Bodie the Dog

My '94 4Runner (automatic 6spd, just over 200K miles, mostly stock) keeps lighting up the dummy light indicating the tranny is overheating. Further, on cold mornings it is really reluctant to shift gears; it takes a couple freeway miles at 65mph before I can feel/hear it shift into the right gear.

This has been going on for several years, I've had my truck in the shop several times, but they can't duplicate the problem and aren't finding any error codes. WTF? Do they really need a dummy light to come on in order to agree with me that there's a problem!?

This used to happen only when I pushed my truck, 75+mph going over Donner Summit on pavement, not towing anything. A transmission flush at the time (about 2 years ago) failed to solve the problem, and mechanic indicated the old fluid looked ok, no metal shavings, not burnt.

Finally I blew my head gasket pulling a trailer last summer, and my mechanic (a Toyotas Only kind of place) fixed it, finding several other problems deep in the engine which a previous shop had missed. He indicated the tranny overheating may have been from transient heat related to my engine overheating, and the problem appeared to go away for several months. Then it started occurring again, consistently, on a road I drive which gains about 3000' in 15 miles of lowspeed curvy road. Really low speed, like authentic 15mph curves, followed by straight stretches where I can get it up to 50mph or so. (Yes, I generally drive it like I stole it, I do work the O/D button for every little bit I can get.)

So I recently took my family to a remote part of the Nevada desert for the first time and wanted to ensure all was reliable. I took it to the shop, they did another tranny flush (and fixed a broken U-joint) but could not duplicate the overheating problem, found no engine codes, nada. As I left the shop (a cold morning), the truck still didn't shift into the proper gear right away. I dragged my kids to the hot lands anyway, and, well, I think you know where this is headed....

Drove 6 hours of pavement (including several major summits) the first day, and 20 miles of generally downhill, high-speed washboard, from Sacto area to Bishop. Big hills, driving fast, loaded down with gear and family, no problems.

Next day we drove (via pavement) over the Inyo Mtns into Eureka Valley, a huge summit, again no problem. Racing down the washboard (2wd) along the flats of Eureka Valley we had a flat (and found our hydraulic jack had blown a seal), so gave the truck about a half hour rest. Then we did a minor bit of crawling up the stairs of Dedeckera Canyon, where I did have some issues but really tried hard not to work my tranny. About 15 minutes later the tranny light came on. We let it cool off a half hour (finding petroglyphs while we waited) and continued, now using 4wd high to climb a moderately steep but long and sandy road, and the SOB overheated within another 30 minutes.

We'd reached our destination, so had a nice hike, etc., then drove back down the dirt hill and stopped at the dunes for another hike. Temps were in the low 80's, not bad. After about 90 minutes there, we continued out along the washboard road along the valley floor; very flat, at about 35-50mph. And 15 miles after leaving the dunes, the overheating light came on again. We took a 15 minute break and drove another 10 minutes before the light came on. Another 15 minutes break, and drove 5 minutes before the light came on. Repeated this 3-4 more times before we made it to a downhill stretch, then 5 miles later we hit pavement and had no more problems. We tried driving in both 4wd high and 2wd, but the overheating occurred anyway.

The next day we had about 10 miles of washboard, but no problems, then drove home, about 8 hours with several really big summits to cross, all paved, and still no problems.

I went back to the shop and told them what had happened. They have no clue ("We can't tell what's going on without an engine code"), and supposedly they're really good at what they do. I don't want a bandaid, I don't want to install a cooler, I want to fix the problem!

Is it possible my temp sensor is broken, and it is giving me bogus alerts? Yet I do have a problem shifting on cold mornings. I'm lucky my kids had a good trip anyway, although I am very sick of hearing them complain about my "crappy" truck. Thanks in advance for your help!

rustyf99

iTrader: (1)

I hate to tell you, but my trans slipping and overheating was the first sign I had a bad head gasket. Since then I've done HG's, new radiator, timing belt, thermostat, water pump, flush and filter on the trans. Seems to be doing OK, at least nothing related to these issues lately.

Yours could need another HG again, or, the maybe it's as simple as the radiator is going bad. Better check that before you get a strawberry milkshake.

With all of your tranny flushes, have they replaced or cleaned the filter? After the first flush I did, mine was completely clogged.

Just some ideas ... Good luck!

ZUK

iTrader: (1)

It's possible that the sensor is 'intermittent' but I see you've already spent alot of time on the issues...this is what I would do. Instead of replacing expensive stuff that may not fix it, I would try to verify a few things.

