95 auto tranny transmission overheating and unrelated towing Q
 

I've just searched the forum for advice on my problem, but only found temporary fixes.

I've got a '95 4Runner 4WD auto v6. The A/T Oil light came on after about 1 hour of highway driving this weekend (2WD). This has not happened in months of driving the exact same roads at the same speeds I traveled this weekend. I was not towing anything, nor did I have much cargo inside. After stopping to let it cool down, I was able to go a little further before it happened again. Each time, I was using cruise and from time to time the tranny kicks down from 4th into 3rd to maintan the speed (75). I understand the torque converter can become overheated in this way, causing the A/T Oil light to come on. I ended up finishing the rest of my drive (another 250 miles) without using cruise and travelling at 60-75 mph. The truck did not overheat once the cruise was turned off.

When I went to get a tranny cooler sized for my truck as a possible remedy, the parts guy noticed I already had a cooler in the radiator, and I know the radiator was replaced by Toyota less than 2 years ago.

Other threads suggested turning off the cruise if the truck feels like it might downshift. Some say to turn off the O/D, making it a 3 speed. Then again, I could always drive at a slower speed. The problem? These methods aren't fixing the problem, but only covering up the symptoms. I want to fix the truck's problem, not throw some cough syrup on it.

My 1st set of questions: What can be done to keep the tranny from overheating, rather than turning off cruise, O/D, or driving slowly? What could be REALLY causing the overheating? How much does Toyota charge for a computer diagnostic?

I heard from a friend that an overfilled tranny could blow a teflon seal (mine is properly filled now, though I bought it used, so anything is possible). A burned out solinoid was also mentioned as a possibility.

My second set of Q's: I have a hitch, but I don't know if it's factory or aftermarket. I was told this matters, as I'll need a tow controller before pulling a medium, covered trailer. True? How much are controllers if I don't have one already? Where can I find the controller on my truck if I already have one?

Thanks!

Have you ever flushed your tranny? The conditions you described should not cause it to overheat. I'm betting your fluid is toasted. Drain a little out and see if it is dark red and has a burnt smell (new fluid is bright cherry red). A flush on your 95 runner is relatively easy and cheap ($40-50) to do yourself.

Your fluid pump could have failed. A way to check this is to remove one of the 2 lines coming into the bottom of your radiator and start the truck. Fluid should shoot out of there really fast and hard. Or maybe the filter in the tranny is blocked (it would be replaced during the flush).

Yeah what he said.....and those stock built into the radiator trans coolers are not the best setups in the world so looking in to an aftermarket one is also a good ideal. I do not think you have a solinoid going out based on what you have noted here.

Not sure what you are asking about on the tow controller.....I think you are implying something to do trailer brakes? if so IMHO if the gross weight of what you want to tow is over 1000LBS you might want to look at some sort of braking system for the trailer or upgrades to the stock braking system...if it is over 1750lbs gross then trailer brakes should be a must....keep in mind the auto towing cap is much than the 5 spd rated towing cap.

Thanks for the quick responses!

I had the tranny fluid and filter changed one year ago, and haven't put 12,000 miles on the truck since then. I watched the mechanic do it...the drain pan looked like new when he was finished cleaning it up. The fluid pump is something I'll check.

Dragon, you said "keep in mind the auto towing cap is much than the 5 spd rated towing cap." Is the auto towing capacity lower or higher than the 5 speed? I'm guessing lower. I'll note the weight of the trailer and my stuff when I tow-thanks for the advice.

I guess the controller I heard about was for braking. Is that something I can install? Any writeups on how to do so?

Also, if I should get an aftermarket tranny cooler in addition to the cooler in my radiator, where should I mount it? How? I have 1/4 inch clearance in front of my radiator, and behind my grill is out, as my A/C condenser has a fan in that space. Any recommended brands, sizes, or places to buy? I looked at one this weekend at a local parts house for $40, the largest of three sizes they offered. I may space above my front skid plate, but I don't know if such a location would have enough wind moving through to do the job.

See if there are any trouble codes in the transmission. A buddy of mine had this problem and the torque converter wasn't locking up in overdrive or something like that. There was a bad solenoid in the transmission that was causing the problem. It did throw a code.

Another time I've seen this problem was when the A/C electric fan on the condensor (in front of the radiator) had failed. This AC fan apparently made a big difference in cooling.

