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Transmission cooler, good idea or unnecessary?

cutehumorcutehumor Member Posts: 137
Hey guys,

I don't tow anything. The reason why I ask is because the auto transmission in this car is on the way out. I bought the car in Oct 98, the previous owner didn't maintain the tranny in this car. In fact, when I bought it, the tranny fluid was black. I presume the tranny fluid was black from running too hot. I changed it immediately, but I can feel the tranny struggle at times when accelerating. Would a transmission cooler be worth putting in this car? Prolong the life the tranny for another year or two? Considering the age of the car and value, I wouldn't want to put a rebuilt tranny in it. any opinions?


  • mrdetailermrdetailer Member Posts: 1,118
    It is placed right in front, not inside of the regular radiator. Why would they do that if there was no benefit.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaMember Posts: 64,482
    Yes, I think a transmission cooler, if it is designed properly, is a great idea for any car. But it has to be installed in the right place (near some air flow), of large enough capacity to actually exchange heat, and of decent quality so you aren't plagued with leaks and clogging.
  • adc100adc100 Member Posts: 1,521
    Cooler is OK but the real reason coolers are needed is that oil oxidizes at a high rate as peak temperatures approach 250 F. For every 15-20 degrees additional- oil life is cut in half. A more practical solution to the problem (and cheaper) would be to use a pure synthetic oil. You could run forever at 300F and higher.

    I am not an expert-but if the oil looked as you suggested the trans has one foot in the graveyard.
  • mrdetailermrdetailer Member Posts: 1,118
    My Mazda Mechanicputs in an after market transmission cooler as a standard procedure.
    Check the Mazda 626 discussion group and you will find out that they have weak (Ford) transmissions and are constantly causeing problems. They need overhauls fairly frequently. He considers it good insurance.
  • mrdetailermrdetailer Member Posts: 1,118
    In a transmission that is truly a scary proposition. I'll bet it smelt burnt too. Generally the worse the condition, the darker the fluid.

    Lubegard reduces acids, so it might be a help to stop current damage. see the site at
  • jlflemmonsjlflemmons Member Posts: 2,242
    This has got to be the cheapest insurance you can give your transmission. Here in central Texas the temps run well into the triple digits on the freeways while you creep along. A good cooler can be had for less than fifty bucks and are very easy to install. I bought a '95 Safari van brand new and asked at the time whether a cooler would be a good investment. The service manager whom is very knowlegeable said it best: "If it were mine, it would have one before the week was out". Six years and 65K and the tranny has not given one bit of trouble. The fluid is still good and the van shifts smooth as glass. Although GM recommends no service for a while yet, I will probably do an oil and filter on it this fall.

  • hengheng Member Posts: 411
    Previous postings alluded to it but plain and clear the damage has been done already. There is no point in adding a cooler now.
  • cutehumorcutehumor Member Posts: 137
    What brands of synthetic transmission fluid do you recommend? I'm not really familiar with synthetic transmission fluid. I know my particular transmission uses Dexon 3 fluid. Is Mercon 5 synthetic? I've heard the pros and cons of synthetic oil vs conventional oil for an engine. Are there any pros and cons for syntheic transmission fluid?
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaMember Posts: 64,482
    HEAT is the enemy of automatic transmissions. Therefore, a transmission cooler is a much better solution than synthetic oil I think for any heavy duty uses, since oil is not a good dissipater of heat. Any oil can be overcome by heat because it cannot get rid of it. Oil, without a cooler, is not a great cooling agent itself, just like water is not without an external radiator. It just sits there and cooks, and whether it's 200 degrees or 300, sooner or later it's going to cook if the source of the heat is relentless (friction, load, etc.).

