At what temp does fuel mileage actually really suffer from running too cool?
#1
Member
Thread Starter
Join Date: Jan 2012
Location: North Salt Lake Utah
Posts: 188
Likes: 0
Received 1 Like
on
1 Post
Year: 1994
Model: Cherokee
Engine: 4.0
At what temp does fuel mileage actually really suffer from running too cool?
Mine runs on the first quater mark of the guage. Solid. After replacing the thermostat.
I put a 180 in it, but from feeling the air when as hot as it gets, it's on the cool sid of hot.
94 4.0 stock motor and electronics.
I put a 180 in it, but from feeling the air when as hot as it gets, it's on the cool sid of hot.
94 4.0 stock motor and electronics.
#4
Member
Thread Starter
Join Date: Jan 2012
Location: North Salt Lake Utah
Posts: 188
Likes: 0
Received 1 Like
on
1 Post
Year: 1994
Model: Cherokee
Engine: 4.0
Because its 200k+ and runs hot while wheeling. I dont need to hear rookie remarks about "meant to run at 210" or higher lol if thats what anyone wants to say. I just need to know when or if the 4.0 obd1 system will run substatialy richer or not and at what temps. Any engine tuners here that know the fuel maps?
Gotta do the radiator anyhow, so the water pump is getting done too. My system flows freely. Nothing is plugged up. Bht the freeze here did in my 250k radiator. I suspect a slightly worn pump impeller too.
Gotta do the radiator anyhow, so the water pump is getting done too. My system flows freely. Nothing is plugged up. Bht the freeze here did in my 250k radiator. I suspect a slightly worn pump impeller too.
Last edited by SiRed91; 12-01-2015 at 02:10 PM.
#5
The engineers who designed the vehicle, designed it to run at 195 degrees. This was done to ensure the engine emissions systems operate effectively, the oil gets hot enough to 'burn off' unwanted contaminates(moisture and any unburnt fuel that may wash past the rings) and adequate heat is available for the cabin. In my experience (20+ years of owning and working on Jeeps) the emission equipped Jeeps, they tend to run much better and get slightly better mileage with a 195 degree thermostat. The computer doesn't even go into open loop (using the sensors to monitor and modify operating parameters) until the engine gets to operating temperature (in this case 195 degrees), it will stay in closed loop and operate off of its preprogrammed parameters (usually a very rich fuel mixture and a very conservative timing setting).
Now I'm sure there are many different opinions and someone out there will swear that I'm a complete idiot, but as an engineer and a former auto tech that's just my humble opinion.
Now I'm sure there are many different opinions and someone out there will swear that I'm a complete idiot, but as an engineer and a former auto tech that's just my humble opinion.
#6
Member
Join Date: Sep 2015
Location: fountain hills az
Posts: 149
Likes: 0
Received 1 Like
on
1 Post
Year: 1999
Engine: 4.0l 310,000 miles
shadowman you are right on the money. It is not a "rookie remark" to say that is how the system was designed. That is how it works,some folks just don't want to understand and accept it. The computer thinks the engine is still in warm up mode. so the answer to the question is that any temperature below full warm up will cause suffering gas mileage.
#7
Member
Join Date: Jul 2015
Location: Nashville, TN
Posts: 134
Likes: 0
Received 0 Likes
on
0 Posts
Year: 94
Model: Cherokee
Engine: 4.0L
Sorry to interupt the thread but then what should I do?
I'm always on the first mark as well, but I have a 195 thermostate and my heats always hot hot hot. If it's an issue to run that cool that worries me because mines never even touched the 190 mark.
I'm always on the first mark as well, but I have a 195 thermostate and my heats always hot hot hot. If it's an issue to run that cool that worries me because mines never even touched the 190 mark.
Trending Topics
#9
Seasoned Member
Join Date: Apr 2015
Location: Denver, Colorado
Posts: 375
Likes: 0
Received 2 Likes
on
2 Posts
Year: 2000
Model: Cherokee
Engine: 4.0
If you're running hot while wheeling there's a problem with the cooling system. What do you mean hot, what temp?The computer wants the temp to be 195 and will keep it rich until it gets above that. No way around that. Don't ask for help then say our help is wrong because it's "rookie". 210 is the highest it should ever get with a properly maintained cooling system.
