Skip to main content ↑ ↓
Topic: Fuel consumption loss with cold engine (Read 709 times) previous topic - next topic

Fuel consumption loss with cold engine

My thermostat went out.  Looked down one day and noticed temp gauge much lower than normal. Selected Coolant Temp on the DIC and watched it on the return from New Mexico. Temps ran from 75 to 184.  Most of the time I was between 110 and 140.  I am just curious how much my fuel mileage dropped. Any guesses?  Coach is at Cummins getting thermostat changed.  I just didn't want to deal with the mess.
Steve DeLange
2005 U320T 40'
Pearland, Texas

Re: Fuel consumption loss with cold engine

Reply #1 –
Quote from: sedelange –
Coach is at Cummins getting thermostat changed.  I just didn't want to deal with the mess.

Steve,

If your Rotella ELC coolant hasn't been changed in the last 6 years, this would be a good time to do so...
Learn every day, but especially from the experiences of others. It's cheaper!  - John C. Bogle

2000 U320 36' non-slide / WildEBeest Rescue
2003 U320

Re: Fuel consumption loss with cold engine

Reply #2 –
How much your mpg dropped I couldn't guess.. I do know my trucks mpg drops in the winter season vs summer.. A cold engine just doesn't burn fuel as effecient.
Dub McBride 1996 270

Re: Fuel consumption loss with cold engine

Reply #3 –
Several reasons fuel economy is poorer in cold temperatures, even with the engine running at proper temperature:

Cold air is denser than warm air (something every airplane pilot knows).  Dense air means you have more aerodynamic drag to overcome.

Winter fuel (#2 diesel diluted with #1 diesel) has less BTU's per gallon than #2 diesel.

Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Fuel consumption loss with cold engine

Reply #4 –
Looks like I pick it up today. I will see if I notice much of a difference.
Steve DeLange
2005 U320T 40'
Pearland, Texas

Re: Fuel consumption loss with cold engine

Reply #5 –
Cummins found line coming from pressure side of pump,bypassing thermostat, going to radiator and returning to engine.  Probably been plumbed like that since new and the previous owner never noticed.
Steve DeLange
2005 U320T 40'
Pearland, Texas

Re: Fuel consumption loss with cold engine

Reply #6 –
Foretravel confirmed engine is plumbed wrong.  Sending missing parts.  Seems like these extra lines are to be plumbed into transmission cooler.
Steve DeLange
2005 U320T 40'
Pearland, Texas

Re: Fuel consumption loss with cold engine

Reply #7 –
Heck of a good catch! ... Can you post any pictures to help show where the lines are supposed to go or are they to buried to get a good shot?
2000 / 36' / U320 / WTFE
WildEBeest / "Striving to put right what once went wrong"

Re: Fuel consumption loss with cold engine

Reply #8 –
Parts from Foretravel arrived yesterday.  They were installed yesterday and finished this morning.  Engine now warms up sitting still.  They are out test driving now. I will post pics of the missing part/parts tomorrow.
Steve DeLange
2005 U320T 40'
Pearland, Texas

Re: Fuel consumption loss with cold engine

Reply #9 –
Picked up Rv and engine ran at a constant 182 degrees. I took pictures of the tube that was removed and the one that was installed. Note the new one has a 1" tee where the old one was straight.  It appears to me that the 1" hose is a bypass of the radiator that allows water pump to just circulate while warming up.  Instead it had been installed at at fitting on the aft end of the radiator, essentially bypassing the thermostat. The tee is installed at the forward end of the radiator just behind the tag axle.
Steve DeLange
2005 U320T 40'
Pearland, Texas