[OFB Cafe] Engine overheating

[Chris Olson]

From: Rick Bowers 
Sent: Monday, July 14, 2008 8:51 PM
To: Cafe 
Subject: [OFB Cafe] Engine overheating

> I do suspect the fan clutch. During my flush/fill session, it 
> appeared the fan was turning slowly, so I used a piece of 2x4 and was 
> able to stop it. I could hold it still with my hands while the engine 
> was idling with little resistance

Well, then it's junk.  The fan clutch is a viscous unit and it should have a fair amount of viscous drag even when it's cold.  The viscous clutch is similar to a torque converter on an automatic transmission.  It has a pump (turned by the input shaft), a stator and a rotor (the part the fan blade is bolted to).  There's a small bi-metallic spring that expands when heated and turns a shaft that's connected to the stator.  The stator either directs the oil contained in the unit back to the pump (freewheel), or to the rotor (which makes the fan spin), depending on its orientation.

With the engine hot (over 200° F) have a helper operate the engine at 1,600-2,000 rpm and observe the fan.  It should be making noticeable noise and be spinning at approximately the same speed as the water pump pulley.  If it appears to be freewheeling at all at that temperature the clutch is junk.
--
Chris