Running 80 mph down the highway with my T-stat sticking open, I'm only running about 140 degrees. Maybe more at idle, but not enough to register on the gauge.

Can this cause performance or efficiency problems? Cause some sort of bad extra wear on the engine? Just curious, thanks..

Taylor,
Are you sure the gauge isn't broken? By saying it doesn't register, does the needle not move at all? Did you ever use one of those laser temperature guns to shoot the intake or heads, or t stat housing at idle? It's hard to believe that an engine won't heat up to at least 160 or so. Unless you live in Alaska or somewhere really cold. I know that if an engine doesn't reach normal operating temperature, sludge forms in the valve covers, and oil pan, and possibly everywhere else. Also, gas mileage would be a little worse to. What kind of cooling system do you have? Well, I hope I helped in some way. Take care.

That's correct. There are a number of problems that occur when the engine is too cold. As suggested, check the gauge. Maybe try another stat.

Actually one reason I was asking is because my gas mileage all the sudden has gone down a lot it seems and a bit of lackluster performance, especially on the highway. It's not supposed to be a rocket by any means, but putting the pedal to the floor just makes more noise than anything. This could be another problem altogether though.

I haven't checked with a laser gun.

What I meant with 'doesn't register' is the needle doesn't move up a slash higher or anything at idle compared to driving/highway. The gauge seems okay and one reason I believe so is when the car is turned off, the temperature rises and gives me normal operating temperature, but doesn't give any odd ball readings, or go all the way to the right or anything. I just thought that was a sign of the stat sticking open and then when the pump was off with the engine the water sat without flow causing temperature to reach 'normal'. Also during driving it will start off below 100 and take a while for the water to warm up but it will start to creep up. I'm guessing it is getting to only 140, or maybe closer to 150. I haven't really gauged the 'slashes' yet to figure out what increments they are.

I've got a new t-stat, but we're not allowed to do any work on cars except check fluids on college campus, so I'll have to wait till labor day weekend or so. But, being curious, thought I'd ask.

Thanks guys.

I recall now I had a similar problem. The car took forever to warm up. But once warm the temps were normal. Changing stats solved it. Labor day isn't far off. I hope that fixes it.

Just curious here, but, what brand gauges are you using? I had a pair of Sunol (I believe that's the name) gauges and after about a year or so, maybe more, they stopped working. The temp gauge just didn't move anymore and my oil prssure gauge started reading lower and lower. I don't really recall if my temp gauge started giving me lower readings, I kinda just remember it just stopped working all of a sudden. I switched over to Autometer and about 4 years later, I haven't had any problems graemlins/thumbsup.gif .........and that's that I bought my oil pressure gauge used from my buddy who had it a couple years before I bought it off him :D

From what I've read, 180 degrees running temp is ideal for power and wear if the fuel octane is correct. If you run it colder the octane requirement decreases but wear increases. Running clearances when the engine is built are based on 180 degrees from what I hear. No expert for sure, just passing on the info I've read. Someone here once had a link to some testing done on this subject.