Keeping your Cool: How to Prevent Overheating

Steve Cassano — 18 April 2019
Things getting a little heated with the engine? Nip overheating in the bud before your components go bust or you find yourself stranded in the bush.

Can you name all the fluids in a 4WD? A typical modern 4WD can have up to nine or even 11 different fluids running through its body, driveline and engine. Not to mention the Coca-Colas in the drink holders. When I give it some thought, I am amazed by how much the average 4WD relies on fluids. 

Of course, each fluid has its place. Fluids are used for several purposes and functions, including lubrication, hydraulic applications, fuel, cleaning, and cooling. Some fluids even have a dual purpose where they act both for cooling and lubrication cohesively.

However, there is one fluid that is used strictly for cooling, and that is coolant. In this article I’ll explain how to keep your engine’s cooling system running as it should be and why this is one of the most critical maintenance tasks that all owners need to understand.


Manufacturers design their vehicles to run at an optimal temperature. This is a set temperature range in which the engine and components perform at their peak. If the engine and components stray too far from this optimal temperature, problems can arise. A vehicle with a poorly maintained or failing cooling system can be detrimental to engine components, resulting in poor performance or – in a worst case scenario – the engine seizing. Best to avoid that happening out in the sticks!

It was an overheating problem that prompted my young cousin Mitch to call me a few weeks ago. His 1994 N106 2.8 Toyota Hilux Ute seemed to be running a little hot; could I suggest what might be the problem? He also mentioned that the temperature gauge was erratic – varying between not working at all and showing high temps. Finally, in typical fashion for a young fella, he mentioned he was in a hurry because he planned to go camping the next weekend. So the next day I dropped over to have a look at his pride and joy.

I wasn’t too surprised he was having issues, as he’s still in his first few years of 4WDriving and loves hitting the tracks regularly, and especially going through mud holes. Detrimental effects from mud holes would have to be one of the most common causes of cooling problems, with mud ingress often clogging up radiator fins, damaging bearings or belt pulleys, and inhibiting adequate airflow. On top of that, he rarely cleans his Hilux; apparently leaving it caked in dirt is a badge of honour. Naturally that exacerbates the problem.

Closer inspection under the hood revealed an apparent small leak from midway down the left of the radiator (leaving a reddish trail) and plenty of crud encrusted in between the main radiator and the air conditioning condenser that sits forward of the main radiator. It was obvious that this was the original metal radiator, so it was time to change it, along with a few other components. The 4WD sure well deserved it; this still-reliable Hilux was 25 years old and had taken him and his mates along many muddy tracks to many distant campsites.


Although my young mate was financially challenged (as he kept reminding me), I strongly urged him that we were best off changing a few other components at the same time to ensure we covered all possible scenarios in the old Hilux’s cooling system; it’s best to do a complete job in one hit rather than bits and pieces over time. So he ordered the assorted goods and, by the following Saturday, a new aluminium radiator from Fenix, a high flow thermostat, gasket, sender unit and 5L bottle of Nulon long-life coolant were all on his doorstep. All up he forked out around $600 for the parts.

My initial inspection of the new radiator revealed that, although the quality was definitely there, it was slightly thicker than the original, which raised a few doubts. Mitch’s only remark was that it was nice and shiny, mmmmm. Only time would tell, so we commenced the task of swapping the components on a wet Saturday morning in Sydney.

I didn’t anticipate any major dramas and knew the whole job should take no longer than 90 minutes. As it turned out, all we needed was a couple of tools, including: a 10mm spanner, 3/8” (or you could use 1/4”) 10mm deep and shallow sockets, a corresponding ratchet handle, a variety of extension bars, and a universal joint plus a flat-head screwdriver – along with some band-aids for the inevitable grazed knuckles!


We commenced with draining the old coolant by undoing the easily accessible bottom radiator drain plug and extracting the bottom radiator hose by undoing the steel clamp with the screwdriver.  Simultaneously removing the radiator cap helped most of the water drain freely. There’s no need to keep the old cap as Fenix supplies a new one with their radiators.

