Hi,

in about two weeks or so I will have occassion to tow a trailer with my 96 Tahoe. The trailer might weigh about 3000lbs, speed will be about 56 mph. I've been reading that I should never ever tow in OD, for the tranny could get too hot and might be damaged.

At normal driving, I usually keep the rev's below 2000rpm, occassionally getting up to 2300. Thus, when towing in 3rd, rev's will be unusually high for some extended period of time.

What am I supposed to be better off with, without breaking anything: towing in OD or towing in 3rd? Are all of you folks towing in 3rd, at even higher speeds?

That will be the first time I'm going to tow a load of that weight with the Tahoe. Previous owners of the car may have towed more weight, probably not knowing that they eventually should do it in 3rd, but I don't know.


GH

Welcome to the site, and I'm just a bit curious if you don't mind? Are you German or maybe just stationed/work over there?


The problem with towing in OD is that you get into situations where the transmission is constantly shifting up or down to accommodate terrain.


Besides the OD being the weakest gear in the transmission and the most susceptible to slipping, the upshift to OD is the prime time for that slipping to occur if it's got quite a bit of load on it.


So what I'd suggest you do, is to just try it out while paying attention to whether or not the trans is doing a lot of shifting in and out of OD. If you're on flat ground, it probably won't do it and should be okay. If you're in climbing or rolling terrain and the trans is constantly upshifting or downshifting, then you better slow down a little and just leave it out of OD.


Hope that helps.

Zeeb,

thank you for welcoming me :)

Indeed, I'm German, so my English will be a bit 'uneven' in general.

That towing to come will be mostly, if not all, on flat ground. I'm always quite carefully with the tranny, so as I avoid hard accelleration and especially downshifts. When going up hills in OD with the converter bridge locked and being too slow to maintain speed, or when slowed down by traffic, I usually take the foot off the pedal before I feel that the bridge will open to keep the rev's up. I guess that doing so is much better on the transmission than making it unlock under load.

Well, sometimes it's hard to tell how much power is going through the tranny, and it unlocks before I get to release the pedal or before I disengage the cruise control.

On my last holiday trip, I've been driving quite a lot through hills and mountains with very small and curvy roads, and I always took care to select a reasonable gear in order to keep the rev's up to flow enough oil through the tranny for cooling, and to prevent it from shifting too much (between 3rd/4th or even 2nd/3rd when having to go very slow).

This worked very well, and I noticed that you actually get more power in lower gears as described in the manual. It seems that somehow converter losses are reduced when you shift to lower gears.

After all, I was more worried when going downhill in 2nd or, sometimes, even 1st gear. The tranny gives much breaking power, but all the energy must be converted to heat, so I was more afraid of overheating it when going downhill than I was when climbing up. Do I really need to worry when going downhill?


When towing the trailer, I'll be doing it very carefully in OD where appropriate, and I'll watch out for exaggerated shifting.

Breaking the tranny would cost about EUR 3500 ...


GH

I wouldn't worry too much about overheating the trans with the loads you are talking about.


Be aware that the RPM's you are talking about running your engine at are way under it's maximum torque and horsepower. Using lower gears will provide more power due to gear reduction as well as increased engine output because it's turning faster.


While higher RPM's will use more fuel, it's actually better on the engine to run it closer to it's power bands while towing. If you're really concerned about trans temps, I suggest you investigate adding an aftermarket trans cooler which will mount in front of your radiator.

Sorry for this posting getting long ... It's the first time that I've
got a chance to ask my many questions :)


> I wouldn't worry too much about overheating the trans with the loads
> you are talking about.

At what loads will I have to worry?

> Be aware that the RPM's you are talking about running your engine at
> are way under it's maximum torque and horsepower.

Hm, from what I've read, max. torque comes at 1750, max. power will be
somewhere at or in the redline. I've never been over 2500; with my
ususal traveling speeds, I'm at 1600--2000 and should be fine, though
it means towing will be at or just a hair below max. torque.

BTW, should I notice the turbo acting in at some point? It seems to be
working so unobtrusive that I do not notice it. Since you cannot even
hear it, I don't know if it works at all.

> Using lower gears will provide more power due to gear reduction as
> well as increased engine output because it's turning faster.

