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Technical Curiosities:
The Hydraulic Cooling Fan

November 7, 2011 by Matt

Hydro Hydraulic Drive Fan Motor Cooling Radiator

I first ran across this one when I was doing the 7M-to-1JZ engine swap in my old Supra Turbo. Before the thought of a swap had even entered my mind, I remember puzzling over pictures of Japanese-market-only Supra engine bays fitted with the 1JZ-GTE from the factory, wondering why they seemed to have not one, but two power steering fluid reservoirs (yes, I sit and ponder things like that). I couldn’t figure it out, but when I finally had my hands on one and was lining up my ducks for the swap, I quickly discovered the reason for the extra container of hydraulic fluid: The car was fitted with a hydraulically-powered cooling fan.

In almost every instance, car engine cooling fans are powered one of two ways: Either directly by the engine off the front of the water pump pulley, or electrically using a large-ish motor. Typically, longitudinal (front-to-back) engines feature direct-drive, whereas engines mounted in a transverse (sideways) fashion, with their accessory belts rotating perpendicular to the ideal orientation for a direct-drive cooling fan, receive electric units. However, in a handful of cars, the engineers decided to grant the cooling fan its own, dedicated hydraulic circuit for motive purposes. In addition to the 1JZ-GTE in my ’89-’92 Supra application (the 1JZ was directly-driven in other Toyotas), the ’92-’96 Toyota Camry V6, Lincoln LS and ’99-’04 Jeep Grand Cherokee all featured hydro fans.

The disadvantages are obvious, but not outright deal-breakers for sensible and careful engineers: The setup adds another layer of complexity to the engine, with more parts to fail, and another fluid level for the owner/mechanic to check and service. As with Audi’s UFO brakes, the rarity of the solution means added expense for parts.

Hydro Hydraulic Drive Fan Motor Cooling Radiator 1JZ 1JZ-GTE 1JZGTE 1JZGTTE 1JZ-GTTE Parts Diagram Schematic Pump

There are some distinct advantages, though: The decoupling, as it were, of the fan from the engine gives the developers some leeway in term of radiator and accessory placement. The hydraulic drive can draw more power from the engine than an electric fan, and thus move more air through the radiator for more effective cooling. And compared to a directly-driven unit, the hydro fan’s speed isn’t dependent on engine speed—the solenoid that controls the flow of hydraulic fluid through the fan motor can opt to run the fan on high speed as the engine idles, for example, or completely freewheel the fan on the highway.

In the final analysis, if you can accept a little added complexity under the hood, the hydro fan combines the best qualities of both directly-driven and electric cooling fans: high power and flexibility, respectively. It’s a wonder to me that it hasn’t been more widely adopted.

Editor’s note: This post is part of an ongoing series spotlighting obscure automotive engineering solutions. Read the other installments here:

Filed under: Technical, Technical Curiosities, Toyota


  1. areopagitica says:

    Biggest reason the hydro-fan was appreciated in the Camry Lexus V6 was the total absence of fan noise or presence when the engine was running. So many large engined cars made more commotion from the fan blades than escaped the valve covers OR the tailpipe. The crappy sound of a Crown Vic accelerating away was one such instance. And as one might imagine the flailing fan was doing useless work before the heat spike ever made it to the cooling jackets much less the radiator surface.

  2. I have a 93 camry and it tries to run ho
    t when climbing a hill or high speed on interstate.would it be easier to put electric fan on it

  3. Car t
    ries to run hot on interstate or climbing hills.its a 93 camry would it be hard to put electric fan on it

    • Matt says:

      This isn’t strictly a diagnostic forum, but if your car is equipped with a hydraulic cooling fan then yes, it would be a challenge to install an electric fan, since you’d have to cap off or re-route the hydraulic lines that power the fan.

      Furthermore, if it runs hot on the interstate, then it’s probably not your fan that’s causing the problem. High-speed travel is when the engine needs the fan the least since the motion of the car is much better at pushing air through the radiator than the fan is. Check out your thermostat or head gasket.

  4. Hunter West says:

    Some of the Grand cherokees had a hydraulic fan. 99 body style v8

  5. Sam says:

    Hydraulic fans are very common in heavy duty trucks, buses, heavy equipment.

  6. Anton says:

    I wonder what HP these things drain. I wonder what power they turn the fan with… ideas?

  7. Ed says:

    Are electric fans really that noisy? I’ve only ever really driven the 3rd gen camry so I’m not too sure what I’m trying to hear when it comes to fan noise, I know the hydraulic fan can get noisy if the engine’s starting to overheat, in fact it was the only indicator that my engine was getting very hot – hearing the fan from inside the car I’d look at the temp gauge to see it steadily climbing to the red and in a panic I’d rev the car to above 2000 rpm to get the water pump to do its thing better.

    The overheating issues were caused by a blown head gasket slowly leaking coolant, and one of the heater hoses having a pin prick hole which would lose coolant after the engine was run hard for some time (thus resulting in increased pressure in the cooling system).

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