Hi Newbie Dave here with another question,
1500 miles on the 09 3500 and pulled the trailer (8500lbs) for the first time . The route was 98 percent flat but did include a pretty steep freeway hill here in Orange County, Calif. , the 73 toll road through Aliso Viejo. Pulled fine up the hill , I think it downshifted once , (...into 4th I assume? I was in tow mode, and doing about 55 up the hill about 2400 rpm) outside temp at 75 and trans temp got up to 180, at the top of the grade there's a toll booth, when I stopped to pay the toll, the engine was still really loud - like a whirling sound. I paid the toll , got under way (going downhill now...) and the whirling sound subsidded. Normal behavior?
Also why are there two batteries under the hood?... one in the front right and one in the rear left near the firewall?
Thanks

dave

Wow.

Ok. The tranny must have downshifted twice from SIXTH to FOURTH, if you were at 2400.

The whirring is the fan. The fan-clutch is temperature sensitive and engages when temps climb. The cooling fan then pulls massive amounts of air (takes about 20-30hp to drive it!) through the intercooler (which is now quite hot with towing boost level), the AC condenser, tranny cooler, and radiator. It is quite noisy.

The two batteries are for cold-start. No, not the cranking part. The glow plugs come on for a short time to warm the cylinders. These draw probably as much as the starter itself. Then, there is an intake heater that also comes on to keep warming the air until the engine gets to a certain temperature.

All of these heaters, on a cold morning, use more than the alternator can provide. If you watch, on a cold start, the voltage gauge will stay in the dis-charging area for awhile.

Unless you were in freaking California and actually towing at or about the 55 mph in tow haul mode did it downshift once.
at 55 - 63 mph in TH it will stay in fifth for me, the minute it touches 64ish it shifts up to sixth...then it will stay there if I drop to 60ish.

That fan'll get ya, huh? Sounds like a turbo prop trying to take off! Although I've never ever had an overheat problem (or even close to it) so I'll live w/ the noise and praise it.

Unless you were in freaking California and actually towing at or about the 55 mph in tow haul mode did it downshift once.
at 55 - 63 mph in TH it will stay in fifth for me, the minute it touches 64ish it shifts up to sixth...then it will stay there if I drop to 60ish.

I was thinking the same thing, but he is saying 2400 rpm. That would HAVE to be fourth.

Towing my 9000lb boat/trailer with full fuel on both (truck and boat), ice chests, luggage, and 4 adults, mine will NOT downshift to FIFTH unless I do it. On the average 6% grade, in tow/haul, at 70, it will just stay in sixth. I tap it down to fifth, as I don't want to heat up the intercooler that much. Even then, it's at about 2200 rpm. If he is 2400 at 55-60, it has to be fourth. I think his trailer is heavier than he thinks and with the DPF - probably during a regen cycle - the truck MAY have been taking a hit hard enough to downshift to fourth??? Just looking for a viable explanation.

Hi guys,
Thanks for the input and the info on the dual batteries.
I was sort of suprised when it dropped the gear. I reminded me of my 04 V10 with that 4r100 tranny that would drop into second and force me to crawl up hills (hence the Duramax purchase). The trailer weight is accurate , I took it to the scales after I bought it. It says 5500 on the mfg plate but actually it's 7600 dry! Those lying rascals!
The grade is pretty steep at that part of the hiway, would it be more than 6 percent I wonder? and the sound like the Saturn 5 lifting off sound was the coolers/fans kicking in. So I'll know in the future what that sounds like.
Anymore feedback ...keep it coming
Thanks again
Dave O

I assume the trailer is a travel-trailer? If so, you are talking about added wind-resistance in conjunction with luggage (clothing), food, ice, full fuel in the truck, people in the truck. You're loaded pretty good. If you had a head-wind whilest climbing said hill, PLUS you were probably easily into a regen cycle, PLUS the fan coming in at the same time: I could see it going to fourth.

Mine without the DPF, plus adding the intake, and running a much more efficient tune than stock won't downshift at all. I am pulling about the same load as you, but probably have 80 more hp and 150 or so more ft/lbs of tq. So, the hp/tq I have gained with exhaust/tuner/intake has neutralized the fan, wind resistance, and most of the load. Like I said, I tap mine down to 5th for the long pulls to reduce smoke and ease up the intercooler temp.

Hi

Yes it's 26 foot Toy Hauler .. so that equals pulling a parachute uphill. It's a 2001 Weekend Warrior ..built like a brick - s***house but rolls like a block of iron.

No head wind fortunately..this time.

...One more question what's a PDF?

Also does changing the intake / exhaust as you did void any warranties?

Thanks!

oh yes,.... what is the regen cycle?

I was thinking the same thing, but he is saying 2400 rpm. That would HAVE to be fourth.

