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Genevatexan · 11-21-2022, 11:04 AM

We recently replaced the engine cooling fan motor (Cassappa) on our2007 American Coach Tradition 40J- Cummins 400, side radiator, AKG radiator stack. this was to attempt to solve a dash air overpressure issue. From there forward we were borderline engine overheat. I picked up a $17 photo RPM light and recorded 358 RPM idle, 401 RPM AC on and 410 RPM ECM cable to the hydraulic control valve disconnected.
That range is very narrow, I have read on this forum we should see 260 idle and 580 disconnected (wide open). This fan is never 'howling'.
What would be the root cause here? My assumption is Power Steering Pump, since there is never as much rpm as we have seen people say was wide open, and the entire electronic circuit was disconnected.
Help diagnosing from here appreciated. Could it be the new valve that came bolted onto the Cassappa fan, or is it power steering pump, or something else?

Genevatexan · 11-27-2022, 09:35 PM

Thought I would update the forum on this challenge- background- we changed the engine hydraulic cooling fan motor chasing an AC problem. The AC is now solved through other means, but the engine now runs 20 degrees hotter. (200). I pulled the wire connector off the fan solenoid valve on our run down to South Texas this week. So now the fan is supposed to run wide open- well, apparently it did, we averaged about 138 degrees engine temp on the trip down. (And our gas mileage dropped dramatically, so we can't leave it unplugged). So we know its not the power steering pump and its not the radiator. Higher fan speeds cooled the engine to crazy low levels. SO, current thought is one of the sensors that sends voltage to the fan solenoid valve, forcing more fluid to the bypass circuit and slowing the fan. I have seen an 'air inlet fan temp switch', and a 'coolant temp switch' in schematics. Can someone guide me on the exact list of what cuts down the fan speed via the ECM and where each sender is?

Ray,IN · 11-28-2022, 10:22 PM

138° coolant temperature means the thermostat is faulty (stuck open, it should remain closed until approx. 170°, then slowly open completely to ~ 190°.
Before going any further, I'd replace the engine thermostat.