First, I would try a good additive that might correct your high mileage shifting...maybe try this
http://www.autozone.com/autozone/acc...er=592808_0_0_


Then, for the temperature issue, I would put in a good aftermarket temp sensor. It does require some work for sure. This is the exact same one I have in my 2001 Tacoma (Auto Meter 7157 C2 Electric Transmission Temperature Gauge ) http://www.google.com/products/catal...d=0CEAQ8wIwAw# You can choose a cheaper one but I like the linear full sweep window and I can see a 2 degree change in temp also. You have to crawl under there and look at where a good spot is to mount the sensor....probably not a good idea to have it on the bottom pointing down....I mounted mine on the side of the tranny pan in a known clear spot and it favored the lower portion of the side so it was always in oil. I mounted it in a spot that allowed for easy routing of the electrical wire to the inside of cab to the meter. To mount it to the pan you have to drill a large hole.....mig weld the steel pipe thread nut in place and then screw the sensor in place with some teflon tape to seal it. Again you should verify the when the sensor is screwed in all the way that it does not interfere with something inside the pan. Check twice and drill once.

The aftermarket gauge will give you the real temp of the fluid that the transmission has to work with. I think the pan temp is the best temp to monitor as opposed to the temp of the tranny output line which changes dynamically with how much throttle you give it.


Stage 3--- If you determine you really do have high tranny pan temps (about 220 degrees or more) then do the auxillary tranny cooler thing.
http://www.autopartsdealer.com/hayde...m_content=rank
Hayden #679......It's 11" x 11" x 3/4" thick.....is way overkill for your applications
Absolute best spot to mount is up against the front of the radiator...or the AC condensor if it has one. Use the 4 push-thru tie raps to secure it. It really does need to be UP AGAINST the radiator for best cooling. Even 1 inch away compromises how well heat gets moved away from it. The front surface of the radiator is not 100% clear but the cooler will fit with some tweaking.

The tranny cooler should go AFTER the built-in radiator cooler. If, for some reason, it's not feasable to put the temp sensor in the tranny pan then the 2nd best place is right after the output of the Hayden cooler I would think.

Hope that helps. ZUK


ps---- I like what Rusty said....think about a new radiator.....I have heard that the Runners have problems with their radiators....not sure why it's just the Runners. The pick-ups/Tacomas don't seem to have the "milkshake" issue mentioned.


psss- The more I think about it the more I think something as simple as the radiator could be the prob.....If you still have the original radiator then that's the first thing you should change out.






.

rustyf99

iTrader: (1)

Zuk's on, be aware the TransTune requires a flush after use if it's similar to the stuff I used.

I also forgot to mention you should check all your cooler lines for clogs, a small constriction can cause a serious fluid flow reduction, which could cause the intermittent overheating. Also check your A/C Condensor fan and make sure it is running properly, which can cause major heating when the AC is on and the truck is not moving or moving slowly.

Lastly, remember in the cool-downs, no trans fluid is being circulated and no fan on the radiator is cooling, if the engine isn't running.

The MAN

I'd seriously consider a new radiator and a dedicated external trans cooler.... if you are doing any towing at all, you have no reason not to have a cooler.... the stock system is marginal for cooling the tranny and any sort of reduced capacity of the cooling system or significant load on it even when 100% condition will cause the tranny to overheat!

make sure there's no air flow restrictions around the front fascia... make sure the skidplate or any other splash shield is there... they help direct airflow

also make sure your fan clutch is working properly.... if it's never replaced or never serviced, then it won't be working right... replace the silicone oil in it! thicker than stock oil helps too

with an external tranny cooler, I recommend a thermostat with it also... and if you manage to stuff it in some weird place, get an electric can for it too


finally, consider switching to synthetic ATF.... it will run a lot cooler and continue to protect the tranny once it gets hot.... if not, then get a bottle of lubegard and run it with the conventional ATF.... lubegard is NOT snake oil, you can read all about it on BITOG... the stuff really works

as for your cold harsh shifts, it's indicative to me that the fluid is too cold or there's a problem with the valve body.... cold fluid = high fluid pressure... I'm more inclined to believe that there's a problem with your cooler/overall cooling system as the trans cooler ALSO acts as a fluid warmer during cold starts.... that's really what the cooler inside the radiator does, it acts as a temperature moderator... not a real cooler in the purest sense

Bodie the Dog

Amazing tips, thanks, now I've got homework. Or my wife does, she's the wrencher in the family.

