B500: How much cooling needed?

[MagnoliaBus]

Could we say that you need to cool the trans oil from 250-300F down to 200F, and maybe it equate to removing 60-80 000 BTU.
The point is oil at 250F will emit a certain amount of BTU and at 300F it will emit more BTU, but you dont have the remove all the BTUs (or the oil would be cold). What do you think ?

[bevans6]

My understanding is the engineers know the temps in and out, the volume of fluid, the energy inputs and the cooling recommendatiions are designed to result in their preferred temps under specified conditions.  So they aren't trying to dump all heat, just excess heat to end up in a good zone for the application.  I think for most auto's that's kind of 200 - 225 F-ish.  If the recommendation is XXX Btu's, then that's what is required to cool it down to 200, if 200 is the goal temp.  Water to oil coolers will probably be specified differently than air to oil coolers.  Water to oil is cooling with 200 degree coolant, so pulling big energy out of the trans fluid into the coolant is different that transfering it to 130 degree air.  Most bus transmissions are designed to be cooled with coolant, not air, and the heat load is added to the engine coolant.  Also helps keep things warm in cold conditions, I imagine.

[buswarrior]

This is one of those complicated topics, with different goals, depending on the busnut.

Engines and automatic transmissions make lots of heat that needs to be dumped overboard.

Stock systems may have been (polite way of saying WERE) lacking right from the factory, busnuts may be putting more heat in than stock, the cooling system is no longer as efficient as it was new.

Typically, we are limited by vehicle structure and packaging, so have fans and radiators that don't readily upgrade.

Those radiators are all different ages and conditions.

Some busnuts want to raise their horsepower via bigger injectors, turbos or a re-power, all of which makes more heat.

Some busnuts want to add an automatic transmission where the original manufacturer did not consider offering one, and the cooling system is not sized to accommodate.

Some busnuts want to operate in the extremes of mountains and deserts without making the compromises that stock set-ups force one into, slowing down to reduce temps being a big one.

How to free up some existing cooling capacity?

Adding an auxiliary hydraulic cooler gives a busnut a way to remove the transmission heat from the cooling system, for whatever reasons one wants more cooling.

Installing properly placed temperature probes so the busnut can surely see the real temp, in and out, makes for good decision making.

In order to avoid making engineering errors, maintaining the stock style tranny oil to engine coolant cooler is a good move. No fancy controls to regulate the tranny temp are required. If the aux cooler is the wrong size, the engine coolant cooler will add or remove whatever the aux cooler didn't do right.

Running cold in winter conditions can't happen, and if the aux cooler can't take it all out, the engine coolant can valiantly try...

A simple fan switch that the busnut engages under high heat conditions does the job.

Busnuts who have installed a decent sized Hayden in the curb side engine access door of the MCI 8 report they never have to turn the fan on, there is enough airflow to dump enough heat without the dedicated fan in Florida conditions.

Note, they set those fans to blow OUT, as there is positive pressure in the engine room from the big cooling fans running at full tilt. Somewhat counter intuitive, cooler outside, hotter air inside, but an electric fan will have a hard job fighting the big squirrel cages, and the effect could be stalled air in the aux cooler, not desirable.

Even for a middle of the road busnut, an aux cooler gives you more room, as your radiators, fans, seals and shrouds age and deteriorate, even if strenuous conditions aren't in your plans.

That's why we roll our own, everything is right, if you are happy with the results!

Typed riding in the belly of a Megabus double decker, for true flavour...

Happy coaching!
Buswarrior

[Iceni John]

When I completely rebuilt my entire cooling system two years ago to solve some ever-worsening overheating problems, I also installed a separate transmission fluid cooler, not so much to cool the transmission itself but rather to help lower the coolant temperature.   It's a Thermal Dynamics DB-00341DC, the largest that would fit the only space I had for it, with 1" ports and a decent 14" electric fan.   And to answer the big question, yes, it does make a difference to the engine's coolant temperature  -  it's certainly a few degrees cooler when the electric fan is running.   The transmission fluid temperature, measured at the top exit hose of the TC housing, now either matches the coolant temperature or is a few degrees cooler, especially when out on the open road when it's locked up in 4th.   The DB-00341DC is rated at only 30-something K BTU, but that's enough to help.   I have a 195-degree temperature switch to turn on the fan, but most of the time I keep it always on with an override switch.

