Coolant temperature issue

95 Windstar was not running at its regular temperature --lower than normal and as a result the heater output was lukewarm. I changed the thermostat but still have the same problem. It is a 192 degree stat which is the recommended one for this vehicle. The thermostat is working, according to the gauge, but it opens too soon.
Feeling the upper hose from the stat to the radiator also indicates a lower then normal temperature. Any suggestions? Thanks

At first I'd say, if the lack of inside heat came on gradually, you may have a heater core plugging up, but you think the coolant is too cool. Is the dash temp gauge also reflecting the lower temp? How do you know the coolant is too cool before you changed the thermostat? You can tell the upper hose is too cool by feel? Hmm. It doesn't really sound like the pump is bad. Could there be something interfering with the thermostat from closing all the way or maybe it's not seated all the way and being bypassed? When you believe it opens at too cold a temp, can you tell there is actually flow? Does the upper hose become firm? Do you know if the original tstat and the one you put in were put in the right direction and the jiggle valve at the top? The larger side with the spring should be towards the engine. When I doubt a thermostat, rather than just buy another, which might be worth doing on a warranty exchange on the one you just bought, I will boil the tstat with an accurate thermometer to check that it operates according to sped. The specs I have from Haynes state that the tstat will start opening in the range 188 - 195 deg F and fully open at 208 - 215 deg F. Ford service manual has 180 -200 deg F for first opening and Fully Open at 221 deg F.

Thanks for your help. The orginal thermostat was the one that came with the vehicle which now has 213,000 miles on it. The temp gauge needle was always in the middle of the word "normal" when the engine reached operating temperature.
I changed the thermostat because the needle reached only to the "a" and then dropped just below the "l" when it reached operating temperature. The new thermostat does tshe same thing, I know that the coolant is flowing as the upper hose was hard and warm. I also know the spring end is in the block, but did not check the bypass little valve to see if it was at the top. Could that by itself by the problem? It just seems strange that the new stat does exactly the same thing as the old. Again, thanks for your input.

Duhhhhhh!!!!! It finally dawned on me what may be going on after reading your last post. It sounds like the ECT, the engine coolant temperature sensor is not working correctly and is prematurely turning on the radiator cooling fans. It's resistance has moved out of its proper operating range and incorrectly senses the lower temp as being a higher temp, thereby turning on the fans prematurely and causing "overcooling" as one poster likes to put it. It sounds kind of funny but that's what it is. If you wish to test it with an ohmmeter, it's range is around 40,500 (40.5K) ohms at around 65 deg F and will decrease as the engine temp rises. From 180 to 220 deg, F expect 3,800 to 1840 ohms. I have measured mine to have a resistance of 2200 ohms when the ECT will signal to the PCM to turn of the fans. This will have to be measured just when the fans come on but with the electrical connector off to protect your meter. You can also backprobe the electrical connector by sticking the meter probes down alongside the wires till they make electrical contact, and expect the voltage to be around 0.45 to 0.55 volts. On mine, it measured 0.485 volts. You should also make sure the ECT is getting the correct voltage to it by removing the connector and checking the voltage at it. It should be around 5 volts for the above voltages to be accurate, otherwise your system voltage to the PCM is below 12v, not good, or the PCM is not able to give the necessary 5v, really not good, but I doubt it as you aren't having other issues that would be related to sensors that would also receive that same 5 volt power supply that would then create similar biased results that would throw off the PCM. So, hopefully you have 5 volts with that rational in mind.

The other possibility is your fans are kicking on to the high setting for engine cooling when they should be on low before they jump up to high when the engine temp gets too high for low speed, so that is something you should try to check. That can be done by watching it as it warms up or is warmed up, and another method that can prove easier, is to remove the electrical connector to the ECT causing the fans to come on automatically as part of the engine cooling failsafe. The ECT is screwed in right next to the tstat and has a two wire connector to it. You should pry it off with the engine running to prove out the fans. It can't be done with just the key on, engine off.

Does the temperature issue occur even while the van is parked or only while moving? The reason I ask is some think the PCM will not engage the fans while the van is moving or whatever, but that runs counter to my understanding of how it works, so I make that distinction to rule that theory out since I can't definitely say the PCM doesn't do that. To me, it shouldn't matter since there already is in place a temp sensing system to regulate the cooling fans on an "as needed" basis that does the necessary job irrespective of the driving conditions. Whatever.

Hope that helps, "love." ;)