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bigbadblazer 09-17-2018 11:10 PM

New member: Hydraulic fan question
Hey guys, newb here. My wife and I recently purchased an already converted 1990 Thomas transit-liner with 8.3 cummins 6cta and allison mt643. We've taken it on a number of trips already and are completely in love with it. Had a hiccup today though... This morning when I started it (luckily from the engine bay), after running for about 1 minute, I gave it a little throttle and the hydraulic cooling fan completely grenaded. I was able to shut the engine off very quickly so the pump was never starved of oil or anything, etc. After a few hours of making a mess and realizing that I'm not used to working on large diesels, I got the motor out and can't find a part number on it anywhere. So my question for you is where do you look up/buy parts from? Google has not been helpful, at least with the search terms I'm using and I need to get one on order. Thanks in advance!:Thanx:

bigbadblazer 09-17-2018 11:15 PM

4 Attachment(s)
Just wanted to add a couple of pictures of our rig.

Brad_SwiftFur 09-17-2018 11:44 PM

Try a Napa, and I don't mean one catering to auto parts. Find a Napa that deals in big truck parts. TruckPro is another possible source.

bigbadblazer 09-17-2018 11:53 PM

Ok, I know of one nearby. Plus it's out now, so I can take it along. Thanks!

Thunderbirdpilot 09-18-2018 05:29 AM

Napa will most likely have what you need, but if not you can just google the parts by the part number or model name and it should show you all the available options. You can also search by make/model/year on, and of course ebay and amazon

The thing is that it's not necessarily bus-only shops, many truck shops may have the parts for your 1990 Thomas too.

TJones 09-21-2018 11:34 PM

If an auto parts store cant get it try a truck or RV specific shop or parts store. Larger truck repair shops have parts counters and may stock your motor or be able to order it for you.


TJones 09-21-2018 11:42 PM


Originally Posted by bigbadblazer (Post 291173)
Just wanted to add a couple of pictures of our rig.

Also when you get your new motor if you have to move the fittings from the old pump DO NOT OVERTIGHTEN. It looks like the failure may have been caused by the fitting being overtightened.

bigbadblazer 09-21-2018 11:57 PM

So I actually spent two days googling the part number from my service manual and came up with next to nothing. Wound up using a company in New Jersey that was able to spec out a new motor and fiberglass fan for me. Should ship next week hopefully. The price was a bit shocking... $1,500. Hopefully this is the last big repair for a while.

bigbadblazer 09-21-2018 11:57 PM


Originally Posted by TJones (Post 291687)
Also when you get your new motor if you have to move the fittings from the old pump DO NOT OVERTIGHTEN. It looks like the failure may have been caused by the fitting being overtightened.

That's what I was thinking as well.

drew78634 09-26-2018 05:08 PM

I feel your pain. When I was bringing my 92 All American home the solenoid unit that diverts hydro oil to the fan went belly up causing my bus to overheat. I was stuck for three days waiting for the $1500 part to come in from Seattle.

cycle61 09-26-2018 05:20 PM

Is it possible to convert it to electric?

Also, I see you're in Tacoma. Would love to meet up some time!

bigbadblazer 09-26-2018 07:06 PM

Balls, that's terrible. I wish my part was in Seattle... I'm in Tacoma. Instead I'm 3 weeks out from New Jersey.

bigbadblazer 09-26-2018 07:08 PM


Originally Posted by cycle61 (Post 292257)
Is it possible to convert it to electric?

Also, I see you're in Tacoma. Would love to meet up some time!

I looked into electric and wasn't convinced it would adequately cool it. Current fan is 30" metal. Was told it could move ~18,000 CFM. So aside from spending gobs of money, it didn't seem feasible at the time. I'll casually keep researching it in the event this happens again.

We definitely should meet up sometime.

Tango 09-28-2018 10:38 AM

I pulled the mechanical fan off my 4BT and went with a shrouded electric. Surprising just how heavy that old unit was and was told they pull as much as 10-15 hp.

bigbadblazer 09-28-2018 10:52 AM


Originally Posted by Tango (Post 292502)
I pulled the mechanical fan off my 4BT and went with a shrouded electric. Surprising just how heavy that old unit was and was told they pull as much as 10-15 hp.

Yeah mine has to weigh 50 pounds.

