99redclassic

So it's starting to get cooler here in Wisconsin. Temps are in the 40-50s in the mornings and on my drive to school, the temp gauge on the dash never gets above the first line after 100. Anybody else experience this, or is that abnormal? It runs just fine, no problems at all that I know of, but I don't know much about these types of things. It also ran a little cool in the summer I thought. Even in 90 degree weather it never rose above the second line unless I was stuck at a red light with the AC cranked up. Any ideas?

djb383

That's too cool/abnormal. T-stat is missing, stuck open, bad gauge/sensor or combo. Factory t-stat is 195F with a 180F available.

99redclassic

I like that picture. Since it has been cooler it hasn't gone over 127.5

djb383

I suspect u at least have a gauge/sensor problem.

99redclassic

Ok thanks for the input. I'm heading home this weekend so my dad and I will try to check it out. Probably a dumb question but will this hurt the engine if I let it be for a while, or does it need to be fixed as soon as I can?

djb383

No, and it does need to be corrected as soon as convenient.

99redclassic

Thanks you've been a big help!

99redclassic

So I drove back from home to school this morning (~100 miles) and it seemed like I went through gas really fast. It was frosty on the ground, temp was in the 30's and the gauge barely got over 100. Could that cause a decrease in fuel mileage or is that just the temperature doing that?

dukie564

yes it could. If it is reading that the engine is much colder then it actually is, it will run rich (similar to when you start up on a cold morning) the entire time, burning much more gas.

Sounds like you have more than a gauge problem. You need a new coolant temperature sensor by the sound of things.

99redclassic

Yes I'm going to get the whole thing looked at. I don't know anything about it so hopefully I can take it to someone who does, unless there is a cheap and easy way to fix it?

alpine.adrenaline

Well, not fixing it is going to decrease your gas mileage and therefore up your monthly gas expense. So fixing it would be the cheap way to go. Test your coolant temperature sensor by removing it and using an ohmmeter, clean it a little in the process. Nonetheless, I'd bet your thermostat is stuck open (pretty common) so your engine doesn't get a chance to heat the coolant well enough before cycling it. Your ECU is providing a rich mixture because it's staying in an open loop mode. This is used primarily when you first start the engine to get it up to an ideal operating temp of 210°. It uses more fuel to compensate for the lower temperatures of your intake manifold.

Those thermostats only run 8-15 bones at most auto stores.

99redclassic

Where is the temperature sensor located so I can look at it? I don't really know a whole lot about cars/engines, but I'd really like to learn and I've heard that XJs are quite easy to learn on. So any advice on how to check it out?

djb383

It's a '99 OBD-II XJ, it enters "closed loop" within seconds of starting up cold, presuming no CEL.

djb383

http://motors.shop.ebay.com/__?_from...+manual&_sacat=

Some of the best/cheapest text books you'll ever find/read. Ask the folks, bet they'll spendy for ya. Easily get your money back. The kiddo and I did a major a/c overhaul this past June using the FSM. Saved $1000 vs having a shop do it.