We’ve all been there. You’re cruising down the track enjoying the scenery when you happen to glance down at the dash and see your temperature gauge needle is right up at the wrong end, and your 4×4 is now overheating. You look back up just in time to see steam hissing out around the bonnet. You take some time to spit out a curse word or three before pulling over to the side of the track and shut the engine down, hoping like hell no lasting damage has been done.
Y’see, it’s no secret that engines hate excess heat – it’s one of the quickest ways to kill your 4X4 and collect yourself a hefty five-figure tow and repair bill. Not ideal regardless of whether you’re out on the trip of a lifetime or heading up the beach for a quick weekend mission. Overheating sucks.
All is not lost however. Chances are it’s something that can be fixed right then and there. Of course, we don’t need to preach to you about preventative servicing and maintaining a healthy cooling system on your vehicle right… right?
Here’s our rundown of what commonly goes wrong with your cooling system and how to get out of trouble when it does.
Cooling systems are designed to be sealed with the coolant being circulated under pressure. This is because fluid under pressure has a higher boiling point than when it’s at atmospheric pressure. Ever heard about water boiling at the top of Mount Everest way under 100ºC due to the low air pressure? It’s the same principle at play – the higher pressure drives up the boiling point and allows the coolant to be more efficient at removing heat from your engine.
It’s your radiator cap’s job to maintain this pressure within the system. If you’re running hot, pull over and allow the engine to cool (have a cuppa) until you can touch the cap with your hand without screaming in pain. Remove the cap carefully (the fluid inside may still be under pressure and squirt out – I actually know someone with significant facial burn scars from opening a radiator that still had hot coolant inside, so take it nice and easy ok) then inspect the gasket on the underside of the cap.
If the gasket is split, perished, hard or brittle it may not be able to seal the system and hold pressure and allow the fluid to boil off, especially once the engine’s shut off. Once the engine is no longer turning the coolant is no longer circulating so it’s not shedding heat and it can be warmed enough to boil. Always carry a second cap with you in your spares kit to avoid any dramas.
It seems kind of obvious, but did you check your coolant levels before you left? Coolant has a higher boiling point and lower freezing temperature than water, although doesn’t displace heat as effectively so a mixture of both fluids is recommended. If you’re using a concentrate only mix it with distilled water. Tap water will rust the inside of your engine block’s coolant passages and can promote corrosion throughout your cooling system, whereas coolants have a corrosion inhibitor in them – radiators hate rust! Coolant also lubricates your water pump and keeps deposits from forming in your water galleries, so it’s important to keep it topped up and change it out every couple of years. In a pinch you can top your radiator up with tap water, but flush and re-fill it as soon as you get home.
Ideally, check your radiator hoses before you leave on a trip – a good trick is to change them out anyway and toss the old ones in the spares kit. You want the rubber to be in good shape and not cracked or brittle, and the hose clamps not biting into the rubber which can cause cuts which produce leaks over corrugations and other off-road vibration producing terrain.
Hoses can also collapse from suction, which most often occurs on the lower radiator hose. It may only happen at speed and not be immediately obvious on a trackside inspection. Check the internal spring hasn’t collapsed or rusted away which is the main culprit here, but a stuck thermostat can also cause them to collapse, which brings us to our next point…
A thermostat is essentially a valve that gradually opens to allow cooling fluid into your engine as the temperature rises from running. It controls the rate of coolant flow and allows your engine to get up to operating temperature before it opens, which’ll only happen at a pre-determined temperature (different thermostats open at different temps).
A thermostat that’s not opening soon enough or too late can cause overheating to occur. If you suspect your thermostat is faulty, you can remove it entirely to get you home, but keep in mind that running without one may not allow your engine to reach optimum operating temperature and damage can occur, so replace it as soon as possible. Not to sound like a broken record but having a spare in your kit is a great idea, particularly if you’re travelling through the desert or other hot-running environments like the beach or when towing a trailer.
As the name suggests, this is what pumps the coolant around your engine. It’s driven off the belt system which is among the first things to be checked once you’ve pulled over and let everything cool down. Look for cracked or torn belts. Because you’re a smart four-wheel driver who’s always prepared, you can simply retrieve a belt from your spares kit and throw it on without too much fuss. If however you’re like the rest of us and didn’t pack it, it’s time to get creative. We’ve seen everything from cable ties to pantyhose used as makeshift belts – just don’t expect them to last. Get two new ones ASAP and chuck the second one in the spares kit like you should’ve done in the first place (yes, we’re guilty of not doing this too).
If that’s not the case, check the pump itself. Failures in the water pump are most often advertised by a leak around the pump housing, usually on the underside. There’s a bearing and a seal inside the pump and if one goes, the other often follows a short time later. Pump life comes down almost exclusively to cooling system maintenance.
