The transmission
Hydraulic automatic transmissions are found in most vehicles these days and the torque converter plays a critical part in the operation. Stuart Kitto, director at Wholesale Automatics explains: “The torque converter is a device that sits between the engine and the automatic transmission. It is referred to as a fluid coupling with two modes – unlocked or free spinning mode and a locked or engaged mode. The transmission electronic control unit (ECU) automatically controls when the torque converter is switched between these two modes. When your vehicle is travelling in a situation where the ECU calculates that the torque converter lockup can be applied, a solenoid is activated sending oil pressure to act on a clutch inside the torque converter which in turn ‘locks’ the engine output shaft and transmission input shafts together so they spin at the same speed. This primarily is to reduce heat build-up and reduce fuel consumption.
Most vehicles are optimised for suburban driving and where towing is the exception rather than the norm. This can result in the torque converter running in the unlocked position while towing when it would be ideal to be locked. The knock-on effect is more slippage, more heat, and potentially worse fuel economy.”
Similar to a radiator, the hydraulic oil passes through a heat exchange with fins to cool it. As air passes through the fins, heat from the system is dissipated.
The brakes
Your tow vehicle brakes are another system that gets hot. The action of brake pads making contact with the brake discs or drums causes friction which generates heat. Brake fade occurs when the brake pads break down, giving off gases that create a microscopic layer between the pads and the disc or drums, which reduces friction and therefore braking performance. A more dramatic brake failure can be caused by brake fluid boil. Brake fluid has the characteristic of absorbing moisture from the atmosphere over time. When brake mechanisms get hot some of the heat is transferred to the brake fluid. If there is enough water in the brake fluid and the brake fluid gets hot enough then the fluid will boil, creating bubbles in the system. These bubbles are easily compressed and effectively stop the braking system from working.
Managing
The first step in minimising overheating is managing the variables you can control. As we touched on, ambient temperature goes on top of your operating temperature. For example, your systems can run 20 degrees hotter on a 40 degree day compared to a 20 degree day. If you can avoid driving in the hottest of conditions, do so. The heavier your rig is the more you load the system. Keeping weight down will not only help keep your tow vehicle running cooler, but it is also good for safety and fuel efficiency too. Take breaks to let the vehicle cool down if you are doing a lot of ascending or descending. Going up makes the drive train work harder and going down asks more of the brakes.
The next one is a bit counter-intuitive. Many believe that by driving in the highest possible gear at the lowest possible revs gives the best results. Stuart from Wholesale Automatics tells us this is not the case and in fact is usually detrimental to heat generation and fuel consumption. Above, we learnt that slippage in the transmission torque converter is a cause of heat. One way to minimise heat and improve fuel consumption is to rev the engine harder. This reduces load and heat generation on both the engine and the transmission torque converter.
Monitoring
In a stock standard car, the only visual reference for heat is generally the engine temperature gauge. Hayden Kelly, sales supervisor from PWR Advanced Cooling Technology says this is a good place to start. “Monitoring the differences in the temperature gauge when towing or not will give you a good idea about how the engine is coping. If you find the gauge running close to red when towing, then you are going to need to change something. A more precise way to monitor engine temperature is to add an aftermarket temperature gauge with a numerical readout. Similarly, a temperature gauge can be fitted to monitor automatic transmission temperatures.”
Arguably this is more valuable than an aftermarket engine temperature gauge, as a standard car provides no feedback on transmission temperatures. Stuart from Wholesale Automatics highly recommends “that transmission temperature gauges are fitted to all vehicles to provide real-time feedback on your driving style’s strain on the automatic transmission. Most importantly, with a transmission temperature monitor you will be able to understand what is ‘normal’ for your transmission during your average day-to-day driving. When you put extra strain on your transmission with an automatic transmission temperature gauge kit fitted, you will be able to see how your transmission is coping and how long it takes to return to ‘normal’ afterwards.” Hayden from PWR adds, “They are not necessarily early warning signs, but hot transmission oil can lead to the transmission making strange noises or the gears not shifting correctly.”
Temperature gauge kit
As far as brakes are concerned if you feel the brake pedal action is getting softer or you can smell the burning of brake pads you are likely sensing brake fade and it’s time to pull over and let the system cool. More dramatically, if your brake pedal goes to the floor when braking then you have likely experienced brake fluid boil and you better start downshifting that transmission fast to slow the vehicle down.
Maintenance
Vehicle maintenance is always important and particularly so for a tow vehicle due to the extra loads involved. Heat and time cause all fluids to degrade. Leaks can also cause fluid levels to drop. Companies such as Penrite play a huge part in developing and supplying quality fluids to keep vehicles properly maintained. According to Brendan Hughes, national technical and sales support manager at Penrite, choosing the right fluids, changing them on a regular basis, and keeping them to the right levels are some of the most fundamental things you can do to keep your tow vehicle running cool and protect against premature wear or failure.
Coolant is the first thing you think of when it comes to managing engine temperature. There are a multitude of specifications of coolants, and it is important to use compatible coolants if you are topping up the system or having it replaced. Mixing coolants can cause chemical reactions which can coagulate the fluids clogging up the cooling system. Coolants come in all kinds of colours and Brendan from Penrite says, “Unfortunately you can’t judge a coolant by its colour as there is no standard for colour and coolant spec. Similarly, it is important to ensure a suitable spec is used for engine oil, brake, and transmission fluid.”
Vehicles that have operated in offroad or outback conditions can end up with dirt or other debris clogging the fins in radiators or transmission coolers preventing air flow and thus overheating. Gentle application of compressed air can be used to clear the delicate fins without damaging them. Engines that have been in service for some time may build up rust, lime, or scale inside the cooling system and require a flush periodically. Other components in the cooling system that need checking or replacing periodically are radiator fans, thermostats, and hoses.
Modification
The final step is to consider fitting aftermarket components to enhance the cooling power of your vehicle. PWR are leaders in this space developing products for motor racing, aerospace, and OEM equipment. Hayden from PWR says a common upgrade is to plumb an additional transmission oil cooler into your system which can be DIY installed. This increases the surface area of the cooling system and introduces more transmission fluid into the system which both aid with cooling. Radiators can also be upgraded with units designed to allow greater flow of coolant through the system and more air to pass through the fins to improve heat dissipation.
Stuart from Wholesale Automatics reckons another modification worth considering is a torque converter lock-up kit. Wholesale Automatics have been pioneers in developing lock-up kits to improve torque converter efficiency “The lock-up kit overrides the factory ECU. The latest models have been developed to automatically kick in the lock-up function at times more conducive to towing. The system can be further finetuned to your needs using a phone app. And for complete control you can lock the transmission manually with the flick of a switch. Lock-up prevents slippage and therefore reduces heat generation. Torque converter lock-up kits also help with reducing fuel consumption while towing on the open road. Plus, you gain 100% engine braking which reduces the reliance on regular brakes on long steep descents. The system is easy to install and can be supplied as a DIY kit.”
No doubt some tow vehicles will benefit from modifications, but it is worth being mindful of the impact on new car warranty where applicable. If in doubt consult with the car manufacturer before proceeding so you know where you stand.