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Poor Gas Milage

T

The Lure Washer

NAXJA Forum User
Location
Bristol, CT
My gas milage suffers. I get maybe 8-10 mpg. Im running pretty stock set up with only exception being 30x9.5x15 tires. All the sensors are pretty much new as well. That being said my temp gauge does flucuate from about 195 down to 150 and then it starts the climb back to 195. Im almost positive there is no air in the cooling system. Ive burped it from the temp sensor at the back of the block and all I get is coolant out of there. So what gives? Is there an easy way to check if its going into closed loop mode? Cause thats my only thought on why Im getting poor MPG.
 
Replace the thermostat, get one from the dealer or an aftermarket one that has the weep hole in the flange, weep hole goes at the 12 O'clock position. Cheap and easy.
 
Either your gauge is inaccurate or your thermostat is bunk.

A 195 degree thermostat will keep your engine running higher than 150 degrees, as it is supposed to open at 195 and close at temps under that.

So, did you check the temp marking on the thermostat or did you trust the box it was in?

Don't know what year/engine you have.

Fan clutch usually fails and doesn't cool, but perhaps yours has locked up and is cooling too much.

Electric fan? Is it staying on constant?

Check, test, confirm.
 
I was wondering about the clutch fan. How do I tell if its locked up? Its definately a 195 thermo stat. I always check them. Its a 1990 I6 4.0. The aux fan is never on.
 
Fan clutch, engine cold (and off!), should turn with a slight resistance. If the fan has heavy resistance the clutch may be locking up on you, causing the fan to pull air when it should be just idling along. This would also cause the engine to be cooler than normal. The fan clutch really should only be engaging when the engine is hot, in town and idle.

When cold it shouldn't be doing much, and at highway speeds the airflow through the radiator pretty much does all the cooling.
 
Non-thermal fan clutches operate strictly on RPM and are pretty much worthless at idle/low speeds.

I would never use a non-thermal clutch unless it was absolutely required for a warranty, and maybe not even then.

Look for the little coiled bi-metal spring on the face of the thermal fan clutch.
 
Not always true, the factory fan clutches use hydraulic fluid and no little spring in front of them. In my experience the fan will roar on a cold startup then quiet down after about 30 seconds, this is the fluid being redistributed after sitting over night.
 
i just swapped over to full synthetic and gained 3+ mpg... i didnt get an accurate check cuz i drove in the snow with alot of hills and was in the throttle a few times.

i have a 00 4.0 with 108k automatic and 235/75 mt's (same thing as 30x9.5's) and i just got 17mpg with stock gears.
 
The Lure Washer said:
My gas milage suffers. I get maybe 8-10 mpg. Im running pretty stock set up with only exception being 30x9.5x15 tires. All the sensors are pretty much new as well. That being said my temp gauge does flucuate from about 195 down to 150 and then it starts the climb back to 195. Im almost positive there is no air in the cooling system. Ive burped it from the temp sensor at the back of the block and all I get is coolant out of there. So what gives? Is there an easy way to check if its going into closed loop mode? Cause thats my only thought on why Im getting poor MPG.
Click to expand...

Replace the temp sensor.
 
if its going up and down etc... that means your thermostat is getting stuck wide open... then unsticks and warms back up basically... its either a sticking thermostat or its a faulty guage or the wire's grounding out or something else electrical i'd trace that and make sure its all ok. if its not the problem... your out what 5 bucks for another thermostat?
 
MaxxXJ said:
i just swapped over to full synthetic and gained 3+ mpg... i didnt get an accurate check cuz i drove in the snow with alot of hills and was in the throttle a few times.

i have a 00 4.0 with 108k automatic and 235/75 mt's (same thing as 30x9.5's) and i just got 17mpg with stock gears.
Click to expand...


They are actually about an inch smaller and narrower than 30's.


My temp gauge won't read sometimes is that a sign that my temp sensor my be going bad.
 
FlexdXJ said:
They are actually about an inch smaller and narrower than 30's.
Click to expand...

well every tire companys different but the bfg a/t ko's have a section width of .3" and overall height difference is only .5 inches... so in my opinion a 1/2" isnt enough to really decide the difference between the 2

and if you do the math 235/ 25.4 it = 9.25... so 235's are only 1/4" difference between 9.5's

at any rate, i'll stick to my 235's long before i pay more for a set of 30x9.5's. when everyone else gets stuck with their wider tire's i get to smile real big when i drive around them and pull them out (all i got is a rear recovery point for now)
 
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