Hydraulic Cooling Fan Issues

Truthseeker4449 · 09-12-2022, 09:19 AM

So my bus overheated a month ago. I saw the hydraulic fan was barely trying to spin. Not having the resources to diagnose and no good place to attempt to work on it, I dropped it off at the dealer. They recognized it as a common issue with hydraulic fans and said there was an update kit. The kit essentially involves replacing the entire cooling fan system and is a couple thousand.

Unfortunately that update kit stopped being produced a few years ago and there were only a few nationwide. Now I'm being told the kit doesn't actually fit my bus.

I just spend a few thousand on new tires the week before this happened and the bus is well spec'd and is absolutely spotless underneath, so now I'm trying to figure out what to do next. Maybe someone else has dealt with this issue before.

cadillackid · 09-12-2022, 09:28 AM

wonder if the fan system for the C7 on an HDX would be able to be retrofitted in. the 3126 and C7 are similar footprint and the HDX is essentially an upgraded updated MVP ER

Truthseeker4449 · 09-12-2022, 09:45 AM

Quote:

Originally Posted by cadillackid

wonder if the fan system for the C7 on an HDX would be able to be retrofitted in. the 3126 and C7 are similar footprint and the HDX is essentially an upgraded updated MVP ER

I'm really hoping the entire cooling package can be swapped out. From memory the two do look very similar on the back end. And the radiator with fan pedestal sits on a cradle bolted to the frame. I would need to take some measurements to verify, then course find a cheap donor bus. And then convince the dealer to do it because I don't have the means to lift the bus high enough to drop the package.

I'm also still awaiting details on why the update kit doesn't fit to start with.

cadillackid · 09-12-2022, 10:03 AM

what part is bad? the notor or the control valve module? the way these fans "*usually*" work is that when the module is void of power or communications to the ECM the fan fails out to high speed..

when its working right, the computer limits the flow of fluid when the fan demand is low thus spinning the fan slower..

the older fan drives was simply a temperature switch and a solenoid.. then the switch was closed (cold) the solenoid was on and the fan spun at low speed.. when the engine got hot the switch opened and the solenoid turned off putting the fan in high speed..

if you unplug your fan control do you not get full speed fan all the time?

if you did, the bus could be driven (albeit noisier and probably a little less MPG).. and it would be paramount to make sure the power steering cooler is clean so the fluid system can cool down..

Truthseeker4449 · 09-12-2022, 10:12 AM

I'm not too sure on what exactly failed. The fan would either barely spin on its own, or you could bump it to make it spin slowly for a little bit. Steering assist was unaffected. I unplugged the temperature sensors in the charge air and upper coolant pipes and it did not have any effect. I did not locate the control module, I think it's underneath the motor and buried in dirt.

My guess is faulty valve block or motor, and because parts weren't readily available, the update kit just involved taking another off the shelf kit and installing it. Whatever the root cause is, it was a common issue and the dealer did a lot of updates.

Truthseeker4449 · 09-12-2022, 12:54 PM

Okay finally got the update on why it doesn't fit, it physically fits but the bus is not J1939 complainant so the fan would run 100%

The service writer mentioned it should be possible to put a toggle switch on the fan, which to me sounds like I could toggle it with a thermostat. Thoughts?

cadillackid · 09-12-2022, 03:25 PM

Quote:

Originally Posted by Truthseeker4449

Okay finally got the update on why it doesn't fit, it physically fits but the bus is not J1939 complainant so the fan would run 100%

The service writer mentioned it should be possible to put a toggle switch on the fan, which to me sounds like I could toggle it with a thermostat. Thoughts?

hmmm.. not J1939 compliant? it sure is! the electronic allisons like the MD3060 and 2000 series run off of J1939.. and I know in 01 they were supported.. now that said maybe they didnt send all the data in EEC 1 and EEC 2 PGN's across? wierd.. that said, the dealer probably knows more than I do about their systems..

cadillackid · 09-12-2022, 03:29 PM

could you put a T-stat on it? all depends on if you can swipe the signal that controls the fan.. if its a PWM signal coming from the controller to the valve then a simple toggle switch / thermostat wont work.. if the controller outputs a simple on or off to a solenoid then yes it should be operable by thermostat..

