Trans cooler fliud route

[LVJJJ]

Although I've been towing for years, and have always had a transmission cooler on every tow vehicle, I can't remember whether the fluid should come from the trans thru the cooler then to the rad and out back to the transmission, or vice versa?

In other words before or after the the radiator?

Recently purchased an '04 GMC Envoy to tow our 4000 TT, has tow package but no cooler. On the Trailvoy forum, there didn't seem to be a consensus as to which way it should be. Since those using their Trailblazer or Envoy for towing was a minority, I'm thinking us RV'ers here would know best.

The climate you live in seems to be the reason for placing the cooler before or after?

[Mark_Kovalsky]

BenK wrote:

In front of the main coolant radiator...it can be over cooled but the
main radiator will then heat up the ATF.

No, the main radiator WILL NOT heat up the ATF. Ever. In any cold ambient. Ever. See my post above for the explanation, I'm not typing it again.

[BenK]

BenK wrote:

Now for rotating shaft seals...sure thing. More so with journal type bearings
(non o-ring or some such). Ditto lots of rear crank seals...heck even some front
crank seals. Some old were packed, many has a coiled spring inside to keep it
tight during the thermal contraction/expansion

Said sure thing for rotating seals and have dealt with water pump weep holes
since I started wrenching engines in the late 50'...early 60's

[BigToe]

BenK wrote:
I'm not buying that synopsis and still say for thermal management of the hottest place on any ICE (piston) and that is around the CC

You aren't buying the synopsis of the purpose of a weep hole on the front of a water pump? You still believe that the weep hole in a water pump pulley shaft seal is for "thermal management around the combustion chamber"?

AirTex, a leading water pump manufacturer, produced a very simple to understand video explaining the purpose of weep holes and weep hole reservoirs on the front of water pumps. It can be seen here:

https://www.youtube.com/watch?v=UpcrfS-x5jA


On one of my tow vehicles, the manufacturer provided a photo explanation that makes it even quicker to understand the purpose:




And as for the "3/32" orifice on the thermostat you mentioned as being the same size as the weep hole, neither orifice is large enough for a bypass port that would allow the pump to recirculate coolant to bypass the radiator until the thermostat opens.

The manufacturer of one of my tow vehicles provided a drawing to illustrate the size of the port for the purpose of "thermal management"... ie, bypassing the radiator so that the engine can get up to operating temperature sooner, in part to reduce smog. The port is many times larger than that of a weep hole. In fact, the manufacture increased the size of the bypass port early on in a design update:




The comparatively tiny orifice on a typical automotive thermostat flange with a little "jiggle" valve through it is for bleeding air, not for coolant bypass. And the orifice in front of a water pump at the pulley bearing is for the shaft seal.

[BenK]

All ICE gaskets/seals/etc face thermal contraction/expansion...some
more than others. Worse if different metals on either side of the
gasket...part of why early alu heads had head gasket issues

I'm not buying that synopsis and still say for thermal management of the hottest
place on any ICE (piston) and that is around the CC

Now for rotating shaft seals...sure thing. More so with journal type bearings
(non o-ring or some such). Ditto lots of rear crank seals...heck even some front
crank seals. Some old were packed, many has a coiled spring inside to keep it
tight during the thermal contraction/expansion

SMOG has really messed up what us civilians can do with the thermal management
system. But for my GMT400, it was only during the early days and did lots of
noodling and thermal coupled my 454

This image is of the final modifications of 180*F thermostats. Wanted 160*F,
but too close to the SMOG mandated control system. The switch from open loop
to closed loop control is right around there and no confident enough to have
full power mode...cuz the computer kept if open loop

Notice all of the holes both in numbers, placement and dia...dialing it in with
a home based lab/tools (borrowed the thermal couple box/recorder)

This lead me to my final thermostat and is a 180*F with a bypass valve and a single
3/32" dia hole...close to the OEM weep hole from the stat manufacturer


thermostat thermostathole

Again, in extreme ambient temps...why lots of diesel's cover all to
a portion of their main coolant radiator...to keep their ICE's up
in temp...as it can be over cooled.

In front of the main coolant radiator...it can be over cooled but the
main radiator will then heat up the ATF. After the main radiator has
the potential of then over cooling the ATF if the ambient is extremely
cold.

Again, today's systems have lots of engineering to cover 'most' of
the bases on this, but note that some OEMs off kits to cover the
main radiator for those who live in extreme cold...

[BigToe]

BenK wrote:


Biggie is to keep the ICE from over heating on startup from cold

Gets a tiny bit to more (dependent on the hole size) flow from the ICE past the
thermostat so that it will open sooner than if no weep hole

Hottest area is typically around the CC and that is normally in the head...which
is insulated to the block by the gasket (of course gasket material factors)

By the time the CC heat brings everything up to temp...no weep hole will have the
thermostat NOT open till whatever thermostat range is designed in. They typically
do not just open/shut, but ramp (hysteresis) open/close

SMOG plays an ever larger component on how they design cooing systems today

Thank you Mark K for stepping in to provide some facts.

The weep hole of a water pump is directly related to managing the performance of the water pump seal, which is dynamic. It swells and contracts with temperature, and, the seal faces must remain wet at all times for lubrication. When the engine is cold, the seal is contracted, and coolant weeps. Newer design water pumps have a small reservoir built in that collects the weepage, so that customers do not misinterpret stains dribbling down the pump as a seal failure. When the engine heats up, the seal swells, and seepage ceases. Heat also evaporates the seepage in the small well designed to contain it.

IF seepage continues when the engine is at full operating temperature, and the contents in the well never evaporates under those conditions, and continues to over flow, then there is an issue. Otherwise, the dynamic seal of a water pump bearing is permitted to seep by design, for seal performance, not as any type of coolant bypass system for "smog" or "until the thermostat opens" purpose.