Update:

I took the Yota to the stealership today. The A/T oil light came on again last week when pulling an empty 5 X 8 trailer for 30 miles. Damn thing. The techie said the truck didn't throw a code. He then showed me how to check my 4Runner for codes- very easy to do since it requires only a jumper wire. If you'd like to know how to check your 95 4Runner for trouble codes, let me know and I'll take some pics to accompany the explanation.

Anyway, the techie advised me to install an aftermarket tranny cooler, which I plan to do after finding a suitable location. I have not yet checked the fluid pump...maybe this weekend?

I think the problem is basicly an engineering flaw with the 3.0/auto. The OD gear is too high for the wimpy power band of the 3.slow forcing the torque converter (TC) to slip to keep the revs up when running in OD. This flaw is made much worse by going to bigger tires unless you regear, are you still using the stock tire size?

I've always (since 1993) manually dropped mine out of OD if the auto tranny downshifts to 3rd. I notice the TC will lock up more and lower the RPMs when I do this. I've never had my tranny overheat but I'm also running an extra Hayden cooler now to keep it nice and cool. Here is where I put my cooler:
http://community.webshots.com/photo/...71697809PxiQaV
http://community.webshots.com/photo/...71697751rirBUC

I would get the biggest (stacked plate) cooler you can find a space for, I started out with a bigger cooler but took it back because I could fit it in anywhere. I then ordered the next smaller size and fit it in in front of my front diff as you can see in the pics. The tube and fin coolers are bigger and don't cool as well as the stacked plate coolers.

I'm also running Mobil 1 ATF in the tranny, but any synthetic ATF should help.

I wouldn't worry too much about checking the trans fluid pump. If it had failed, the trans is dead in the water. Trans can't function without pump pressure. As others sugested, check fluid condition and level first. The cooler in the radiator is good for most applications, and normal driving shouldn't be a problem heat wise. It is possible that the radiator cooler has become blocked, and is no longer working. It basically consists of a small tube that circles inside the radiator. Fluid flows thru it to transfer heat to the coolant and then return to the trans. There are two basic types of add-on trans coolers. One is the biger, tube and fin type which are usually mounted in front of the radiator, and they come in several sizes depending on the amount of cooling you vehicle will need. The second type is a stacked plate design, which is much smaller in size, but work much better than the other type. Do a search on trans coolers, and you will find many threads on this topic with a wealth of info. The stacked type coolers also don't have to be in a direct air flow position to work, so you have more mounting options.

The usual method of adding additional cooling is to put the add-on cooler in the return line to the trans from the radiator cooler.

mt. goat, I am using a P235R15, one size up from the stock 225 that came on my Runner. I’ve noticed from the inside of my Runner that the front floorboard and tranny hump under the center console get amazingly hot after driving it for an hour or longer, whether using cruise or not. It’s such an issue that I’m thinking of removing the carpet and insulating the floorboard to limit the heat in the cab. This is my 1st 4Runner, so I don’t know if this floorboard heat issue is common or not. :dunno:

From the pics you provided, it appears as though you’ve rigged a slim skid plate in front of the tranny cooler. Am I correct? I guess I could fab something like that or cut my stock skid plate down on each side for increased air flow.

Also, does the tranny cooler block the removal of, or access to, anything important in that area of the underbody? I’ve heard mechanics bit¢h and moan about having to remove the skid plate to access this and that.

I hadn’t considered using a synthetic tranny fluid…that might be the answer…



TechWrench,

How can I check the rad. cooler for a blockage? How would I clear such a blockage? (coat hanger-snake, etc.) I’d like for the rad. cooler to work with my soon-to-be-added aftermarket cooler, rather than replace it.

Thanks to both of y’all for the stacked plate info. That definitely sounds like the type I need. Now I’ll know what I’m looking at when shopping for parts.

I also saw someone on Yotatech that had attached a fan to the added tranny cooler to maximize its efficiency. Your thoughts?

I'm in the same boat, wiseguy. The tranny never overheated before. In the past few years it's gotten progressively worse. I've installed a tranny gauge and can get the tranny up to 250F if I try...I just need to find a steep long grade and let the torque converter unlock. Even up to around 250 the tranny light does not come on. I don't want to push it over 250 so I take it out of OD and it cools right down.

I'm still not sure what the cause is and I do have an aux cooler. Keep us posted.

Yeah my hump use to get pretty hot too, haven't noticed it getting too hot since I added a body lift and the extra cooler.