I dont know without seeing the wiring to it.. sounds like it takes in J1939 (which is a data link) and then operates the fan... if thats the case then connecting a thermostat would require some research..

Truthseeker4449 · 09-12-2022, 05:14 PM

Yeah it's impossible to tell without knowing what the configuration actually is. I could be mistaken but I think 2001s are setup for 1708, or at least the engine and trans are on a dedicated 1708 link. My other bus (another 2001, with the HDX Bodystyle but apparently not actually called the HDX at the time) had issues with a bulkhead connector going into the rear run box and they said it was the 1708. I do hope it's possible to set it up to be variable, but for now I'll tell them to leave it stuck at 100% (I don't plan to take any trips any time soon) and give me the documentation. I'll check back in when I have more information. Thank you for your input thus far.

Iceni John · 09-12-2022, 07:13 PM

Some years back I completely rebuilt my entire cooling system to address some ever-worsening overheating: I replaced the hydraulic fan motor, the hydraulic/PS pump, the solenoid directional control valve, and plenty more. If your PS is working OK, the hydraulic/PS pump is probably also OK, but is the pump's priority flow divider valve working right? It sends a guaranteed minimum to the PS at all times, with the remainder going to the fan motor. If this flow valve is part of the pump, like in my Webster KB, you can try replacing the O-rings on the shuttle, but also check the two springs in there that decide how much fluid goes to where. If you have an external flow valve, like the one made by Prince, check and/or replace it. If the fan motor is internally leaking past the gear lobes it's usually not repairable. Motor repair kits address leakage past the end plates, but won't help if there's too much clearance against the inner shell. Hydraulic motors are readily available from suppliers like Eaton and Parker, but they'll likely have a straight shaft with a keyway; fans typically use a tapered shaft with a nut on the end. At the very least, have a hydraulic shop flow-test and leak-test the motor, and see what they say. If you have excessive back-pressure it could slow the motor a bit, but there would have to be many time's normal back-pressure to make much difference, and that would probably blow off the return hose anyway! Motors typically use up to 1500 PSI, but back pressure is (you hope) less than 100 PSI - my Webster YC motor's BP is about 40 to 50 PSI, and that's running through an additional Baldwin full-flow hydraulic filter that I installed before the fluid reservoir. (This is why installing a pair of pressure gauges on the fan motor's supply and return lines is useful to help trouble-shoot problems.)

As has been said, the solenoid directional control valve blocks half the flow when power is applied to it. If it's working OK, don't futz with it: the setting of its internal pressure relief valve is critical, and if you mess with it you'll destroy the motor (or worse). If it's a Danfoss 7WA110 you won't find any more of them these days, so a whole new cavity block will be needed for whatever else you replace it with. No big deal!

Good luck.

John

cadillackid · 09-12-2022, 08:01 PM

I’ve never seen an Allison newer than mid 98 that ran in 1708 (WTEC-II),
The diagnostics is very likely to be 1708.. it’s also possible they ran a linkage to a throttle box for the Allison.. however I thought the 3116 was the last one to use that old method..
again it may be that the correct data isn’t sent in the transmission 1939 to run the fan..

1708 is what likely goes through the bulkhead and handles any communicating gauges, diagnostic port. Possibly ABS control (they were made both ways)..

If you have an MD3060 trans you prob have 1939 active..

This is the best I could do for a diagram but appears it’s only wired if it’s required..

https://f01.justanswer.com/NicholasM..._R115-6581.pdf

Truthseeker4449 · 09-12-2022, 09:57 PM

Quote:

Originally Posted by cadillackid

I’ve never seen an Allison newer than mid 98 that ran in 1708 (WTEC-II),
The diagnostics is very likely to be 1708.. it’s also possible they ran a linkage to a throttle box for the Allison.. however I thought the 3116 was the last one to use that old method..
again it may be that the correct data isn’t sent in the transmission 1939 to run the fan..

