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Thermostat dropping temp randomly?


NewShockerGuy

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Have a bit of a weird issue/quirk going on...

I have an ultra gauge in the truck so I can monitor various things via the OBDii port. Engine temp is one of them. Since I have a 2001 2.3L autoit has a cylinder head temperature sensor rather than an engine coolant temp sensor. Temp will read higher. It reads about 220’ F which is normal.

What I can’t understand is depending on the drive. Normally coming home, then temp will drop to about 170’ F after I am more than half way home (40-minute drive). It will sit there for about 10 minutes or so then eventually come back up to normal temp at 220’F. I have replaced the electronic thermostat thinking that was the cause. Still proceeds to do the same finicky behavior. I changed out the cylinder head temp sensor yesterday and today still experience the drop, then eventually come back to temp. Coolant bottle isn’t low, and new degauss bottle, cap, and radiator all replaced with in a year. Everything is OEM Motorcraft.

Not sure what else to check so looking for any advice. I have zero check engine lights/codes and zero pending codes. I will get CEL if I unplug the thermostat sensor so I know the parts are working correctly. Truck gets up to temp fine, blows heat. Blows cold air when AC is on. It never goes higher and it doesn't spike/overheat. No clue on this weird behavior however. This doesn't happen going to work for some reason, normally only coming home from work.

For some reason I want to say it's some type of electrical thing going on but I really don't know. With no codes being present and the truck drives fine it's hard to figure out.

Thanks for any help.

-Nigel
 


adsm08

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Is this new behavior or has it always done this?
 

NewShockerGuy

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In the time I've owned the truck, about 6+ years now I never once noticed this. I will note I haven't had the ultra gauge up until about a year or two but never noticed this temp drop like this. I want to say this is in fact new behavior.

I drove to work today. No problems with temp going down. I drive home today and not turning on the AC thinking that might trigger it and I got past where I normally have this happen, and sure enough I see the temp dropping. Goes down to about 170-180 F'. I pull into my drive way with the truck still running, pop the hood and jiggle wires around the thermostat/harness. No change in temp.

I open up the rad cap on the degaus bottle and you would think that after 40 minutes of driving the coolant would start to raise up and over flow but it didn't do that. I heard a small hiss of air come out the bottle and then that was it. The fluid didn't raise at all, which makes me think that's not normal. I have opened up the cap before and if I didn't screw it on fast enough coolant would have come out the top of the bottle while the truck was running.

I put the cap back on, turned the truck off, then turned it back on 5 seconds later. Sure enough the temp start rising to normal operating temperature...

I don't believe there is air in the system because the coolant degaus bottle is filled to the proper line, and doesn't get sucked down when I turn the truck on or if it's been running.

I really don't want to keep throwing parts at it because I want to figure out what is happening. Just seems strange to me.
When I felt all the hoses they were hot, so I know the coolant is circulating through the truck. My temp doesn't spike up or overheat. No hydro carbons in the degaus bottle when I tested it and no milky oil/vise versa coolant. Coolant is super green and clean.

Thanks,
-Nigel
 

greg2u4

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Seems possible you could have a bad temp. sending (gauge controlling) unit (different than the cyl. head temp sensor you replaced).

Maybe a fairly simple check, other than changing temp sending unit, would be to install one of the non-electric thermostat versions (about $25) and see what happens. Switching to the non-electric version is addressed in some of the other threads, and some recommend it. I did this recently (2003 B2300) and have had no known problems.

If you decide to try the non-electric t-stat, keep the electronic one you have connected to its wiring but strap it out of the way for road testing. The non-electric ones maintain a lower running temp., closer to 190 deg., which should show up on your ultra gauge. The lower temp may not be ideal for your engine's calibrations, but at least you could see if you get a temp. fluctuation.

The electric t-stats seem prone to issues, and maybe why they were only used a couple of years on the duratecs. Still, it seems somewhat unlikely the new one you installed would be defective. The non-electric one was apparently used from mid-2003 on.
 

NewShockerGuy

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I ordered a new sending unit. That should get here in a few days but I don't think that's the problem. I say that because the temp gauge goes up on the cluster. From what I have researched if it was bad it would fluctuate a lot of the times. Where this actually goes up as the temp goes up or goes down as the temp goes down. IE: My ultra gauge isn't showing 220 'F but the cluster is showing cold... but who knows.? lol I wish I would have replaced it when I had my valve cover off when I was painting it. Would have been way easier to get to. Just looking at it now I have no clue how I am going to reach it.

I have read a post or two of people using non electric thermostats in their 2.3L. That might be an option down the line but even replacing it with a good one I still had that issue here and there so it leads me to think it's not the case.


I'll be probing stuff this weekend hopefully.

-Nigel
 

RonD

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There is a Resistor in the engine fuse box for the temp gauge on the 2.3l Duratecs, it connects to PCM pin 19 and to the instrument cluster Temp gauge

It could cause temp gauge to go up and down but not PCM temp reading
 

NewShockerGuy

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Ok so I decided to take the ranger up to my parents house in PA... about 4 hours from me.

It's quite hilly/inclines throughout the trip and of course the truck sometimes just struggles to get up some of the hills unless it's floored almost.

I start writing things down on my phone every time the temp dropped back to 170 'F.

1:55pm-2:08pm - 13 minutes the gauge read at around 170
2:15pm-2:29pm - 14 minutes the gauge read at around 170
2:43pm-2:50pm - 7 minutes the gauge read at around 170
3:18pm-3:24pm - 5 minutes the gauge read at around 170
3:28pm-3:35pm - 7 minutes the gauge read at around 170
3:46pm-3:53pm - 7 minutes the gauge read at around 170
4:18pm-4:32pm - 14 minutes the gauge read at around 170
4:40pm-4:45pm - 5 minutes the gauge read at around 170

Note all of the above was up and down going through the mountains...
After the last one the next time it happened was:
5:37pm-5:50pm - 13 minutes the gauge read at around 170

Each time this happened it was after going up a large hill with quite a bit of throttle... which makes me wonder is it something the PCM is doing to cool the system down?

Like I said before all my previous drives/commutes have been on pretty much level high way, very minimal inclines and didn't take much effort to move.

Once the temp went from 170, it would go back to normal at around 220-230 cylinder head temp reading. The truck doesn't over heat at all, doesn't go above that, and doesn't spike up. Which makes me believe that perhaps something is doing this?

lol

-Nigel
 

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