I'm sure a fan would help if the cooler is somewhere that doesn't get good airflow or if you are overheating while going slow.

That is my Superlift skid plate in front of the cooler. I do have to remove the cooler to service my front diff but it's not that hard to unbolt it and move it out of the way enough to check the gear oil.

TechWrench,

How can I check the rad. cooler for a blockage? How would I clear such a blockage? (coat hanger-snake, etc.) I’d like for the rad. cooler to work with my soon-to-be-added aftermarket cooler, rather than replace it.

Thanks to both of y’all for the stacked plate info. That definitely sounds like the type I need. Now I’ll know what I’m looking at when shopping for parts.[/QUOTE]

There are two lines from the trans to the radiator cooler. Usually, the line closest to the front of the trans is the pressure side going to the radiator and the one closer to the rear of the trans is the return side. Try removing the return line, put in in a catch bucket, and start the engine. At an idle, you should get a steady flow of fluid from the line. If there is flow (it is not a high pressure circuit, but the fluid should come out in a steady stream), then the radiator cooler is not blocked. If not, then try removing the pressure side at the radiator and again check for flow. If you have flow on the pressure side, then the radiator cooler is probably blocked. The cooling line inside the radiator is only a narrow coiled tube, so trying to 'snake' it out with a coat hanger won't work. You could try using low air pressure in the reverse direction through the cooler and see if that clears it up. Othwerwise, you will probably have to take the radiator to a shop, or just replace it.

I called every auto parts store in the area- none had stacked plate tranny coolers. Any suggested sellers? Any brand or model # recommendations? One thread suggests a Hayden cooler from Makco Distributing. I'm looking through their website now.

I was hoping a store in my area would have the part, to avoid shipping and the time it takes for delivery. :yawn:

Also, I forgot to mention earlier that my fluid was checked at the stealership last week. The techie said it looked and smelled fine and was at the proper fill level. He was perplexed by the problem and couldn't offer any ideas as to the possible problem. That's ok, since he didn't charge me anything for the diagnostic- it usually costs $65-$90. I'm carrying a jumper wire with me to see if it will throw a code the next time it overheats.

Mine is a Hayden 1678 it's (7.75" x .75" x 11"). I first tried the Hayden 1679 (10" x .75" x 11") off the shelf @ Pepboys but it was too big, so I returned it and ordered a 1678 from Autozone. I have since bought another 1678 for another application off e-bay.

You need to go in there and personally look for the coolers. I never trust those guys. Most of the time they're just kids working after school to pay for toys.

Just ran across this, maybe 250F is too hot: http://www.txchange.com/heatchrt.htm

Funny, I've seen a similar chart recently too. I should say that although I can get it up to 250, my "normal" operating range is 160-220. Stop and go traffic is the worst and it'll stay near 200-220. If it gets near 230-240 on the long grades I drop out of overdrive and the temp goes down to "normal".

So far my amsoil fluid seems fine, not burnt at all, but I think it's about time to change it.

With Amsoil or other synthetic ATF that chart may not be very accurate. :think:

Deja Vu Tranny overheating
 

I was looking for info about the tranny overheating in the second generations because I have been blessed with the same problem. After reading through this I was wondering what step I should take next. I have a 4inch lift, 33 mud terrains (upgraded to 16), the tranny has been rebuilt (that tranny is a MOOSE), fluid is fresh and not overfilled, x-tra tranny cooler installed, new radiator, new hoses, no blockage anywhere. I took it for it's first long distance drive yesterday since the tranny cooler install and the first time it did fine in overdrive doing about 60 (and that is fast for Mr. Yoda). The second trip I went a little farther and it made it about 20 minutes then the A/T oil temp light came on. Other than being pissed I pulled over and waited for it to turn off and went with my "formula" for the rest of the trip. The "formula" is to turn the overdrive off and keep the rpm's from going over 3000 (thats where and when the tranny gets hot in or out of overdrive). So driving 45 on a 70 isn't the best idea, but it got me where I needed to go without overheating.

Now I want to take the next step in solving this overheating. I am planning to add 2 more inches of lift and 35's in the future so I feel I should change the gearing and possibly get a more beefy radiator? What gearing is best if I do need to go that route? I'm not sure so any knowledgable input would be greatly appreciated. By the way .... the radiator was from 1-800-radiator, and quality issues with them? What's a girl to do? THANKS