Use fresh coolant every couple of years and flush the entire system while you’re at it. These should last the life of the engine so they’re not a regular cause of overheating, but they do let go occasionally. As such, they’re not often found in spares kits so you’ll need to limp back to civilisation to swap it out for a new one. Make sure the coolant is regularly topped up and the heater is on high while you’re driving (the heater core is effectively another small radiator which will bleed heat from the cooling fluid for you). It’ll be an uncomfy drive, but it’s better than paying thousands for a tow.
Most 4X4s have either electrical fans or viscous clutched fans that are bolted directly to an engine pulley. They draw air through the radiator and are an important determining factor in its overall cooling ability. Clutched fans are able to work at low vehicle speeds, such as when negotiating a tight section of track in low range, and then essentially switch off at higher speeds when the air is flowing faster through the radiator fins.
There are a few tell-tale signs that a fan clutch is on the way out. Check how much free-spin it has when the engine’s stopped. If it freewheels more than three revolutions on its own after you spin it the clutch is probably not working. Also, if your air-con is not working that well when the vehicle is travelling at slow speeds then there may not be enough air being pulled over the condenser and AC performance will suffer. Also visually inspect the fan for fluid leaks and to see if there’s too much play in the bearing or if it spins roughly or grinds – all signs you’ve got a bad fan.
On electric fans, check the wiring and fuses as well. While you’re under the bonnet, inspect the fan shroud for damage from stones or branches being kicked up. The shroud directs hot air away from the radiator, so if it’s damaged, the hot air may not be able to escape and lead to a rise in engine temperatures.
This is the big one. The radiator is the main component in a vehicle’s cooling system and is what cools the fluid down after it’s circulated through the engine collecting heat. Inspect it closely for leaks and if possible, patch them with metal putty. Try to avoid using stop-leak fluids that you pour into the cooling system as they can often clog cooling channels…but if all else fails you may have to throw some in.
Dirt, mud and grass seeds can all clog a radiator’s fins so make sure you regularly wash them out with a hose from the back side of the radiator. Also look for bent or damaged fins, as they can affect the cooling efficiency. Some careful work with the needle-nose pliers can get them straightened back out.
It’s a good idea to get your radiator professionally flushed every year or two. Corrosion and lime scale can build up and impede coolant flow, which is not going to do your cooling ability any favours. If you do find yourself with a pierced radiator out in the scrub, try dropping a raw egg or some pepper in the fill-hole. When they cycle through and contact air at the place of the leak, they should swell up and seal the hole. I’ve seen this work first hand, but it’s a temporary fix at best.
If there are bubbles in the coolant, oil mixed in with the cooling fluid, or a milky slime under the oil cap, chances are you’ve done your head gasket. Best bet here is to drop a tube of stop-leak type stuff in and hope for the best, but either way it’s time for the head to come off and have a new gasket fitted in place. Make sure the head is machined flat before you bolt her all back up too.
Heads are an expensive repair, no way around it. If you’re a bit suss on it before you leave, or are losing coolant without any apparent external leaks, get a compression test done, or even better a leak down test before you head off. That’ll let you know whether it’s time to look elsewhere for the problem, or put the trip off for a week or two in order to get it fixed.
In some cases a cracked head gasket can lead to an air bubble being trapped in the water pump causing it to stall. It may be worth trying to run your vehicle without the radiator cap on tight to stop pressure from building and allow coolant to bleed back into the pump, but this can also result in exhaust gasses being pumped into the coolant (depending on where the gasket has broken), making the problem worse so it’s not a fix-all solution by any means.
Other things that can cause overheating
- DIRTY ENGINE AND RADIATOR
You don’t need a degree in thermal dynamics to realise that an engine and radiator covered in a healthy layer of mud are not going to radiate heat as efficiently as one that’s not. Make sure you hose your radiator out from behind after every trip and keep your engine bay clean.
- TOO MANY ACCESSORIES UNDER THE BONNET
Engines partially rely on airflow through the front grille to keep them cool. If you’ve got five batteries, a compressor, winch control box, pie warmer and a big block V8 crammed into the space that was designed to accommodate a 4-cylinder, you may run into problems. The engine needs to be able to have efficient radiant release of heat. Cramming accessories around it won’t let it happen.
- POOR TUNE
If you’re running a poor tune on your engine it can lead to things running hotter. If you’ve isolated all other possibilities, it may be time to book her in some dyno time with someone reputable. Older diesels in particular can fall out of tune and need adjustment. Similarly, if you’ve installed a cheap, cobbled together “performance chip” you may want to consider plucking it out and repurpose it for stopping your bin from floating away. There are far better options, and reputable power modules available.
- ENGINE COLOUR
Believe it or not, black is the best colour to paint your engine. It comes down to the fact that it is the most capably dissipative colour on the infrared spectrum. Lighter colours can actually absorb heat as well as dissipate it, and far less in the infrared spectrum than black. It’s not enough to overheat an engine on its own, but if you’re wondering why your freshly painted lime green powerplant isn’t running as efficiently as it used to – now you know.