50 hp radiator fan myth

April 06, 2017, 12:05:56 am

Ok it's time to debunk this myth/old wives tail. Cat litiature is for for 525 hp coach weighing 40-50 thousand lbs. Doesn't exactly apply to a 25,000 lb coach. Cummins literature is for a tractor trailer. Tell me your engine hp and your fan(s) diameter. I can reverse engineer this and be within probably 20% of the actual hp consumed. Charge air cooler and radiator thickness can help. But when it's all said and done the ability of the belt drive system may be the limiting factor.

Re: 50 hp radiator fan myth

Reply #1 – April 06, 2017, 10:06:06 am

Not wanting to beat this to death but, most of us have near 35,000 lb. coaches you need the number of fans, diameter, pitch and rpm, pressure and flow to drive the fan at that rpm. I am not sure what the engine HP has to do with the calculation, but I am not an engineer. The later coaches have gear drive pumps on the engine and the latest have PTO driven pumps off the trans. My guess is all of the later ones have 450 HP or more.

Re: 50 hp radiator fan myth

Reply #2 – April 06, 2017, 11:43:30 am

The more HP the more cooling is required

Re: 50 hp radiator fan myth

Reply #3 – April 06, 2017, 12:31:31 pm

My cummins dealer shop foreman looked at our 97 and the 180 degree hydraulic fan thermostat and thought the setup continuously consumed 37 hp at the normal cruising rpm of 1400 by being at full speed all the time the motor is at 180 degrees.

the dynamatic hydraulic fan controller can be configured differently.

The beaver/Monaco people use a 199 degree controller where the fan is on "idle" speed at 184 degrees then as the temps go up the fan speeds up.

Second variable is the engines rpms. Engine spinning faster causes the fan speed to change depending on the fan controllers specs.

Two variables.

Older coaches have a low/high electrical controller also with its other variable speed being the engines rpms.

Engine temp at 180 or over and at 1800 rpm you probably are consuming more than the mentioned 37 hp.

Fifty would be my opinion.

Changed my controller to the industry standard 199 degree unit as did Bob Rozen here on his u320 and the added power and mpg is very noticeable.

My thoughts was that this horizontal radiator was a new design and the factory opted for the max cooling possible at all times.

Less possible phone calls "my temp gauge moved" "my cars gauge does not move"

My temp gauges show basically the same temps with the 199 degree as the 180.

Engine thermostat starts to open at 180 fully open at 195.

M11 electric fan switch on engine that turns on a front mounted radiator fan on a big rig is set to turn the fan on at 210.

Bob and I both noticed excellent mpg at low speeds in perfect conditions.

Over 11 mpg.

I drag raced our coach to Las Vegas and back to OC in high winds and at 36,000 pounds combined and averaged 8.2 mpg.

Over 9 mpg at 70 towing on the Vegas to OC side.

The silver leaf was a major help in the over driven fan diagnosis as stock it would show short stretches of 11 mpg on flat ground at 60 towing.

Seems the hydraulic fan finally went back to "idle" speed for those stretches

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