GM Truck Club Forum banner
1 - 20 of 25 Posts

·
Registered
Joined
·
36 Posts
Discussion Starter · #1 ·
I have an 11k camper...going up big hills/long grades I generally try not to hold the rpms past 4k (red line for the 8.1 big block is about 5k I think). 160k miles...engine is midly worked. Am I being overly cautious? I think on i70 in Colorado, I held it at 4k for like 15 minutes straight. Probably one of the more extreme examples. I'm not worried about overheating -- I'm worried about engine wear, especially the crank/rod bearings. I run 15w50 btw. I would like to push it 4500. At 4k in 2nd gear on the really big hills, I lose momentum. Perhaps at 4500 I could hold it. Idk. What do u guys think?
 

·
Registered
2001 Suburban 5.3L, 296k miles
Joined
·
1,648 Posts
I agree with Ray.
What made you decide to use 15w/50?
On a 5w/30 oil, what was your oil pressure?
At higher rpms, you need oil flow between bearing shells and journals. Using heavier oil than what was specified will result in more resistance to flow thus less oil flow even though you are seeing good oil pressure.
Oil pump is a positive displacement type so if there is less oil flow between bearings and journals, excess oil volume will just bypass thru the relief valve.
Oil flow also helps remove heàt from bearings and journals esp at higher rpm .
 
  • Like
Reactions: wjkirk and RayVoy

·
Registered
Joined
·
36 Posts
Discussion Starter · #4 ·
Lots of write-ups and performance builds recommended the full synthetic mobil 1 15w50 for the 8.1. Helps more then just oil pressure. I only brought it up to note that I dont cheap out on oil. I firmly believe that 5w30 is only recommended because it gives the best gas mileage...an EPA thing...not a 'best protection for the engine' thing. That said, thanks for your thoughts on the oil weight ...I will consider it...but I don't want to turn this into an oil thread. Let's just please move forward assuming I did my research and am using the best oil for my application.
 

·
Registered
2001 Suburban 5.3L, 296k miles
Joined
·
1,648 Posts
Its safe to keep the revs up when towing, better than lugging at a lower rpm.
Look at the rpm-torque curve on your 8.1L and stay there. You maybe over the max torque-rpm .
One time I was considering getting a suburban with the 8.1L and I remember the max torque is below 2k rpm. You are way over revving.

Edit:. Max torque is at 3200rpm
 
  • Like
Reactions: RayVoy

·
Registered
Joined
·
4,049 Posts
I'm having a hard time picturing thicker oil being optimal at high rpms.

I just did some quick research on the oil for an 8.1. lots of people are using the thicker oils based on oil consumption. but I also read where the oil consumption has been fixed over and over with new head gaskets and new bolts. people say these engines just burn a little bit of oil, its normal and it's fine. others use thick oil to prevent consumption. then theres the marine mechanics who say use 5w30 but first fix the head gaskets.....

If I was concerned with my RPMS I would surely want to make sure the oil can flow as freely as possible.

I'm not saying your doing anything wrong as theres lots of people doing the exact same thing but that doesn't mean its right either.

One thing I couldn't find was anything in regards to thicker oil and high rpms.

Anyways, I know you dont want to talk about the oil but I summed it up and I do believe its relevant to your question.

GM recommends 5w30.

keep us updated......

take care.
 

·
Registered
Joined
·
16,460 Posts
Well, like it, or not, I think we've turned this into an oil thread

The 454 has burned oil from day one, so has the olds 455 and the Buick 455, I'll suggest it is a big block fault and GM wouldn't spend the money to fix the problem.

And if any one wants my 2 cents, backyard cures are not favorable to engine health. Oil flow to bearings is important, lots of flow. And high flow will provide cooler oil. Synthetic oil is a must.
And, unless your a liberation engineer, follow the owners manual.
 

·
Registered
Joined
·
523 Posts
I’m curious about the transmission temp during these long hill pulls at high rpms? My 8.1 has a 4:10 gear ratio which helps. Is your 4:10 also or the 3:73? If I remember correctly the 3:73 max trailer weight is 10K. The 4:10 is 12K.
 