If I had space for a second one of these coolers (they're about 18" x 24", about 8" deep over the motor), I would also have one for the engine oil which now always runs about ten degrees hotter than the coolant, but I haven't any more space.   Too bad.   The new transmission cooler and the original Hayden 10421 hydraulic fluid cooler now sit behind the driver-side rear wheels, at a slight angle to catch the airflow under the bus while driving, but protected by the wheel well and mudflap from being hit by stones or road debris.

John     

[chessie4905]

So you DON'T have a coolant transmission cooler anymore?

[Jim Blackwood]

Buswarrior, Where does a '96 lie on that timeline? Should I be thinking about an aux trans cooler? (I may have one if I grab it today.)

Jim

[buswarrior]

Yes, '96 had problems.

Now, that being said, you aren't a hired steering wheel holder, and you aren't dragging 55 passengers around.

You know to use the transmission along with the retarder on long downhills, to keep engine fan and coolant moving, not just yank back on the joystick.

You want to know what your coach is programmed to do. How much retarder percentage, activated by the joystick, activated by the brake pedal, activated by throttle lift.

4 position joystick?

It all depends what the last fleet's brake life goals were, and what they thought of their drivers' abilities to use the equipment on their own to achieve that, or just programmed it to act all the time.

I wouldn't think twice, the small cost of a good cooler vs the game ending cost of a reman makes a great justification.

Heat is what kills all auto trannies, big and small.
Take the heat out, they live long lives.

Happy coaching!
Buswarrior

[luvrbus]

The first generation B500 had short lives anyways not much you can do to save one most series 60 in their life had at 3 behind them before the series 60 gave up

[Jim Blackwood]

Well now that's an interesting perspective. The seller said he thought it likely the transmission had been replaced, but when I looked at it, it seemed pretty crusty compared to the engine so I just assumed it hadn't been. Maybe it had. Do you think the history in the DDEC3 controller would tell me anything about that? After I get it registered one of my first trips will be over to the neighborhood Freightliner shop to check that out.

I pulled that oil cooler yesterday. Don't know how much help it would be, it's probably pretty small in relationship to bus parts. But it does have rather large lines, pretty close to 1" and the core is probably something like 16" square by an inch and a half thick so it could reject some heat. But maybe not much more than a drop in the bucket for this beast. Anyway I snagged it.

I think the retarder control is the 4 position you mentioned. I didn't exactly count but my impression was 5 so you are probably right. No idea how it might have been programmed, guess I should add that to the list. Also of course being in the east there are only a few long downhills steep enough to challenge it I expect. That one headed down the east side from Va into NC would be the one I'd see the most of.

Jim

[lostagain]

I have driven many S60/B500 buses. I don't think heat is a problem. Yea you can see the transmission temperature go up when using the retarder, but it quickly goes back down when you're done. Isn't transmission oil good to like 300F ?

Transmission oil temperature in a 2 stroke affects the coolant temperature much more, because the engine puts out twice as much heat as a 4 stroke.

JC

[6805eagleguy]

Got some good comments over the weekend!

I do not have a retarder!
Which is just fine with me! I would rather use the jakes any day, even though they are not quite as smooth.
So, judging from the comments here, cooling is minimum without a retarder.
Cliff said it was 5500btu's a minute with the retarder.
What is the max heat with out a retarder? (I do not have an Allison book, need to order one)

[luvrbus]

I have driven many S60/B500 buses. I don't think heat is a problem. Yea you can see the transmission temperature go up when using the retarder, but it quickly goes back down when you're done. Isn't transmission oil good to like 300F ?

Transmission oil temperature in a 2 stroke affects the coolant temperature much more, because the engine puts out twice as much heat as a 4 stroke.

JC

The synthetic's will stand a little more heat than 300F it is the only reason some people use in the B500, I cannot see where the B500 last any longer using the high dollar stuff  over 15/40

[luvrbus]

Got some good comments over the weekend!

I do not have a retarder!
Which is just fine with me! I would rather use the jakes any day, even though they are not quite as smooth.
So, judging from the comments here, cooling is minimum without a retarder.
Cliff said it was 5500btu's a minute with the retarder.
What is the max heat with out a retarder? (I do not have an Allison book, need to order one),download a Mechinic Tips for the B500 is all you need a lot of info is only found in the Application Manuals and they are to come by

I posted it for you 530 BTU per minute for sump cooling and gave the size of the cooler inside the radiator from the Allison manual 

[chessie4905]

Even though the synthetic fluid will stand more heat, the lip seals are still the same. They are robust, but can gradually degrade with extreme heat.

[lostagain]

I like Jakes way better than a retarder.

JC