I've got a problem with my 94 940 that I wonder if anyone has seen before.

The transmission oil cooler in the radiator has apparently failed and dumped transmission oil into the cooling system.

My troubles began about a week ago, during the recent cold weather.
The transmission became sluggish to shift into gear.

My first thought......120K miles...transmission never serviced.....transmission oil has thickened and cold weather is adding to the problem.

I flushed the radiator with new fluid....complete flush....and topped off the fluid.
When I was finished, I compared the amount taken out to the amount put in and realized that the transmission was about 3 quarts low to begin with.
What the hey?

Anyway, the tranny shifted good again, and since it was so cold, I didn't look further.

2 days later when I was checking the fluid level again, there was transmission oil all over the engine.....what the h###?
The upper radiator hose was split at the connection to the thermostat housing, and it was spraying "muck"....oil and coolant combined....all over the engine.
Where was the oil coming from? The Transmission.
The engine temperature gage showed normal through all of this.

I checked the engine oil, it was clean and the correct level.
Checked the transmission fluid, it wouldn't register on the stick.
The transmsission oil was leaking out of the oil cooler inside the radiator and filling the cooling system.

The fluid that I had flushed out 2 days before showed no indication of contamination with coolant. Thanks goodness the liquid was flowing in the direction it was and not the reverse....coolant flowing into the transmission.

Anyway, I have a new radiator on order, and I won't be driving the car...or even cranking the engine until it is installed.
I plan on flushing the engine before installing the new coolant.
Any recommendation on the type of radiator flush to use?

Sorry for the long post
steve

Just curious. Do you know the maker of the failed radiator?

Prestone Super Radiator flush claims to "help remove rust deposits and oily residue" . It may be a good candidate.
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Paul NW Indiana '89 744 Turbo 145K/ '90 745 turbo 127K

Providing your transmission survives (I hope) I wonder if it would be possible for you to pry off the end cap on your rad and determine what exactly was the cause of death.


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Art Benstein near Baltimore

Time flies like an arrow. Fruit flies like a banana.

Hello Art

I finally finished replacing the radiator on my 940.
I got a great deal on a new radiator.....$89......freight included....shipped to Georgia.
Send me a E-Mail if you want the name of the source. It's a good quality (aluminum and plastic) radiator too.

Anyway, I removed the side of the (old) radiator to expose the oil cooler.
The oil cooler in my (OEM?) radiator doesn't look like the one in your picture.
Mine actually looked like a small radiator about 2" wide and 12" long.
There was a tiny pin hole somewhere between the cooling fins.
I suspect it had been leaking (slowly) for a good while, and when I flushed the transmission with new fluid (see my first post), I must have opened it up some, because it really dumped the oil into the cooling system after that.

I flushed my cooling system several times, and got all of the oil out of the system, I then installed the new radiator and coolant.

I drained the pan on the transmission (again), and found no trace of coolant in the transmission. So far, I've flushed about 5 gallons of new fluid thru my transmission since this all started.
Since the repair, I've driven the car about 200 miles, and the transmission is as good as new.....shifts smoothly, and doesn't slip.
The fluids (oil and coolant) have remained clean with no sign's of contamination in either.

Anyway, I believe that I have the problem resolved.
I intend to keep a check on the transmission oil and engine coolant regularly in the coming days.

steve

Art,

I take it that is the tube that the transmission fluid flows through? Did the transmission tube fail on this one? Is it missing a plate on the end? Never saw the insides before. It actually looks to be a stout tube. Was this a blackstone?
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Paul NW Indiana '89 744 Turbo 145K/ '90 745 turbo 127K

Hi Paul,

That is indeed the transmission cooler from a Blackstone, original rad in an 89, that survived 21 years before its upper neck cracked.

No, I've never experienced a transmission cooler failure. I dread it, that is why I'm interested in the failure mode, and can't offhand recommend anything for Steve to use for flushing the coolant of oily stuff. My concern would not be for the cooling system having a little oil in it, but for the transmission having a little coolant in it. Supposedly it dissolves the bond used to attach the friction surfaces.

