mmcpeck

So I pulled my boat out yesterday and towed it the 30 miles to where I store it for winter. Basically it's just two relatively flat highways from one location to the other, as Long Island isn't very hilly.

This is the first time I did it with my '91 4Runner, 3.0, Auto(obviously), since I got it in April. I started off with the O/D off but after a few miles of running it at 3K at like 55mph or so, I figured I'd hit the O/D button, just to see what happened. It dropped down to the normal RPM at 55-60mph, about 2300 - 2500.

Now I usually never use O/D on any of my vehicles when I tow, but just wanted to check it out in this Runner. After about 6-8 miles, it had locked and un-locked about 5 times or so, and I figured it was enough and I didn't want to hurt anything, so I hit the button off again, and just went about 50mph with the RPM's at about 26-2800. Then I decided to turn the ECT on, even though that wouldn't make much difference while on a highway.

Then when I exited onto the next highway, it was a relatively steep on ramp to the next highway, and when I merged onto the next hwy, the RPM's went up over 4000 RPM's before shifting, because of the ECT, and a minute or so later my A/T temp light came on.

I pulled over and put it in Park, and eventually it cooled down and the light went off. I kept going about another 10-12 miles or so with O/D off going around 50mph and it was fine. It didn't act any differently, didn't shift any differently, didn't have any smell, nothing.

When I got where I was going, I checked the fluid and it didn't look or smell burned at all, and the level was correct, the fluid wasn't even all that hot to the touch on the dipstick.

The tranny worked fine as usual on the ride home also.

So I guess my question is, what could I have done to the tranny by getting this light on? What should I do in the future? What is the best way to tow, with O/D on or off? Some things I read say that TC lockup makes the tranny run cooler, so does that mean having O/D off make it run hotter? I always thought the TC locking and un-locking created a lot of heat so that it was better to tow with O/D off? Could the ECT have made it run hotter?

Just a little confused as to what actually creates the most heat in the tranny when towing, and what the best way to tow is.

Thanks.

abecedarian

Likely you didn't hurt the trans at all. You took all the standard precautions- turned O/D off and kept your speed low.

Using O/D around town or when not loaded is recommended- it puts the trans into the highest possible ratio to get the best mileage. A trailer will put more strain on the trans and will add heat to the fluid. So, maybe an external trans-fluid cooler would be a good thing (one placed after the fluid leaves the radiator).

Hayes

I will answer the questions I know the answer to...

Leave OD off.

install another trans fluid cooler/

If the temp light was only on for a short period of time, there shouldn't be any damage. I would probably change out the fluid just to be safe. The light should come on right before there is a serious problem...

Marc

How much does the boat weigh?

I've often towed 3000 lbs on flat ground, 100 miles in summer. Always with O/D off and usually with ECT on.

When O/D is off the TC will still lock up.

thook

Definitely get a tranny cooler. Very easy and practical modification.

mmcpeck

The boat weighs about 2000lbs (with motor), the trailer maybe 6-800lbs, so I would say I was towing about 3000lbs at the most.

Do you think having the O/D on for 8 miles or so and having it kicking on and off, is what heating it up, or do you think the ECT allowing the revs go up to over 4K heated it, or maybe just put it over the edge?

What exactly is O/D? I thought O/D was when the TC locked-up, but Marc says the TC will lock-up with O/D off also....so now I'm confused.

mmcpeck

Will running the A/T out of O/D create more heat because of the higher RPM or will having it in O/D create more heat because of it going in and out of O/D, while towing?

What exactly happens when the A/T goes into O/D?

FredTJ

O/D (Over Drive) is the same in an auto tranny as in a manual tranny.
What do you think the O/D is in a manual tranny ?
It's the top gear (usually 5th gear) with a ratio less than 1:1 ..
Same with the auto tranny.
It's the top gear (4th in this case) and has a ratio less than 1:1.

The T/C locking up has nothing to do with it (as in a manual tranny which doesn't have a T/C, obviously ).

Most 3 speed auto trannies without an O/D (that is the top gear ratio is 1:1 or greater) still have lockup torque converters.



Fred

FredTJ

It, in this case, shifts into 4th gear.



Fred

abecedarian

/nevermind.

abecedarian

let's let it suffice to say that the trans will not shift into O/D if the vehicle speed and engine torque are not enough to to do it.
If you find the trans shifting into and out of O/D a lot, like several times per minute, then you should disengage O/D and let the engine rev up a bit so you have power to tow your load.

mmcpeck

Maybe I should have phrased it better.

I understand what O/D is, I just thought that O/D was the only time the TC locked up. But I am just trying to understand if having the tranny in O/D while towing will cause extra heat in the tranny or will not having it in O/D and running higher RPM's create more heat in the tranny.

