Jensen Monday Club

Modulated Fan Temperature Controller


Since fitting the high performance Sandon air conditioning compressor, Steve had noticed that the engine temperature had started to creep up due to the extra heat being generated by the air conditioning condenser which is mounted in front of the engine radiator. This combined with the extra heat generated by using unleaded fuel was giving Steve cause for concern.

Steve looked around car parts suppliers to find fans that were the same size as the original Jensen fans, but with a higher air flow rate (CFM). He found that fans for the 1990's Audi 80 and 90 models, with engines larger than 2.3 litres, had a fan the right diameter, but giving approximately 2100CFM rather than the Jensen's 1400CFM (approximate).

This would give 4200CFM, which is the same as the Jensen triple fan setup used on later Series 4 cars, but without having to modify the front chassis to take the larger Series 4 radiator setup.

These could be mounted onto the Jensen radiator shroud using VW Transporter Van mounting arms, which look as if they were made for the job.  

Steve installed the fans, and was impressed with the way they cooled the engine as they reduced the temperature much more quickly than the old fans.

As a precaution he used a clamp-on Ammeter to check the current being drawn by the new fans. He was shocked to find that the 2 fans were pulling  55 amps!

Steve was concerned that during town driving when the fans would be used the most, the alternator wouldn't be able to supply the amount of current the fans required. Some means of controlling the fans to lower the current consumption was needed.

Some research on the net led Steve to Delta Controllers who make temperature sensitive speed controllers. Rather than as in the standard setup, where the engine gets near the high temperature limit, and the otter switch bringing in the fans to reduce it to a safe level, the Delta controller constantly alters the fan speed to maintain a constant temperature. This then reduces the amount of time the fans need to be on as the upper and lower limits are much closer together than with the otter switch.

Delta Variable Fan Speed Controller

Steve brought the FK60 From Delta, which is designed to maintain a constant 180 degree temperature, and is rated at a 60amps continuous, with 100amps for up to 30 seconds. This is controlled by a probe which fits in the side of the radiator, and the controller runs the fans at varying speeds to maintain the 180 degree temperature. As the controller can handle 60 amps, no relays were required.

As a belt and braces back up, Steve has used an output from the ECU of his Holley Commander fuel injection system to operate 2 relays which activate the fans if the ECU detects the water temperature has reached 195 degrees.  If you have a car with no ECU, the standard radiator otter switch could be used to do the same job. Steve also has a manual fan switch in the car to override the automatic systems.

Steve has found that due to the Delta unit keeping a tight control over the temperature, the engine runs cooler, and the fans run for less time, reducing the load on the alternator. We just need some hot weather for a proper test!

An alternative option is an electric water pump, which is controlled by a similar temperature sensitive speed controller. Click on this link to see the article from the JOC magazine. You will require Adobe Acrobat reader to view it.