My feeling was like the following: Going up a steep hill in 3rd with
the lever in OD is different from going up the same hill in 3rd with
the lever in 3rd. The tranny feels much firmer with the lever in 3rd,
tough it's actually using the same gear. The same seems to be true for
2nd: With the lever in 3rd or 2nd, 2nd gear also feels firmer than it
does with the lever in OD.

Gears in use are the same, engine output is the same, but responses to
throttle are better/firmer. It feels as if the tranny puts more
resistance onto the engine with the lever not in OD, sending more
power to the wheels.

> While higher RPM's will use more fuel, it's actually better on the
> engine to run it closer to it's power bands while towing.

Hm, on flat ground, the most resistance comes from the wind drag, and
German highways are very flat MOTT. In my particular application, I'm
going to tow a car trailer with a cabin of a Nissan Patrol (K160) on
it. The cabin is has no windows --- a friend of mine bought it off of
ebay to rebuild his Patrol. Wind drag will be low on it.

I would be running 56 mph at 1650 rpm in OD with tranny locked. I'm
allowed to go 50 mph, but that's just the speed when the tranny is
about to lock when not towing. I avoid cruising at that speed because
the tranny would lock and unlock quite often.

50 mph is too slow on German highways anyway, even the large trucks
would have to pull over. They run 54 to 56 (they're allowed 50, and
are limited to 56 by a speed-limiting device required by law).

Thus, I could go 56 at 1650 rpm, but the point where the tranny will
lock might be shifted just to that speed due to the resistance of the
trailer :( Going faster is not a good idea because I'd have to pull
over at the trucks, but the oncoming traffic on the fast lane would
MOTT not allow me to do so. Going a bit slower (in OD without the
tranny locked at 1600 or 1700 rpm), I'd be making a significant
obstacle in traffic.

Thus, I might have to go 56 in 3rd at higher rpms, maybe 2200 or 2400,
never tried that. This would be closer to the power range of the
engine, but I did never run it for some extended period of time with a
load on it at such high rpms. But on www.62-65-dieselpage.com they say
that you should be at 2500 rpm when towing ...

You see the problem? I don't mind the fuel comsumption, but anything
could happen, like the injection pump going out or the tranny getting
in trouble. I've just no idea what would be the best way to go.

On the other hand, that trip will be very good for testing. It's about
100 miles only with the trailer each way. I'm really looking forward
to it --- if my Tahoe performs well, I might be thinki

Hmm....


I guess I should have asked you, but I assumed you were running a gas engine, is your Tahoe a diesel? If so, then the RPM's are closer to what they should be, but running closer to the max HP RPM will work better towing.


You will notice a firmer trans if you pull it down into the gear you want as opposed to letting it run in that gear with the selector in OD.


Trans coolers are built into the radiator from the factory and HD means you get more capacity from a bigger radiator and more surface area for the fins. If you're mechanically inclined installing an aftermarket unit is not tough, but may be a bit time consuming. Usually they are hooked up in series with the existing setup in the radiator, so the ATF goes through the auxiliary first, then the radiator, then back to the trans. This prevents the ATF from getting too cold when not towing or in Winter temperatures.


As far as tow weights to think more about, usually when you get to about 75% or higher of rated capacity for your vehicle is where you want to pay more attention to temperatures. Just guessing, I'd say your Tahoe is probably rated for somewhere around 7500 lbs. or so?

Olee,


Welcome to the forums.


I would greet you in German, but I will not embarass myself and insult you at the same time. http://www.dieselplace.com/forum/smileys/Big Smile.gif


Is your Tahoe built and sold in Germany or, is it an American Tahoe that was imported to Germany and sold there?


Also in the same question as Zeeb, is that a Diesel Tahoe?


Those are just my questions.


I used to tow a 1200 Kg trailer at 100 kmh with my U.S. made 1990 S-10 Blazer. I added an external Transmission cooler in series with the transmission cooler built into the radiator. I did not tow in Overdrive and did not worry about the power band. My engine was a 4.3L V-6 and I believe the engine was turning about 2500 RPM's. This engine was a gasoline engine not a Diesel.


If your tahoe is a diesel, the proper towing RPM's would depend on the torque curve of the engine you have in your Tahoe.


The State of Ohio has the same terrain as Germany without the mountains if I remember, so you should be fine towing in OD if you have a Diesel, and not towing in Overdrive if you have a gasser.

