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Towing and transmission coolers.


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Ok, so maybe this would go under towing, but a question.

 

Tow vehicle overheats when towing out west, at elevation, going uphill.

 

No transmission auxiliary cooler, which, according to Griffin Radiators engineer, is the first thing one should add.

 

All diagrams online show auxiliary cooler in return line from radiator to transmission, to protect transmission.

 

If one were trying to reduce heat load to radiator, would the auxiliary cooler be better placed PRIOR to radiator, in line between transmission and radiator?

 

Any thoughts welcome, David C.

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I have added a few extra trans coolers to trucks hauling the horse trailers so the line is before the radiator. I’ve hauled 4 horse trailers all over the Rockies with out a problem. 
 

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The heat exchanger in your radiator

is your primary cooler for your transmission.

 

It may be plugged.

 

That is the best way to cool

your transmission - make sure

it is operating correctly.

 

Then add supplemental coolers.

 

 

Jim

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28 minutes ago, SC38DLS said:

I have added a few extra trans coolers to trucks hauling the horse trailers so the line is before the radiator. I’ve hauled 4 horse trailers all over the Rockies with out a problem. 
 

Ok thanks, that makes sense to me to add it BEFORE the radiator, to reduce load on the radiator, just asking thoughts.

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8 minutes ago, Trulyvintage said:

The heat exchanger in your radiator

is your primary cooler for your transmission.

 

It may be plugged.

 

That is the best way to cool

your transmission - make sure

it is operating correctly.

 

Then add supplemental coolers.

 

was stating a problem with two possible solutions and wanting opinions on the two solutions.  Radiator not plugged in any way. Thanks 

 

Edited by trimacar (see edit history)
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I also put the auxiliary cooler as far forward away from the radiator but still in a good air flow as possible. I assume you would realize that but just wanted to be sure as I’ve seen them right next to the radiator. 
dave s 

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9 minutes ago, Trulyvintage said:

The heat exchanger in your radiator

is your primary cooler for your transmission.

 

It may be plugged.

 

That is the best way to cool

your transmission - make sure

it is operating correctly.

 

Then add supplemental coolers.

 

 

Jim

I was stating a problem with two possible solutions and wanting opinions on the two solutions.  Glad you’ve never had problems.

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"The heat exchanger in your radiator " so when the engine gets hot, it heats the transmission fluid.

Best way to keep tranny cool is to keep the lockup engaged. If you do not have a lockup trans you are beating a ded horse.

An external oil cooler is a good idea.

A transmission temperature gauge is also good - do not exceed 190-200F (my tow car has one in the dash)

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Talk to an experienced honest transmission repair shop.

 

The heat exchanger in your radiator 

cools the transmission fluid in the

summer and warms it in the winter.

 

It is the best way to cool the transmission fluid as it leaves the pan and cycles through to return.

 

Auxiliary coolers are not as efficient and are not a substitute.

 

They are a supplemental cooling add on.

 

I just learned this on my last transmission rebuild.

 

The owner of the truck before me did not have the factory heat exchanger on the radiator thoroughly flushed after they had rebuilt the transmission so there was a restriction in fluid flow.

 

This led to premature failure of the transmission they had installed before I bought the truck.

 

Coincidently I had disconnected and bypassed the factory heat exchanger in the radiator when I installed two supplemental coolers.

 

That bought me a little extra time but my transmission repair shop explain to me the best heat transfer took place with the factory designed and installed radiator cooler.

 

On my truck that is located under the radiator.

 

if you are towing a trailer a properly installed in line temperature gauge on your transmission line is a must.

 

 

Jim

 

 

Edited by Trulyvintage (see edit history)
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A over heated transmission transfers heat to the engine.  You can

have a transmission cooler seprate form your engine radiator with its own finned little radiator unit.

