Fan runs all the time?

[Audiomaker]

Hey all, I mentioned this in another thread, but I don't think anyone noticed, and it's bugging me, so I figure I'll start a dedicated thread...

I have a 6L-71TA/MT-654CR in a rig with a front mounted radiator, and remotely powered hydraulic fan.

The fan is controlled.  You can start the motor without the fan running.

In my new-to-me rig, I start the motor and somewhere between 5 and 30 seconds later, the hydraulic fan will come on, and it will stay on until the motor is shut off regardless of engine temp'.

What I'm wondering is if it's supposed to do this?   If the fan came on all the time (i.e., with the motor), I would think it was just a substitute for a directly linked fan, but since it controlled, I would expect it to be thermostatically controlled (which it isn't unless it turns on at 50 degrees).

Pondering this, a friend suggested it might be turning on "once the appropriate hydraulic pressure had built up" and is supposed to be on all the time?   That doesn't pass my logic test (he's not a mechanic or anything, just grasping at straws).   I don't see hydraulic pressure as a reason a solenoid would kick the fan on...it would just start turning.

Ok Ok... so I'm seeing this as a problem with what I think should be a thermostat controlled hydraulic solenoid, but before I get in there and start turning set screws and banging stuff with my Crescent wrench...

Is there any reason one could see that the fan would be set to be on all the time with this combo?  It doesn't overheat or anything.
I don't want to burn out the "whatchamagigger" I didn't know about that depended on a full time fan, but if nobody can think of anything, I guess I'll get in there and tamper because I'd rather have it come on at about 190 than always.

Oh... I should add that in the outgoing (cooler) radiator hose that returns to the engine, there is a decent sized heat exchanger that looks like it goes to the transmission, and lastly, before you ask... the transmission temperature gauge is the only one in the truck that doesn't work.

Ideas?

[Iceni John]

I have a 2-speed thermostatically-controlled hydraulic fan in my bus.   The temperature sensor that controls whether full-flow or half-flow hydraulic fluid goes to the hydraulic fan motor is one of three on the passenger-side of the engine, and it actuates a valve inside an aluminum block to which all the hydraulic lines are connected.   If I undo the wire from the sensor, the fan defaults to full speed.   Is your sensor or wire still connected and working?   As for the delay after you start the engine, maybe the hydraulic pump is building sufficient pressure for the steering before it then starts producing pressure for the fan??   What make of pump and fan motor do you have?

John   

[TomC]

Since you have a front mounted radiator, it is very important (to your fuel mileage) that you have a working thermostat on the hydraulic fan. Otherwise, that's about a 20hp draw on the engine at all times. You can also install a dash switch so you can over ride the thermostat if you want to turn on the fan.

From reading about all the hydraulic systems you have, it's no wonder you have no power going down the road. Except for power steering and the radiator fan, I would eliminate all other hydraulic systems driven off the main engine. For any other hydraulics you want to keep, just get a pump that will work off the genset-whether that be belt driven or electric motor driven.

The big cooler is for the transmission. All Allison powered vehicles have these big coolers. Whether it be in line from the radiator, built into the bottom tank of the radiator, or an air to oil cooler mounted in front of the radiator. The main time the transmission creates lots of heat is in torque converter mode. Once the torque converter has locked up, the transmission only produces about 4,000btu/minute (can produce up to 20,000btu/minute at stall [yes that's per minute, not per hour]). Good Luck, TomC

[Audiomaker]

I have a 2-speed thermostatically-controlled hydraulic fan in my bus.   The temperature sensor that controls whether full-flow or half-flow hydraulic fluid goes to the hydraulic fan motor is one of three on the passenger-side of the engine, and it actuates a valve inside an aluminum block to which all the hydraulic lines are connected.   If I undo the wire from the sensor, the fan defaults to full speed.   Is your sensor or wire still connected and working?   As for the delay after you start the engine, maybe the hydraulic pump is building sufficient pressure for the steering before it then starts producing pressure for the fan??   What make of pump and fan motor do you have?

John   

This sounds similar to what I have ( a box with hydraulic lines and an electric solenoid).   I haven't traced the solenoid electric line as in my "L" configuration, the passenger side of the engine is now the top (and hard to get to).  I suspected this box to be the hydraulic fluid flow control whatever that control might be.
The power steering works immediately upon the start of the truck, but I get that it's possible there is some relation such as a fail sensor where if the hydraulic pressure fell off, that it would kill the fan first.  My experience with other machines though is that hydraulic pressure shouldn't need to "build", it should be almost instantaneous unless there's a failure or considerable air in the lines that needs to purge. I can get 20 seconds before the fan kicks on after starting the engine.
Two things are striking me here... start at that box is #1.
#2 is that you say your fan has 2 speeds.  Is there an "OFF" as the 3rd speed, or does it always run in "Low" unless hot?
My temp gauge has never shown what I am used to as a "HOT" diesel fan kick in level (about 210-220).  I may have managed 200 once.
I'd hate to find out what I currently have is "low" because it blows pretty hard even at idle.  If there were a "high", I might be able to launch from a carrier simply from thrust
May I ask about your experience in the low/high/(off?) scenario?

[Audiomaker]

Since you have a front mounted radiator, it is very important (to your fuel mileage) that you have a working thermostat on the hydraulic fan. Otherwise, that's about a 20hp draw on the engine at all times. You can also install a dash switch so you can over ride the thermostat if you want to turn on the fan.

