Just how does tranmission fluid get into coolant?

I had transmission fluid show up in the engine coolant reservoir of my 1999 Chevy Tahoe. I first noticed this sometime after also noticing an intermittent rattling (washboarding) which sounded like it was coming from
the transmission. I made the mistake of continuing to drive, and about 25 miles later the entire transmission went out (only neutral "worked"). (BTW, the vehicle has TWO auxiliary transmission coolers in series with the cooler in the radiator.)
Different shops give me different explanations as to what happened. I'd like to get YOUR experiences/opinions!
Theory 1: The transmission was failing (possibly torque converter going bad), causing bits of metal particles and debris to plug the transmission cooler part of the radiator, which caused fluid to spill into the overflow reservoir (just how I don't know).
Theory 2: The transmission cooler in the main radiator developed a leak and allowed fluid to leak into the coolant and coolant to leak into the fluid. The coolant, once getting inside the transmission, ruined it.
Theory 3: ???
At any rate, when the transmission got rebuilt the shop also bypassed the main transmission cooler so that I am now using only the two auxiliary coolers. I am posting separately with questions about this.
I'd like to get your opinion on which theory above is most likely, but my main question is: If only the transmission cooler in the main radiator developed a leak and not the engine coolant part, then how can the transmission fluid get mixed in with the coolant? (It *did* happen -- I'm just trying to understand *how* it was possible.)
--S. Miller
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The transmission cooler is submerged in the engine coolant (water). When it leaks, the two are connected via the break.
DT
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# 2, possibly aggravated by the internal cooler plugging up with debris........pressure in the cooler circuit will rise to line pressure (up to a couple hundred pounds) if the cooler is plugged; up to the point at which it is stopped up

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Basic concept at work in this one: "If you can't dazzle 'em with brilliance, baffle 'em with bullshit." Although your TC *MAY* have been chewing itself to pieces, which *MAY* have been forming a blockage in the tranny-cooler section of the plumbing, there's no possible way (As in none, zero, zip, nada, zilch) for transmission fluid to "spill over into the overflow reservoir". Somebody was feeding you a line of shit in an attempt to appear wise, when in actuality, they were clueless, and hoping you were too.

*MUCH* more likely. A hole in the loop that goes into the radiator would allow exactly this sort of thing to happen.

There is no theory #3. Theory #4: NO POOFTERS! Oh, wait... wrong skit! So sorry, old bean! :)

Probably because they figured out that there was a leak in the transmission cooler section of the radiator. Hopefully, they also sealed the in/out from the tranny at the point where it enters/exits the radiator when they did the bypass. If not, you're in for coolant leakage. Exactly how much/how bad isn't predictable from the information I've seen you give so far, but there will be leakage.

The tranny-cooler part of the circuit is usually (I'm sure there are exceptions, and I'm just as sure somebody will point to them in an attempt to "prove" me wrong) just a loop of tubing inside the radiator that the coolant flows around. There is no "separate compartment" or whatever that deals strictly with the tranny fluid. The loop is simply run into the radiator, and sits there submerged in the coolant that's normally present. No "magic" going on - It's just "Dump the heat from the tranny juice into the water in the radiator, then let the radiator worry about dealing with it."
A hole in the loop, whether from rust, mechanical trauma, or whatever other source lets tranny juice out, and water in. The result is (sooner or later) a dead tanny and a cooling system with transmission fluid mixed in.
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Did they plug the transmission cooler lines coming from the radiator? If not, there has to be coolant running out the tubes OR there is nothing wrong with the radiator.
In any event, in cold weather the transmission fluid needs to go through the lines in the radiator to warn it, so I'd have a radiator shop clean and test it for leaks for peace of mind.
Tom J
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|
| | |> |> At any rate, when the transmission got rebuilt the shop also bypassed the |> main transmission cooler so that I am now using only the two auxiliary |> coolers. I am posting separately with questions about this.| |Did they plug the transmission cooler lines coming from the radiator? If not, |there has to be coolant running out the tubes OR there is nothing wrong with |the radiator. | |In any event, in cold weather the transmission fluid needs to go through the |lines in the radiator to warn it, so I'd have a radiator shop clean and test |it for leaks for peace of mind.
If you do not replace the radiator and restore the radiator loop to the transmission cooling circuit, you might consider moving the auzillary coolers behind the radiator, near the top if there is room. That will impart some heat to the trans coolers in cold weather. Rex in Fort Worth
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Tom,
Why, praytel, does the ATF need to be heated by the coolant? The ATF heats itself (that's the reason why you have ATF coolers). All the coolant does is keep it at 195* after the truck's all warmed up.
Doc
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Cold fluids not as efficent as warm fluid, too thick, and in sub zero temps, it can pay to have the engine run for a while heating the fliud for a few minutes before putting the auto in gear and moving off. Totally unessesary in Florida, but can be vital in Alaska.
at least thats my understanding from lurking around elsewhere.
rhys