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I installed a stacked plate auxiliary cooler on our Suburban 2500 that we use for towing. I installed it after the factory cooler. My thinking was that the transmission typically runs cooler than the engine coolant so if you put the cooler ahead of the radiator, the radiator will just be putting heat back into the transmission fluid that the auxiliary cooler just took out. I think the amount of heat that transmission fluid adds to the radiator is negligible given the differences in thermal mass (the amount of transmission fluid in the radiator vs. the amount of coolant). Most radiator-based transmission coolers are only one or two passes inside anyway. Plus the radiator is on a thermostat while the transmission is not, so the radiator will typically be warmer.

 

With the auxiliary cooler after the factory cooler, our transmission typically runs at 165-180 degrees in the summer with a trailer, while the engine stays at a fairly normal 195-200 (for a GM vehicle). The only time we really stressed it was going through the mountains on a 90+ degree day with my '29 Cadillac in the box, but that was pre-cooler. Coolant went beyond 220 and the transmission was about 215 so we stopped to let it cool off for a while. Never had temperatures close to that after the auxiliary cooler was installed, although I'll admit we haven't hauled anything that heavy through the mountains again, either.

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If I was doing much towing I would add a trans cooler following the manufacturer's instructions.

 

You do not state what kind of tow vehicle, how old it is etc. I would start by blowing out the rad from behind with compressed air, there could be a lot of dirt and bugs blocking air flow. Then put on a 7 blade fan with no clutch. If this did not solve the problem I would be looking for a bigger radiator. The aluminum rads they make today are efficient and not too expensive.

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You start out saying your "tow vehicle is overheating"... When was the last time the cooling system was serviced?  New radiators are relatively inexpensive.  I would get a aluminum radiator and add a row of cooling (if it is two row go to three row) and flush the system.  Most tow vehicles offer a towing package from factory, I would start with that radiator and trans cooler.

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Vehicles today are designed to have the transmission fluid cooled or warmed by the coolant in the radiator.  That is why manufacturers put the transmission heat exchanger in the radiator.

 

If the system is working correctly, the fluid temp even when towing will probably not go above about 245degF.  Just an estimation.  That is because if the cooling system on the vehicle is working correctly, the high target temp would be about 215degF for the coolant.  

 

I said "OR WARMED" also.  The system is set up to warm up the transmission fluid if it is really cold outside.  That is because transmission shift quality is affected by the temp of the trans fluid.  If you are "tuned in" to the transmission shift points, you might notice different shift points when the vehicle is cold.  Warming the fluid helps to get the fluid up to temp quicker.

 

This controlling the fluid temp helps to increase durability of the transmission.

 

Trulyvintage is absolutely correct about having a CLEAN transmission cooler. I have lost count the number of repeat transmission failures caused by plugged transmission coolers that I have seen.  Talk to me sometime and I can give you some examples.   You ABSOLUTELY must flush the transmission cooler EVERY TIME you have transmission work except a filter & fluid change.  If in doubt, replace the heat exchanger or the whole radiator.  As noted, a new radiator is not that expensive, especially if you can afford to tow around an antique vehicle.

Edited by Larry Schramm (see edit history)
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2 minutes ago, nickelroadster said:

Out West and at altitude.  What kind of altitude?  When you start getting four to eight thousand feet, you really need to advance your timing a bit. 

 

New fuel injected vehicles take care of all of the engine control variables for best performance and fuel economy including timing advance.  Most timing inputs are taken off the crankshaft and fed into the engine control module.

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Sorry,

I don't have any new cars that this would be true.  I used to work in a foreign car repair  shop at over seven thousand feet.  We did a booming tune up business in the summer time and would tell the people to get the timing set back when they got to lower altitude.  I guess I wasn't thinking when I posted.

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Ok, so full disclosure, I purposely made this a generic question so I could get opinions here.

 

2013 Grand Cherokee, 3.6 L with no factory tow package, towing a 2000 pound Aliner trailer.  Radiator is not an issue as far as regular driving, tows all day long no issues.

