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Overheating is a common problem, but the cure may be at hand.


Many new 4WDs have electric cooling system fans, but nearly all older-generation 4WDs are fitted with thermal clutch cooling system fans. These are not everlasting items, so will need periodic maintenance or replacement.


Replacement fan assembly and standard one


When we had our LandCruiser 75 Series 1HZ engine rebuilt, we had a new radiator fitted, but even with the injection pump only mildly tweaked to match the after-market turbo’s boost we found that the engine temperature needle climbed when the engine was labouring.

With our slide-on camper on the stretched ute tray ‘Harry’ HJ weighs around 3.3 tonnes, for which we have GVM-upgrade approval. We found that long uphill grades, in hot weather, made the temperature needle move upwards – not to the red danger zone – but more than we liked.

We suspected the viscous fan hub wasn’t working properly, so the fan wasn’t getting up to sufficient speed and checked out what was needed to remedy the situation. Dismantling the hub and replacing its silicone fluid was a possibility, but the fan had done more than a half-million klicks, so we thought a replacement was in order.

It’s well-known that earlier Japanese 4WDs had marginal cooling systems. When loaded and run at Australian highway speeds many of them overheated and it took the 4WD community many years to convince Toyota and Nissan engineers, in particular, to respond with higher-capacity cooling systems. The introduction of factory-fitted turbos forced their hands, eventually.

However, those of us who like the simplicity of older 4WDs are stuck with the need to improve cooling system capacity when even mild tuning upgrades are done. Larger radiators and bigger cooling fans are common after-market fitments, but larger radiators with standard fans don’t usually work very well.

The starting point should really be with thermal fan improvement, cooling system specialists have told OTA.

For those unfamiliar with the operation of a thermal clutch fan, here’s a summary, courtesy of Davies Craig:

A thermal clutch fan operates using silicon fluid as a viscous coupling medium. (Viscous fluid is thin at low temperatures, but thickens as it gets hotter.)

When the clutch is cool and disengaged, most of the silicon fluid is stored in the reservoir allowing your fan clutch to slip relative to your water pump shaft, thereby spinning at lower rpm than the water pump. This saves you money because the horsepower from your engine is not wasted driving a clutch fan when it’s not needed. 

As your engine heats up, the thermal spring on the front of the clutch expands, which opens a valve, allowing the silicon fluid to drive your clutch at increased rpm. This provides more air flow through your radiator, preventing your vehicle from overheating.

Our initial thought was to replace the older fan and hub with a genuine Toyota replacement, but we were actually seeking more fan performance than standard, because the turbo we’d added to the engine increased its coolant load.


QIKAZZ fan assembly is slightly longer than standard


A complication in the case of older 70 Series LandCruisers is that the engine bay shape wasn’t optimised for airflow. I remember many years ago that Victorian after-market specialist Rob Kay moulded a replacement see-through bonnet for his own 70 Series and dotted stuck-on tell-tales around the engine bay. He was able to see from above that even when the standard fan was working properly, airflow inside the engine bay was minimal.

The mechanical workshop that looks after Harry – A J Automotive in the NSW town of Bowral – suggested an after-market fan kit that offered around twice the air volume capacity of the standard fan. This QIKAZZ kit combined a quality-made hub with a larger thermal surface than standard, in combination with a Mitsubishi fan. (Mitsubishi is one of the world’s largest producers of fans, in addition to the group’s automotive expertise.)

So, on went the QIKAZZ fan replacement, aided by an adaptor with centre spigot, to ensure precise alignment. Notably, the replacement is slightly longer than standard, putting the fan closer to the radiator core, but the quality fan is warranted not to distort and contact the radiator.

One of the fan belt pulleys was replaced at the same time, the coolant refilled and, although the thermostat worked OK, a new one was fitted.



We loaded Harry to the gills and headed off on the Hume and Federal Highways to Canberra, from Moss Vale, running at 110km/h. The ambient during this 500km return trip was 36 degrees. Perfect.

Our normal driving procedure was to downshift from fifth to fourth for long grades, to increase water pump speed, but for this test we left the engine in fifth and kept the right foot flat to the floor. This driving mode used to get the coolant needle rising, forcing a downshift to improve coolant flow, but, with the QIKAZZ fan working, the coolant needle didn’t budge.

We sat behind B-Doubles, lugging the engine in that reduced airflow; we drove in heavy traffic around the ACT; we ventured off road and we sat idling with the aircon on full in the hot sun. The engine temperature needle looked like it was glued in place!

Obviously, it’s early days for the QIKAZZ fan installation, but our first impressions are all-positive.



























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