My car was first warmed up nicly and I drove it for like an hour. Then suddenly the Water temp gradually dropped below C then go back up to middle . It happed twice that night......... So I wonder what happen. This has never happened to me before.

 

your gauge is junk most likely, old stock gauges arent known for being very accurate

 

hmmm so what should I do?

get another gauges??

 

Check the connection at the housing. It is a single wire. Most likely the culprit. Over time the wire covering gets hard & brittle with the vibrations it can break or become loose. Pretty common problem on any older car.
I just had the same prob on my 240. Just driving down the street it started. Seemed like every time I accelerated the temps went up, when I stopped the gauge dropped. Driving steady it would stabilize. I knew right away it was the wiring. Popped the hood & sure enough the wire was hanging on by a single strand of wire. New connector & all is well. Funny thing is that it happened as soon as I bought my water temp gauge. So I hooked up my new temp gauge & fixed the stock gauge.

 

i c. Thanks alot

 

i'm thinking it's the temp sensor, the single wire one. that one is for the gauge, the other is for the a/c fan.

 

so when you say the wire. Do you mean the wire on the coolent temp sensor? or the wire on the gauge?

 

coolant temp sensor

 

yes by single wire i'm referring to the temp sensor with a spade connector. there are two temp sensors right next to each other. the one with a spade connector (single wire) is the one for the temp gauge. that sensor is most likely bad. i don't believe you have a problem with the wire to it or the gauge but rather your temp sensor is bad.

that is not to say that the other things mentioned are not likely causes, but based on what you've said i believe it's just a bad temp sensor.

 

hmmm... also note that my car has rough and low warm idle, too. Could the bad water temp sensor cause this problem as well?

 

sorry you're allowed only one question per thread.



ok not really but no, the sensor (sending unit) only gives a reading for the gauge to display.