 

Above 5000 feet and pulling up a hill, engine starts heating up, in some situations (AC off and heater even blowing), 25 mph up a hill to keep from overheating engine.  Have even had engine computer shut engine down.

 

So, called Griffin Radiators, they make a heavier duty radiator, but will give no numbers on how much more efficient than a stock radiator.  The engineer’s first question was whether vehicle had an auxiliary transmission cooler.

 

My tow vehicle is a Suburban with 8.1L, 2500, temp gauge and cooler and all that, so this is not about me knowing how to tow.  Thanks David C.

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1 hour ago, Trulyvintage said:

if you are towing a trailer a properly installed in line temperature gauge on your transmission line is a must.

DITTO!  I added mine to the transmission pan. Interesting to see it heat up with converter unlocked and cool back down when in lockup.

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If you ever have an automatic transmission failure & rebuild ...

 

Remove & replace any aftermarket transmission coolers you have installed - don’t attempt to flush them.

 

You may have to be adamant on 

insisting the transmission repair shop

replace them.

 

Also be prepared to replace your radiator too if the heat exchanger is not thoroughly flushed - the only way you can tell is by the pressure of fluid that comes thru on the return - some shops just run a short flush and cal it a day.

 

I service my own transmission.

 

I always run a full synthetic fluid.

 

My truck is a 2WD and I replaced

the stock pan that had no drain plug with a 4WD pan that was deeper and had a drain plug.

 

Starting at 25K after my transmission was rebuilt - I drain the pan when it has been running awhile & the fluid is hot - it holds (7) quarts so when I do

this I am replacing about 1/3 of the total tranny fluid.

 

Then I do it every 3K to 5K.

 

Dirty fluid & heat = premature transmission failure.

 

 

Jim

Edited by Trulyvintage (see edit history)
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2 hours ago, padgett said:

Best way to keep tranny cool is to keep the lockup engaged. If you do not have a lockup trans you are beating a ded horse.

 

Can't do that with vehicles I have towed with, they are designed to unlock when under heavy load and use the converter. Don't think the lockup clutch can stand heavy towing except on the flat with a moderate load.

 

My latest is a 97 K2500 Suburban. These late models are a whole different animal, especially the HD models with diesel. They may pull in lockup, don't know.

Edited by TexasJohn55 (see edit history)
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Not worried about protecting transmission in this case.  Want to reduce load on radiator.  Auxiliary cooler add, before radiator, or after radiator, was basic question.

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5 minutes ago, trimacar said:

Not worried about protecting transmission in this case.  Want to reduce load on radiator.  Auxiliary cooler add, before radiator, or after radiator, was basic question.

Before. Then the radiator can warm it if overcooled.  Yes! That can happen in cold climates. This is an old discussion, there will be opinions both ways.

Edited by TexasJohn55 (see edit history)
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The last transmission that I replaced I used a power washer at the end of the lines by the transmission.  When I first started to try to flush with soap, nothing would come out.  I then turned the soap off and still nothing.  I kept alternating between the two lines and eventually the big slug of junk came out of the cooler/line.  After alternating back and forth I eventually got a clear stream.  I then ran air through the cooler system for a while to dry it out.  Never had another transmission problem after that.  You must flush the transmission cooler during any transmission repair.

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8 minutes ago, TexasJohn55 said:

Before. Then the radiator can warm it if overcooled.  Yes! That can happen in cold climates. This is an old discussion, there will be opinions both ways.

Thanks, that seems to be a common sense approach....thanks for all the replies...dc

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On my truck now 👍

 

After the factory radiator heat exchanger - installed on the return line to the transmission - I have two auxiliary coolers.

