Oil, engine life and towing

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I have a question for fellow BITOG experts. I'm curious about heavy engine load and it's affect on the oil and engine stress. My particular example is for my GM 5.3L Silverado (2012 which has the 6 speed and 3.42 rear gear) where I tow a 7500lb travel trailer. When I'm towing the trailer and come to a long and steady hill (let's say a long 6% grade as an example) I have two options. Going up the hill I can climb it at WOT and it will hold 3rd gear around 4k rpm. It won't accelerate but it will hold the speed at 45mph (It's not a race to the top and I can regularly pass Semi's). The second option is to downshift to 2nd gear which brings the rpms up to ~4.5k. Under this condition I can hold the 45mph with 50% throttle and can easily accelerate up the hill (with rpms rising accordingly). At 4.5k rpm the engine is really working but still well under redline. All of these numbers are estimates and what I remember off the top of my head. So, my question is this - which is easier on the engine and the oil? What is happening to the oil under these conditions? Is the oil better protecting the engine with less wear if I down shift and run at higher rpm (and thus need less throttle)? I usually downshift in this case but it got me wondering what is happening to the oil in this case. Your feedback and technical information is appreciated.
 

Ndx

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I would worry more about transmission then engine ... I would make sure that ATF is changed frequently ... This is serious car that can tow a lot more ...
 
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Thats a great question, and being a coastal resident I cannot answer it directly, but I agree the trans is of far more concern than the engine. The 5.3 is one of the most bullet proof ever made. My 2000 Siverado has 215K and works like its new. 7500 lbs is a "workout" for your truck but it is not pushing it to the max. Its within its capabilities. So, change your trans fluid often, and get a trans cooler if you don't already have one. I would tow in 2nd up the hills, and reduce speed to 40 instead of 45, lowering the throttle and RPM's just a bit. I don't like pushing WOT for any extended times. Personally I would run a good stout 10-30 (like PYB) in this application, with a max of 5000 mile intervals.
 
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I would also agree that it would matter more to the transmission than the engine. With respect to the transmission/torque converter, if the speed of the vehicle is kept constant, would the higher RPM (lower gear) cause more heating of the ATF?
 

pbm

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I'm only guessing here but I would prefer option 2....lower gear and higher RPM. As long as your well below redline it shouldn't be a problem. PS: I agree that your A/T would be more of a concern.....
 

Nate1979

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Thanks for the feedback so far. For the ATF I change it often and have added a secondary cooler (in addition to the stock ATF cooler) so temps do not get too hot. In this situation the worst I see is 220F (the addition of the secondary cooler has had a big affect on the ATF temperature during towing and making it much less of a concern). Under both conditions the coolant temp also rises above the normal operating temperature to ~230F but doesn't rise further (and is explained in the owners manual as normal). I believe the fans kick in at that temp and help keep it from rising further. I don't know under which option the temps of either the coolant or the ATF rises faster as I haven't been in the situation enough times to accurately say. During these climbs I'm carefully watching the gauges along with the strange look on the face of my wife as she hears the engine screaming at 4500 rpms! Another point of information is that the OLM doesn't really kick down much faster towing compared to not towing. While I burn twice as much fuel while towing the rpms are not twice normal rpms (except on hills) so I think the OLM is watching rpms more than fuel burned. Regardless if you look in the UOA section I have posted some under towing conditions and the OLM has proved to be very accurate under severe conditions (short trips, towing, etc).
 
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The choices I get from this is either: WOT at 4000 rpm, or 1/2 throttle at 4500-5000 rpm. Easily the part throttle and higher rpms are not as hard on everything. Running the engine faster with less load causes less wear than the marginally lower rpms with the engine working as hard as it possibly can. As far as all the warnings you've received about the transmission, keep in mind that it is the shifts under load that cause the wear; so if you shift down prior to the hill, it will be easier on the trans and fluid than it would be if you shifted say 1/2 way up the hill.
 
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Originally Posted By: pbm
I'm only guessing here but I would prefer option 2....lower gear and higher RPM. As long as your well below redline it shouldn't be a problem.
Agreeing with pbm, and here's why: Your oil film in the crank bearings is thicker with the extra RPM and less piston force (torque) there. Oil film thickness is higher with higher RPM and lower piston force on each stroke. Thicker viscosity also increases oil film thickness, yet the latest 5.3L V8 in new Chevy pickups specify 0w-20, albeit they might have slighly widened the journal bearings to get that to work, not sure. Still a ways from redline, like you say.
 
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The effect on oil at 4000rpm vs 4500rpm is negligible. Both scenarios are heating up the oil. In the same scenario I feel half throttle in second is better than full throttle in third.
 
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Originally Posted By: Nate1979
Another point of information is that the OLM doesn't really kick down much faster towing compared to not towing. While I burn twice as much fuel while towing the rpms are not twice normal rpms (except on hills) so I think the OLM is watching rpms more than fuel burned. Regardless if you look in the UOA section I have posted some under towing conditions and the OLM has proved to be very accurate under severe conditions (short trips, towing, etc).
When GM created the OLM algorithms, they mostly penalize you if you keep operating the vehicle without it warming up, resulting in much more acid formation.
 
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Originally Posted By: FetchFar
Originally Posted By: Nate1979
Another point of information is that the OLM doesn't really kick down much faster towing compared to not towing. While I burn twice as much fuel while towing the rpms are not twice normal rpms (except on hills) so I think the OLM is watching rpms more than fuel burned. Regardless if you look in the UOA section I have posted some under towing conditions and the OLM has proved to be very accurate under severe conditions (short trips, towing, etc).
When GM created the OLM algorithms, they mostly penalize you if you keep operating the vehicle without it warming up, resulting in much more acid formation.
How does that affect acid formation unless its also short tripped?
 

Nate1979

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Originally Posted By: Kuato
As far as all the warnings you've received about the transmission, keep in mind that it is the shifts under load that cause the wear; so if you shift down prior to the hill, it will be easier on the trans and fluid than it would be if you shifted say 1/2 way up the hill.
Thanks for the feedback. I hadn't thought about this point before. Usually when I see that 3rd gear and WOT can just hold the speed up the hill I let off the throttle a little and then downshift to 2nd. The shift to 2nd is pretty hard but with tow haul mode you can tell the shifts are firmer (which I think is to reduce wear).
 
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7500lbs is a lot for a 5.3 with the 3.42. 4:11 would be the way to go. I'm suprised you can climb hills at all. I'm towing 5000 with a 3.73 in the avalanche and i wish i had 4:11's. I have thought about the cost of going to 4:56. Heavy lugging will hurt the bearings. Its better to run rpm a bit, i just would'nt drive at redline.
 
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Nate1979

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Originally Posted By: spasm3
7500lbs is a lot for a 5.3 with the 3.42. 4:11 would be the way to go. I'm suprised you can climb hills at all. I'm towing 5000 with a 3.73 in the avalanche and i wish i had 4:11's. I have thought about the cost of going to 4:56.
I guess you have the 4-speed? The 6-speed makes a big difference.
 
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Originally Posted By: Clevy
How does that affect acid formation unless its also short tripped?
...meaning it never warms up, gets shut down to fast.
 
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Originally Posted By: Nate1979
Originally Posted By: spasm3
7500lbs is a lot for a 5.3 with the 3.42. 4:11 would be the way to go. I'm suprised you can climb hills at all. I'm towing 5000 with a 3.73 in the avalanche and i wish i had 4:11's. I have thought about the cost of going to 4:56.
I guess you have the 4-speed? The 6-speed makes a big difference.
Probably so, i do have the 4 speed.
 
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