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Old 07-23-2017, 02:46 PM   #1
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Cooling issues

Wanted to pick some brains for ideas/suggestions. I recently purchased a 03 Bluebird transit bus we are converting. It has the 8.3l cummins and has 6th gear disabled. I'm currently waiting on bluebird to authorize 6th gear to get the tcm reflashed. With this being a transit bus while I'm on the highway my engine temp reaches 220* F at about 60mph 2200rpm. It triggers the warning system that will shutdown the engine eventually. I have yet to reach that point. I'm curious if my problem is adequate airflow through the side mounted radiator, or hydraulic fan inefficiency due to design of intended use. What radiator is used on a "highway" coach? Should I go to electric "pusher" fans? I'm a certified auto tech by trade and a fabricator, so I'm not intimidated by necessary "modding". I'm just not familiar enough with "busses". Any help would be greatly appreciated. Thanks in advance.
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Old 07-23-2017, 04:45 PM   #2
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i would check the cooling system, n radiator as u r 35 degrees too warm. of course there can be engine issue as well. If you have constructed street rods or even buy and sell from like say IAA, you know that fabbing up radiator supports for another radiator, n redoing the inlet and outlets is not difficult. I personally would not use elect fan, instead would either repair my system or make new ..
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Old 07-23-2017, 05:17 PM   #3
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an electric fan is unable to move as much air as an engine powered fan. i'd fix the problem first.
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Old 07-23-2017, 05:22 PM   #4
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Do you know if there are any differences in a otr re bus vs transit in the cooling system? I'm quite certain there would be due to the different operating conditions. Just need to know what I need to change. Engine runs well and exhibits no mechanical issues that are evident at this time to indicate mechanical problems.
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Old 07-23-2017, 05:40 PM   #5
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School buses tend to use medium duty parts, where transit buses typically have larger engines, engineered for sustained highway speeds and ascending steep hills at highway speed. They often have much greater capacity cooling systems, both in terms of how much coolant they contain as well as how much heat they can dissipate. That said, rear-engine school buses and transit buses may use the same type of cooling setups (even if they don't use the same parts).
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Old 07-23-2017, 05:41 PM   #6
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i "know" cooling can always an issue with an RE. some one is an expert here, they'll pipe up soon.

i'd start with the usual suspects. verify your fan clutch is working. thermostat. water pump. rod the radiator.
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Old 07-23-2017, 06:01 PM   #7
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And the simple thing, such as simply cleaning between the radiator fins (externally). Some build up a lot of junk and dirt and removing it can make a difference. I use a pressure washer, just be very careful not to wash "from the side", you don't want to bend the fins. If possible, I wash from behind, push the dirt back they way it came in.
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Old 07-23-2017, 06:16 PM   #8
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I recently completely rebuilt my entire cooling system due to perennial overheating problems that were getting worse. I'm guessing my bus's cooling system is not much different than a BB transit bus's - I have the info for BB pusher school bus's cooling systems, and mine is broadly similar. I had a new radiator core made, powder-coated both radiator tanks and the surge tank, had a new 9-blade fan made by Multi-Wing, had a new Webster YC hydraulic fan motor made by QCC, replaced my Webster KB hydraulic/PS pump, replaced the Danfoss solenoid directional control valve, moved the hydraulic cooler to a different location, added a separate second transmission cooler, added a hydraulic filter, replaced both thermostats, replaced a lot of hoses, added a hydraulic pressure relief valve and two pressure gauges, and did a lot of other associated work as well. Now the bus doesn't completely overheat at the sight of a slight hill, but the temperature still isn't quite where I would like it to be. I'm now toying with the idea of adding a second radiator, either on the right side or at the back, but I need to know what heat rejection I could expect from it before I start a project like that - if I turn on my heaters I see an immediate drop in temperature, and they are 150,000 BTU/hour total. My engine requires about 12,000 BTU/minute (720,000 BTU/hour!) heat rejection through the coolant, but a Cummins 8.3 will be less than that.

