Chrysler Repair: cooling, coolant temp, heater coils

Question
I have a 95 Chrysler with a 2.5 V6 and it doesn't heat up.  I have replaced the thermostat and flushed the system and it still doesn't heat up.  The temp gauge comes up to the first mark and the heater blows cold.

Thanks

Scott

Answer
Hi Scott,
I would suggest that you verify that the coolant temp is really below normal by thermometer, so that we can separate that from the possibility that the heater is not controlling the air over the heater coils properly. If the car is truly running cool, about the only explanation I can suggest is that the engine coolant temp sensor is off-value so that it is overestimating the temp of the coolant and thus turning on the cooling fans prematurely which overcools the radiator and prevents the temp from reaching its normal operating level.
So see if you can get a reading of the coolant when you believe that the engine is as warm as it is going to get. If it is really that cool it should be safe to open the coolant filler cap and insert a thermometer but be careful just in case it really is hotter than you think. If the temp is below 180 and the fans are running then your engine coolant temp sensor is off-value, or the fan relay is stuck "on".
If you have an ohmmeter you can check the resistance of the temp sensor. It is located between the coolant fill pipe and the thermostat housing. Is should read 700 to 1,000 ohms when the coolant is at 200F.
There may be corroboration of that problem via a fault code stored in the engine controller memory.
The most useful thing to do would be to try to get the fault codes that may stored in the engine controller memory to readout. Try using the ignition key: turn it "on-off-on-off-on" and leave it "on" (doing this quickly, no longer than 5 seconds). By "on" I mean just the normal position when the engine is running, not the cranking position. The 'check engine'light will remain on when you leave the key in the "on" position with the engine still not running. But then watch the 'check engine' light to begin flashing, then pause, flashing, pause, etc. Count the number of flashes before each pause and keep track of the numbers. Repeat the readout and verify the counts are correct. Then group them in pairs in the order that they came out, thus forming two digit numbers. You may notice that the pause is shorter between the digits of a given number, and longer between the numbers themselves. Then send me a 'follow-up' question telling me the results of your readout. By the way, 55 will be the last number (two groups of 5 flashes each) and that is the code for "end of readout". A code 17 would support a too cool operation of the engine, but why that is needs to be determined.
There is also an essay on fault codes at the site:
http://www.allpar.com/fix/codes.html
which gives the meaning of the code numbers. But then you need to get specific info for what exactly might be the diagnostic tests or parts to replace to complete the repair.
So verify the items I listed above and write back with the results. The fans should not be coming on except if you have the AC running if the engine is running as cool as you believe it to be.
Roland