Rapid temp fluctuation 95 Explorer, but does'nt overheat yet...

[vett82ce]

Anyone got any ideas:

I have a 95 Explorer and we had a hard freeze here in Ga. last night. It went to 20 degrees which is abnormal for around here. This morning while driving to work, which is a 35 mile trip, the temp gauge constantly went up and down. It would go up to just a little above it's normal operating temp then fall rapidly and then begin it's climb back up in temp... and then fall again. It did this the whole 35 mile trip. The gauge was constantly on the move. The height in temp before it would fall was never high enough to overheat and the temp was definitely changing (it was not a gauge problem) because the heat coming out of the ducts matched what was going on in the gauge.

After work, on the return trip home when it was 55 degrees, it still did it some but not near as dramatic when it was 20 degrees this morning. Not sure what it might be but I know it is having trouble maintaining it's temp at the sweet point it wants.

 

[joesilvia92]

id try the thermostat. its seems that its not opening properly

 

[mritz]

On my 96 5.0 that is how the guage acts in cold weather,really drives you crazy if you watch it too much.in summer it stays right around mid range and does not change much as soon as cold weather starts it goes past mid range and down about 1/3 constantly changes ..pleanty of heat and never overheats .about 2mos ago we did timing cover gasket for the famous water leak and did all the hoses and new tstat and it is the same as last winter

 

[4rd Xplora]

I had air in the coolant system on a Cougar once that did the same. The sensor would register the coolant's temperature but when the air would pass, it wouldn't register anything, so the needle would bounce between normal and cold.

 

[yavapaires]

On my 96 5.0 that is how the guage acts in cold weather,really drives you crazy if you watch it too much.in summer it stays right around mid range and does not change much as soon as cold weather starts it goes past mid range and down about 1/3 constantly changes ..pleanty of heat and never overheats .about 2mos ago we did timing cover gasket for the famous water leak and did all the hoses and new tstat and it is the same as last winter

My 96 4.0 is doing the same thing. New Tstat, same thing, coolant level is full. I have driven a lot af big trucks that do the same thing. IMHO, just drive it, as long as it's NOT loosing coolant.

 

[SoNic67]

Thermostat is not opening smooth enough.
Even a "new" one can do that, especially on extreme temperatures. I did pull out a "new" Stant T-stat that was doing the "dance" on my Sable and replaced with a Motorcraft one and that cure it.

 

[Radar2819]

My 97 sport did the same thing. My temp would move like crazy only in winter and when I had the heat on. I thought air in the system,so i bleeded the air out and still same problem. What it ended up being was a clogged heater core and/or hoses for the heater core. I would say check the hoses first then the heater core itself.

 

[koda2000]

probably defective t-stat or you could be low on coolant. check the rad not just the overflow tank for level.

 

[vett82ce]

will change the stat Saturday and see if that puts it back to a controlled temp.

 

[yavapaires]

My 97 sport did the same thing. My temp would move like crazy only in winter and when I had the heat on. I thought air in the system,so i bleeded the air out and still same problem. What it ended up being was a clogged heater core and/or hoses for the heater core. I would say check the hoses first then the heater core itself.

Thanks for the heater core suggestion, never thought about that.

 

[vett82ce]

Replaced the stat 2 weeks ago and it immediately stopped the gauge fluctuations and the temp stayed at it's sweet spot perfectly. So, a new gauge definitely fixed the problem.
Since the stat change, weather here has been normal (mild in Georgia). But last night it went down to 35 degrees and now the temp is up to it's up and down revolutions again. The 35 degree weather may just be a coincidence and not play into the problem and the problem was going to resurface again anyway. I tend to think so because 35 degrees is just a frost.
Anyway, I'm boggled at this. The gauge change definitely stopped the fluctuations. At the time the stat was changed the temp and gauge was up and down constantly and it was a balmy 75 degrees outside.
I wonder if something is corrupting the stat? I'm sure the radiator could stand to be changed out. Has anyone ever had "particle" problems in an older radiator where the contaminants could alter the stat?

 

[joesilvia92]

My 96 4.0 does the same thing in the cold. Everything's new. the only thing I can think of is I have a small crack in the top of my radiator. Maybe that's messing with it somehow.

 

[SoNic67]

On cold weather, the T-stat needs to be almost completelly closed and that makes it less effective. If the T-stat is completelly closed, it will not regulate the temperature. The circulation thru heater core will be enough to cool the engine in low temperatures.
Probably now the fan is blowing air when it should NOT and under-cools the engine. The fan has a temperature-controlled clutch. If that is not working and is always "locked" on, then it will overcool the engine at that low ambiant temperatures.

 

[vett82ce]

The fan has a temperature-controlled clutch. If that is not working and is always "locked" on, then it will overcool the engine at that low ambiant temperatures.

That clutch was changed about 9 months ago (not because it was causing any problems but just because I had never changed it before). How can you tell (in different conditions) whether that clutch is all that it should be?