temp gauge fluctuates

[fiz101]

hey guys

i bought a 1996 explorer about a month ago, its an xl - my winter beater. car is pretty mint everything works except ive noticed if i drive longer distances i notice the temp guage is dead center, and then it will drop ..not bellow the cold line, but almost right on it.. and it will come back up, and will drop again.. and come back up, even if i drive it for 60 miles,(100km) it does the same thing. i tried to search, but cant find an answer, any help would be great.

 

[Stinger357]

Not that this is the solution but just experience I have had with a fluctuating temp gauge on a pontiac...when it was happening to me exactly as you described it was the Thermostat in my pontiac had to be replaced since it was bad...once I did this it went away. So just an obervation I noticed. Not sure if it is the same on ex...but just might want to check it it is an easy replace...it took my 20 min and I am not handy with tools nor an engine there are great videos on youtube about how to change the thermostat if that is actually what might be the issue.

 

[fiz101]

thats what i thought as well, but just wanted to confirm, this isnt normal with the ohv explorer is it?

i assumed the thermostat opened up, the coolant that flows through may be cold, and therefore shocks the sensor into dropping the temperature. however, this could cause the ecu to dump gas into the engine to warm it up. any thoughts?

 

[Hartman]

My truck does a similar thing...it will warm up right to the middle and then drop down to probably 1/4 level....mine does not drop all the way to "C" like yours does. I just changed my thermostat so I'm thinking it may possibly be my fan clutch. Seems that once the thermostat opens, the engine is getting too much cooling (fan spinning all the time).

 

[justanother1]

My wife's 96 4.0 ohv does the same thing. I have had multiple thermostats in it. i have taken the clutch fan off and added an electric fan. Nothing seems to keep the temp gauge at a 1 stop. I'm thinking this is normal for the ohv motor. My 97 4.0 sohc cam motor does not have a fluctuation with the temp gauge. I know this doesn't help but if anyone solves this, I'd like to know how.

 

[Hartman]

My wife's 96 4.0 ohv does the same thing. I have had multiple thermostats in it. i have taken the clutch fan off and added an electric fan. Nothing seems to keep the temp gauge at a 1 stop. I'm thinking this is normal for the ohv motor. My 97 4.0 sohc cam motor does not have a fluctuation with the temp gauge. I know this doesn't help but if anyone solves this, I'd like to know how.

It's definitely not normal for an OHV or any motor for that matter. My old 95 OHV warmed up to the middle and stayed there, and that's how it should be.

 

[fiz101]

My truck does a similar thing...it will warm up right to the middle and then drop down to probably 1/4 level....mine does not drop all the way to "C" like yours does. I just changed my thermostat so I'm thinking it may possibly be my fan clutch. Seems that once the thermostat opens, the engine is getting too much cooling (fan spinning all the time).

it drops to above the line on the cold end of the gauge, so its not at the C, but drops roughly a quarter as well

 

[fiz101]

My wife's 96 4.0 ohv does the same thing. I have had multiple thermostats in it. i have taken the clutch fan off and added an electric fan. Nothing seems to keep the temp gauge at a 1 stop. I'm thinking this is normal for the ohv motor. My 97 4.0 sohc cam motor does not have a fluctuation with the temp gauge. I know this doesn't help but if anyone solves this, I'd like to know how.

It's definitely not normal for an OHV or any motor for that matter. My old 95 OHV warmed up to the middle and stayed there, and that's how it should be.

im thinking that once the thermostat opens, it should close once the temperature changes, it shouldn't allow the temperature to go down that far?.... unless the temperature is being read from a different position than where the thermostat is..

also

does the ecu rely on the signal the temp. gauge uses to dump fuel into the engine to warm it?

 

[budwich]

i will throw my "hat" in to this one also as my ex does the same thing even after the T was changed a while back. I recently hooked up my computer and monitored the temp... according to the data collected, the temperature didn't appear to be as big of a "swing" as the gage seemed to indicate but I would need to be a passenger instead of a driver trying to watch the road and the computer screen at the same time... yikes... to get a better look.

 

[budwich]

Took a short run today.... looks like the gage doesn't start showing anything til about 175F and at 192 its only at about 1/3 so it would likely mean that the instrument reading might be on the low side (actually the sensor). On the engine side, I can see that perhaps my T stat is sticking a bit as the temp rides to about 200F before it falls back to around 183F... it appears to run (in the cold weather here) at about 185 for a while then "cycles" up to 195ish and then drops again to 185 and then sits there are bit. This is slow driving in suburbia. So... I would think I probably need to look at getting a new Tstat to see if the fluctuations are reduced especially the "high side" ones.
Comments???

 

[OneLever]

Before I replaced my thermostat I checked the coolant temperature with a scanner (Actron CP9180) from a cold start and then idling. Took about 10 minutes to reach 200*F with ambient temperature of 75*F. The coolant temperature would rise slowly to 206*F and then drop quickly to 192*F. Then after two minutes it would reach 206*F again and repeat the cycle. What I believe was the stock thermostat had around 159,000 miles. Upon removal and visual inspection it was still intact. This was observed for four cycles. Interior heat was off during these tests.

After replacing it with a Stant 195*F thermostat the engine would warm up to 190*F and then stay steady at that temperature. There was no cycling. Also the stock thermostat had 192*F stamped on it, but 195*F was all I could get a hold of and decided it was close enough.

If your coolant gauge fluctuation is not solved by replacing the thermostat then look at the coolant temperature sender. Also, consider getting a failsafe thermostat. When you get the new one place it in a pot of boiling water to make sure it opens correctly. It won't be much of an opening but its worth testing. If that part is bad out of the box it will lead to an overheated engine.


Edit 1: I should note that even with the scanner temperature fluctuations of my old thermostat. The gauge on the dash was completely steady and did not flutter.

Edit 2: Went through my work log and my memory was a little off. Data above has been revised.

 

[bulldog18]

I have a 97 ford ranger... in a semi cold day.. my heater is blasting hot... on a very coldday...it barely heats up the truck... and I've noticed that the temp gauge will go up to where it should be but then drops... I don't think it goes below the c mark or at least haven't seen it drop that far.

 

[koda2000]

it could be your thermostat is sticking, or your fan clutch is bad, or your rad may be low on coolant.