Towing my 9000lb boat/trailer with full fuel on both (truck and boat), ice chests, luggage, and 4 adults, mine will NOT downshift to FIFTH unless I do it. On the average 6% grade, in tow/haul, at 70, it will just stay in sixth. I tap it down to fifth, as I don't want to heat up the intercooler that much. Even then, it's at about 2200 rpm. If he is 2400 at 55-60, it has to be fourth. I think his trailer is heavier than he thinks and with the DPF - probably during a regen cycle - the truck MAY have been taking a hit hard enough to downshift to fourth??? Just looking for a viable explanation.
It's so weird how some trucks built the 'same' can have such different attitudes. If he was doing the speed limit in MY truck it would have been cruising in fifth in TH mode.
So if it downshifted once from fifth to fourth (that would be how my truck reacted if it decided to downshift) that sounds right on the RPM range.
It does take some work for mine to kick down from 6th, but, it's usually speed related rather than load related... my truck is a mutant ;)

Hi

Yes it's 26 foot Toy Hauler .. so that equals pulling a parachute uphill. It's a 2001 Weekend Warrior ..built like a brick - s***house but rolls like a block of iron.

No head wind fortunately..this time.

...One more question what's a PDF?

Also does changing the intake / exhaust as you did void any warranties?

Thanks!

I share your pain towing a 'brick' :) My horsetrailer has a bit of a V in the front, but, NOT much.

It's actually a D P F - A DPF is a Diesel Particulate Filter. It's a new smog/emissions device for the 07.5 + (the new body style) trucks. It is what calls and performs the 'regen cycle' (When the computer tells it to).
It traps the nasty ugly smoggy soot according to the EPA :)

oh yes,.... what is the regen cycle?
Ok, I'm going to try this, and someone correct me if I'm wrong!

The regen cycle is triggered by the ECM (Engine Control Module) of your trucks' computer. The DPF has two sensors that track flow from the exhaust...one in the front one in the back. When it senses that flow is becoming out of specification (a parameter written into the computer) It
then tells the truck to start a regeneration cycle (it also has preset things, that you have to be in drive above a certain MPH and other parameters set by GM) it then commands the truck to do a regenerate mode.
The regen mode after it gets the ok from the computer then puts raw fuel (yes, I know it's waistful) into the exhaust and it gets the DPF HOOOTTT.
It gets hot enough to burn off the soot it had collected and put them out the exhaust stream as unharmful obliterated cooked and baked soot particules.

Close - but it doesn't put RAW FUEL into the exhaust. There is no way to do this. It alters the injector pulse rate to INJECT more fuel into the motor and also adjusts the vanes in the turbo. I am sure timing and other things are changed also, but the end result is 1100-1200 degrees of exhaust temp, even at idle, to burn off the soot. It takes alot of fuel, and reduced power output to complete a regen cycle.

I have been in for two warranty items. One was an ECM issue and the other was a leak. Dealership had no problem with my exhaust, tuner and intake. They said none of those things had anything to do with my specific problems. They could see the glitch in the ECM was prior to my first tune application and the leak was a factory flaw.

on the 7.5+ truchs there are 3 injection events that are possible.
1. Pre injection, all trucks have it, makes the truck quieter, and better fuel economy.
2. main injection. all trucks have it, This is all the power.
3. post injection. lmm and later 07.5+ have it. inject fuel on the exhaust stroke so you don't get any power, but heat the crap out of the cat and dpf. This is the dumping raw fuel into the exhaust.

There are 2 pressure sensors, 1 in front and 1 behind the dpf. when the difference in pressure reaches a certain point, it trigers a regen.
there are temp sensors in the exhaust, to make sure it cooks at the right temp. If you are pulling a hill at 1200 or 1300 degrees, just the act of driving will cook off some of the soot, saving regen fuel for later, or if you are in a regen cycle the computer won't have to add as much fuel to hit the temp it is going for.

That grade up the 73 is very steep. I towed my 21 ft toyhauler loaded to 8000 lbs and my truck went into 4th gear as well. I have the Juice/Attitude setup and monitor my trans gears. My fan was howling as well when I got to the top. It shuts off fairly quick once it notices that the temp isnt climbing any longer.

I have an 2008 Chev and a 32' Travel Trailer (12,000lb) and after towing our travel trailer for 20,000km last winter I have noticed a anecdotal observations I thought I would share re. some of the items mentioned.

I have noticed that the fan kicks on when:
1. the engine temp rises, OR...
2. when the transmission temp rises.

The engine temp can be normal and the fan kicks in if the transmission temp reachs around 200F. The fans will stay on until the trans cools even if engine temp is normal. With repeated heating and cooling of the trans temp if you are pulling up and down rolling hill terrian the fan will start to kick on at lower and lower trans temps and after a while will start kicking in in the high 180F range. The whole rig seems to recognize if certain situations are happening repeatedly and it seems to start anticpating what cooling may be required.

The fan does not always kick in at the same spots. On average the fan will kick in to cool the engine at about 112F (according to my gauge) and shut off at around 100F. The fan can also kick in at different times if a regeneration is in progress as I guess the heat rises a lot faster if the regen is in process.

