For some reason my '93 90CS won't warm up past the 1/4 mark...I've driven it for up to an hour at a time, but absolutely nothing higher. I just changed my filters and got an oil change, so I don't think that is the problem. Any ideas?

 

Sounds like a thermostat.

 

temp sensor or the fan is running too much ... bad thermostat or a bad water pump would command overheating

 

I have the same problem. Actually, sometimes it shows right temperature and sometimes subzero. For example, I start engine which is cold of course. Then after a while it shows that is still cold though it is obviously warm. Then I drive and in the middle of that, it rises and shows the right temp. Then I stop forcouple of minutes and turn off the engine,and start it again and it shows subzero again. It must be something about wire connections. Or, maybe even the gaugeworks occasionally. Anyway, method of elimination should be conducted.

 

you need to check the thermostat, when you belive that the engine is hot, check the upper and lower hose for heat. The upper should be higher that the lower. the lower should be hot too.

if it is, then probably the sender is bad, or the sensor for the heat.