From reading about all the hydraulic systems you have, it's no wonder you have no power going down the road. Except for power steering and the radiator fan, I would eliminate all other hydraulic systems driven off the main engine. For any other hydraulics you want to keep, just get a pump that will work off the genset-whether that be belt driven or electric motor driven.

The big cooler is for the transmission. All Allison powered vehicles have these big coolers. Whether it be in line from the radiator, built into the bottom tank of the radiator, or an air to oil cooler mounted in front of the radiator. The main time the transmission creates lots of heat is in torque converter mode. Once the torque converter has locked up, the transmission only produces about 4,000btu/minute (can produce up to 20,000btu/minute at stall [yes that's per minute, not per hour]). Good Luck, TomC

Agree.

I don't know what hydraulic systems I have though.   The levelers and gate are already on their own pump.  There is some line routing intermixing so it gets confusing.
As far as I know, the only hydraulics on the engine pump are PS and Fan, but this isn't a 2 hose deal... it's more like 3 hoses, and a box, and a splitter...it gets hard to count.  You know how it is... it could be a really simple thing, but throw in a  bypass, maybe a filter, and a couple T's and now you're trying to trace the flow of something you can't see (hydraulic fluid).
Not knowing these trucks, I don't know if something else is using it... like PTO..etc.

Maybe it's as suggested above, that it might always be on with a high/low setting and mine is stuck on high.  I'll have to dig in there knowing of this possibility.
Once I find out that nothing but the fan is dependent on this "on state" hydraulic pressure, I would be ok with tampering...even modifying it so that it had an "off".

It comes down to possible design choices in 1983 that I'm attempting to decipher.   On a vehicle of this type, it is entirely possible that fuel economy wasn't critical and having a low/high (or even just an "on") would be acceptable.  I don't think they ever planned on RV use,  or much highway use, so all it takes is for one engineer to go "just throw a high/low in there", and it lives like this.
30 years later, and $4 diesel prices later, one might like to get that extra 1mpg by adding a 3rd stage of fan operation (off).

The problem is not knowing all that the fan might be cooling or what that fan hydraulic pressure might also be powering.
The engine temp could be completely cool, but the fan pulls air past the A/C, and perhaps other exchangers in there that need this right from startup?
From the pressure side, I have to make sure that someone here doesn't pop up and say "No!, the hydraulic pressure to the fan motor *also* powers the *****" before I tamper and shut it down at below 200 degrees engine temp'.

Where I'm at now is this...

The system might be "always on" and requires air to purge from the lines before kicking on the fan hydraulics.
.
The system might be 1 speed, and stuck on. (which does not account for the delay after starting)

The system might be 2 speed, and as suggested, a problem has it stuck in "high". (also doesn't account for startup delay)

or some combination of those with a faulty temp' sensor that kicks in at a ridiculously low temp which is almost immediately reached (unlikely... there is always a delay).

<sigh>

[Iceni John]

Two things are striking me here... start at that box is #1.
#2 is that you say your fan has 2 speeds.  Is there an "OFF" as the 3rd speed, or does it always run in "Low" unless hot?
May I ask about your experience in the low/high/(off?) scenario?

My fan always runs.   Immediately after engine start it's at low speed, and the full speed kicks in at about 190 degrees and kicks off at about 185 (as best as my crummy short-travel temperature gauge shows.   I plan on replacing it with a full-sweep gauge to better know exactly how hot the engine is.)   Until the thermostats open there won't be any coolant going through the radiator anyway, so I assume that takes the place of an Off setting for the fan.

A good-running 6L71 with a front radiator should never have overheating problems, as long as you don't lug it.   At highway speeds on level ground the fan should not need to run at all.

John

[TomC]

Front ram on the radiator is so important, this is why Freightliner stopped making the Century/Columbia models and superceded them with the Cascadia that has a bigger front opening on the radiator.

Course now the engines require less cooling. So what used to take 1650sq/in radiator is handled by a 1400sq/in radiator. If it were me, I'd use the optional 1750sq/in radiator. Less fan time, better fuel mileage. Good Luck, TomC

[Audiomaker]

My fan always runs.   Immediately after engine start it's at low speed, and the full speed kicks in at about 190 degrees and kicks off at about 185 (as best as my crummy short-travel temperature gauge shows.   I plan on replacing it with a full-sweep gauge to better know exactly how hot the engine is.)   Until the thermostats open there won't be any coolant going through the radiator anyway, so I assume that takes the place of an Off setting for the fan.

A good-running 6L71 with a front radiator should never have overheating problems, as long as you don't lug it.   At highway speeds on level ground the fan should not need to run at all.

John

Hmm... ok, so either mine is running correctly (comes on with a delay at start) and I've never had it click to "high" yet (which would be scary considering how strong and loud "low" is), OR it tries to come on at "low" at startup, but a bad sender sends it immediately to "high".

I'll tell ya this... it's loud, and the hydraulic motor for me is right under the doghouse in the cab'.
My own experience echo's what you guys are saying...  on a front radiated diesel, the fan should only come on at low speed on a grade.

Because of the noise, I would modify the circuits and senders so that "low" came on at about 190, and "high" at about 210, or if it is a single speed, just come on at about 200.
It's either this, or try an electric @$1000, or possibly adapt a coupled driveshaft with a clutch to the crank pulley (which looks doable).

Unless I discover that there is indeed a tolerable "low", I think I'll go ahead and modify the system.

[TomC]

Your last statement is what I would do. Use only a big enough Vickers pump for the power steering then shaft drive the fan through a fan clutch and get rid of all the hydraulic stuff. Good Luck, TomC