Help! Engine temp is on the fritz on my 94 Civic Dx!
 

Hello my good people. A few weeks ago, my engine temp was HOT! On my dash, it went up past the H. So, I bought some engine coolant. That didn't do the trick. Lucky for me, I was parked at a Pep Boys. For them to take a look at it was $50. No way Jose. So, I figured buying a thermostat would do the trick. Well, it did... Until today. So that's the back story; here's the problem. When I go to drive it, my engine temp on my dash will start out normal, go up, go down, then it will stay in the middle, then go up to H to the level it was at, then go back down. Would anyone know why this is happening? Thank you in advance! =)

Cluster may be needing replacement, or most likely the temp sensor sending the signal to the cluster is damaged.

Have you bled all of the air out of the system since replacing the Tstat? Your fans come on, correct? Do you overheat while sitting at idle, or only when driving?

Yeah, fans come on and AC works great. The more I look into it, and viewing your post, it looks like what I need is a ECT sensor

I assume the temp gauge remains consistent when sitting at idle? You have bled out all the air, correct? Any white smoke out of the exhaust on start up, and oil/coolant mixing?

Right now, I am thinking dead ECT sensor, bad water pump, or blown HG. Leaning towards one of the first two however.

When the engine is cold, open the radiator and make sure it is full. If not, find out where the coolant is leaking out.

The ECT sensor does not affect readings on the gauge. The temperature sender does. I suspect though that the engine really is getting hot.

I just solved the problem this morning. Turns out that when I installed the thermostat I broke my radiator cap, thus spilling out antifreeze from my radiator. It didn't occur to me that turning the cap an unlimited amount of times wasn't good. But it was a cheap fix so that's good. Thanks to everyone who responded!

Keep an eye on your radiator fluid level. Getting your motor that hot was a bad thing. You may have gotten really lucky and noting happened. Or you may have warped your head and blown the head gasket.