I have a replacement motor in my 96 SSEi and the engine run good but ive notice now the temp is going from 200 to 170 then back up to 200 the whole time im driving. I replaced the thermostat and the coolant level is full, Im not sure what to look for next..... Before the motor change the temp held steady at 200. I hope someone can point me in the right direction....

It'* not a problem. Tells me the thermostat is opening and closing right. A stock thermostat is 195*

The temp does the same thing with a 180* and a 195* thermostats. My concern is the fact that it held steady before the engine change and as ive searched this forum ive read that the PCM is looking for a certain temp. Im wondering about the emissions, fuel economy, ETC...

If your using a different temp sensor, that may explain it. If you have a 195*, then the stock set points will be fine. Even with a 180*, the set points are close. The fans are only needed when car is not moving. Does the temp do this when driving as well?

Yes the temp does that will driving, i havent let the car idle long enough to see if the fans turn on on there own but they do turn on when i turn the A/C on.

I find this an interesting problem.

The radiator itself is full.
The thermostat is in place with the wax cartridge toward the engine.
The thermostat housing has been bled of air.
The thermostat is inserted into the groove in the middle cut of the rubber gasket.

Yes to all of that. I even flushed out the heater core. Im kinda leaning towards the engine temp sensor at this point.

Sounds like air in the system (bleed it some more), a defective thermostat, an incorrect thermostat (what temp did you install?) or a bad temp sensor.

That does sound like it still needs a burp. Some air can stay trapped indefinitely, up in the stat housing.

My SE tends to nail the temperature and sticks. My SSEi and SSE both tended to do what you are talking about. But it had to do with the 180* stats. (both have the same sensor and dash gage, too FWIW). But after they got where they were warmed up for a while (10 min or so), they would peg at 185 or so. (I put my scanner on the temp, because the dash gage has proved to be a little wiggly.)

I stopped it dead in its tracks, but this is kinda' a last resort thing if the moving really bothers ya.

I tend to do things to the cars just "because". One day on a shopping visit to the yard, I happened on 2 aftermarket radiators which were the 3800 radiator frame size. "Cept they were near new, and had 1-1/4 inch aluminum cores. (Yeah, I know it'* probably cheap Chinese fab. But more and newer aluminum is cooler. Just don't monster torque them in, and don't strain the trans lines connections.)

Long story short. The thermal fidgeting stopped. It warms up, the stat opens, and the gage goes and sits in one place. My trans oil runs cooler during familiar conditions, too. i left the trans-cooler off of the SSEi.

Oh also i seem to have intermitent heat. Sometimes it works and sometimes it dont.