1708 is what likely goes through the bulkhead and handles any communicating gauges, diagnostic port. Possibly ABS control (they were made both ways)..

If you have an MD3060 trans you prob have 1939 active..

This is the best I could do for a diagram but appears it’s only wired if it’s required..

https://f01.justanswer.com/NicholasM..._R115-6581.pdf

At least I'm not the only one who thought it was weird that J1708 was the primary then. The Diag port is the J1939 plug. Any ideas on how to verify what is in use?

Both buses have MD3060s. TCM is located in the dash electrical compartment on the HDX, under the floor in the MVP iirc. Electronic accelerators on both, the MVP has a Williams iirc.

Thoughts on a using a J1708-J1939 convertor box? Apparently it's not uncommon to find in boats trying to modernize their dashboards.

Booyah45828 · 09-13-2022, 07:31 AM

A 3126 could be either, or both, depending on what options were selected.

If it has a 6 pin connector, it's j1708. With the 9 pin, it's likely j1939 or both. Very rarely do you see the 9 pin with j1708 only.

If your old fan clutch was a mechanical unit, they might have to check a box or two in cat ET enabling electronic fan control, and they might have to run a harness from the ecm to the new controller. I'd say them telling you that it isn't compatible is them running out of labor hours on the job and giving up on it.

It's not right for them to return to you a bus that isn't correct, especially after the thousands you've spent, but it's hard to argue with them without being there.

cadillackid · 09-13-2022, 08:27 AM

Quote:

Originally Posted by Booyah45828

A 3126 could be either, or both, depending on what options were selected.

If it has a 6 pin connector, it's j1708. With the 9 pin, it's likely j1939 or both. Very rarely do you see the 9 pin with j1708 only.

If your old fan clutch was a mechanical unit, they might have to check a box or two in cat ET enabling electronic fan control, and they might have to run a harness from the ecm to the new controller. I'd say them telling you that it isn't compatible is them running out of labor hours on the job and giving up on it.

It's not right for them to return to you a bus that isn't correct, especially after the thousands you've spent, but it's hard to argue with them without being there.

if he has an electronic transmission wouldnt it have to be J1939 capable? im interested to learn as ive been iunder the impression that J1708 allison transmissions were gone since 98.. the ones i found on earlier cat motors ran off of mechanical throttle linkages.. and it may be that they placed a mechanical linkage on so,e of the 3126's also.. it seems in the sachool bus world about the time I think ive seen it all some new combo shows up on a forum or board.

Truthseeker4449 · 09-13-2022, 09:07 AM

I think in all fairness, this bus is ancient tech compared to what the dealer has been working on for the last 20 years, especially in the last five or ten years. This is evidently not an issue they've run into before and this bus is very different to what the local schools have. Therefore the techs would be spending tons of time trying to figure it out and the average tech doesn't deal with in depth communication issues like this beyond bad wiring. The labor rate also isn't cheap, $150 an hour, and I would rather have bus not overheating but isn't working as new over it being a lump of scrap.

Besides, people seem to get more interested in weird communication issues like this and wanting to engineer a solution. And as these buses get older, someone else is bound to have a similar issue and we have the opportunity to solve it.

cadillackid · 09-13-2022, 09:32 AM

What transmission is in it ?

Truthseeker4449 · 09-13-2022, 09:52 AM

Quote:

Originally Posted by cadillackid

What transmission is in it ?

Per the data plate, MD3060. The last time I was underneath it sure looked like one. It has had 6th gear unlocked by copy pasting the flash file from the 2001 HDX I had, the flash file itself having come from an Allison tech.

cadillackid · 09-13-2022, 10:59 AM

3060.. yeah that should be J1939....

Booyah45828 · 09-13-2022, 01:55 PM

CAN, and j1939 wasn't really used until 2000, and wasn't used widely for a few years after that. Before that ecm-tcm comms could have occurred on a j1587/j1708 link directly between the two modules. With Allison transmissions, wtec2 was stricly j1708, wtec3 could be j1708 or both. They phased wtec2 out in 98, so him being 01 would likely be wtec 3, unless someone swapped in a 4 or 5 ecm. A lot of wtec3 used j1708 as the primary module-module comms, with 1939 being enabled but only used for diagnostics. So if 1939 is available on his bus, it might only serve as comms to one or both the modules for diagnostic comms, and not actually sharing operating data on it.

