EGT's vs. RPM's-Stock ETH

[T Peterson]

Can't quite find the answer I'm looking for with the search, so please forgive me if this is a much asked question. I will be pulling a 22' TT for a friend this weekend, about 450 mi. each way. Question is will my EGT's be lower pulling 1700-1800 rpm in 6th, with foot on the floor or 2500-2600 in 5th? How much? TIA



Tom

 

[HBarlow]

Tom:



The common wisdom is that EGT will be lower if you downshift and run at a higher rpm.



However, I have not found that to be true with my truck. My truck, an HO/6 speed with 3. 55 gears, will not generate lower EGT by downshifting, only by reducing throttle input. If I start up a long steep grade pulling my TT in 6th gear with cruise control engaged, and EGT reaches or tries to exceed 1300 degrees, I have tried downshifting to 5th direct. But if after downshifting I apply sufficient throttle to maintain road speed, EGT rises again. The only way I have found I can reduce EGT is by disengaging cruise control but remaining in 6th gear and backing out of the throttle a little, giving up road speed.



Harvey

 

[Diesel Gunner]

I had no problems pullin my TT, EGT wise, until I put the 295/75 Nittos on. I have 3. 55 gears and the temps will get high if I try pulling in 6th. So, I slow down to 55 and run in 5th. Here my EGT stays at about 800 and engine temp stays normal. Trying to run 65 in 6th will cause the EGT to go up to about 900 and engine temp goes up but does not exceed normal. Just does not feel right to me, so I slow down and relax

 

[dvaughan]

Tom, the 24 valve engine produces maximum power at an rpm less then governed speed. Placement of maximum power has been changed on the 24 valve to encourage operation in the most fuel efficient engine speed range. The changes in the 12 valve engine has accured largely in part to stricter emissions regulations handed down by the EPA. The 24 valve engine likes to be driven hard. It preforms best in higher rpm ratings. For on highway cruising and no load, maintain 2000-2200 rpm for best fuel economy. For optimum performance while pulling a heavy load, run up to 2800-3200 rpm. You can hit the hill at 3000 or 3200 rpm and allow your engine speed to drop to 2300 rpm before downshifting. This will you to maintain good recovery and power. You can not have optimum fuel economy and prefomance at the same time in a diesel. It's one or the other.

I would not tow a heavy load in 6th at 1700-1800 rpm, you will heat up. For fairly flat highways I would run around 2400-2500 rpm

 

[T Peterson]

Thanks!

That was the info I needed. I see most of you are pretty much stock for the engine, my truck is completely stock, don't even have guages yet (I know) do you think I'd have a problem with EGT's pulling at 2800 RPM in 5th with my foot in it, or do you still have to back out of it with a stock HO? TIA



Tom

 

[Diesel Gunner]

My experience is just as dvaughn stated. If I try to pull the TT at 1600=high heat. Although, I do not pull at 3200, which seems extreme to me, I have had no problems pulling at between 2100 and 2500. Traveling MT it seems to me that I wil burn more fuel by keeping my RPM in the 2300 zone than using 6th gear and letting it run along about 70mph and 2000rpm.



Experiment and be resonable. Your truck will tell you what it likes.

 

[LFarrar]

You should not have problems pulling such a small trailer anywho!

 

[T Peterson]

Thanks Again

I installed a Jordan Ultima yesterday afternoon and we hooked up the TT and drug it around the patch a few times to adjust the brakes and jumped on the freeway just to see if was going to "buck" with the expansion joints, it was quite smooth, I thought I'd have to put a few hundred lbs. in the back to smooth it out. While on the freeway I noticed what you guys are saying, it takes alot of peddle at 1700 RPM to go up a small incline in 6th, so I'll take all the good advice and a keep her 2000 or above. Thanks again, I'll sleep better knowing I'm not screwing something up.



Tom

 

[JyRO]

Fuel economy...

dvaughan -



I'm going to have to respectfully disagree with some of your reply.

Placement of maximum power has been changed on the 24 valve to encourage operation in the most fuel efficient engine speed range.

Its true that the best performance range can be tuned somewhat, but the primary reason for the most efficient rpm being located where it is, is due to the dynamics of 24V vs. 12V engine.

For on highway cruising and no load, maintain 2000-2200 rpm for best fuel economy.

I do agree with you that the engine is using fuel more efficiently at this rpm range. But that does not mean that you get the best fuel economy cruising at this rpm. Here's a basic example, these numbers are made up, but are relevant.



Let's say the engine is running at 2,200 rpm for a mile on level ground in 6th gear at 75 mph. During that mile, the engine consumes 210 milliliters (mL) of fuel. Of those 210 mL, 45% is used to drive the piston. The rest is wasted.



Let's say the same engine is running at 1,800 rpm for a mile on level ground in 6th gear at 65 mph. During that mile it consumes 172 mL of fuel. Of those 172 mL, 40% is used to drive the piston. The rest is wasted.



In this scenario, the engine was more fuel efficient at 2,200 rpm (45% versus 40%). But the fact is, it used more fuel at 2,200 rpm to go that mile than it did at 1,800 rpm ( 210 mL versus 172 mL).



Therefore it is more fuel economic to drive the slower speed.



- JyRO

 

[clem]

I don't think a 22ft TT will load your truck enough to worry about EGT unless you try to tow at 70mph in a big head wind. You have a strong engine. Not a FORD!