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Never fill 100% coolant into your cooling system!
The manual specifies the limit to max. 60% - the lower threshold is 35%.
Coolant has a lower heat capacity than water, but a higher viscosity, so change in both parameters due to a higher coolant concentration will boost the negative impacts on the heat transfer.
The lower heat capacity will lower the heat transfer rate, which is even further compromised by a lower water pump capacity due to the higher viscosity. Therefore the higher the coolant concentration, the lower the heat transfer.
In down under we don’t need to protect the cooler system against minus 30 deg C - conversely an extreme good heat transfer capacity and the rust inhibitors in the coolant is required.
The minimal coolant concentration specified in the manual - 35% - is just fine for hot climates and will give a much better heat exchange rate compared to a 65% or even 100% fill, especially when going up a steep hill with the camper in tow.
The colour of the coolant is not really important, but issues can be caused by the different types of corrosion inhibitors different brands may use. The different corrosion inhibitors can neutralise each other compromising the corrosion protection.
Owners and inexperienced - or lazy? - Hyundai mechanics - get often fooled by this: it is not possible to check whether there is sufficient coolant in the system by just opening the filler cap. Also if the coolant level reaches the filler neck edge, there can be still air bubbles in the system.
The air bubbles will compromise the water pump performance and heat transfer heavily, and will finally cause overheating. The system can “somehow” deaerate itself via the filler cap - but IMO it is not advisable to rely on this.
Air bubbles remaining in the system will expand when heating up pushing coolant into the reservoir; when the engine cools down the coolant get sucked back into the system. A heavily “breathing” expansion reservoir is a good indication that there is not enough coolant in the system.
To fill the system completely via the open radiator cap with an idling engine can take 5 - 10 stints and quite some time. I know from one owner, who experienced overheating and who was able to fill additional several liters back into the system following this procedure.
The right coolant in the right concentration is mandatory! The Terracan requires an ethylene-glycol based coolant.
If you live in Australia or other countries with a warmer climate:
The CRDi engine takes 9.4 liters coolant (the petrol even 11 liters) in total, but when you do a coolant change you can only drain approx. 5-7 liters via the drain plug at the radiator.
Consequently you can only fill these 5-7 liters (if nothing was missing) back in. The 2-4 liters remaining in the system sit in pockets and cavities and for a complete change flushing of the system is required.
The petrol engine - check page 6-10 and 6-11 of the owner’s manual! - requires to remove the engine cover and to unscrew the bolt for the water drain to equalize pressure and to allow a 100% refill.
The refill can be tricky. Owners who just fill it to the edge of the radiator cap thinking that’s it get it likely wrong and might experience overheating due to lack of coolant.
To avoid sever burnings, draining and refilling has to be done with a cold engine!
Filling coolant back takes a while and a running engine / working water pump too; when filled to the edge, with a running engine and water pump the level will drop after a while allowing to add more coolant.
Note: coolant at the edge of the filler neck doesn’t mean automatically that there is enough coolant in the system!
Conversely I experienced some overheating issues in the earlier days of my ownership after a service conducted by a Hyundai dealership. These issues were solely caused by an improper filling of the coolant system. IMO the cause of most overheating issues lies in an improper coolant refill respectively air in the system.
Consequently measures like replacing the genuine radiator with a bigger one as discussed in one of the forums or replacing the thermostat with one that opens at lower temperatures will likely only mask the real culprit and beside wasting money might even compromise other realms.
Without a precise temperature reading via a suitable scan tool a decent assessment isn’t possible, and as a first measure for everyone experiencing overheating issues I highly recommend a ScanGaugeII (or a similar tool) to overcome the flaws of the genuine gauge.
Some owners also recommend to increase the revs to avoid overheating. Wrt any “recommended” threshold it needs to be considered that the CRDi engine provides its max. torque of 345 Nm in a wide range from already 1,750 till 3,000 rpm.
On our recent holiday trip (2 adults and 2 kids, car fully loaded with a packed roof rack and CT in tow) the highest temperature on the ScanGauge was 98 deg C on steeper hills (e.g. Tamborine-Oxenford Rd - QLD) with an outside temperature of 32 deg C.
I have to admit so that the relative low temperature (at this temperature the thermostat is still not fully open!) was achieved with the help of my “light foot” as I always aim for an optimised fuel consumption.
However, with still 17 deg C below the threshold where the ECU switches into limp mode it clearly indicates that there are sufficient reserves in the system.
Based on my experience, the cooling system of the CRDi with an auto gear box - I can’t speak for the petrol and manual versions - is good enough as it is, also for towing a camper up a steep hill in hot conditions.
I drove up the Snowy Mountain / Monaro Highway, up the Jamberoo Mountain Rd (Jamberoo Pass) and up the Macquarie Pass, each time with a fully loaded car (4 adults and 2 kids) with the CT (approx. 1.5 t) in tow without any overheating issues.
Therefore different types of ethylene-glycol based coolants shouldn’t be mixed.
IMO the best is to use distilled water for topping up if required. For a coolant change try to stick to one brand and type, as flushing isn’t so easy with the Terracan and there will be mostly some residuals of the old coolant left in the system. Note: the same colour alone won’t guarantee that it is the same type of coolant!
It is also good practise to check the concentration of the coolant from time to time.
In former time I used a density meter, but now it is much easier to do it with coolant test stripes, e.g. from Castrol.
These stripes give you not only the coolant concentration, but they also indicate whether there are enough corrosion inhibitors left in the system.
Higher revs might indeed worsen the situation as the engine will provide more power (power = function of torque x revs … CRDi: max. 120 kW at 3,800) which means a higher heat load the cooling system has to cope with.
Keeping the revs below the 3,000 rpm mark for the CRDi will significantly help to keep the temperature at a healthy level. It might require to slow down, but as long as the revs are between 1,750 and 3,000 rpm the engine operates at its “sweet point” or better in its “sweet range”, minimizing also wear and tear and fuel consumption too.
For the petrol with a max. torque of 302 Nm at 4,000 rpm the revs can be higher, but the physic is the same.
If you experience overheating (temp. verified by a scan tool!) check first whether the coolant expansion reservoir is “breathing” respectively whether the level changes distinctly - if so it strongly indicates that you have air in the coolant system that compromises the heat transfer.
A note for those who have a body lift: the radiator will sit now higher than the filler cap and you can’t fill the system properly. For the required mods read here.
The thermostat will start to open at 87-90 deg C coolant temperature and will be fully opened at 100 deg C. While cruising with 100 km/h on the highway the temperature should be around the 90 deg C mark. Towing up a hill or hard work in sand can increase the temperature to 105 - 110 deg C.
Above 115 deg C the ECU will send the engine into limp mode to mitigate the risks associated with overheating.
The genuine temperature gauge in the dashboard is quite useless to monitor the temperature. If you really want to know what is happening in your cooling system get yourself a ScanGaugeII.
Not only will it give you the precise temperature, it will also allow to recognise overheating issues before the engine is sent into limp mode and to adjust the driving style to the conditions.
After reading on various forums about overheating issues Terracan owners experienced, I restructured this page a little bit making an attempt to address those topics better.