Thermostat Problems

Hey,
I put a new 195 degree thermostat in my '93 XJ. Now my temp gauge is fluctuating - when it gets up to running temp (about 200+-5) it will fall roughly 40 degrees - it takes about 15-20 seconds to get back up to running temp and falls again about 2-3 seconds. When its cold, the temp will fall even lower maybe 50-60 degrees. I noticed this fluctuation almost immediately after I changed it - So, I put another one in. It does the exact same thing.
I also have a small leak in my radiator - however, I don't think that has any thing to do with my temp.
I am open to any ideas.

Please Help!!

Thanks

Did you put in in the correct way? The side with the spring goes into the head.

Hey,
I put a new 195 degree thermostat in my '93 XJ. Now my temp gauge is fluctuating - when it gets up to running temp (about 200+-5) it will fall roughly 40 degrees - it takes about 15-20 seconds to get back up to running temp and falls again about 2-3 seconds. When its cold, the temp will fall even lower maybe 50-60 degrees. I noticed this fluctuation almost immediately after I changed it - So, I put another one in. It does the exact same thing.
I also have a small leak in my radiator - however, I don't think that has any thing to do with my temp.
I am open to any ideas.

Please Help!!

Thanks

What you are seeing is the thermostat cycling open and closed. The temperature changes are exagerated when its really cold out. What happens is the thermostat is closed until it reaches opening temp of 195, then it will open suddenly allow a rush of cold (COLD) coolant thats been sitting in the radiator into the engine and across the temp sensor and thermostat. When the temp drops through the thermostat, it will cycle closed again.
The 50 degrees you speak of does seem excessive, its probably no more than 20-30 degree difference you are actually seeing.
Some thermostats open and close faster than others. It seems some slam shut, especially when new, while others just sorta slowly fluctuate. Give it some time, I'll bet it settles down after a hundred miles of so.

I used to watch that happen every morning on my way to work in the winter. I would notice about 3 temp drops before it stabilized. The first one was the largest drop, as the rush of cold sub-zero coolant enters the engine, and then the 2nd and 3rd temp drop were of less magnitude as the coolant temp levelled out. Completely normal I'd say.

My temperature never cycles down as it's warming up, except when I switch the heater on. Then I will see a drop on the gauge as the cold coolant from the heater core enters the rest of the system. As posted above, not all thermostat units are the same. If you put one into a pot of water on the stove you can watch it open as the water heats up. When I did this I watched mine open slowly. You could even use a cooking thermometer to confirm opening temperature.

Once, after installing a new thermostat, my car kept overheating. When I removed this thermostat and did the above stove top test, I found that it would not open more than a very small amount even at full boil. After buying, testing and installing another new unit the problem was cured and everything worked fine.

Thanks for all the replies.

I am now seeing a rise in temperature when I come to a stop; about 20-40 degree over running temp.
Should I look at buying a different brand (manufacturer) thermostat? If so, what brand should I buy?

Thanks

I just replaced the thermostat, coolant temp sensor, temp switch sending unit, water pump, upper and lower radiator hose, heater bypass hose, and engine block freeze plug on my 92 xj inline 6 and it does the same thing that your's is doing. Give it time and drive it some just keep an eye on the temp gauge to make sure it doesn't redline overheating and it will eventually even itself out once the thermostat has broken in real good. Almost every car I've had and changed the stat in did the same thing for about the first week or so and then equaled out.