Correct Thermostat Temperature -- 4.0 OHV

[lobo411]

Anyone know what the correct thermostat temperature should be for a 1996 4.0 OHV? My engine has been running cool ever since I installed an Autozone 198 thermostat last summer. The gauge used to get right between C and H and stay there, but now it gets to the low 1/3 and stays there.

I'm going to check the exact temperature using my scan tool today, but there seem to be a ton of different thermostat temps listed as "correct:"

Haynes Manual: 192-199 F
Autozone: 198 F
Rockauto: 195 F (OE Temp)
Rockauto: 198 F (OEM Recommended Temp)
Fordparts.com: 197 F

 

[AP9]

195°F nominally. AAP sells a 180° thermostat as well, and I'd imagine AutoZone probably does too, are you sure you didn't install one of those?

 

[swshawaii]

OEM Motorcraft RT1161 is 190*. Engine cooling systems, like spark plugs, are optimized to run at SPECIFIC temperatures.
More Information for MOTORCRAFT RT1161

 

[lobo411]

195°F nominally. AAP sells a 180° thermostat as well, and I'd imagine AutoZone probably does too, are you sure you didn't install one of those?

Nope, Autozone only carries one thermostat for the 96 explorer 4.0 (at least, their web catalog does, and that's how I ordered it).

I ran the car today--about 10 mins of city driving followed by 5 mins of highway, then I parked it for 2 hrs, and then another 15 mins (5 highway/10 city).

According to my scan tool, the ECT never topped 187 degrees F. I even raced the engine while parked after a total drive time of 30 mins, and I couldn't break 187 degrees. Ambient temp was 50-60 degrees.

I'm thinking this isn't right...? According to these readings, the thermostat never opened in 30 mins of driving. Maybe it's stuck open?

 

[lobo411]

OEM Motorcraft RT1161 is 190. Engine cooling systems, like spark plugs, are optimized to run at SPECIFIC temperatures.
http://www.rockauto.com/catalog/moreinfo.php?pk=383902&cc=1119653

Hmm..ya I see that, and it's also listed as their "popular" part so others must be using it. On the other hand, the Ford parts catalog is 197 F. Yeesh!

The car actually runs great right now--idles fine, and I get the usual 12-15 city mpg and 20 highway. No codes. The two problems that do concern me are:

Knock/ping on heavy acceleration (basically only on two 8% grade mountain passes I drive on my commute)

High NOx on my last smog (with 2 ppm of failing). Next smog check is May.

 

[lobo411]

I ran the car 350 miles yesterday with the scanner attached, and the coolant only touched 190 a few times. Mostly it hung out in the 180-185 range, even on an 8% grade or with the air conditioner on. Air temp was 50-80 degrees, so I think I to have gotten up to thermostat-opening temperature (195-200), right? I ordered a new one.

 

[lobo411]

Well, I'm not sure what did it, but now my dash gauge operating temperature is back to normal. It's also displaying more "normal" behavior--IE, before the engine was getting to the low 1/3 on the gauge that was about it. Now it gets up to the 1/2 point, and then I see a decent drop as the thermostat opens, and then it comes back up.

I changed the lower intake manifold gasket, replaced the thermostat, flushed the radiator (had a minor but still worrysome amount of brown sludge), and refilled. I don't know which of those might have done the trick, but I'm happy with the outcome!

 

[mhanglow]

Excellent post. I have the same problem with my 1995 4.0 ohv.

 

[bigred4x4]

My temp gauge on my 96 fluctuates within the middle third section a lot and from lower third to upper middle third seems like only a few degree difference in actual coolant temp in that range I'm going to install a new temp sender ($10 why not) to see if that changes anything, there are two sensors for coolant temp one for the gauge and one for the pcm. I'm glad you fixed your problem, but 187 is better than having overheating problems lol as for the ping on acceleration there is a tsb on carbon knock (carbon build up in combustion chamber) I would look that up I forget what the exact fix is, also smog could be many things from a number of sensors to a going bad catalytic converter. I'm just thankful I don't have smog test because with these older vehicles (especially mine) I know id be screwed.

 

[239]

My temp gauge on my 96 fluctuates within the middle third section a lot and from lower third to upper middle third seems like only a few degree difference in actual coolant temp in that range I'm going to install a new temp sender ($10 why not) to see if that changes anything, there are two sensors for coolant temp one for the gauge and one for the pcm. I'm glad you fixed your problem, but 187 is better than having overheating problems lol as for the ping on acceleration there is a tsb on carbon knock (carbon build up in combustion chamber) I would look that up I forget what the exact fix is, also smog could be many things from a number of sensors to a going bad catalytic converter. I'm just thankful I don't have smog test because with these older vehicles (especially mine) I know id be screwed.

I just installed a new motor craft sensor yesterday and the temp gauge is still below halfway when the truck warms up. I’m guessing I need to change my thermostat again.

 

[bigred4x4]

The explorers factory owners manual will tell you this is normal that the gauge can fluctuate with in the "normal" band. If you want more accurate readings you'll have to go through the pcm to get an actual number the gauge is just relative at best basically just let's you know when your about to start overheating once it reaches the top of the normal band is how I see it.

 

[239]

I wonder how hard that would be to do. I wouldn’t mind having a numeric display for coolant temperature.

 

[bigred4x4]

Check out the Scan gauge 2 other than that it'll be a round auto meter type gauge but the scan gauge is way easier to install and gives you a lot more than just coolant temp.

 

[mhanglow]

My ect gauge is reading below the bottom normal range line. Heat is good. I just recently replaced the fan clutch. Any ideas ?

 

[96eb96]

Check out the Scan gauge 2 other than that it'll be a round auto meter type gauge but the scan gauge is way easier to install and gives you a lot more than just coolant temp.

For a bit more than a scangauge you can get a 7" Android head unit and run forscan, have 100s of gauges. You can even read out Engine Torque!

My ect gauge is reading below the bottom normal range line. Heat is good. I just recently replaced the fan clutch. Any ideas ?

Mine always read low. It is a common issue if you search. I tried another Tstat, it improved a bit. My ECT sensor matches the Dash, so the temp is right. My theory about these engines is they all have small cracks in the heads, push air into the coolant. There was a TSB many years ago about a bypass kit and steam formation, to stabilize temperature. Probably related to that issue.

That causes the temperature to stay low or wander below normal. I never overheated. Forscan says one of my cyls has a higher misfire count, and I blew air into the spark plug hole and noticed the coolant rose a bit.

 

[lobo411]

I haven't had an issue with my gauge since I posted this thread, for what it's worth. The dash gauge reads perfectly: it slowly rises on first start, gets a little above middle, drops down as the thermostat opens, and comes back to right about middle.

 

[mhanglow]

What about engine fan on all the time, I think that has a lot to do with engine temperature. And like I said, I already replaced my fan.

 

[mhanglow]

Also my idle stays at 1000 rpm’s. I think it is all connected.

 

[96eb96]

I haven't had an issue with my gauge since I posted this thread, for what it's worth. The dash gauge reads perfectly: it slowly rises on first start, gets a little above middle, drops down as the thermostat opens, and comes back to right about middle.

How much does it drop?

 

[mhanglow]

Needle stays at bottom line normal range or a little below