No, I never run my air conditioning. No freon.

Radiator was recently damaged by fan blade after another shop installed the shroud improperly. Which is why I'm paying so much for the "experts" at the Toyotas Only place. Hmm, maybe this does go back to the radiator....

Almost took off my skidplate, but good tip regarding airflow, so I'll leave it. I work on PC's and for the same reason you should leave your case on, air flow.

Just seems indicative of something that it usually only overheats on dirt. Something about the clutch working extra hard because of all the wheel bouncing? (Told you I'm not a wrencher.)

I'd hope a competent shop would detect a head gasket problem, although maybe that also depends on a code being generated. Nuts.

No tranny cooling when engine turned off?! I guess when the light comes on I should pull over and idle?

I've asked the shop to give me some ideas. I'll add to this thread when I learn more.

The MAN

there's no clutch in the traditional sense in an auto... it has a torque converter, which directs power from the engine to the drivetrain... it's a fluid coupling gizmo, which when used produces a lot of heat... hence why the necessity of a cooler... the rest of the transmission (clutch packs, gears, etc) produce negligible heat as far as everything is concerned

the reason why it "only overheats on dirt" is because you're going slow, which means less air flow through the radiator, and if you're crawling, the torque converter is producing a lot of heat from the engine torque loads

like I said, replace the radiator, replace the fan clutch fluid, replace the thermostat with a toyota one (aftermarkets suck), and install an external trans cooler (along with a thermostat for it)

sure it'll cost money, but it'll save a lot of headaches... even if it won't fix it, any rebuilt or replacement tranny will like what you did


and finally, I forgot to ask... is the kick down cable adjusted properly? if it's not, it will cause harsh or late shifting

Bodie the Dog

So I went back to my "toyotas only" shop and showed them the advice from this thread. They sneered at "the Internets" but promised they would discuss this/do the research and get back to me. I have been using this shop for close to 15 years now, spent thousands of dollars, and yet they haven't bothered to get back to me. Been driving the minivan in the dirt, but that won't last long.

Time to go back and poke them in their conscience. I don't think they liked it when I asked, "Are you telling me you can't diagnose the problem without the dummy light coming on?"

I did do a full day of mixed pavement/dirt last week, in warm temps, and had no problems, but was really babying it.

swampfox

A friend of mine had a t-100 that the trans light would come on when towing ,he done a filter and fluid change that fixed it . The problem was the fluid that the po had used wal-mart brand trans fluid, Some brands are better than others. Also you might try trans medic additive at orielly's, A transmission shop recommended it to me after my s-15 jimmy quit shifting after a fluid change. They told me that the manufacturer uses an additive that gets lost or diluted after a fluid change , it fixed mine completely in 150 miles. It was around 5 dollars a bottle.

skypilot

iTrader: (1)

I think you are on your own with this.

I do not understand even how your trans is still operable at that milage. I junked my A340H (200,000 miles +)without even batting an eyelid. I think a new converter and overhaul are in order since mine never last over 100k unless I get really lucky. YMMV

Perhaps you need to get a Russels or Earls plumbing kit for that trans, and put a really big fan cooler (w/ thermostatically controlled fan) on the return leg. At least pull the valve body and overhaul that.

ZUK

iTrader: (1)

Hey Bodie-
Have those mechanics replace your radiator. That will keep your engine temps rock stable and keep the tranny cooler.

wiseguymmiv

@ skypilot- I have a '95 with 200,000 + plus miles on the original tranny with no major work done to it, so it is not obvious that a rebuild is required.

@ Bodie- 6 years ago I had tranny cooling issues when using cruise control at interstate speeds on hilly highways, and when pulling even empty uhaul trailers. The mechanics kept telling me they couldn't replicate it, and couldn't diagnose it without an error code. I installed a $50 Hayden tranny cooler and have never (knocks on wood) had the tranny temp light come on again. That was 70,000 miles ago. I know you say you don't want to install a cooler, you want to find and fix the problem. Maybe the lack of sufficient factory tranny cooling IS the problem, as noted above by other posters. Chalk it up to poor design (like the woefully underpowered 3.0 engine). At least that's it from my viewpoint. Every great vehicle has flaws. If something so easy and inexpensive could increase the likelihood of not being stranded in the desert, why would you not consider it?

