Skip to main content ↑ ↓
Topic: Hydraulic Cooilng Fan (Read 685 times) previous topic - next topic

Hydraulic Cooilng Fan

Hi All,

My hydraulic cooling fans sometimes surge.  Can even hear it driving down the road at highway speeds. It happens infrequently.  I have experienced it at idle a couple of times.  Also a couple of times over the last year they seem to stick at high speed.  Shutting down the engine and restarting seems to correct the problem.

Hydraulic fluid and filters were changed a year ago,  Likely for the first time.  Current mileage is approximately 80,000 miles.  Although I don't think it makes much difference, the service facility used 15w-40 oil when I asked for 10w-30 as recommended.

Ideas?
Don & Sue
2009 NImbus 38
2020 Jeep Grand Cherokee toad

Re: Hydraulic Cooilng Fan

Reply #1 –
Hopefully some member with a Nimbus (or a newer model coach) will respond with more specific knowledge.

I'm not familiar with the mechanical layout of your newer model coach, but it is likely your cooling fans have a electric solenoid valve somewhere in the system that controls the speed of the fans.  I would suggest aiming your trouble shooting efforts at that device, if it exists, if you can find it.

IMO, the slight deviation in oil weight should not be a problem (especially in the summer), as long as oil level in the reservoir is correct.
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Hydraulic Cooilng Fan

Reply #2 –
Don,

Slow day at my house, so did some poking around the Forum archives looking for clues to your problem.

Most late '90's model Foretravel coaches had wax valve fan speed controllers - I suspect your Nimbus OEM fan controller is electronic.

Found this article which may be of some interest, as it shows where you might look to find your "FDCA control unit":

Source Engineering Inc | Custom RV Chassis | Eugene, OR


1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Hydraulic Cooilng Fan

Reply #3 –
Turned up another document.  If you DO have a electronic speed control device (FDCA) in your cooling fan hydraulic system, it may be similar to the one described in the link below.

https://assets.danfoss.com/documents/DOC264103728182/DOC264103728182.pdf
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Hydraulic Cooilng Fan

Reply #4 –
I've owned two Nimbus' and I too have had the hydraulic fan come on intermittently and at idle as well. I also notice it kicks on at approx 189*. In my case all gauges are in normal operating range and I just chalk it up as something the ECU or other temp sensor system feels the need to kick on.

A problem I would be concerned with if it the fan stays on - and does not allow your engine to maintain enough proper engine temp heat. My answer might be inadequate for your scenario - but this is my own experience with mine.

Re: Hydraulic Cooilng Fan

Reply #5 –
Quote from: pibutler –
A problem I would be concerned with if it the fan stays on - and does not allow your engine to maintain enough proper engine temp heat. My answer might be inadequate for your scenario - but this is my own experience with mine.

NO, that would not be a problem (engine maintaining proper operating temperature if fans are on HIGH).

The thermostat controls operating temperature,  If the engine is below thermostatically controlled temperature the thermostat merely closes (partially or completely) and does not sent coolant to the radiator.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Hydraulic Cooilng Fan

Reply #6 –
The Sauer Danfoss Fan Drive Control Assembly(FDCA) on my Country Coach controls fan speed based upon three input data points. They are:
1. Coolant temperature
2. Charge air temperature
3. Chassis air conditioner high side pressure

It may be that yours is the same and that, at idle, the fan speed is changed based on A/C pressure. While moving down the road any of the three will effect a change in fan speed. All are perfectly normal.

It also may be that you have a separate condenser fan setup in which case never mind.
George and Jan Sanders
2003 Country Coach 42 Ft Magna

Re: Hydraulic Cooilng Fan

Reply #7 –
Mine has always done the same thing. It will switch to high speed at idle sometimes and during high engine RPM too. It relates directly to air temperature across the cooler and intake air temperature. Running the dash A/C will kick it into high speed mode too. Only time you need to be concerned with it is if it stays locked in High Speed mode.
Previous coach - 2007 Phenix 45'

Re: Hydraulic Cooilng Fan

Reply #8 –
Quote from: brrving –
Only time you need to be concerned with it is if it stays locked in High Speed mode.
Which, Don says (in the initial post), happens occasionally:

"Also a couple of times over the last year they seem to stick at high speed."
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"