 

One is a tube type:

 

DB71D8F1-8308-49FA-894F-CF6AA2CB3DD5.jpeg.1bcb564c21dece83f26247dee33778bd.jpeg
 

The other is a plate type:

 

3E10EF78-C115-4B12-B5CE-8151548F888A.jpeg.20045768ffac855788f740a2574c1eb7.jpeg

 

Both are mounted in front of the ac condenser and radiator where the front grill was 😉

 

 

Jim

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Well, again, that’s helping the transmission, but it’s stealing cooling air for the radiator.  Quite an installation, though, should help the transmission a lot!

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20 minutes ago, Trulyvintage said:

Both are mounted in front of the ac condenser and radiator where the front grill was 😉

Wow, that looks like overkill. Do you have a guage? It may overcool without reducing radiator load from OEM cooler.

With 2 coolers, you may not need airflow from fan but don't change it if it works for you.

Edited by TexasJohn55 (see edit history)
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3 hours ago, TexasJohn55 said:

Before. Then the radiator can warm it if overcooled.  Yes! That can happen in cold climates. This is an old discussion, there will be opinions both ways.

 

Yup.  My old Suburban has the factory aux tranny cooler option.  It is plumbed BEFORE the in-radiator cooler for this reason.

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The OP’s tow vehicle has a 5000 pound rated tow capacity - but that is probably with the larger engine and factory tow package.

 

The absence of a factory auxiliary transmission cooler would indicate that Jeep model was not designed to tow.

 

In addition to an auxiliary transmission cooler and perhaps a different transmission on the larger engine - there perhaps is also a larger radiator and suspension - rear differential differences between the models.

 

I have a 1998 Jeep Laredo with a 5.2 liter V-8 and factory tow package.

 

It has a 5000 pound tow capacity.

 

But I don’t consider my Jeep as a tow vehicle.

 

 

Jim

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Jim, in a lot of ways you are correct, this Jeep is not really a tow vehicle. 

 

It does great on level ground and gentle hills.  But, as I pointed out to my brother (who owns it), 25 people can make a 82 ton 757 airplane move on level ground (Dulles yearly airplane pull competition).

 

Its just on inclines at elevation that there are issues, all related to overheating.

 

He’s going to install an auxiliary cooler before the radiator and see how that works.

 

Thanks, good discussion.

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Trans temp is your friend or enemy. By putting the extra ( not the only) cooler before the radiator the exchanger can raise or lower the temp to the required temp. One other thing, all two or three of these I installed (it’s been a few years) we’re set up with the proper fittings so it could only be attached one way. I guess they were trying to make it idiot proof so as not to be sued for destroying transmissions. I believe they called those days the law suit happy society days. 
dave s 

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Gee so many different opinions. All I can say is what works for me. Been towing since 1972 (mostly race cars) and never with the largest engine (this century all have been gasoline six cyl engines with lockup torque converters).

 

Yes the lockout will drop out under PE (Power Enhancement) aka heavy load, usually over 53% throttle position (viewable with torque pro). How do you avoid PE when climbing a hill ? Use of a little known technique called "downshifting" (people with old VW campers may have heard of it). Modern automagics make it easy, on my tow car just push the shifter sideways to go up or down manually. True with a tandem axle trailer with a Corvette onit (most of my early towing) it can get slow but in my experience steep uphill grades are a small part of towing and have little effect on A to B time.

 

By keeping the trans in lockup except for short bursts, the transmission runs much cooler (helps to have an transmission oil temperature gauge). The other part is that 3000-4000 rpm for long periods is no big for an engine with a 6500 rpm redline and a really flat torque curve.

 

Don't disagree that an external trans cooler can help but if you drive to keep the whole drivetrain under 200F it is not needed so much.

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On 1/24/2021 at 7:38 PM, padgett said:

"The heat exchanger in your radiator " so when the engine gets hot, it heats the transmission fluid.

...

A transmission temperature gauge is also good - do not exceed 190-200F (my tow car has one in the dash)

If your desire to keep the temp. below 200, I think the best place is to place the cooler after the radiator. 

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