    So if you are towing or driving in very severe heat conditions, and you expect synthetic oil to match the efficiency of a good external cooler, I feel you will be disappointed. But for a little extra security under normal conditions, a synthetic oil might help, sure.
  • adc100adc100 Member Posts: 1,521
    I use Mobil 1 only because I know they make a very good motor oil and its available and not overpricy. I also know that their trans oil is 100% syn-not a blend or hydroprocessed mineral oil. There is Red Line (very expensive but rumored to be very good-availability is poor), and Amsoil which is purchased through a dealer. Be leary of Pennzoil and Castrol-they play games with the word "synthetic"

    I still say syn oil is a good choice because it gives you at least a hundred degrees of reserve. I can't imagine a transmission so misdesigned that it runs 100 degrees higher than its supposed to. Don't forget it also has a cooler in the radiator and as the transmission heats up-heat rejection improves. Towing may be the exception where a cooler is absolutely required.
  • lngtonge18lngtonge18 Member Posts: 2,228
    Just curious, how effective are transmission coolers that just run through the radiator? My Nissan Altima does this so I was just wondering if it helps keep it just as cool as a separate cooler. Any thoughts?
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaMember Posts: 64,482
    No, not as effective since the hot water part of the radiator can heat up the oil part. This is a very old solution going way back to the early days of the automatic. Better than nothing, but not much.

    Of course transmissions go over their acceptable heat range...that's why they burn up, and that's why you need a cooler for either a) towing, b) severe service, or c) possibly even for "weak" units that are notoriously unreliable. If your trans is overheating badly, no oil is going to save it---at best, it gives you just a few more minutes until the catastrophe happens or until you can react (hopefully in time) and give it a rest or a service. If say a racing engine running syntheetic is pushed to its design limits (over-revving, detonation, etc.), it doesn't matter what kind of oil is in it.
  • adc100adc100 Member Posts: 1,521
    lubricated machines fail because the oil failed. The transmission burned up because the oil failed. That auto trans would run at 400 degrees if the oil could take it. (seals are good for that). Plain and simple-unless there is a clearance problem with heat, lubrication failures cause the machine fail many times. More than likely when they go beyond their "acceptable heat range" they went beyond the acceptable heat range of the lubricant.

    As far as over reving a race engine thats a different story. More than likely its a delivery problem where oil can not physically keep a surface lubricated or the high speeds broke a rod or physically deformed a bearing even though there was lubrication there.

    Having said all that-I may investigate a transmission oil cooler myself. Who makes good ones??
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaMember Posts: 64,482
    If a transmission gets hot enough, lubrication will fail no matter what I think. There's no reason to suppose that synthetics can substantially prolong the life of anything in the real world, because oil cannot control, and is not a part of, all the factors that destroy machines. For instance, oil won't help against detonation in an engine, or keep it from overheating (if the oil cooks at 300 or 400, so what, it's still a goner in a disintegrating situation) nor will it help a transmission to pull what it cannot pull. It's just one part of a more complex series of events.

    Nor, for that matter, can an oil cooler be thought of as a guarantee of long life. It's just another hedge, like synthetics might be, or good driving habits and good service. You add 'em all up and hope for the best, I think.
  • q45manq45man Member Posts: 416
    Generally syn ATF [Mobile 1] helps by improving flow at the cold end of spectrum and a bit more stable above the 176F - that all AT should run at. The glue that hold the friction material to the metal plates [clutches] is temperature sensitive, excess heat will allow the material to break down and flake off into the ATF [this is why it turns black] the high temps will oxidize the chemicals in ATF this is the brownish red burnt smell in ATF. All fluid has a combo of these depending upon miles....the color and smell are the major indicators of problems some trans need an annual total change, some can go 30k, a white paper towel and your nose are the 2 best indicators.
    The extra external air to ATF cooler can lower peak temps by 20-30F thus doubling the time between color changes from bright red to dull red.
    After 20,000 miles my ATF looks like brand new [compare color] but it gets changed [full flush Mobile 1] anyway since the goal is maximizing life and $200 every 20,000 miles [annually] is nothing compared to a $3500 unscheduled replacement.
    If owners would just change all their fluids annually [plus the regular 3-4k or 90 day oil changes]..brake, coolant, ATF, ps, diff, traction, etc they could easily get 250,000 miles out of most vehical systems!
  • self_mechanicself_mechanic Member Posts: 95
    I have a 2000 Honda Odyssey, and the manual state
    that "use only Honda ATF. if Honda ATF is not available, other brand of ATF can be used temporarily. It needs to be flush out as soon as possible and replace with Honda ATF". I am planning to use Mobil sync ATF on my Honda, and
    is there any truth to the Honda claim? Or it is a another gimmick to sell expansive Honda ATF.
  • mrdetailermrdetailer Member Posts: 1,118
    g45man. One word. Amen. Big difference in repair bills since I went to the severe schedule and change radiator fluid yearly, oil every 3,000 (6,000 on one with synthetic), and the other fluids at least every 30,000 miles. Guess that's more than one word.