I'm going off generics for MD/HD as a whole, not school bus specific. I could be wrong. The OP himself said it's all 20 years old. I can't tell you the last time a 3126 or even a md3060 was in for diag work, it's just too old to be seen anymore.

The number of pins he has at his DLC will determine everything. If he has 9 pin, and 1939 available at the diag port, he should be able to build a CAN and have the fan controller as a node on the network, and then enable the ecm to transmit the data on it for the controller to operate. The trans would also be on the network, and could also be turned on to communicate over it if high trans temps are experienced, requiring more fan speed/cooling.

But as it sits, he might not have a CAN bus on it, and maybe he has the 9 pin plug, but without the CAN bus present, and that's what they mean by saying it doesn't have 1939.

Do you by chance have ABS on this? If not, it's even more likely he doesn't have a CAN bus. If it does have ABS, I don't think I've ever seen ABS without a CAN bus and active comms on it FWIW.

cadillackid · 09-13-2022, 02:31 PM

Quote:

Originally Posted by Booyah45828

CAN, and j1939 wasn't really used until 2000, and wasn't used widely for a few years after that. Before that ecm-tcm comms could have occurred on a j1587/j1708 link directly between the two modules. With Allison transmissions, wtec2 was stricly j1708, wtec3 could be j1708 or both. They phased wtec2 out in 98, so him being 01 would likely be wtec 3, unless someone swapped in a 4 or 5 ecm. A lot of wtec3 used j1708 as the primary module-module comms, with 1939 being enabled but only used for diagnostics. So if 1939 is available on his bus, it might only serve as comms to one or both the modules for diagnostic comms, and not actually sharing operating data on it.

I'm going off generics for MD/HD as a whole, not school bus specific. I could be wrong. The OP himself said it's all 20 years old. I can't tell you the last time a 3126 or even a md3060 was in for diag work, it's just too old to be seen anymore.

The number of pins he has at his DLC will determine everything. If he has 9 pin, and 1939 available at the diag port, he should be able to build a CAN and have the fan controller as a node on the network, and then enable the ecm to transmit the data on it for the controller to operate. The trans would also be on the network, and could also be turned on to communicate over it if high trans temps are experienced, requiring more fan speed/cooling.

But as it sits, he might not have a CAN bus on it, and maybe he has the 9 pin plug, but without the CAN bus present, and that's what they mean by saying it doesn't have 1939.

Do you by chance have ABS on this? If not, it's even more likely he doesn't have a CAN bus. If it does have ABS, I don't think I've ever seen ABS without a CAN bus and active comms on it FWIW.

if you look at how WTEC-III works it talks the J1939 language... not saying allison didnt run some bastardized version.. however J1708 and J1939 are physically different.. the levels are different.. you cant intermingle J1939 and J1708 on the same pair of wires.. and WTEC-III TCMs only had CAN-1 (not the second set of pins for CAN-2 that the 4th gen has).. the WTEC-III shift panels come up as J-1939 controller address 5.. the ECM is 1.. and ive witnessed this myself by tapping into the trans links..

on my IH the connector that goes from engine to trans is Pure J1939.. ive decoded it, ive measured it.. and that is a year 2000... any allison that got connected to the link in said year was WTEC-III.. in fact IH released the J1939 Trans connector and software for the NavPak in 98 (ironically coinciding with the year WTEC-III was released)...

WTEC-II was J1708 in its root with a bunch of proprietary PID's used to handle better transmission diagnostics and the language between the TCM and shift panel... Most WTEC-II integrations used a mechanical throttle but some like IH put the trans on the J1708 interface on the 466E.... and it worked sort of OK for the tech at the time..

after all when the world-series came out in 94 the whole realm of electronic shifting automatics was a pretty new thing..

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