By the way, I'm on my 3rd radiator since the truck was new. They continually spring leaks on the top. This time I bought an aftermarket one with a plastic top. So far, so good. Drop a new one in yours. It's much cheaper than rebuilding the tranny.

Wiseguy

Bodie the Dog

So fast forward a couple months, I've been staying close to home and off big grades so things are fine. Then I hear about a transmission mechanic said to be really good, the kind of guy who can often diagnose the problem just by taking it for a drive, and who won't rip you off. I stop in to see him, he echos a few suggestions here, and on his advice I also get a infrared thermometer so I can shoot my tranny pan and get a rough estimate of the temperature. We verify together I have a good flow of coolant returning to the tranny. Nice guy, no charge.

Life happens and I have to make several quick drives down to LA, about 7 hours at sustained 80-85mph. Interstate 5 is generally level, the only time I really mash down on the gas is when passing on a grade. I make it over the Grapevine no problem.

I return from LA via Hwy 395, with no problems until I make a sidetrip up a 5000' grade, a windy road where I can't get my speed above 35mph very often. Not much air cooling going on there. Near the summit my transmission temp light comes on. I pull over and find a huge SETI-type installation hidden behind the hills, and my tranny pan temp is showing as 280 degrees. Rest of the drive was uneventful, including some huge highway grades from Bishop to South Shore Tahoe then Placerville area.

Another trip a month later, same variables, except instead of the grade I did some 4 wheel low in deep sand, without bothering to air down. Not much, a couple intermittent miles. Light never came on. A week later I turn right at an intersection, I feel a clunk, and I've lost my drive, just spinning in place. I still have 4W low, so pull into the local roadside fishing hole. AAA estimates 2 hours to meet me for a tow, so I drive at 10mph in 4W low to my regular "toyotas only" kind of shop, which is conveniently enough less than a mile away. I park in front of a different shop, because my old shop, well nevermind what I have to say about them.

The new mechanic says I need a new tranny, there's no pressure in the flux capacitor, or something. Screw it, I give up, ok. He quotes a new tranny for about $5400 or a remanufactured one for $3600. I call my new transmission guy and he says he can get me a rebuilt for about $1000 and $900 labor. I get my truck to the transmission guy and he helps me order the correct rebuild. He's impressed with how clean it looks, opens the pan and sees no problem, torque converter looks new, so puts it in. I test it with 1.5 hours of high speed pavement, then dirt, but temp light comes on within 20 minutes of being on dirt. I used 4wd maybe 5 minutes. After letting it cool, 5 minutes later I went to use 4wd low to get up a snowy hill, but it wouldn't engage, it was like being in neutral. I still had all other gears.

Back to the shop, my mechanic orders a new tranny, finds metal in the pan of the old one (tranny #2). The new one arrives and he puts it in. He charges me $70 for the fluid and asks for a $100 donation so he can take his wife out to dinner. I test it by heading up a nearby hill that's given me problems, and sure enough, the temp light comes on even earlier than usual. Bad road, so it takes me a couple minutes to find a place to pull over. Tranny pan temp shows as 265 degrees. I let it cool to 165 before continuing, but it comes on again within 5 miles. I modify my trip, but still find some nice quartz before driving home, pissed.

Two days later I go to back out of my driveway, and have no reverse gear. Just like being in neutral, all I have is 4W low. Good thing I have a pull thru driveway. I can't afford to tow my truck 18 miles, so drive in 4W low down backroads to my mechanic. He is once again waiving his labor charge, wow. He now has the tranny pulled apart and found metal in the pan again.

Now the tranny supplier is being difficult (well, they were with the last one, too) and proposing the problem is due to my driveshaft being screwed up. But the truck is drving great, no shudder, good alignment? WTF? My mechanic has been doing this over 20 years in a small town, learned the biz from his dad, I think he's good. He's going to check for wear marks in the same place on both my old and new trannys, to see if the driveshaft is the culprit.

Otherwise, he's convinced me a cooler is probably a good thing, can't hurt. I need to check on formfactor, though, as finding a place to install it up front may be difficult.

So any ideas, suggestions, general wisdom?

Grant Baker

So you are asking in general what to do-or you want suggestions on install locations for the "trans" cooler?

Since this vehicle is NOT OBDII compliant, there are very few trouble codes unique to the transmission(these codes are related to the solenoids and speed sensors only). The A/T oil temp sensors can NOT be seen on a scan tool as serial data and do not have trouble codes related to them. In order to see the voltage signals that the ECU is seeing, you must measure voltages at the ECU or wiring. The ECU makes the decision to turn the A/T OIL TEMP warning lamp ON/OFF.