    Honda ATF is different. But a transmission specialist or your dealter should have a synthetic available.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaMember Posts: 64,482
    Those are all very good points, thank you.

    I just wanted visitors to avoid a false sense of confidence from synthetic oil alone, as if to say "well, I've got synthetic in there now, so I can forget about good driving habits and maintenance". Bad idea!
  • q45manq45man Member Posts: 416
    will only provide 10-20% at most improvement in basic design life because heat is the killer in AT, the Mobile 1 can better handle the heat but other parts still react to the heat!
    Even Mobile 1 with an external cooler starts to change chemical composition around 20,000 miles [the red color starts to get washed out] and the smell changes. Depending upon how long you want the tranny to last thinking about a full flush exchange should begin and in no case should the ATF be allowed to remain for more than two years even if you don't drive much.
    The best OEM warranty is only 6 years or 70,000 miles [most are still around 3/36k] the dealer would love to sell you another AT anytime after that. We have been sucessful in extending transmission life to the 175,000 plus range [on cars that normally failed at under 100,000 miles]by almost forcing the customer to do flushes and use premium fluids [we make the same profit on multiple flushes [say 5 plus cooler install] but the customer saves big on the transmission.
    Either way we're happy but it's nice to save the customer money.
  • lbthedoglbthedog Member Posts: 198
    There's a very good reason that the manufacturers use the radiator tank to "cool" the transmission. Unlike the engine, the transmission does not have the capability to regulate it's temperature, there is no thermostat. Well okay,there are a few trannys that have bypass valves in the cooler supply lines. And most are running with some sort of thermo elements to maintain levels. But the coolant in the radiator is a fairly consistent temperature. And it is warmed by the engine in cold weather. Transmissions like warm oil. Cold oil is tough to pump and apply bands or clutches. Valve bodies hate it too, need to get everything at the same temperature. The oil to water coolers are far more efficient than air to oil. And of course, far cheaper. But if you are so inclined to install a additional cooler, be sure to plumb it so it feeds the cooler in the radiator. If it's after the radiator cooler, you may lower to oil temp too much. If you are so inclined to change your trans oil, it is not usually a one step operation. Some but not many trannys have drains in the torque convertor, Some convertors hold as much as four to five quarts of oil. It does not drain down when the motor is off. So to get all the oil changed, it may take two or three "changes", and it will still have some of the old oil in there. Be careful how you plumb a cooler too. I've seen where some people do a haphazard plumbing job and put kinks in line, rubber hoses with sleazy clamps, use rubber lines that aren't rated for high pressure or oil, in other words, they do more harm than good. For the most part, the factory parts do well, many of the after market stuff is good but if you find the cheapest way out, you found something that isn't worth doing.
  • bretfrazbretfraz Member Posts: 2,021
    First, thank God Dennis (aka Q45Man) chimed in here because his knowledge about extending transmission life (among other things) is incredible.

    Post #21 by LB was a good one too. It is important to realise that the so called "cooler" in the bottom of the radiator is really a heater. LB is right; trannys don't like cold fluid. Radiator heat is used to warm up the tranny fluid until the tranny itself gets hot enough to be happy.

    The problem is that trannys get too hot and the radiator cannot cool it. That's not what that thing was designed for.

    Prolly the best thing to do in the AM is let your car warm up gradually before driving off. That way the tranny has had time to feel good and will operate as best as it can. This is especially important in cold winter climates as cold temps will kill a tranny about as quickly as hot temps.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaMember Posts: 64,482
    Yes, that's what I meant about good trans cooler design. If it's well engineered some temperature stabilization is provided for. I've seen some very primitive junk out there that you woudn't want to use.
This discussion has been closed.