95 Wrangler, 4 cyl, 5 spd.

Knocked a hole in the radiator, so I just put in a new OEM radiator and hoses. Also, flushed out the coolant and replaced.

Before this, the temp gauge showed a steady 195-200 once she warmed up. Now, temp keeps going up to about 215, then drops to about 190, over and over. I assume the thermosat is opening and shutting repeatedly (I know I should have replaced it while I was in there).

Will this hurt anything if I don't get around to replacing the thermostat for a while? If it fails completely, is it more likely to stick open or closed?

Thanks.

It is more likely to leave you beside the hiway somewhere at 3:00 in the morning! Of all the parts that should be replaced immediatly, you have stumbled on the easiest and most necessary of them all.
It is 20 minute job under your tree! DO IT NOW! You just might be frying your head gasket and valves every minute!
You got bout $2.000. for a new engine? <img src="/forums/images/graemlins/smile.gif" alt="" />
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />

Ps It sounds like you did not get it FULL of coolant, and have some air in the top of the radiator. Have you took the cap off and LOOKED?

I was told that the thermostat was not neccisary, unless you need the heater. I removed mine and now my temp runs at a steady 150. I even replaced the factory gauge with an after market to see if there was a difference and it read the same.

note to my above reply

I'm not a mechanic, I asked a few friends of mine that are and that was the response(thermostat not needed). It seems to work for me and my situation.

Yes, you can operate w/out a thermostat. But is doing so the best thing for the engine? Essentially, you're pulling more heat away from the engine than the coolant system is designed to do. The engine is running cooler. But is this a good thing? No. We've had some discussion on this board about this issue. The thermostat maintains the engine effluent water about 195 degrees F; supposedly, at about this temperature you engine will run more efficiently, improve gas milage, and with less wear. I'm sure some of the mechanics will eventually address your comments with better detailed information. Good post, and an important question. <img src="/forums/images/graemlins/kewl.gif" alt="" />

Your friends are nuts! If it WERE better the factory would save their money! You are operating your coolant pump at it's maximum. Allowing the coolant to WHOOSH thru your system. Even racing vehicles use a restriction of some kind in there cooling system. Your motor oil is formulated to run better at hotter temps. With no thermostat you are causing the oil to form sludge and deposit itself in all corners of your engine. Your warm-up time is waaay too long and most likely you are runing a richer mixture much longer than you should. This is costing gas milage and carbon deposits in the engine. Not to mention the temp of the engine is varied throughout..top to bottom..
Put a 195* thermostat in there and you will like what happens. Tell your silly friends to do that too.
Your engine is NOT TOO HOT untill it pukes it's coolant out the overflow. If it does not do that the temp is fine.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

Makes sense. Installing thermostat this week. <img src="/forums/images/graemlins/cheers.gif" alt="" />

Sorry for taking over the thread. I installed the new 195 thermo and watched as the temp climbed to 195 and whoosh, dropped back to around 160 or so. Putted around town for a bit and the temp stayed at about 185/190. Haven't noticed any changes in performance but then again I haven't done a long term gas milage study on the thing yet, other then it get 11 mpg prior to the removal of the thermostat. Since my gas gauge doesn't work I'll have to watch my milage closely so I should be able to see something this weekend(taking it for it's first trip to the Ocala National Forrest in FL). Thanks again. <img src="/forums/images/graemlins/cheers.gif" alt="" /> <img src="/forums/images/graemlins/kewl.gif" alt="" />

BTW the engine doesnÆt start running closed loop until about 140. If you are running less than 140, the computer will ignore the O2 sensor and run basic MAP cold weather programming.

Basically the computer will run rich because it thinks it is still warming up...