·
Registered
Joined
·
36 Posts
Discussion Starter · #10 ·
Hi jaercole, 410's...12k. I think the highest a saw the trans temp was 215. however, I have aftermarket coolers, lower thermostat and real time digital monitoring with aftermarket guages. No overheating issues.
 

·
Registered
Joined
·
36 Posts
Discussion Starter · #11 ·
As for every one else-- im looking for answers to at what rpm the 8.1 engine can be comfortable pushed during heavy towing or at what point its being hurt. All the answers so far have been completely off topic or flat out condescending and offensive.
 

·
Registered
Joined
·
523 Posts
Unfortunately I cannot speak on your question from experience. In my area I can tow my 7K lbs trailer easily on the highways without resorting to lower gears. The only time I’ve pushed her was climbing some mountains in north GA. And even then I think was in 2nd gear around 3K rpms.
 

·
Registered
Joined
·
16,460 Posts
As for every one else-- All the answers so far have been completely off topic or flat out condescending and offensive.
I think we need to set the record straight.
You asked if we thought running your engine above 4k was a good idea.
The correct answer is: your fine as long as you can keep it lubricated and cool.

Now excuse us if we are offering our opinions on how we think you can keep it lubricated and cool.
Be assured, none of us are interested in wasting our time being "flat out condescending and offensive"; but we can be if pushed beyond 4k.
 

·
Registered
2001 Suburban 5.3L, 296k miles
Joined
·
1,648 Posts
Its safe to keep the revs up when towing, better than lugging at a lower rpm.
Look at the rpm-torque curve on your 8.1L and stay there.
Max torque is at 3200rpm.
Past 4k rpm, the torque drops.
Rectangle Slope Font Plot Parallel
 

·
Registered
Joined
·
36 Posts
Discussion Starter · #15 ·
Yes bazar01, torque indeed drops above 3200 but peak hp is 4200. It's not possible to go up steep grades and stay at 3200 rpm...it would never shift out of gear. I forget the relationship between tq and hp but I think Torque gets u to the point where horsepower is usable. But I could be wrong. And u have gearing involved there too. Also, I have a 4 speed 4l80e...it needs to get up to those higher rpms so it still can be in the torque curve after the upshift.
 

·
Registered
Joined
·
36 Posts
Discussion Starter · #16 ·
Rayvoy-- thanks for responding but even if we knew 100% if it was cooled and lubed properly, I don't think u would suggest I run it at redline for 30 mins straight! At least not with 160k miles on it....
 

·
Registered
Joined
·
36 Posts
Discussion Starter · #17 ·
And speaking of upshifting, here is some context: I was stuck behind a motorhome on a fairly steep incline once. I was in 1st gear at 4k rpm. It was too steep to upshift into 2nd at 4k because the computer knew the shift would have landed 2nd gear too low in the torque curve. So...I thought about pushing it to 4500 and passing him (power was there, I could have), hoping 4500 or so would allow it to go into 2nd. But, I was afraid it may not have still shifted and then I would be stuck doing 4500 till I got over the mountain (or slow back down to 4k and look like an idiot and make him have to go around me after I passed him). These situations happen all the time in the mountains.
 

·
Registered
Joined
·
16,460 Posts
I've never driven in Colorado, so I'm not aware of the hill/grades that your talking about; but I don't understand the need to consider using 2nd gear.
I would think that engine would pull 11k in 3rd gear all day long. It's used in motorhomes, it's used in big trucks, I thought it was designed to pull big weight at highway speeds.
 

·
Registered
Joined
·
36 Posts
Discussion Starter · #20 ·
Different gearing in 'big trucks'....yes, I can do 70 mph in overdrive with torque converter locked, but not on a 7% grade at 10k feet above sea level in the mountains. Then your in 1st (if u have a 4l80e) or 2nd (if u have an allison) at high rpms, with a lot of hp loss due to high elevation.....sometimes for 20 miles or more at that grade. Hence my question of at what point and what conditions do things start to break in this particular engine. Maybe I can run redline all day long. Idk.
 
1 - 20 of 25 Posts
Top