I replaced the temp sending unit and my gauge only reads 110-120 degrees tops.  I grounded out the gauge and it pegs out, so the gauge checks out.  I bought a new thermostat but I haven't replaced it yet.  I drove the car a couple of days ago and of course i couldn't tell the engine temp.  The upper hose was hot, hot, hot and steam was was coming from the radiator plus it was hissing.  Does anyone know where I might start..... I definiately don't want to drive a car that doesn't have a functioning temperature gauge

First, be sure you have the correct sender. Sounds like you're overheating regardless, the radiator shouldn't steam. The hose should be hot, but not so hot you can't put your hand on it for a few seconds. Start with the t-stat, I've started buying the "failsafe" type. Just a few more bucks. Some people drill a couple of small (1/8th) holes in the t stat also, it kind of helps get air out of the system, also, somebody help me with this cause I'm not totally sure, but I don't think the sender will give an accurate reading if it doesn't have coolant to it. Hot air won't read. Start there and let us know what you come up with.

Sounds like you should start with a new thermostat! The gauge will not read steam or an air pocket. I hope you don't have a bad headgasket.

Denny

Don't assume a new sending unit is good!  I tried 2 new ones before I got one to work. A resistance reading can be checked with an ohm meter.  You would have to get those values from the manufacturer.  I  agree with those above, you need to tackle the overheating issue first.  A t-stat that does not open will cause overheating. Replacing it may solve your over heating problem. Hissing is not a good sign ! The age of your radiator could be a factor.  As they age, deposits build up that limit the radiator's ability to do its job.  Is your fan clutch operating properly?  When the engine is hot and you turn it off, there should be considerable resistance when you rotate the fan by hand.   Just a few thoughts!!

Good Luck,

Mel

Ditto for me!!
Change the t/stat, and either get one with a "bypass/bleed" hole, or drill it yourself. It will allow the air in the engine to purge itself, and you'll get a full coolant system easier.

Dave & xfire are correct. The sender unit will NOT give an accurate reading if there is no liquid on it. If you have a system that is low on coolant, the gauge will usually fluctuate, hot to cold, pretty quickly, depending on how low the coolant level is.

Also, be aware that a lot of "new"(replacement) sender units are not calibrated to work on every vehicle. There are differences in the calibrations of the gauges, in respect to the sending units. I have found the Paragon Reproductions units to be the most trusty, but I'm sure there are others.

You may need to have the temp read with an infrared temp. reader, or install a mechanical gauge temporarily, to find the real temp.
Then, you can install a resistor in the wire for the gauge, to compensate for the calibration offset.
But first, get the overheat problem fixed!!
Change the 'stat, make sure the system is full, and go from there.

THANKS FOR THE INPUT GUYS. WILL CHANGE OUT THE T-STAT. I DON'T NEED TO DRAIN THE SYSTEM DO I???

You'll need to remove some coolant, but just enough to lower the level to below the t/stat. Usually, only a gallon, or so. If the level in the rad. is down about 6"-8", you should be good to go. You don't have to drain it at all, but it does make it a lot less messy! Adams' Apple38658.2485763889

It might not be a bad idea to go ahead and flush the system while you're doing the t stat. Fresh anti freeze and some water wetter.

My question is did you have all this steaming and hissing before you replaced the temp. sender? When ever you drop the coolant level for any reason make sure you purge all the air out of the system before capping it. You can just run motor with cap off until stat opens, then top it off. I agree with Adam on the infared thermometer. Take a reading right at the sender and see if its close to the guage reading. But only when the system is full. Terry

Where do I drill the bleed hole on the t-stat????