Tropical Fan Clutch vs....D24 Fan

[DieselScout]

Does the Aisin Tropical Fan Clutch pull more air over the radiator when engaged, compared to the direct driven fan on the D24 NA?

Also, any idea why the D24T was equipped with a fan clutch and the D24 NA was not?

[v8volvo]

The direct driven fan will move at least as much air as any clutched fan, if not more. The tropical fan clutch (or any fan clutch) can only ever spin the fan as fast as the belt will drive it. In other words, the direct driven fan always runs at the same speed that would be the maximum possible speed of any fan with a viscous clutch, tropical or not. In still other words, when the fan clutch is engaged, a clutched fan BECOMES a direct driven fan. The difference is just that the clutched fan has the ability to disengage the fan drive in low cooling demand situations (e.g. light load and cool ambient weather), when extra airflow from the fan is not needed, whereas a direct driven fan runs at all times when the engine is turning, regardless of whether fan operation is actually needed or not.

Adding a clutched fan to a 240 would be an upgrade in the sense that it would make the car run a little quieter when the fan is not engaged, and would maybe give a very marginal fuel economy benefit also when not engaged. But it wouldn't add anything to the engine's ultimate cooling capability versus the direct driven stock setup, and when the clutch is engaged the other two benefits would not apply either. There would be no cooling performance advantage from adding a clutched fan, tropical or not, if that is the reason for considering it.

Why the 7 series got the clutch fan and the 2 series did not? Good question, who knows. Might have mainly had to do with cost, as the 7 series had a higher sticker price and might have had more room in the budget for extra features aimed at refinement like a viscous clutch for the fan (or a turbo on the diesel engine which the 240 also never got). It might have had to do with the available space in front of the engine also, maybe the direct fan is a little slimmer and fits the tighter 240 engine bay better, but then again I think some people have bolted 740 viscous clutch fans onto 240 diesels with no fitment problems so that seems less likely.

[DieselScout]

Would the D24T fan (7 blade) pull more air through the radiator than the D24 NA fan (5 blade)?

[v8volvo]

Probably would move more air, it is a more modern and quieter fan blade design also.

I don't know how you would adapt it to the direct driven D24 fan hub though, unless you added the viscous clutch also. The 740 style fan has wider spaced mounting points for attaching to the outer perimeter of the viscous clutch unit and wouldn't bolt directly onto the skinny hub spacer from the D24.

But you do raise a good point: maybe swapping in the complete 700 series D24T viscous fan setup would actually improve cooling capability, not because of the viscous clutch drive, but because of the different fan blade section itself. I hadn't thought of that.

Only one way to find out -- try it and let us know! If you have trouble finding a D24T fan setup, the fan blade is identical to what is used on any gasser 4cyl 240 or 740 so you could harvest one of those from a JY also.

[DieselScout]

I tried the B230F fan (1317465), which is also listed as the same fan for the d24T and it is slightly too large to fit in the D24 240 engine bay. It measures 16" (406mm)

I noticed that there are two other fans listed for the D24T engine, 1257443 (380mm/15 inches) and 1274964 (430mm/17 inches). The latter will be too large, but can anyone confirm if the former (1257443) will fit in the 240 D24 engine bay?

[v8volvo]

Where was the interference with the 16" one you tried that didn't fit? Was it too large in diameter for the shroud? How close was it to fitting?

What is the inner diameter of the shroud?

I'll measure one of the D24T fans I have and see what the size is.