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Old 07-02-2019, 10:44 AM   #1
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Accessory transmission cooler questions

A recent thread got me thinking...

When adding an accessory transmission cooler to a bus already equipped with the factory cooler (tied into cooling system), what's the best practice? Run the second cooler in series, or eliminate the original cooler entirely?

In the first case, would it be better to run it upstream or downstream of the OG?

In the second case, would there be issues relating to the ECM / sensors?
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Old 07-02-2019, 01:31 PM   #2
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A recent thread got me thinking...

When adding an accessory transmission cooler to a bus already equipped with the factory cooler (tied into cooling system), what's the best practice? Run the second cooler in series, or eliminate the original cooler entirely?

In the first case, would it be better to run it upstream or downstream of the OG?

In the second case, would there be issues relating to the ECM / sensors?
On my 91 t/c 2000 in series with the original heat exchanger and used a thermostat to control flow to the auxillary cooler. The stock cooler is more of a heat exchanger to keep the trans within limits. When the transmission heats up under heavy load it is the extra capacity in the engine cooling system to keep the trans within operating limits. I put mine on the return line from the engine cooler and before the filter. ECM / sensor issues? IMHO cooling transmission fluid has no bearing on the ECM or any sensors
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Old 07-02-2019, 04:06 PM   #3
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Ona bus with a 545 you want to add a cooler between the trans and radiator to lower the temps of the coolant going into the rad.
That's what I'm doing anyhow.
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Old 07-02-2019, 10:06 PM   #4
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Thanks for the info, guys.


It's a 2000, but I've already had some low gear heat-related problems, so considering our climate adding another cooler is high on our priority list. With any luck that & a full service keeps it chugging along.
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Old 07-08-2019, 05:37 PM   #5
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Any auxiliary air to oil cooling capacity needs to be placed before the oil to water cooler or heat exchanger.

That's how I've always done it, and have always seen it done by oe manufacturers.

Never eliminate the oil to water cooler. That thing will pull more btu's of heat out of the fluid then even the largest oil to air coolers.
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Old 07-09-2019, 08:34 AM   #6
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Any auxiliary air to oil cooling capacity needs to be placed before the oil to water cooler or heat exchanger.

That's how I've always done it, and have always seen it done by oe manufacturers.

Never eliminate the oil to water cooler. That thing will pull more btu's of heat out of the fluid then even the largest oil to air coolers.

Many thanks, Booyah. I'll take your advice on both counts.
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Old 07-09-2019, 12:54 PM   #7
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OK this is how the auxillary oil cooler is plumbed on our 91 Bluebird 5.9 AT 545 The temperature controlled valve has 10% flow through it all the time . It will be interesting to see the split between the 3 temperature guages. The oil cooler fan will be connected to an HOA switch.
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Old 07-09-2019, 02:01 PM   #8
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What's the purpose of preventing flow through the aux below a certain temp, Rivet?
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Old 07-09-2019, 02:02 PM   #9
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OK this is how the auxillary oil cooler is plumbed on our 91 Bluebird 5.9 AT 545 The temperature controlled valve has 10% flow through it all the time . It will be interesting to see the split between the 3 temperature guages. The oil cooler fan will be connected to an HOA switch.



THIS!! always use the thermostat.. esp if you eliminate the existing cooler..



the electronic allisons esp dont like to run too cold.. it does concern me that your 2000 heats up.. I barely see more than 190-195 in my 1000.. although there is a difference between 95 degree heat and 120 degree heat outside..



does your trans Lock up in 2nd?
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Old 07-09-2019, 03:16 PM   #10
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Yet another "Thanks for saving me" moment. I never would have thought about adding a thermostat. I do intend on keeping the stock unit.


Yeah, the trans concerns me as well, but not nearly as much as the first day I got her. Coming out of Austin in the afternoon the coolant temps were getting up to ~220. Everything was fine in high gears, but every once in a while you'd come into a town with stoplights, and then things would go to crap. In low gears (not sure if it was 1st, tor 1st + 2nd) as you'd slow to a stop it would lurch. Then coming off a stop it would slip like crazy, spinning up high rpm and just baaaaaaaarrrreeeeely moving, to the point I was sure I'd be stranded in the intersection. But eventually it would get some speed, shift up, and once back at a descent clip appear to be fine. Once out of Austin I ran on the freeway for another couple hours - no problems in high gear - and then exited onto some slower back-roads to reach my first day's destination, where again the low-speed slipping occurred. By the time I reached the ranger station (state park) the 'check tranny' light was on, and I shut her down figuring she very well may not move again once I fired her back up. But after 30 minutes or so cooling down, she started back up no problem (light gone), and had no problem in 1st... like nothing had happened. The campground was right down the road, so I parked for the night.


The next day no problems up to the freeway. Even though ambient kept increasing the further I traveled, the coolant temp stayed lower than the day before... ~180 or so mostly, up to a max of 210. Every time I'd stop for gas or other stuff I'd expect more problems, but never had any. Like the day before never happened. It wasn't until the end of the day - in El Paso rush hour traffic - that it started to lurch a little bit again in low gear. This is when the temps were ~210, with alot of stop & go. But nothing like the day before. Day 3 was the hottest (ambient) yet, and I reached home without any problems at all.



Even if the trans was brand new, I'd still want to add auxiliary cooling capability considering our location. As it is, I figure it might keep it alive a bit longer before a rebuild. I'm waiting until we get the 2nd cooler to service it so I don't fill it with fluid just to drain it a week later - and I'll be filling it with TransSynd when I do. I'm hoping (probably hopelessly) that the issues I experienced could be 'fixed' by a service. Why they got better over the course of my trip instead of worse has me extremely puzzled. But either way a cooler makes sense.


Any input regarding the behavior I experienced, or its potential cause, would be very much welcome.
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