Zeeb,

sorry, I should have pointed out what I have. You can see it in the signature now, it's the 6.5 TD.

Today, when going back home from work, I checked the rpms. I'm going 56 @ 1600, not 1650 as I said before. But more important, at a traffic light, I shifted into 3rd and afterwards found that in 3rd I'm doing 56 @ 2100. Thus, 3rd seems just to be made for towing :)

But at the same time, you see me confused. The tranny actually seems to be shifting 4 gears, not only three as I expected. Depending on how much I put onto the pedal, there was an unexpected shift into a higher gear once at about 53 mph, the other time at about 40 mph.

What might be going on there?

> You will notice a firmer trans if you pull it down into
> the gear you want as opposed to letting it run in
> that gear with the selector in OD.

How comes?

> Usually they are hooked up in series with the existing
> setup in the radiator,

Hm, would an additional cooler be worthwhile? The oil temp would be about down --- or up --- to water temp before the oil enters back into the tranny unless even the stock HD cooler is insufficiently designed. The cooler and the pipes would add to the flow resistance of the system, eventually slowing down the flow of oil. And there are already quite a lot of coolers on the front.

Maybe a backup canister holding about two gallons of transmission oil, hooked into the line like the engine cooler has one, could help more? The total amount of transmission oil would be larger, and it would cool down a bit in the backup canister.

> your Tahoe is probably rated for somewhere around 7500
> lbs. or so?

Original rating is 6667 lbs (2700 kg), but I received information on the car from GM/Opel that the capacity is actually higher --- 3170 kg, afair, i. e. 7827 lbs. In case I would need it, I'd check further into the issue and eventually have the papers of the car updated so that I can legally tow 7827. But it depends on the hitch; I'm not sure if it's strong enough for that. If it isn't, I would have to get a stronger one or to stay with 6667.


GH

Olee,


I think the other "shift" you are feeling is the torque converter locking up.


If you hold the trans in a lower gear, it usually delays the shifts below that gear, meaning higher RPM, and you should get a torque converter lock up sooner. I thought you might find that towing in 3rd gear would work better for your particular situation and towing speeds.


As far as weight ratings on your hitch, if it's like the factory ones here, you have to have a weight distributing hitch to go over 5,000 lbs. and then you can go up to 10,000 lbs. There is also a tongue weight limitation without the weight distributing hitch. That information may be stamped on the metal on top of the receiver of your hitch. If you can't see it by looking down on top of it where it sticks out behind your bumper, it's not there.


In case you didn't know, the weight distributing hitch is an accessory that mounts to the trailer being towed and works with the vehicle hitch.


Edited by: Zeeb

> Welcome to the forums.

Dave, thank you! This seems to be a nice place here :)

> I would greet you in German, but I will not
> embarass myself and insult you at the same time.

Hm, insult me by greeting me? How would you do that? ;)

> Is your Tahoe built and sold in Germany or, is it an
> American Tahoe that was imported to Germany and sold
> there?

Well, I don't think that any Tahoes and the like are being built in Germany. What a very few dealers sell here are all the gasolines ones, and, afaik, no Suburbans.

My Tahoe has been imported, Canadian version with kilometers on the speedometer, miles in small letters. According the VIN, it must have been made in Mexico.

> Also in the same question as Zeeb, is that a Diesel
> Tahoe?

Yes, it is --- I updated my signature yesterday, it's a good idea to use it for that information :)

> I used to tow a 1200 Kg trailer at 100 kmh with my
> U.S. made 1990 S-10 Blazer. I added an external
> Transmission cooler in series with the transmission
> cooler built into the radiator.

Did you have a gauge to show transmission temp? It would be interesting to know if and additional cooler will make a difference.

> If your tahoe is a diesel, the proper towing RPM's
> would depend on the torque curve of the engine you have
> in your Tahoe.

Going at what point of the curve is best for towing? Hm, I didn't find a complete curve yet, I only know that max. torque should be at about 1750.

> The State of Ohio has the same terrain as Germany
> without the mountains if I remember, so you should be
> fine towing in OD if you have a Diesel

Thanks, I'll try it out --- most/all ppl here seem to agree on that I can safely tow in OD on flat ground, so I guess I'm worrying too much about it :)

But, it's much better to worry and to ask in advance than just going into it and breaking something :)


GH