#10
CF Veteran
Join Date: Oct 2013
Location: Denver
Posts: 1,589
Likes: 0
Received 1 Like
on
1 Post
Year: 99
Model: Cherokee
Engine: 4.0
I believe the motor goes out of their fuel-rich loop @ 90F or so. I remember a thread a year or two where someone ran their scanner tool along side the temp gauge. Lower engine temps will cause other issues but its not in "warm up mode" AFAIK. Anyone care to corroborate? I thought it was CCKen or someone else with the know how.
Do still believe a 180F will end up with some smaller longer term issues due to the engine not running at its full temp.
Do still believe a 180F will end up with some smaller longer term issues due to the engine not running at its full temp.
#11
CF Veteran
Join Date: Jan 2015
Location: Oregon Coast
Posts: 1,508
Likes: 0
Received 4 Likes
on
4 Posts
Year: 1999
Model: Cherokee
Engine: 4.0L I6
If you're running hot while wheeling there's a problem with the cooling system. What do you mean hot, what temp?The computer wants the temp to be 195 and will keep it rich until it gets above that. No way around that. Don't ask for help then say our help is wrong because it's "rookie". 210 is the highest it should ever get with a properly maintained cooling system.
#12
Seasoned Member
Join Date: Apr 2015
Location: Denver, Colorado
Posts: 375
Likes: 0
Received 2 Likes
on
2 Posts
Year: 2000
Model: Cherokee
Engine: 4.0
If you use a more accurate gauge than the dash gauge it actually fluctuates a lot and a bit higher than that. Mine will do swings between 210 and 215 all day down the highway having its upswings going up hills. When you push it hard the coolant will go higher. The electric fan turns on at 217. Mind you during all of this the gauge hasn't moved a wiggle. By the time the gauge moves the engine is closer to 220-225.
#14
Senior Member
Join Date: Mar 2012
Location: Racine, WI
Posts: 974
Likes: 0
Received 8 Likes
on
7 Posts
Year: 1997
Model: Cherokee
Engine: 4.0
Fine, you don't want to run so hot. The thing is: a 180 deg stat won't change that. Those of us with 195 degree stats are not running at 195 degrees, are we? Nope, our engines level off at 200-210, and with a 180 deg stat, yours still will, too.
The thermostat merely sets the minimum running temperature of an engine. That's it. It's the cooling system that sets the maximum temp of the engine, and assuming your water pump and radiator are in proper condition, it's specifically the fan clutch (or switch if you have an electric fan) that sets the maximum temp of the engine.
If you do force your engine to run cooler, your computer may never move out of its preset closed loop settings because it never reaches a temp required to do so. Your fuel efficiency may suffer. Your spark plugs may foul. Carbon deposits may increase. Moisture bits that accumulate every night from condensation in your oil won't burn/boil off as quickly. Your oil itself won't be hot enough to be performing optimally.
The thermostat merely sets the minimum running temperature of an engine. That's it. It's the cooling system that sets the maximum temp of the engine, and assuming your water pump and radiator are in proper condition, it's specifically the fan clutch (or switch if you have an electric fan) that sets the maximum temp of the engine.
If you do force your engine to run cooler, your computer may never move out of its preset closed loop settings because it never reaches a temp required to do so. Your fuel efficiency may suffer. Your spark plugs may foul. Carbon deposits may increase. Moisture bits that accumulate every night from condensation in your oil won't burn/boil off as quickly. Your oil itself won't be hot enough to be performing optimally.
#15
^^^Very well said! As many have stated the dash gauge can be horribly inaccurate. My '92 is at operating temp (verified with an infrared temp gun) when the gauge has just passed the first quarter of its sweep while my '99 is at operating temp (again verified by infrared) just past the middle of the gauge. I usually do not worry about the temp until the electric fan kicks on, then it's time to back off a little. As others have stated, as long as the cooling system is in good shape (it must be maintained just like the other systems of your Jeep) you should not have any problems. If it has been a while since it was serviced, no time like the present! A little quality time on maintenance now will save you a lot of heartache (and money) later.