Bad T-Stat?

1994 Jeep Cherokee Sport. 4.0I6HO 29.5" A/T 0" Lift 139,8XX Miles

Ever since I got my Xj, my gas mileage has dropped, it's now getting around 6-8mpg. For the longest time, I thought this was normal,being a 15 year old machine, until I started talking to my buddies with Xjs, who told me it was far from it. One of them suggested I replace the O2 sensor, which I did and saw no improvement. Changed my oil about a month ago and the other day went to check all of my fluids; found the usual. Low power steering fluid and windshield washer fluid. What wasn't normal was that I was 2 quarts low on oil. I promptly filled it and checked it yesterday and was about a half quart low again. Filled it up and left for work this morning. It was a nice day, 65 and sunny. During the 25 mile drive to todays job sight, I noticed my Jeep no longer gets up to temperature. I stayed below the 110(I think that's what it is) line the entire time. I turned the heat on during the ride to see if it was working and it was pushing out some real nice heat. I thought, "Hmm, maybe the thermostat is stuck open? That would definitely explain the horrid gas mileage and burning oil." Then I started to think, if the thermostat was stuck open, then I would constantly have coolant flowing and the engine would cool down, which should also kill most of my heat. I also remembered, that in the 3 years i've owned the Jeep, i've only put coolant in it once, and it hasn't budged since. I am at a loss right now with this Jeep, I don't know what to do. I'm not a mechanic, just a do-it-yourselfer with a chiltons, a father that used to be a mechanic on the side, and friends who know their fair share about vehicles. Hopefully somebody here can better inform me of what the problem might be. I'm hoping it's the T-stat; that's a $9 part and a $0.99 gasket.

If it isn't getting up to temp it is most likely your thermostat. If the gauge is reading I doubt the gauge sender is to blame. The gauge sender cracks or seperates you will get an incorrect "off of the scale" temperature reading.

110 is really low. If the therm wasn't opening you wouldn't have much heat. I would check the temp sending unit. You could ground out the wire going to the sending unit and see if the gauge spikes as well. If the thermostat hadn't been opening for a while then yes your mileage would suffer because the computer would not pull timing and such(closed loop as opposed to open loop).

Probably the tstat. I'd put in the Stant Premium model myself. 45359 part number is what you want. It's $5 at Rock Auto. Pretty expensive because it's twice the price of the standard one ($1.76). Why not go for broke?

http://www.stant.com/common/printthi...global=St ant

http://www.stant.com/common/part_loc...=LOCATOR_STANT

Change the t-stat, make sure it has a small hole in it, sometimes with a brass toggle rattling in it. It goes at twelve oclock to burp air out of the system.

Check to see if the clutch for the mechanical fan hasn't siezed up tight. If you don't have a working mechanical fan clutch it will cool too much and really drag mileage down. It's the finned aluminum rotor the fan bolts to. It should be loose when cool, and stiff when warm. (Check with the engine off . . .)

Otherwise the mileage loss could be from using 4LO all the time.

winterbeater said:

Probably the tstat. I'd put in the Stant Premium model myself. 45359 part number is what you want. It's $5 at Rock Auto. Pretty expensive because it's twice the price of the standard one ($1.76). Why not go for broke?

http://www.stant.com/common/printthi...global=St ant

http://www.stant.com/common/part_loc...=LOCATOR_STANT

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I've never seen a Rock Auto in my area, but Autozone is very common. Plus, they know me by name:wave1: (Damn Jeep...). I will be buying a Duralast unit. What temp should I get?

What do you guys think about these? I'm all for high performance parts. Especially with the way I drive! =P

http://www.autozone.com/autozone/ca...ryDisplayName=&parentId=cat10018&questions=[]

195 degree tstat. Rock Auto is mail order internet. Mr. Gasket doesn't make thermostats, neither does MOPAR. They buy them from the cheapest source they can find. Tstats are a sideline for them. Obviously any of them SHOULD work.

I wouldn't use AutoZone. I got a "lemon" thermostat from them once that didn't give me any hot heat. I am talking about Duralast or Valucraft brand. I did not know AutoZone sold MrGasket. I have heard others with good results from MrGasket!

Plus they are cheaply constructed.

You are much better going to Advance Auto and buying a Stant thermostat or going to the dealership and getting and oem thermostat. Much better quality over AutoZone!

However I was thinking that since he was getting any reading on his temperature gauge at all and especially if it moved up from the left the gauge sender would most likely be ok. However if the gauge doesn't move at all it IS likely that the sender is at fault! Even without a thermostat or a fully stuck open thermostat the temperature would gain a little bit at the very least.

I drove it again today and got a good look at what it is doing. The T-stat is sticking some times, and others it is fine. Went for a drive, it got up to temp and dropped to 1/8" above the 100 degree mark. Went for another drive and it stayed in between the 210 and 100 degree mark the entire time. Went for a drive later after it cooled down outside and it stayed at the 1/8" above 100 degree mark the entire time, not even getting up to temp. I also went from a half tank to below a quarter today -.-

So what is the deal with these Mr Gaskets? Why are they "race only"?

Race only might be low temperature. It is a common method of tricking the computer to let the mixture be extra rich which can allow retuning for more power. It doesn't do any good unless you are running nitros or boost. Just wacks out your stock motor.

It says its a 195 degree thermometer. That's what's confusing me. If it's 195, then what declares it a "race only" thermometer?

X9x A T I x7X said:

It says its a 195 degree thermometer. That's what's confusing me. If it's 195, then what declares it a "race only" thermometer?

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They are probably claiming higher flow through it.

Be sure and check your accessories--power steering pump, water pump, idler pulley, alternator. When one of these starts to fail the bearings will put quite a load on the engine. Do a search on JP Magazine website. They were testing the mileage on an XJ to see what mods made things better, and what mods made things worse.

I already know my idler pulley and PS pump are going. The idler pulley has been replaced multiple times and the bearings start to go in about 2 weeks after installing the new one, so I am not replacing it anymore until it breaks again. And my PS pump i'm not going to replace until it dies, simply because I do not have the funds. I am in the process of moving and am out of a job, so I have no better choice.

Check your cylinder compression before you spend more money.

winterbeater said:

Check your cylinder compression before you spend more money.

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I do not have a compression tester.

At Murray's, you get to use it for free.........buy and bring back for refund. Autozone has rental. If your rings and valves won't hold compression, you're wasting money on the other stuff. If compression is good, it's worth repairing.

All the temps quote by most of us are because we fully trust the temp sender on the side of the block.

I had a customer in last night with a 87, had a "cold" thermostat that wouldn't warm up the motor. He stuck a thermometer in the radiator tank and measured 195* coming inot the rad. Don't know how he did that, but nonetheless, Hmmm. He changed the temp sender and voila, the low temp problem was fixed.

Make sure you're trusting a trustworthy gauge reading.