Side Radiator Cooling Fan

[Andy Clark]

My hydraulic engine cooling fan varies its speed with engine RPMs. Is this correct? Or should it have 2 speeds (lo and hi) that are switched on and off with engine temp variations? Reason I ask is that recently going over Stevens Pass (Wa), the engine very gradually warmed to 215deg (65deg ambient, 4th gear, 1900rpms), then the overtemp light and buzzer came on right at the top of the pass. I could not hear the fan running at hi-speed when I stopped to check things. Nothing obvious found- no leaks and the coolant level was correct. Light/buzzer went out/off almost immediately that I stopped, and temp gauge came down slowly.
It certainly never did THAT before. Any suggestions?- normal operation or might I have a failed thermosticallycontroller fan sensor/switch?

1995 Cummins 8.3 side radiator which has recently had its fins cleaned out.

Thanks
Andy

[Edward Buker]

Andy,

I'm not sure if all coaches are similar. I believe the way mine works, based on several temperature monitors on my computer, is the wax valve sends little or no fluid to drive the hydraulic fan motor until your engine reaches temperature. In my case that is 194F, in Gerald's case maybe 188F. It would appear that once the fan motor is turned on it stays on and the engine thermostat then controls the engine temp. I say that because the intake manifold temperature varies dramatically with the fan air flow and will heat quickly if the air to air intercooler does not have adequate air flow through it. Mine will hover at 80 degrees, + some degrees on hills, nearly all day at about a 70 degree ambient cruising at 63MPH. You may not have an intercooler or that readout but I am just using that as a tool to sort out how things work.

Given the hydraulic fan is run off of the hydraulic pump, there would be some variation in pressure with RPM, but you were holding high RPM so one would expect adequate pump speed and pressure. You may want to start looking for simple things that can change over time that could limit the cooling before going to the main components. The radiator is clean so next might be the hydraulic filter. If it was plugging some that may cut the fan speed you could achieve. The engine thermostats may be not fully opening is also a possibility. Not sure if a restricted air filter might limit the speed you could attain and impact intake air flow and cooling affect and help drive the temperature up. These are some of the things that come to mind.

I have never owned a coach like yours with a Cummins and those owners would have some hands on experience that may be more direct at finding the true source of your problem.

Later Ed

[Andy Clark]

Thanks, Ed.

My hydraulic reservour had a new filter and fluid last year, thermostats are less than 10 hours old, and the air restriction guage runs at about 8"Hg, so I've mentally eliminated those as causes. Also the radiator and CAC fins are clean.

If I read you right, you're saying that once the wax valve turns the fan on, it stays on, but speed does vary with engine (pump) rpm.

I have read about folks with a 2 speed fan that goes to "high" when the engine temp reaches normal levels. Am I misinterpreting something there?
Thanks for the help

Andy
................................
I'm not sure if all coaches are similar. I believe the way mine works, based on several temperature monitors on my computer, is the wax valve sends little or no fluid to drive the hydraulic fan motor until your engine reaches temperature. In my case that is 194F, in Gerald's case maybe 188F. It would appear that once the fan motor is turned on it stays on and the engine thermostat then controls the engine temp.
....snip.....
Given the hydraulic fan is run off of the hydraulic pump, there would be some variation in pressure with RPM, but you were holding high RPM so one would expect adequate pump speed and pressure. You may want to start looking for simple things that can change over time that could limit the cooling before going to the main components. The radiator is clean so next might be the hydraulic filter. If it was plugging some that may cut the fan speed you could achieve. The engine thermostats may be not fully opening is also a possibility. Not sure if a restricted air filter might limit the speed you could attain and impact intake air flow and cooling affect and help drive the temperature up. These are some of the things that come to mind.

snip..................
Later Ed
[/quote]

[Edward Buker]

Andy,

I can't tell you exactly how your hydraulic fan works for yours, just how mine works based on observations of readouts. If you have an intake air temperature readout on an Aladdin or Silverleaf, that readout can give you some insight as to what is happening by monitoring it during the start up and while driving through until warm up. My intake air temp is so stable on the road after the wax valve kicks on, that the fan has to be driving constant air flow through the intercooler. BCS might have some understanding of how your wax valve and hydraulic circuit works. This is one of those problems that is hard to sort out between air flow driven by the fan or coolant flow issues within the engine. There are foil reflective tapes that can be put on the fan blade to measure RPM with a hand held tach but we have no reference to compare to. There are some good folks in Bend that have had some write ups on the forum about solving this kind of problem. Wish I had better info for you.

Later Ed

[Gerald Farris]

Andy,
Your radiator cooling fan is temperature controlled. If the engine cools down below the set point on the wax valve, your cooling fan should run at low speed. However, if the engine coolant is above the set temperature, the fan should run at high speed. There is not a good chance that you can tell what speed your fan is running at from the driver's seat, so if you continue to have an overheating issue, have the fan properly check. Do not through parts at a condition until you know what you are fixing.

Gerald 

[Edward Buker]

Andy,

If you have an intake air temp readout it could possibly help sort some things out. I would think that under the condition that you are getting poor fan speed both the Intake air temp and coolant temp would be rising together beyond normal limits. If the cause of your overheating was caused by coolant flow issues (plugged radiator core, collapsed hose, bad thermostat, bad water pump) but you had normal high air flow I would think that the intake air temp would not be rising out of control. It may be climbing some due to the turbo boost involved but with good air flow I would think the temp would still be in control. It would be great to have some reference values from a similar coach doing a hard climb.

The high and low fan speed with wax valve turn on and off Gerald mentioned should also have the caveat that when the wax valve is on sending fluid to the fan, your fan speed is then a function of the pump pressure/speed which would have wide variations based on engine RPM.

Later Ed

[Gerald Farris]

I do not think that the hydraulic fan speed is directly tied to engine speed on our coaches. Since the hydraulic pump powers the power steering as well as the fan, the pump will maintain adequate pressure to fully power both at any driving speed. The pump should be equipped with a flow control valve to release excess flow at higher RPMs into the low side of the pump. If the pump was not designed to supply adequate pressure at all driving speeds, the power steering would not have even assist at all speeds.

Gerald

[Edward Buker]

Thanks Gerald, that makes more sense then the systems having to rely on varying pressure with engine RPM. Your wisdom is always appreciated. Hope Andy can find an easy fix with this problem that is not so easy to diagnose.

Later Ed

[Andy Clark]

Thanks so much, Ed and Gerald. Some clarity is coming into my thoughts re this problem. I think it's time to take the coach to freightliner where they can check the fan speed controller. I cannot do that at home.

Thanks again, guys.
Andy