Once the water had been cleared, we removed the top radiator hose, again using the screwdriver and gently prising it off. We were surprised that both hoses were still in excellent condition and decided that they could be easily reused (with a small modification; see below). It was also reassuring to see the drained coolant was clear of any contaminates.

Once the radiator and overflow hoses were detached, removing the radiator shroud was the next task. The shroud’s function is to funnel the airflow for more efficient cooling, just like when you’re blowing on hot chips to cool them down before feasting... Undoing just the four supporting bolts using a variety of 10mm configurations was a bit of a challenge due to the confined space. Luckily, after a few expletives and with one person holding a torch, we managed to extract the shroud by lifting it vertically out of the way. 

Once cleared, the radiator had similar requirements with just four 10mm bolts supporting the whole assembly. With a fraction more space to work in, Mitch slowly screwed the four bolts out while I held the heavy unit to avoid damaging other vehicle components. A short time later we had the old radiator sitting on the ground. It looked pretty sad and sorry, with many damaged fins and about 30 per cent being clogged by mud from the 1990s.

At this time, I had Mitch hose out the area, including directing water spray through the air-conditioning condenser. Again, plenty of dirt came flowing out, which highlighted the need for Mitch to perform regular cleaning after a day out playing in the mud.


After the obligatory morning tea with biscuits and a discussion of all things 4WDing, we commenced on changing the sender unit and thermostat. After unclipping the electrical connection and using a deep socket, we extracted the old sender. Again, it looked pretty awful, so luckily we had the new one. We screwed it in easily, then reattached the connection.

Next, after loosening the turbo and inlet hose mounts to gain access, we undid the three 10mm bolts to get access to the thermostat housing. To our surprise, after pulling it out, we found that the internal rubber thermostat seal had actually split and parted to a point where it had jammed the thermostat closed. How lucky we’d decided to buy a new one! 

But then, it wasn’t that simple. The replacement, when compared to the old one, was actually the wrong one, completely the wrong size. A quick trip to Repco had us back with the right unit. After a quick clean of the thermostat housing with a small wire brush, we decided to lay a line of sealant (plucked from our magical bag of tricks), rather than use the gasket. Then we positioned the replacement thermostat in its place, tightened the three housing bolts and reassembled the overhanging turbo and inlet pipe.


By now we were on the home run. I held up the new radiator, ready to install, and immediately noticed how light it was. I’d guess the new radiator was about a third of the weight of the old metal one and that can only be a good thing, even though it was still distinctively thicker, by about 15mm. I dropped the new unit into its place with caution, careful not to damage any fins or the fan. After a concentrated effort we managed to place it in position and get all four mounting screws sufficiently tightened.

The shroud was next, and again, with patience, we placed it in position and screwed it in place (this is when most of the band-aids came into use).

The bottom hose fitted like a glove and was tightened accordingly. However, due to the thickness of the radiator, which resulted in the top hose inlet being offset a little, we decided we’d trim the top hose about 20mm to avoid any kinking. It then fitted like factory, as did the overflow hose.


With the finish line in sight, we added about three litres of concentrated Nulon coolant, which has a life of seven years, and supplemented it with some clean water to top the system. After the initial fill, and having the engine run to normal temps, we added a little more coolant mixture, and topped the overflow bottle. We estimated the Hilux’s cooling capacity to be around 8.5 litres, so the Nulon 3L concentrate would be more than ample for its needs. As a final note, if you’re doing this yourself, remember to dispose of the old coolant in an environmentally friendly way.

That’s all there is to it. Maintaining your cooling system is a very simple and effective DIY job that anyone can do with basic tools and patience. I recall Mitch being happy with the final result and uttering “it’s real shiny” as he headed towards the next bog hole, intent on making it less shiny once more... Happy wheeling.


technical how to guide 4wd overheating engine cooling radiator