I would assume that if you were lugging it in O/D and it kept having to downshift and then go back into O/D, then that shifting back and forth would cause extra heat, but would running the higher RPM's when not in O/D create any less heat, even though the TC will be in lock up?

Am I asking that right?

Really just trying to figure out what I did to cause the Temp light to come on in the truck. When I had it in O/D, it went in and out of O/D maybe 5 or 6 times in 10 minutes before I pushed the O/D button off. But the light came on after going up a semi steep entrance ramp and then merging onto a road and working it out to like 4200 RPM.

So basically not sure if the culprit was having O/D on or having the ECT on and winding up high RPM with the load on it....or the combination of both within about 7 or 8 minutes of each other.

In any case I will probably throw an external cooler on it before the Spring anyway, just something that was bugging me, trying to figure out how I heated the fluid up.

Also, at what temp does that idiot light kick on? I read somewhere on here that it is up at like 300 degrees!!!....which is scary.

Thanks.

abecedarian

If you have O/D turned on, the transmission will try to upshift as soon as it can. It won't try to hold a gear longer, or shift to the next gear any sooner than the system is capable of handling. Overall, keeping it in O/D won't make it overheat (on it's own) but if you have weight, the constant shifting in and out will add heat to the system.

First thing I would do is add an external cooler to the transmission in the line before the trans fluid enters the radiator, then see how it goes. IF it doesn't get any better, then maybe put the cooler 'after' the fluid leaves the radiator.

mmcpeck

Thanks Abe.

Ok so the TC will lock-up even when O/D is not on right? I know that when the TC locks up, the ATF temp goes down because there is less friction on the fluid when it's locked. So if having O/D off will still get the TC to lockup, then that would seem the best way to tow, seeing as how you will have lower ATF temps and you won't be causing the tranny to upshift and downshift all that much.

In all honesty, with the 3slow, I can only get up to about 55-60mph and then when I let back on the gas the O/D will kick in and I start losing speed back down to under 55mph and then when I give it any little amount of gas, it upshifts out of O/D until I get back above 55mph.

With the O/D off, I can go 50mph with the RPM's at like 2700, so I will just go 50mph, and maybe it will take me an extra 3 minutes to get where I'm going. Hell it's only twice a year anyway, in the water in the Spring, back out in the Winter.

Thanks for the help/advise.

By the way I put the Air Lift 1000 in before I pulled the boat, and with 30psi the truck stayed completely level and rode real nice. At about 18psi or so unloaded, it rides nice and the sag is gone.

slosurfer

When you install your aux tranny cooler, go ahead and install a good tranny temp guage. I installed mine so that it was reading the temp before the fluid gets to the coolers, so I'm reading the high temp. It will really help you figure out how to drive and keep your temps down.

OD off, will keep your temp down.

ECT will raise your temp pretty quick, but shouldn't be a problem unless you are holding those high rpms for too long.

More than likely, your running it with OD on heated up the fluid some, even though you then ran it with OD off after that, it may have stayed at a slightly higher temp and then the high rpm pull was enough to trigger the light. The aux cooler will really help to get your temps back down quickly when you do need high rpms and the temp goes up some.

mmcpeck

Thanks slosurfer. I was just reading someof your posts in a thread from 2006 about temps in the A340. Read a lot about the cooler and gauge, sounds like a good idea.

Yeah I'm pretty sure I don't have a need for the ECT to be on, so from now on I will tow the boat with the O/D off and ECT off also.

Thanks for all the info guys.

slosurfer

I still do have to use ECT from time to time, but I just keep an eye on it. Mainly it is in the mountains climbing grades, not really at highway speeds.

Marc

I don't see how using ECT will raise the trans temp.

It's just holding the shift point longer.

I use it when pulling a heavy trailer to make sure the mighty 3.0 is always in it's power band.

It doesn't mind revving.

mmcpeck

Haha...the mighty 3.0, I like that.

Yeah there aren't too many mountains on Long Island, not even really any hills for that matter, so I doubt I will ever really Need ECT, but it's good to have it if I do.

Marc....I figure the ECT would add extra heat by allowing the higher shift point. If the engine is revving higher, then so is the tranny. More pressure and friction on the fluid pushing that TC around.

slosurfer

Get a tranny temp gauge and you will see!

You're right, it isn't the ECT, it's the higher rpms that it is holding it in. When it is in its powerband, it is creating a lot of heat in the tranny. The engine doesn't mind the revving but your tranny does get hot while doing it.

Edit: ^^^he beat me to it and explained it better haha