The reason I changed out essentially everything was because I don't want to have to deal with this ever again! The fan motor was slightly leaking internally, the pump probably also was the same (it has visible wear to its gear lobes), the heavy old 6-blade metal fan made more noise than moved air, and the radiator had some cold spots and the beginnings of corrosion. After I got everything back together I realized that the fan was still not turning fast enough even at full speed, and it turned out to be the $35 hydraulic control valve that was leaking internally - just changing that alone made a big difference.

Hydraulic fan systems are not intrinsically complicated, and they can work very well. However, age and wear take their toll, and small amounts of degradation here and there will add up to a significant reduction in overall cooling ability. If one specific item is not working right you can replace it alone, but in my experience everything just wears out at the same rate, meaning that you may need to just bite the bullet and change out everything. Yes, it's a lot of work, but I'll never have to redo what I've now done, ever.

Here's Blue Bird's information on their hydraulic fan drives, I assume for school buses. I expect their transit buses and Wanderlodges use something similar: http://www.centralstatesbus.com/2003...s/a3hydfan.pdf If you have any other questions about hydraulic fan systems, feel free to ask me - I'm not an expert, but after working on mine I think I understand the basics!

I notice that the new bendy-bus transit buses here have a bank of nine electric pusher fans, and those fans are at full speed every time the bus comes to a stop, but after a minute or so the fans slow down a lot. What's adequate for a transit bus that stops every minute for a rest may not be suitable for a bus traveling at sustained speed. I can't imagine that those transit buses would do too well climbing Baker Grade on I-15 northbound when it's 115 degrees outside! There's good reason that long-distance buses use hydraulic or belt-driven radiator fans - it takes up to 40 HP to power a fan, and no electric motor(s) come close to equaling that. The subject of using electric fans for primary cooling is discussed every few years on the BCM forum, and the general consensus of thought there is that electric fans simply will not work on a RE bus that's driven continuously in all weather conditions and over any grades. It would have been a lot cheaper and easier for Blue Bird or Crown or Gillig to slap on a few electric fans and call it a day, but they didn't do so simply because it would not be sufficient. In other words, fix what you have, and don't second-guess the original engineers!

John

PS - if your bus uses a Danfoss 7WA110 solenoid directional control valve to vary fan speed, I can tell you where the last two in this country are for only $35 each (less than a tenth of their original SRP).
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Old 07-24-2017, 03:03 PM   #9
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I have visually inspected hydraulic system and cooling system to find no external leaks at all. Do you know the test procedure for the fan clutch and valve? The bus can run all day at high idle and stop and go 105* weather all day with both engine driven a/c units running. Which led me to believe I have a high speed air volume problem. I was even considering building a 3" tall by 4" wide 24" across "scoop" or deflector to help force more air volume through the core at highway speeds. I am going to rod the radiator regardless. I just wanted to pinpoint and address my actual problem if possible first. I appreciate your time and help. I'm fairly new to RE setups and busses all together.
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Old 07-24-2017, 04:48 PM   #10
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Rated Cap: 37,400 lbs GVWR
On pages 16 and 17 of Blue Bird's info there are tables of fan speeds for any given engine RPM. With a simple hand-held tachometer you can measure fan speed, then you'll know if it's running too slow or not. If it is too slow, then there's internal leakage in one or more places (pump, valve, motor). Some pumps and motors can be resealed, but if their lobes or casings are worn there's nothing to be done except replace them. Is the engine's water pump working well? Sometimes their impellers are loose on the shafts, or the impellers are worn because of cavitation. Does the radiator have any cold spots? What temperature difference is there between the inlet and outlet hoses? Is the coolant at no more than 50% concentration? (Has it been tested recently? Does it need SCAs?) Is the radiator shroud absolutely 100% airtight so no air can be drawn through any gaps there (all the air must come through the radiator)?

Radiator scoops is another of those much-"debated" subjects on BCM. Like misters, some folk swear by them, some folk swear at them, and everyone has an opinion. You could try making some different temporary designs from plywood to see what happens, but they won't solve other cooling issues. Apparently i's easy to make scoops that work well at 60 MPH, but will they also work well at slower speeds, or will they obstruct airflow when stationary? Good luck!

John
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