cincydiesel

Just got back from a camping vacation in Virginia. This is the first time I've had to run any step mountains with the f'ver. My question is, is it ok on the transmision to coast down the backside of a mountain to help cool the engine back down? Does idleing provide enough pressure to a hot transmision coolant line or do I need to give it a little gas now an then? Man I need gauges.

whitebuffalo

im not sure if this answers your question....but on my truck, the egts come down WAY faster if im engine braking (as opposed to just kicking her into neutral and coasting.) the engine is pumping more air that way without heating it up with fuel. if i missed ur question entirely, i apologize....

JyRO

whitebuffalo - I'm not sure about the auto trucks, but with a manual tranny, when you are coasting (in gear) there is NO FUEL injected. That will bring the temps down real quick. If you put it in neutral and coast, fuel has to be injected to idle. Plus, coasting in gear turns the motor faster. So with no fuel, and more air (more air versus idling) its only natural the EGT will come down quicker in gear with a manual.

Cincydiesel - Admittedly I don't know the auto's but I would bet that either locking the O/D out, or pulling it down a gear (whichever is more rpm appropriate) would turn the motor faster, which may turn the fluids faster and cool them off more effectively. Not sure though, but that would be my bet.

- JyRO

DMH

Not only that, but I think in most locations, it is illegal to run with any vehicle out of gear. That is considered "not being in control of your vehicle".

I may be wrong, and we seem to have a few members who are in law enforcement, or who know someone who is in law enforcement and they will be able to either confirm or deny my comment.

DMH

v8440

All of you guys seem to have hit it on the head. I'll add that if engine rpm goes high enough, friction seems to contribute a significant amount of heat to the coolant. If by "engine temp" the original poster meant egt's, then yes, coasting in gear will certainly pull them down faster. If you meant coolant temp, that's still probably true, but not completely for sure. Like I said, it seems to be at least partly rpm dependent.

HotRod82

First, why do you need to cool the engine down? If it is getting hot, fix what is broken and leave it in gear. I have run my truck flat footed on several cross country trips pulling between 10 and 12K and I pretty much never lift off the throttle. That is what these trucks are built for. The only time I cool down the truck is before shutting it off. Also, having your truck in neutral going down hill with a trailer is just a bad idea IMO....

2500CTD

On the auto the engine drives the tranny pump, well actually the converter does... which in turn is what moves the fluid. I pulled 24K before my built tranny and always coast down hills. My EGTs are never a problem, unless I lugged the engine.

cincydiesel

I'm not worried about EGT's and I didn,t shift into neutral. Sorry I dont think I explained myself very well. I was worried about the transmission not cooling down because of coasting in gear (48re) down 5 to 6 miles of 5% grades. I didn't know if the transmision needed a little throtle to build pressure in the trans or if it ran directly from RPM's.

RATTLINRAM

Your 05 with the "Tow/Haul" engaged should keep the TC locked up even when you have lifted your foot off the throttle. This means that you should feel some engine braking effect and the trans should cool down due to very little heat build-up from the converter.
On my 99 with a modified 47RE, I always use the "Mystery-Switch" to lock the TC, plus I will set the cruise control for the speed I want to maintain down the mountain. (I tow in the mountains of VA quite a bit.) This has worked great for me. On my trips on I-64 over Afton mountain, my trans temp really doesn't heat up because of the TC/VB modifications. Your 05 48RE should manage all this automatically,,,,,, (that's what DC claims anyway,,,,). Your best option,,,,,, A tranny guage is not expensive and easy to install,,,,,,,, Then you will know for sure.
I know that some folks don't care for the way that the 2005 Tow/Haul function works and yet some folks say it's great. The reason was that you can not lock-out overdrive on that year transmission. However, I will say that my Dad traded his 2000 V-10 with a 47RE, in on a 2005 CTD auto and then towed his 30' 5er to CA, up to WA, then WI and back to VA. He was very impressed with the 48RE auto and said it was the best automatic trans he has ever driven. (I'm after him now to get gauges installed.) He did say it just takes a little time to learn how to feel the throttle and apply it to avoid gear hunting in some situations.
Maybe some more responses from folks with the 2005 48RE that run gauges will shed more light on the subject.

Foxborough

Once you get up to speed the transmission stays cool (100-140*). I tow #6300 boat and even in the Ozarks the transmission did not climb going up those hills. I always keep it in tow/haul mode when towing. I would get EGT and Transmission gauges. It really helps, I realize my weight is about half of what some are hauling.

Jezzhuntin

I just click the OD button, it helps control speed which also keeps you off the brake. I wish they had that option on the jake brake like the 07's do for $300, that will be a sweet option, one benefit I see on the 07. if the only, time will tell.

signature600

What do you mean NO FUEL injected...the pump can't stop pumping fuel, unless you turn the key off. The fuel is injected at idle fueling levels...which is equal to the APPS at 0% travel...the truck doesn't know the difference between idling, and coasing in gear, there are no sensors on the tranny!

That being said, it does cool better "coasting" at higher RPM...more air moving!

Chris

JyRO

OK, I should've been more clear. I don't know factually that there is NO FUEL being injected, but that is what I have read here and on the TDR. I'm no pump designer, but if a pump can pump various levels of fuel (idle, full throttle, in-between), then why couldn't 0% fuel pumped be one of the levels? The pump would still be turning, but not pumping fuel. Dunno, but I suppose it could be the case.

I would imagine that if the rpm is ~2,000, and you let completely off the throttle, the ECM can see that throttle is at 0% but the engine is well above idling and can trigger the pump for 0% fuel (manual tranny). However, on an auto tranny, it would have different ECM programming. On those auto trannys that unlock the TC when off the throttle, the rpms will not stay at 2,000 rpm. The rpms will drop to close to idle, and because the engine is near idle, the ECM will have the IP add fuel to idle the engine so it doesn't stall.

- JyRO

signature600

The pump has to pump fuel anytime it has fuel coming into it...remember, we are talking about a PUMP...if the key is on, it will get fuel. If the key is off, no fuel.

All it does is pump...the elctronics contol how much extra fuel is moved, but there is a preset "bottom" end to the fueling...called idle. Why do you think it try's so hard not to stall when you let the clutch out, without your foot on the pedal...that "romp, romp" that some people call it. It can't go below that level, or it dies!

Mechanical, or electronic, it doesn't matter...it has to pump something ALL the time.

Chris

RATTLINRAM

OK,,,,,,,, and I think the original question was,,,,,,,,,,,