Odd temperature behavior

[MythX]

The other day, I noticed my '94 explorer sport getting warmer than normal. Then it would drop back down. In another moment, it would be back up toward the top. It wasn't going beyond the normal range, but approaching it. I checked the coolant level, it was low...about 1 gallon low. I topped it off. I'm still getting the same behavior. Ambient temps have been 30's - 50's. What should I be looking at here? Thermostat? Fan? I don't know how else to explain the wildly varying temperatures.

Truck had been sitting in driveway for about a year waiting for a tranny rebuild. I was surprised when it fired right up without any problems. That was a week ago. Now I'm having some problems. Hoping they're easy to fix.

Thanks in advance

 

[Anime]

Try a new thermostat. With the coolant having been that low, and the engine getting up to higher temps, it can permanently damage the wax that's in them, so do a coolant drain, change the thermostat (A 195 degree Stant SuperStat is fine), add in a gallon of new coolant, fill the rest with distilled water, and do the air purge/burp procedure, keeping the radiator cap loose, starting the engine, letting it get up to operating temp, waiting until the needle falls, then let it cool, refill radiator/overflow reservoir again, and repeat one more time.

If the coolant that comes out when you drain it is brown or dirty, you should refill the system with distilled water, do the air purge/burp procedure, and drive it like that for a few hours, which will flush and clean the system. You can also use a radiator flush kit with a hose.

 

[MythX]

Thanks, I think I'll try that. Do you know where I can recycle my used coolant at? I live in Colorado Springs, CO.

 

[Turdle]

Try a new radiator cap also. Cheap insurance.

 

[malohnes]

X2 on thermostat and cap.

Search for info on what stat to get will yield lots of info. I suggest you read up on some of the threads...worth your time.

 

[Anime]

You can probably take your used coolant to a radiator shop or perhaps even a general auto repair shop. If you can't find a radiator shop in town, call around and ask the repair shops what they do with the used coolant when they do flushes.

A new radiator cap can help things too, though I'd suggest a new Motorcraft one from the dealer since they actually are fairly inexpensive, very close to what an aftermarket one costs, and the aftermarket ones aren't very good.

You can get a factory Motorcraft thermostat, but they are $20+. A Stant Superstat is ~$5. The 195 degree Stant runs ever so slightly warmer than the 190 degree factory Motorcraft one, but does the job. I liked the Motorcraft 'stats, but got sick of them failing like clockwork after 2 years, so far the Superstat has been a good choice, especially for the price.