The heat exchange tube is not stout, but very thin material to promote quick heat transfer. It is double-walled, maybe about 1/8" between inner and outer, where the transmission oil flows. My concern is whether stress at the nipples or corrosion from the coolant side commonly causes this vital part's failure.

I think about this every time I do the transmission flush procedure, where someone frequently gives the advice to use a counterhold wrench when removing and installing the flare fitting.
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Art Benstein near Baltimore

A chicken crossing the road is poultry in motion.

hi art

actually what happens in the dreaded coolant in the trans is the coolant vaporizes to steam under the heat of the transmission while driving and it is the steam which destroys the transmission as MUCH from lack of lubricity as from any other factor.

typical trans fluid BOILS at 599F versus 212F for coolant

transmission fluid is extremely slippery stuff. water into steam inside a hot transmission literally dissolves the slippery film not to mention displacing the trans fluid so the transmission eats itself from friction.

I intend to do just that.

I can't conceive of any other thing that would cause the symptoms my car is experiencing.

There is oil in the radiator (and cooling system), and the transmission is low of oil.
The cooling resevoir is coated inside with a frothy mixture of oil and coolant, along with the outside of the engine where it sprayed from the split hose.
I don't believe the hose ruptured from overpressure.
I would expect to see coolant in the transmission oil if this had happened.

I did drain the oil pan (again) on the transmission, and there is no sign of coolant in the transmission oil......although the oil level was low.

I plan on flushing the engine block and heater, installing a new radiator, hoses, anti-freeze and topping off the transmission with fluid.
I will watch the engine and transmission closely for the first few miles to make sure there is no problem with cooling, or with coolant in the transmission fluid.

Any suggestion on what to use to flush the oil from the cooling system?
It seems like I would need a detergent of some kind.

Thanks for the reply
steve

How old was the radiator? I recommend changing it preemptively every ten years or so.
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See the 700/900 FAQ at the drop-down menu above right.

your first order of business is to flush and re flush the transmission AFTER opening up the drain plug on the pan to search for particles and foreign matter. if the pan fluid is clean....then flush and reflush after you have installed a new radiator. then get to the engine flushing. do not add any soaping agents to your engine flush and make sure you have the heater dash controls all the way open and remove the thermostat.

the only serious damage you want to ascertain if it exists is from your transmission. if you have none there you dodged a bullet

Can you give me some details on your advice not to use a soaping agent? Do you mean don't use soap, or just not to use it along with an over-the-counter flushing agent?

I ask because, for oily stuff, I flush with liquid laundry soap. I have done it on a variety of vehicles and it always seemed to work great while having little toxicity risk.

Charley

my reluctance to use soap is the all the bubbles created which can be hard to flush out.

I see. I never had that problem, but I flush with the thermostat removed. Then I run it with an open drain while feeding fresh water with a garden hose. Also, laundry soap is somewhat low sudsing so that the washing machine doesn't overflow with bubbles.

The first time I used it was on my Autocar that had developed a crack in one of the oil cooler tubes. It very quickly pumped 3 or 4 gallons of motor oil into the cooling system. Since the cooling system holds about 12 gallons, it was much more affordable to buy a giant bottle of laundry soap instead of flushes from the auto parts store. Also, I was not dealing with any scale build up, just oil.

Thanks,
Charley

I use washing soda, or sodium carbonate as a coolant flush. Commonly used as a booster for laundry where water is hard. Cheap if you buy it in the detergent aisle. It is a primary ingredient in many coolant flush products- at a higher margin.

"Thanks goodness the liquid was flowing in the direction it was and not the reverse....coolant flowing into the transmission."

I think there is a chance for "reverse flow" when the engine is off. The coolant system retains some 12± psi for a while, which could theoretically drive coolant thru the leaky cooler and into one or both fluid lines.

Given the possibility of coolant in the return line, I'd flush the tranny if it was mine.


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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.