Viscous hub constantly engaged

2008 MITSUBISHI TRITON
150,000 MILES • 3.2L • 4 CYL • 4WD • MANUAL
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KERODE
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the viscous hub seems to be constantly engaged, car has decreased power/fuel economy and the has the typical roaring sound while revving, which is constant from a cold start up until normal operating temperature, which is about half way on the temperature gauge.

I replaced the fan with a new aftermarket unit but the car still has all the same symptoms! am I right in assuming that the suspect may be that the temperature gauge may not be accurate and the car may actually be running hot?
Mar 9, 2020 at 1:58 AM
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KASEKENNY
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Unfortunately we don't have this vehicle in the USA so I don't have specific info on it. This means I am going to have to rely on you to inform me of what components you actually have on the vehicle. When you say you replaced the fan, did it include the clutch assembly? The reason I ask is these Mitsubishi viscous clutches have a metal spring inside them that allow the fluid to flow out of the storage chamber to engage the clutch. They don't actually have a sensor that engages the clutch. This means if the new one is doing the same thing then either we didn't replace the correct parts or have a defective one. I find it unlikely that you got a second part doing the same thing so let's start with what part you replaced. Can you get a picture of the old one you took out?

As for it running hot, it could be but if I understand correctly the fan is running on high when you first start the vehicle and cold then it can't be running hot yet. So if the fan is engaged when cold, this is not the issue.
Mar 9, 2020 at 2:22 PM
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KERODE
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Hi mate and thanks for taking the time to respond. Sorry for the lack of clarification. it was the viscous clutch that was replaced (Dayco 115543) there was one notable difference between the OEM and aftermarket unit, the OEM version doesn’t have the typical coiled spring but a bi metallic strip. I am lead to believe that it shouldn’t matter provided they are set to operate at the same temperature. If it helps the motor is a TD 4M41 which is used in numerous other models of Mitsubishi's. I am starting to suspect that the original wasn’t actually faulty and there is an underlying issue or i was just unlucky enough to get a faulty replacement. I have read numerous reports to indicate that other people have had defective Dayco units.
Mar 9, 2020 at 11:20 PM
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KERODE
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OEM clutch.
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Mar 9, 2020 at 11:20 PM
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KASEKENNY
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I agree with you that it seems like there is another issue. However, these clutches operate like a concealed unit. Meaning they don't have anything that controls them other then the spring or bi metallic strip. You know this because there are no electrical connectors going to it, correct?

Here is a guide and a video that goes into the detail. The video is worth the watch because it has really good illustrations on how these work.

https://www.2carpros.com/articles/fan-clutch-symptoms

https://youtu.be/UwM4OqsLek4

May be worth getting them to exchange it if the fan is roaring at start up.
Mar 10, 2020 at 5:45 PM