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Actually, the coolant isn't 195F by the time it gets to the ATF cooler in the bottom of the radiator, even though it entered the top of the radiator at that temperature. Wouldn't be a very good radiator if it didn't cool the coolant!
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Others have already given you the answer, but if transmissions didn't need that liquid to liquid heat transfer, maybe you can explain why all automatic trans equipped vehicles come equipped from the factory that way
Tom J who is not trying to reinvent the wheel!!
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All automatic trans equipped vehicles *don't* come from the factory that way. My '99 V10 has no connection to the rad . . . just a cooler. I would presume that if cold transmissions were a problem, they they would need new trannies every year in Alaska where the average tranny temp never even gets above 0F when the ambient temps are hanging around -40.
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if the in-radiator cooler is SO necessary, perhap someone can explain why I've not had a problem with totally bypassing it in EVERY truck (and a lot of cars) in which I've overhauled the transmission SINCE 1997.
the VERY FIRST ONE, an F-350 7.3 PSD (Turbo) has over 330k on the overhaul, with only two fluid changes (hey, the owner 'doesn't have time' to have it done), and is still going strong, hauling a 30-foot stock trailer all over the country. This was equipped with a pair of Hayden 1679's, the big mothers, plumbed in series.
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I really have to wonder about that. How cold are you talking? 10C? 0C? -20C? -40C?
You can warm the fluid in the transmission easily. Put it in drive and keep foot on the brakes. The torque converter is turn horsepower into heat and that's circulating through the fluid...
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most likely the trans cooler thats made as part of your radiator is leaking... have radiator shop pull trans and replace the cooler.
Elbert
wrote:

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Fu**...
mistake... correction
have the radiator shop pull the radiator and replace the trans cooler that is made as part of the radiator...
sorry about the mixup
On Tue, 21 Oct 2003 16:35:57 -0500, Elbert Clarke

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Perhaps a bit of a sidebar to this:
At some point in the past couple of years, Monaco moved to an aluminum radiator. There have been numerous failures of the internal transmission cooler, with subsequent transmission failures. The story as I've been told is that it is an electolysis problem with different metals used.
In any case, a full recall affecting hundreds of vehicles was issued. Fix was a kit to mount a separate auxiliary cooler and cap off the internal cooler.
I received my recall notice about two weeks after I had the kit installed; I saw one on an unsold-but-built-later version of my '03 Safari, and since I was having transmission overheating problems I called to see about getting one. They didn't mention the failure problem to me, but were very quick to get me a kit and pay for the install. Overheating problems are very much gone, and it does take a long time to get very warm. Fortunately I don't do much (any if I can help it) cold weather travel, but from other posts here it sounds like there may be a different problem for Monaco when the cold weather hits in force.
One guy who I talked to who got the recall notice 9 days after his transmission had failed said Pacific Detroit Allison told him they had replaced 450 (with rebuilds) so far.
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Don Bradner wrote:

A friend in Texas had that experience with his Monaco. His first trip was trouble free-- the next 3 were disasters and he got towed in. As of the first year Monaco has spent $30,000+ rehabbing his new coach. He took it to Monaco factory in August, haven't learned what all his results were but I know he spent a week at the factory. This was AFTER he had the engine and transmission replaced. LZ

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the radiator tank, physically surrounded by coolant. When it leaks, coolant gets in the trans, and ATF in the coolant. Not uncommon at all.
The Engine radiator is a Air to Liquid heat exchanger. The transmission cooler is a liquid to liquid cooler. The transmission cooler is located inside the "return" tank of the radiator. This water has already been cooled by the radiator and is on its way back to the engine. The engine coolant at this point is cooler than the ATF, so the coolant removes heat from the ATF.
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Most US vehicles have the automatic trans fluid running through the radiator for cooling.
I would buy a new radiator and get the line hooked back up to it.
I would have your transmission serviced every 50,000 miles. maybe 30,000 with lots of towing?
I hear of lots of GM vehicles loosing their auto trans before 100,000 miles. After a good rebuild at a good trans shop they seem to run much longer?
Many large Ford, GM and Dodge trucks are all coming with beefier transmissions now.
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