Re[2]: {Chrysler 300} 61G fan clutch question

Well, the issue is what's correct for the car vs. what actually will work well. Non-thermal is correct for a G, but they are always engaged at lower rpms, which means a little less hp and fuel economy, bu they also slip more than a thermal when engaged - so less effective at hot idle/low speed - when you need it most. They tend not to last as long either (always engaged at lower speeds). At higher speeds, they free wheel - you shouldn't need a fan at high speed with a clean cooling system and radiator, hence, "silent flite" - no noise , no loss of hp, brute goes faster! During the 1963 model year, they made a running change to thermal fan clutch for the J - it's better.

There are (at least) two types of thermal clutches - standard duty and heavy duty. Thermal clutch will begin to engage at a predetermined AIR temp at the coil (not radiator/coolant temp!) - the modern ones usually around 175 degrees. That may equate to 200+ degree coolant temp - really a little too high (designed for modern emission controlled engines - run hotter). However, they will spin the fan much faster than non-thermal. The heavy duty clutch, when fully engaged, is almost like a direct drive fan (like 80 to 90%) (maybe makes more noise, maybe not), and may start engaging at lower temp (good). However, some may be sensitive to fan blade pitch, and never disengage also (not good).

Then there are water pumps with different number of impellers, how well they match to water manifold, etc, etc. - John Grady has discussed that before, can have huge impact on cooling, and some water pumps are "taller" than stock also (Summit Racing pump, for example), then you need that Jaguar clutch with the short shaft (more difficult to install as well). But most (all?) G applications should be ok with longer shaft clutches (Hayden 2705 - std duty, or Hayden 2747 - heavy duty). I have used both - the HD clutch is far more effective, much more "spin resistance" and the 2747 (so far) has not been noisy or robbed more hp). I installed a 7 blade fan and 2747 clutch on my 62 300, big difference - will engage at lower temp than std duty, keeps coolant below 190 and brings temp down fast, 7 blade fan will move a LOT of air, no fan shroud. Longer shaft gets the thermal coil closer to radiator, engages sooner. Fan shroud would help a lot, of course, but non A/C 300G didn't have one (that I know of).

------ Original Message ------

From "John Nowosacki" <jsnowosacki@xxxxxxxxx>

To "300 Club" <chrysler-300-club-international@xxxxxxxxxxxxxxxx>

Date 8/19/2025 10:20:48 AM

Subject Re: {Chrysler 300} 61G fan clutch question

Further checking fan clutches on Autozone site lists 'non-thermal' type for G and 'thermal' type for Hurst, so maybe the difference in the amount of spin resistance at room temperature is just different between thermal and non-thermal?

On Tue, Aug 19, 2025 at 10:08 AM John Nowosacki <jsnowosacki@xxxxxxxxx> wrote:
Checking around under the hood yesterday, I did the standard grab of the fan to check if there was any play in the water pump bearing, and found none. However, the fan did wiggle back and forth a bit, and the play was in the fan clutch (non-A/C car, but we all know there is one on non-A/C G's) where the shaft goes into the clutch mechanism. I went over to the Hurst for comparison, and there wasn't the same amount of movement that was on the G. I also did a spin test on each fan (cold engine), and while there was some resistance on the Hurst fan even when cold, there was almost no resistance to spinning the fan on the G, so, question(s):
Are the fan clutches of the same type on a non A/C G and an A/C equipped Hurst?

Should the G fan clutch be thermostatic or centrifugal? I think thermostatic based on what I see in the manual? (Does thermostatic imply some type of ferro fluid?)

If I look on the NAPA website, they list both thermostatic and centrifugal types and say both are 'exact fit' for a G. Thermostatic is $20 more than the centrifugal, but I just want to get the right one.
Given the play I'm sensing on the G fan clutch, and the lack of almost any resistance to spinning when cold, is it time to replace it before it flies off into my radiator and carves up my belts/hoses and dents my hood, or is it operating properly?
Down here in TX, many Mopar folks have actually removed the fan clutch and used the spacer from a non-A/C car to have a fixed, solid shaft connection to the water pump in an effort to combat the 100 degree temps that can be found in July/August.
The club tech page says non-thermal, so I guess I should be getting the centrifugal (cheaper) one, but just wanted to make sure. The word 'centrifugal' doesn't appear on the tech page, only thermal, non-thermal, and direct.
One other data point- I have owned the car since 1998 and have never changed the clutch. I have no idea how long the existing unit has been on the car. It had approximately 40K on the odometer in 1998, and about 80K now. I suppose it could be the original that is currently on the car, but I have no way of knowing.
Thanks,

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