to many rpms

Aythya · 08-07-2002, 11:56 PM

I am towing a 17' 6" boat about 3500#s. Doing 70 mph on the interstate I am turning 4000 rpms. Stock tires and gearing. In my opinion thats way too many rpms for an extended drive ( 3hrs to the lower coast). Any ideas on adding horses etc.

Thanks in advance!

evergreen · 08-08-2002, 02:42 AM

k&n cold air intake, new exhaust system. there isn't alot you can do thats going to give you dramatic results.

xoc · 08-08-2002, 03:33 AM

What gear are you in ?

A 5 speed will turn 3000 RPM at 70, and an automatic will turn 2700.

OffroadX · 08-08-2002, 07:51 AM

If you're turning 4000 RPM at 70 in an automatic and you have the overdrive on, you're killing your transmission. It should be turning about 2600 RPM at 70 if the torque converter is locked up in 4th (overdrive) but if the converter unlocks it will turn well over 3000 RPM depending on the load. Running under sustained load with the converter unlocked will roast your transmission in no time.
Turn off the overdrive when towing. Your RPMs won't be much different, but the transmission will be operating much more efficiently and won't generate near the amount of heat. It kills your gas mileage either way, but at least not at the expense of the transmission.

Also, be sure to check if the "A/T Oil Temp" light on the dash lights up when you first turn the key. If it doesn't, it is probably defective as several others have discovered, necessitating a replacement of a circuit board in the dash. This light will warn you if your transmission is getting too hot!

Brent

OffroadX · 08-08-2002, 09:36 AM

Hmm, I did some testing on the way in to work this morning. I wasn't towing, but it appears there's no way to run 4000 RPMs in 4th in an automatic at that speed, it shifts to 3rd before it climbs that high. 70 MPH in 3rd with the converter locked is about 3600 RPM, and 3rd unlocked is 4000 RPM. 3rd unlocked is pretty rare, about the only time I get that combination is if I turn the overdrive back on while I'm still hard on the gas under load, it won't shift to 4th until you back off a bit. If you're spending a lot of time in 3 unlocked, I'd be surprised. It's better than 4 unlocked, but still not something that should go on for long.

Brent

redxseven · 08-08-2002, 09:41 AM

I towed my 2900 lb. car on a full size U-haul trailer, so I was around that weight as well. I called Nissan and asked about towing with or without overdrive because I was concerned about the same thing.

If you are turning the engine around 4000 RPM with overdrive on you are ok but if you back off a bit you should be able to get the torque converter to lock up and that is good.

The Nissan people told me that by turning the overdrive off you are avoiding the full load downshifts (bad for the torque converter). i.e. you are cruising along with the TC locked up and you start to head up a hill, step on the gas and you get a snap shift from locked up TC to unlocked 3rd gear (i think).

Their suggestion was to turn off overdrive at the same time of backing off the throttle (and transmission load) when approaching hills or passing situations. worked like a charm for me. you should be able to cruise @ 70 with it locked up though.

OffroadX · 08-08-2002, 11:02 AM

Lockup on a level steady cruise at 70 should be no problem, I agree. Buf it for whatever reason (headwind, slight grade, etc.) you end up out of lockup for more than a while, the main threat is heat. The prolonged fluid shear in the torque converter generates a lot of heat.
Haven't heard of the shift issue, but I don't think I've yet managed to force my tranny to shift from 4th to 3rd-unlocked, it always goes directly to 3rd-locked.

Brent

redxseven · 08-08-2002, 12:57 PM

I don't think I've ever got mine to shift from 4th locked to 3rd locked...? Always feels like it's going from 4th locked to something un locked. i.e. RPM's will increase approximately 500-700 more than locked with slight throttle increase, transmission is clearly no longer locked though.

I'll try some full WOT to see if it kicks to 3rd locked. - which would be even worse if towing.

When I was towing if I ever noticed a speed change I would always turn the O/D off before any significant throttle inputs. You can get a pretty good idea when the tranny is going to shift based on throttle input.

Don't try to do this with cruise control on either...

OffroadX · 08-08-2002, 01:17 PM

Could be, maybe it's just locking up within a few seconds of the shift and I'm not noticing.

Brent

redxseven · 08-08-2002, 02:14 PM

You're right I just tested over lunch and anywhere from roughly 1/3 to 2/3 throttle it will go to 3rd locked.

I think WOT will go directly to 2nd...

Hmm, anybody have shift maps?

OffroadX · 08-08-2002, 03:25 PM

http://home.us.net/~stimpy/xterra/mi...s/AT-shift.gif

Brent

Aythya · 08-11-2002, 04:43 PM

Thanks for the replies!

Brent, Apparently I am spending time in 3rd unlocked. I have been turning the overdrive off way to much weight to tow with OD on. Also, that was with cruise on. Perhaps the right coniditions were met to put me in 3rd unlocked and with cruise on it held for the entire trip?

Not sure though.

OffroadX · 08-11-2002, 05:14 PM

Could be. As a general rule, cruise when towing is a bad idea anyway.

Brent

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