As far as electric, I called a few places that do electric fans for buses and didn't get much solid info as far as cfm and how adequately electrics would cool my rig. My current fan is a 30" metal 8 blade. I was told it moves 18,000 CFM. So I never found any electric fans that claim to move near that much. So unfortunately at this time I am keeping it hydraulic.

cycle61 09-28-2018 12:18 PM

I wonder if 18,000 cfm is needed, or if some kind of shroud would help. These guys build electric fans for semi's and buses, seems they might be able to advise: 12- & 24-VOLT BUS & OFF-HIGHWAYELECTRIC COOLING FAN ASSEMBLIES - Electric Fan Engineering - The Highest Standards in Cooling

Their Semi truck setups are rated in terms of HP and GVW:

Here's an older one mounted on a Detroit Diesel powered bus:

Admittedly, I'm more comfortable with electrical than hydraulics, so my opinion is biased.

bigbadblazer 09-28-2018 12:23 PM

That's actually who I wound up buying the new hydraulic unit from. He didn't sound confident that an electric would move enough air. So staying hydraulic was cheaper than one electric pulling and one pushing plus a higher output alternator.

Tango 09-28-2018 01:03 PM

Not sure how yours was set up, but my 4BT never had a shroud, so even with a high volume fan, only a tiny fraction of that air was being drawn thru the rad. A shroud makes a huge difference, My electric is only about 2800 but it's 100% thru the fins.

bigbadblazer 09-28-2018 01:43 PM

Mine has a shroud and it's a nice fit around the fan. It definitely moves a bunch of air. If I drive down a dirt road it's like a damn sand storm.

Iceni John 09-28-2018 03:54 PM

I also have a hydraulic fan motor in my bus. My old motor was showing some slight signs of internal leakage, so when I completely rebuilt my entire cooling system to solve some serious overheating issues I took the opportunity to replace the motor and fan. MultiWing made me a new 9-blade fan that moves a lot more air with a lot less power and noise than the original old metal 6-blade fan that looked like it came from a pre-war Russian farm tractor or something equally archaic, and to help airflow I also reversed the direction of its rotation. The old Webster YC motor was replaced by another YC, custom-made by Quality Control Corporation, but on the first test-drive after installing it the entire motor casing split apart after just six miles! It took a month of arguing with QCC until they finally agreed to make me a replacement, only because they couldn’t prove that the failure was of my making. To ensure that nothing like that ever happens again I installed a Prince RD-1875H pressure relief valve that prevents the motor getting more than 1500 PSI, and I also replaced the Danfoss 7WA110-2 solenoid directional control valve assembly that controls the motor speed - I found someone on eBay selling them for only $35 each (originally they were almost $800 each!), so I bought his last three and now have two spares for the future. To ensure the new motor receives as much flow and pressure as possible, I also replaced the old Webster KB hydraulic/PS pump with another (only $135 from eBay!) and reused the priority flow divider valve assembly off the old pump that was still good; if I had bought exactly the same complete pump as before it would have cost more than $1000, so using the old flow divider saved me about $900. Yeah! The old pump’s drive gear and gear coupling were very badly worn: I’m glad I changed them out when I did otherwise they could have failed on the road with dire consequences. I replaced some of the low-pressure hoses and both the high-pressure hose assemblies, moved the hydraulic fluid cooler to a new location next to my new transmission fluid cooler, added a Baldwin 10-micron filter to the motor’s return hose just before the reservoir, and put two pressure gauges on the motor’s feed and return lines to tell me now exactly what pressures it’s seeing.

Yes, it was a lot of work, along with having a new high-efficiency radiator core made by Atlas Radiator, powder-coating the radiator tanks and the coolant surge tank, reinforcing the radiator’s mounts, thoroughly re-sealing the radiator shroud to prevent any air from leaking past the core, adding three new temperature gauges to tell me the temperature of each cylinder bank and the radiator outlet, replacing both thermostats and their seals and housing gaskets, and finally making a distilled-water mister system for the radiator just in case I still need some extra cooling when climbing long grades in hot weather. At this point the engine cooling is where I want it to be, but I’m still toying with the idea of adding an entirely separate second radiator on the opposite side to take care of unusually hot conditions, such as climbing I-15’s Baker Grade in 115-degree heat, not uncommon in the Mojave Desert. We’ll see - there’s always another project or two to think about!

The subject of replacing stock cooling systems’ fans with electric fan motors is perennially discussed on the BCM forum and elsewhere, and the general consensus of thought is that they will not provide sufficient cooling capacity for over-the-road use, especially in hot weather. What works for city transit buses in stop-and-go use will not be adequate for continuous long-distance use, and everyone who’s tried electric fans has not had happy results (or worse). A RE bus fan takes as much as 40 HP to drive it - there are no electric fans that will move as much air continuously as an OEM system, regardless whether it’s direct-drive with a torus such as GM used for their V-drive buses, belt-drive such as used by MCI, shaft-drive used by Eagle and others, or hydraulic drive used in school buses and transit buses. Many folk have tried over the years to make an effective electric fan drive for RE buses, but I’ve never heard of one working well. Remember that what is OK for a front-engine truck is not OK for a RE bus that has no ram-air effect at speed - all the bus's air must be pulled in at 90 degrees from its flow direction, a very hard task.


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