The circuit related to the A/T OIL TEMP warning lamp has 2 temperature sensors. One for the transfer case, one for the transmission.

You already know the temperature was too high when you measured it ("265" & "280" you mentioned). Which pan were you measuring? Trans or transfer? I'd be interested to know because the transfer temp sensor is supposed to cause the warning lamp to come on at 257F while the trans temp sensor won't turn it on until 302F.

My 4R(90, 3VZ, Auto trans)...has a factory-installed cooler for the transfer case fluid. Does yours? Mine is protected by a sheet metal shield and is below the passenger front floor board. The cooler for the transmission is internal to the radiator. Which one did your mechanic flow check during your first visit to him? The transfer case has its own fluid pump and valve body.

You did not say WHY you had your current mechanic replace the transmission with the rebuilt unit when he said it looks surprisingly clean, etc. And did he also supply a rebuilt transfer case with the rebuilt transmission? If the trans supplier is being difficult, its because your mechanic is giving them reason to believe he has not done sufficient testing. I know because trans suppliers and extended warranty companies do the same thing to me when I want to replace a trans.

Has anyone checked the fluid level in the transfer case at normal operating temperature(158-176F). It is checked separately at the fill plug on the transfer case.

skypilot

iTrader: (1)

Your coolers (two) must be plugged. Also when that warning light goes on the fluid is toast. Metal in the pan is bad, but you have something wrong that caused it to fail. I bet the radiator cooler is plugged with clutch material or metal. (Ford Exploders are notorious for this). I worked in a tranny shop and seen my share of bad coolers, my boss even had us install aux coolers since the customer would not go for the radiator.

These trannys are not cheap to overhaul and that may be why they are giving you a hard time.

vasinvictor

iTrader: (3)

I had a trans temp light come on every time I was on the freeway, finally traced it to a plugged up transfer case cooler under passenger side front door. The fins were all plugged up with grease and oil and dirt. Dropped it down, cleaned it and never overheated again. Just follow the trans cooler lines to find it.

ZUK

iTrader: (1)

Thanks for spending the time to update this thread, Bodie. I get this feeling that alot of money could have been saved if you had a real tranny gauge that monitored the pan temp.
When the light comes on, it's too late.....the damage has been done. 280 degrees is hot

vasinvictor

iTrader: (3)

No doubt 280 is HOT, but mine came on a lot. I just kept pulling over and leaving it in park until the light went off. The transmission was original with 230k, and shifted perfectly for 30k miles that I had it, and I still see it running around town. I changed the fluid a couple times to be careful, but just so future searchers can relax a bit, it wasn't the end of my transmission after the light came on. These Toyota autos are TOUGH.

Bainbridge_Runner

Thank you Grant Baker, Brodie, Vasinvictor and others for the excellent information.

My AT light comes on after about 5 miles up a dirt, mountain road - low speeds and either 2 or 4WD. This happens reliably. I pull over, engine off, wait a few minutes and the light goes off.

Most of the cooling system incl. radiator was replaced when I had the engine rebuilt (blown head gasket) about 22k ago.

The Runner never runs hot, always low to middle on the gauge.

Based on the excellent information here, I'm going to:

1. Clean up the transfer case cooler.
2. Either add something to the tranny fluid and/or upgrade it from whatever is being added by JiffyLube when they change the oil, etc.
3. Use a heat gun on the tranny pan to see what the temp is. I'm heading out on Saturday and will be doing this then.
4. Drain and replace radiator fluids. How frequently should this be done, BTW?
5. If none of these things does the trick, add a tranny cooler. I'm saving that for last because its about 30 degrees in the mountains right now - and if the tranny warms up now, then its going to warm up in the summer when its 85, regardless of whether I have a cooler or not because I only get about 20 degrees of cooling from the cooler (correct?).

Questions:

1. What do I use to measure the tranny fluid temp down the dipstick hole, as mentioned in one of the posts?
2. How come no one mentions replacing the transmission temp sensor?
3. Will the color of the tranny fluid change to yellow when it is toast?

Thank you to everyone who takes the time to make this forum so helpful. The AT light is the only issue I'm having and really want to get this solved. We go out every weekend on family trips and I need the Runner to be very reliable.

Mandy Tuning

what stall speed your converter is making. a worn converter "less efficient" heat the oil very bad.