I have had to drop to 5th gear on the flats once on a hot day as the regen must have been happening and with 100F outside the truck could not maintain normal temperature.

Regenerations happen far less often than normal if you are towing a heavy trailer over long distances, as some of the soot is burnt out of the DPF due to higher exhaust temps.

If a regen happens when you are pulling up a hill you can probably expect to drop another gear than you might normally pull up the hill.

2c worth hope it helps.

I have an 2008 Chev and a 32' Travel Trailer (12,000lb) and after towing our travel trailer for 20,000km last winter I have noticed a anecdotal observations I thought I would share re. some of the items mentioned.

I have noticed that the fan kicks on when:
1. the engine temp rises, OR...
2. when the transmission temp rises.

The engine temp can be normal and the fan kicks in if the transmission temp reachs around 200F. The fans will stay on until the trans cools even if engine temp is normal. With repeated heating and cooling of the trans temp if you are pulling up and down rolling hill terrian the fan will start to kick on at lower and lower trans temps and after a while will start kicking in in the high 180F range. The whole rig seems to recognize if certain situations are happening repeatedly and it seems to start anticpating what cooling may be required.

The fan does not always kick in at the same spots. On average the fan will kick in to cool the engine at about 112F (according to my gauge) and shut off at around 100F. The fan can also kick in at different times if a regeneration is in progress as I guess the heat rises a lot faster if the regen is in process.

I have had to drop to 5th gear on the flats once on a hot day as the regen must have been happening and with 100F outside the truck could not maintain normal temperature.

Regenerations happen far less often than normal if you are towing a heavy trailer over long distances, as some of the soot is burnt out of the DPF due to higher exhaust temps.

If a regen happens when you are pulling up a hill you can probably expect to drop another gear than you might normally pull up the hill.

2c worth hope it helps.

You do realize that the 99% of the tranny cooling is done inside of the radiator, right? If engine water temp is up, so is tranny. The trans cooler is submerged in the coolant. The other one percent or so is just ambient cooling from the lines and (stock) pan.

You probably won't regen at all if you knock down to 5th for up-hill towing. With my 9000lb boat/trailer, mine won't down shift on it's own - even in tow/haul. But, not having a DPF, even with the stock tune there is a significant amount of smoke during that pull. It is greatly reduced by dropping to 5th.

So, that smoke is still there in yours, but the DPF catches it. The more smoke, the more regen, etc, etc.

pa32rt:

You do realize that oil and water heat and cool at different rates right? And that trasmission and engine generate heat seperatly as well as a combination of the two together right?

Your engine temperature can be at normal and your transmission temperature elevated if you are climbing. The transmission temperature will also rise if you are downshifting on a downhill. With the engine holding the vehicle weight back through the transmission the energy (heat) has to go somewhere. The transmission temperature will stay hotter far after the water temp has reduced and hence the fan will come on. It takes about 2 minutes with a stock truck for the engine temp to rise when climbing and the fan may come on as much as 2 minutes after that. Once the fan kicks in even while climbing often the water temp will return to normal with the extra cooling (still climbing) the trans temp whoever will continue to rise as you climb, so even after the water temp has returned to normal the fan stays on until the trans temp falls again which could be many miles after you have been downhilling let alone running on the flats.

Regens happen whether you drive in 5th up a hill or not. Whether you are towing or not. My point is simply that regens will probably happen less often when towing a lot due to higher exhaust gases generated.

pa32rt:

You do realize that oil and water heat and cool at different rates right? And that trasmission and engine generate heat seperatly as well as a combination of the two together right?

Your engine temperature can be at normal and your transmission temperature elevated if you are climbing. The transmission temperature will also rise if you are downshifting on a downhill. With the engine holding the vehicle weight back through the transmission the energy (heat) has to go somewhere. The transmission temperature will stay hotter far after the water temp has reduced and hence the fan will come on. It takes about 2 minutes with a stock truck for the engine temp to rise when climbing and the fan may come on as much as 2 minutes after that. Once the fan kicks in even while climbing often the water temp will return to normal with the extra cooling (still climbing) the trans temp whoever will continue to rise as you climb, so even after the water temp has returned to normal the fan stays on until the trans temp falls again which could be many miles after you have been downhilling let alone running on the flats.

Regens happen whether you drive in 5th up a hill or not. Whether you are towing or not. My point is simply that regens will probably happen less often when towing a lot due to higher exhaust gases generated.
All very true. Maybe I was being too "layman" with my terminology.

I guess my specific point was that the water temp goes up until the fan comes in. So, yes, the trans was probably coming up prior to the engine, but now the water that runs across the cooler tubes is (at least temporarily) warmer than it was before and cannot extract temp from the trans fluid quite at efficiently as before. Vicious cycle.

And yes, regens will still occur. I simply meant there would be even less chance of provoking one in fifth uphill instead of sixth. As I said, even on a stock tune you can see smoke coming out of the exhaust in sixth. If I tap down to fifth, it goes away unless I really stand on it. Which, there is no need for.