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What is this sensor?

spetch

Full Member
Joined
Jan 11, 2004
Messages
1,140
Location
Gainesville, VA
While changing my spark plugs, I found that a little plug was disconnected and hanging free.  It plugs into the bottom of the coolant reservoir, and the wires trace back into the MAF sensor wiring harness.  I plugged it back in.  Anybody know what this sensor is?  Is a coolant level sensor?  Temperature sensor?

Anyway, I've been trying to find the cause of a sudden poor gas mileage issue.  I have a 2004 4x4 5.3L.  I'm getting 10 mpg, where I was getting 14.  It happened after I did an engine flush, dropped the pan, and removed a bunch of sludge from the bottom.  The sludge was from an old coolant leak due to a cracked head.  There is no CEL, and the fuel trims look okay based on watching them on my Bluetooth OBD2 scanner.  I changed the oil and filter twice since then, replaced the spark plugs with new Iridium ones, changed Bank 1 and Bank 2 O2 sensors #1 (upstream), cleaned and oiled my Spectre conical air filter, and cleaned the MAF with MAF cleaner.  I wonder if this little coolant sensor was important to the fuel mixture calculations.
 
It looks like a coolant level switch.
 
Has absolutely no effect on gas mileage.

Drop in mileage may well be due to engine damage caused by coolant getting into oil, although it could be something else much less dire...
 
enoniam said:
Has absolutely no effect on gas mileage.

Drop in mileage may well be due to engine damage caused by coolant getting into oil, although it could be something else much less dire...

Thanks. The coolant in oil problem happened due to a cracked head at 36k miles. Now I'm at 178k miles, and this poor fuel economy just happened all of a sudden, so I tend to think its unrelated. It did happen right after I used engine flush and dropped the oil pan. Do you think engine flush could have washed away gunk that was providing good sealing around the rings?

The DIC reports average fuel economy around 13, but I'm really getting about about 9-10 mpg based on calculation from miles and gallons used to fill back up. The DIC must be making incorrect estimates of fuel used.

Only other thing I can think to do is use some injector cleaner.  If that doesn't work, I'll do a compression test to see if my engine is just worn out.  Any other advice?
 
What type of engine flush?  Oil or fuel additive?  Seafoam or something else into a vacuum port?  Coolant flush?  Need some more info.
 
enoniam said:
What type of engine flush?  Oil or fuel additive?  Seafoam or something else into a vacuum port?  Coolant flush?  Need some more info.
I used Motor Medic Motor Flush by Gunk. I poured the quart bottle into the oil and ran the car for 10 minutes according to the instructions. Then I drained the oil and dropped the pan. There was a lot of old stuck on crud at the pan bottom.

I have never used seafoam or other intake cleaner. I used a bottle of fuel system treatment (don't remember which) in the gas tank about 30k miles ago. Coolant was flushed and replaced with the water pump about 30k miles ago. All levels are good. No CEL or stored codes.
 
This is my oil pan right after I dropped it.  I got all the hard gunk off the bottom.  Also cleaned the uptake oil screen.
This is the bottom of the engine now.  I didn't think it was all that bad.  Opinions?
 

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Only thing coming to my mind that your flush might have done is get some gunk into a lifter(s) and/or oil passages to lifters preventing one or more of them from pumping up and hence not opening a valve(s) fully.
 
enoniam said:
Only thing coming to my mind that your flush might have done is get some gunk into a lifter(s) and/or oil passages to lifters preventing one or more of them from pumping up and hence not opening a valve(s) fully.

I've had one noisy lifter for a long time that sometimes bleeds down overnight and takes a minute or so to pump back up.  I just put in the first full tank of gas after doing all this maintenance, and my ride to work and back reported 15 mpg on the DIC.  I never trust that, but it's higher than it has been reporting.  Maybe things are better.  We'll see after I've gone through a full tank.
 
I used that exact brand on a 70k mile engine from a junk yard on an install of an LT1 into my caprice... After 500 miles a rod started knocking... Was told it was possible the motor flush likely broke something free...

Ended up trading the motor in for about $100 on some parts and found out it spun a bearing...

So I am not so fond of doing a motor flush...

Rodney
 
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