Strange Temp Gauge Behavior
 

2001 Ranger 2.3L, 209K miles.

This week I noticed an odd coolant temperature pattern in my Ranger. It occurred on a drive from central VA to Fayetteville NC, which involved many miles of slight uphill heading south through VA and then downhill from Greensboro to the destination.

When at a cruising speed, 45-70 MPH, on flat ground, it takes very little throttle to maintain speed and the temp gauge is right on the center position, with the icon covered by the needle.

Going up a slight-moderate incline, it doesn't take much more throttle to maintain speed, but the temperature rises to a disturbing level. But if I floor the gas pedal, the truck doesn't accelerate much but the temp quickly declines to below the mid-level. I can see the needle move down as much as 1/4 inch in less than 10 seconds.

When stopping for gas, upon restarting the engine the temp gauge was within 1/8 inch of overheating. But as I accelerated hard to merge onto the roadway, the temp also quickly went down and stayed down.

What do y'all think this is?

I did replace the water pump about 5K miles ago (with an OEM part), and two weeks ago the local dealer replaced the heater control valve which had cracked. Radiator and hoses were new last year. There are no coolant leaks.

Thanks.

Sounds like it could be your rad fan.. Do you have a clutch fan ??? Try spinning the fan by hand with truck not running and see if it is easy or hard to spin,,,also give it a wiggle or wobble test while spinning !!!

If clutch is going bad would explain why stepping on gas would make it spin more and cool down your truck.

The logical first thing to check when the temp gauge wanders without rhyme or reason is the coolant level and to verify that the cooling system has been purged of ALL air. This because, the pickup on the temp gauge sending unit is designed to function when immersed in liquid and NOT air. This especially because, the cooling system has been serviced a few weeks back and therefore came the opportunity for poor purge/refilling to have occurred.

Well, it wasn't the fan clutch, and the serp belt is in good condition. Where is the fitting from which to bleed the coolant?

Also, where is the thermostat on my engine? On other cars I have found it easily near the top radiator hose.

Thanks.

On these 2.3L Duratec engines there is no bleed fitting. You use/remove the coolant bottle cap to burp the system.

The thermostat is near the bottom of the driver's side of the engine block connected to the bottom hose on the radiator. The 2001.5 - 2003 2.3's used an electrically heated thermostat and are therefore quite spendy to replace IF you use one of those. There is a lot of information online regarding these 2.3L Duratec electric thermostats. You can use a much less expensive 2004-2006+ non-electric thermostat however the ECU will pop a code if there is nothing plugged into the harness.

If you have A/C these 2.3's also have an electric fan in addition to the clutch fan. Were you running the A/C during your trip? You might check to see if the electric fan actually works when the A/C is on.

Thanks. No, it happens whether AC is on or not. I have just ordered a Scantool cable and installed Forscan on a laptop, will get data once that's set up.