[BenK]

Don't think centrifugal vane water pump has a min flow. All the ones I've designed
in can go all day at zero flow (blocked)

Yes, burping is one, but not the biggie

Biggie is to keep the ICE from over heating on startup from cold

Gets a tiny bit to more (dependent on the hole size) flow from the ICE past the
thermostat so that it will open sooner than if no weep hole

Hottest area is typically around the CC and that is normally in the head...which
is insulated to the block by the gasket (of course gasket material factors)

By the time the CC heat brings everything up to temp...no weep hole will have the
thermostat NOT open till whatever thermostat range is designed in. They typically
do not just open/shut, but ramp (hysteresis) open/close

SMOG plays an ever larger component on how they design cooing systems today

[Sport45]

BenK wrote:
Okay...fun stuff now...lets get or continue into Thermal Dynamics of automotive
heat rejection systems

Why does all ICEs have a thermostat ? Some are preset/fixed while others
are variable...and...why do all have a weep hole ?

I'll take a stab at the weep hole question and guess it's there to meet the water pump minimum flow requirement. Or it could be there to aid in letting air migrate to the top for bleeding when refilling the cooling system.

[BenK]

Gale Hawkins wrote:

smkettner wrote:
Better get two. One before and one after. :B

That was funny. 🙂

X3...LMAO !!!

Cool, and thought would have been a dumb thing to close the auto tranny
off when started seeing the dip stick with a rubber/synthetic plug seal
Around the time BMW said their auto trannies were sealed for life
and never needs ATF top off or flush.

The reason many diesel owners block off their coolant radiator during
very cold weather is that the engine oil and the ICE itself works best
within it's design temp range. Ditto ATF and why said that a few posts
back

Why also said or asked if anyone knew why there are thermostats on our
ICE coolant systems...to keep them in their design temp range...even
in temperate ambients...because their capacity/ratings are based on
the worst case (withing specifications, which outlines worst case
via ratings).

Meaning that it will over cool the coolant/ICE without a thermostat

[Gale_Hawkins]

smkettner wrote:
Better get two. One before and one after. :B

That was funny. 🙂

[time2roll]

Better get two. One before and one after. :B

[Mark_Kovalsky]

BenK wrote:

Most all of today's automatics have a better closed venting system, so
humidity intrusion is not as high, but it is still there

Wrong. All automatics are vented to atmosphere.

BenK wrote:
As I said earlier:

In extreme ambients...with the ATF external aux cooler AFTER the main
engine radiator, will have the AFT cooled down too low and out of it's
temp range

This is why I think installing the ATV external aux cooler before the
main radiator in extreme ambients will warm or heat up the AFT

No, it will NOT heat up the ATF. Routed this way it won't cool it as much. But why install a second cooler if you don't want additional cooling? Routing it the way you propose is just a lower efficiency way of cooling the ATF. In colder weather it doesn't cool the ATF as much, and in hot weather it doesn't cool it as much. Either spec the second cooler smaller and route it correctly, or just leave the secondary cooler out of the picture all together. You're spending money for a second cooler, then neutering it's function. That doesn't make any sense.

BenK wrote:
In the closed metal tubing and synthetic tubing...there is no 'air'
pocket for any moisture in there to vaporize. It needs a chamber where
there is a gaseous volume to receive the moisture/vapor.

Correct. The air is in the transmission, and since it is vented to atmosphere it can and will pick up moisture from humidity.

BenK wrote:
Again...in extreme ambient (cold). If not in extreme cold...then makes
no matter which...before or after the main radiator

Wrong again. It does make a difference.

You're doing a lot of thought experiments. Get some vehicles and a few hundred thermocouples and run your own tests like I did. Then you'll understand.

[BenK]

Not really, but really due to buddies work at Chevron. Chem Scientist
specializing in lubrication with their modifiers his main assignment

Sub specialty in friction modifiers just because he wanted to work on it

But really still there...in spite of buddies work...just not as major an issue
from my days when I still had hair... 😞

ATF is hygroscopic at elevated temps and now that folks here say it is okay
to run ATF up to IIRC 240*F...H2O will go into solution with ATF above a certain
temp, but not up on that, yet

Again, key is NOT the base ATF, but the additive package. The friction modifiers
one of the biggies with H2O, but not the only one of them.

Think of brake fluid in a closed tube...AKA vapor lock when it reaches temps to
vaporize (in braking boiling point, but for ATF, AKA...vapor pressure)...similar
happens in ATF tubeing/hoses *IF* there is H2O emulsified in the fluid

[Turtle_n_Peeps]

Moisture in ATF creates acid over time and accelerated with heat...but
that heat is the way moisture is vaporized out. Preventing moisture
intrusion is the first and best way to manage this

Not really.

Unlike an engine, there is no combustion in a tranny so there is no acid build up. This is why we get the change our ATF every 100,000 miles in our tranny's and we have to change our engine oil every 5 to 10,000 miles.

As far as a few drops of water in the system from condensate, it's no big deal. We are talking about a low pressure hydraulic system here not a diesel fuel system with 30,000 PSI pressures.

All in all, you don't want your tranny to run too cold or too hot and with modern tranny's this is not too difficult. Even my old 93 4L80E has a strategy for keep the temps just right and it's over 20 year old technology now.

[BenK]

Okay...fun stuff now...lets get or continue into Thermal Dynamics of automotive
heat rejection systems

First, why does some vehicles and/or owners block a portion of their main engine
radiator ?... Where or what ambients do they drive?

hy does all ICEs have a thermostat ? Some are preset/fixed while others
are variable...and...why do all have a weep hole ?