I've got a 98 f-150 with the 4.6L and an automatic transmission. I tow a 2800 pound boat with it. I had to go on the freeway today, so my speed was around 65-70 mph. My rpm's were around 2700-2900. Is it going to hurt anything to drive like this for a couple of hours? My temp guage stayed in the same place as always, but I am concered with excessive wear on the engine, waterpump, etc... I can put it in OD, but it won't keep up to speed and likes to downshift. Any thoughts?

 

Your doing the right thing by not using OD if it always hunts for the lower gear.

As far as the RPM's go, I don't think that range will hurt anything.. You could always slow down to the 60-65mph range if your concerned..

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Y2K F250 XLT SC 4x2 5.4L 5sp 4.10LS

 

I currently have an '89 Bronco with a 5.8L and C-6 (no overdrive) tranny. With 350k miles and counting, I've been running that RPM on the highway for almost 12 years now. Doesn't seem to have caused any problems in my case. Just stay on top of your oil changes and I don't see any problems with it.

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Boss™

Just Ordered 2001 F-150 Lariat Wht/Slvr medium graphite leather, 4x4, SC, SB, SS, 99L 5.4L, 44E tran, 7700# payload, Class III Tow, 3.73LS, Skids, Capts chairs, 4W disc ABS, shift-on-fly, keyless, HD everything
Planned Mods:
Westin Chromed Stainless Nerf Bars, ARE LS II bed cover, Bedrug™, Gibson Swept Side Cat Back, K&N filter w/airbox mods, Headman headers, Superchip, 3" body lift with at least 33's, alarm/pager/auto start system, stereo system

 

Thanks for the informations guys. I just wanted to make sure that I wasn't hurting anything. I'm sure the only thing that I'm hurting is my gas mileage. I get about 13 mpg towing in drive and not OD. Thats still better than a 85 bronco I used to drive. It had a 4 speed manual, and a 4.10 rearend. The tires were p235/75/15. It had the 300 in it and 11 was the norm. Loaded or unloaded, it didn't matter. I just didn't know if they manufacured todays engines to take the abuse like that old bronco would.

 

Not hurthing a thing.

Let's assume that all things were equal except for 2500 RPM vs 3500 RPM.

If it took 60 HP to pull your rig at speed.

At X MPH and 2500 RPM, that would mean 5,000 piston pulses per minute (2500 / 4cycle * 8cyllinders).

Whereas at that same X MPH at 3500 RPM, it would then mean 7,000 piston pulses per minute (3500 / 4 * 8).

The significance is that each pulse at the higher RPM is only 5/7 or 71% as strong for the higher RPM 60HP -- and it means that the stresses (torsional, vibration etc) for those faster and shorter pulses are significantly less than for the slower turning engine speed.

Since it is almost a 'trip back in time' moment to actually catch a vehicle burning oil out the tailpipe -- the conclusion is that rings simply live a long time -- so the possible argument for spinning slow to avoid ring wear is almost a moot point.

Transmissions can be made smaller and do the same amount of Work if the power pulse intensity and duration is minimized.

Keeping the same amount of work (in this case -- your vehicle at speed X) while moving the engine RPM range merely transfers the 'challenges' around the rest of the drivetrain. Spin the driveshaft realy fast and you need a smaller pinion gear -- which, by it's sheer lack of size can mean extra wear on it -- BUT the torque requirement for mainting your 60HP at X RPM is smaller than if you spin the driveshaft really slowly, the torque on the pinion gear is great, the size difference between the pinion and the ring are less (comparated to the former example), the size of the gear is great (translated: costly), and the gear reduction of the transmission is significant.

Do a similar calculation on your 2,900 vs 2,000 RPM scenario and you can see why your transmission 'self-limits' by downshifting. You simply don't have the HP available from your engine at 2,000 RPM - and if even if you did, your transmission would not stay in gear and let you bang at it with those big pulses (smart guys those Ford Folks).

I have not even touched the benefits of spinning the engine where more HP is available (your 2,900 RPM) -- but just look at http://www.woodhouse.com/images/triton3l.jpg and you can see that you have about 150 HP available to you at 2,900 RPM whereas you only have 100 HP (2/3 -- 67% !) available to you at 2,000 RPM.

If you've guessed that it's not simple - You WIN! Many people earn a pretty good living by helping/advising customers/owners on these very issues.

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Y2K™ Jim Gorka

Toreador Red, Keyless XLT SC SB 5.4L E4x4 4wDisc/ABS, 3.73LS, Skid, HD 7700# Towing, LT-245's on Chrome, Tube-Steps, Captain's, 6CD, Tonneau, named: "Nick"


(oops - had to fix stupid spelling error)


[This message has been edited by Y2K 7700 4x4 (edited 07-16-2000).]

 

To all,
Lets not forget a decent insurance policy for any automatic trans. A big-*** oil-cooler. Why doesn't the factory put them on all autos? Because it would put a lot of tranny shops out of business.

Keep it cool and change the fluid every 30K miles or better. Then you will not worry whether you are in OD or 3rd. Also, the modulated TC lockup will be much cooler.

birdman