Did you have it scanned for stored codes? Advance and Autozone do it free of charge. You might have air trapped in system. With engine cold park on incline ( front end higher)and remove cap and run till at operating temp to see if get any air bubbles in reservoir. Did the replacement thermostat come with a warranty? Maybe you got a dud. Do you have a infrared hand held temp sensor? Could take a reading at radiator when it's not acting up versus a reading when it does.

 

tried that and problem still existed. Also, the temp of the fluid in the coolant reservoir is warm, but not boiling hot. I would estimate 100-120 degrees. I was able to put my finger in it and it wasn't unusually hot.

 

03 Maz B23, I will bring it back to Advance auto and to see it there are any stored codes. When I stopped there yesterday, the guy said he didn't think the system would pick anything up, but I will push them to check it anyway.

I am thinking it is something electrical because the temp in the reservoir doesn't seem too high.

Also, I do not have an infrared scanner. Is there another, low tech way to do this check?

 

Check those electrical connections on the thermostat housing for a good corrision free fit. The temp scanners are the only way to check temp that I know off. Just trying to confirm whether you might have a slight clog in radiator hindering the flow. If they give you a hassle on a code read take it to another store. The next time it acts up check temp of both radiator hoses. If one is significantly colder you may in fact have a dud thermostat.

 

I just read in the manual that the 2001 and later 2.3L Rangers have something called an Cylinder head temperature sensor as opposed to an Engine Coolant Temp sensor that is part of the emissions control system. Any chance this is related?

 

The cylinder head temp sensor is totally separate from Engine Temp Sensor. The cylinder temp is a protection device that if engine runs too hot it puts engine into the limp home mode to avoid engine damage. If the replacement t stat is good then the water pump,radiator, fan clutch ,trapped air have to be the cause. Only other cause would be a head gasket and I hope it hasn't got to that stage.

 

I read in Duratec 2.3 specs that it has an aluminum head and block with cast iron cylinder liners hence your cylinder head temp sensor and protection circuit. Also read it has a 191 degree stat. I read in a post (link below 4 cylinder forum) that someone else had a similar overheat problem and some of 2.3 Duratecs had a casting problem. In this case there was actually a coolant leak and not sure you ever had that issue .

https://www.ford-trucks.com/forums/5...-question.html

 

Thanks 03 Maz B23, I just took the truck out again and ran it hard for 30 minutes with no issues. Yesterday, I drove it 2 minutes around the house and it pegged hot. I didn't do anything major to it except to take the cap off the reservoir and squeeze both radiator hose to check for temp as you recommended. I am glad it is not pegging hot, but am concerned that this thing seems to be so fickle. I need reliable trans back and forth to work (30 minutes each way). Any thoughts/suggestions?

 

If it acts up again shut it down and let cool off so don't risk engine damage (head gasket etc.) My temp gauge stays dead center and never varies once warmed up. If you drive highway speeds you are keeping radiator cool by air flow thru the front. If this is happening at slow speeds visually check your fan clutch to be sure it is engaged. It should freewheel at higher rpm and engage at lower rpms. Keep an eye on your overflow container to be sure coolant level is full.

 

My 03 was doing this and I found the electric fan was disconnected. Mine would only do it if you ran the rpm's up pulling a grade it would go up fast and come down just as fast but never felt like I was in limp mode. I did it all replaced t-stat water pump upper and lower radiator hoses. Getting the electric fan hooked back up took care of this for the most part, but no completely if i pull my 6 by 8 foot trailer and pull a long hill (1/2 mile) with a lot of throttle it will still do it. I personally think there is a design flaw here but can't quite pin point it and I haven't found a TSB on this. The only thing I haven't done is replace the radiator. But I can't convince myself that is the problem since it doesn't run hot in 100 + degree weather with AC running full blast. And fyi the water pumps on these are a PITA to change. My motorcraft t-stat was $52.00. My one theory is that these t-stats are on the cold side of the radiator at the water pump and are opened by an electric heater, that is what the wire connector is for, And I think that the ecm at times can not react fast enough to get the t-stat open when the load conditions are high. The temp sensor is in a housing on the back of the head . The Shop manual tells you to change it you have to pull the Tranny WTF. Remember this engine was designed for transverse mounting then they stuck it in the Ranger.