Under "what I did with my Ram today", I changed the spark plugs in the 2001 1500 Quad Cab Truckster with 5.9L engine (they didn't design #7 plug to be torqued, no combination of extensions and flexes and torque wrench was going to get around the PB booster). Installed Champion RC12LC4 gapped to .040". Started up, ran fine. About an hour later, started up and drove across town six miles to my destination for the day.

Three hours later, left destination to return home. CEL came on within first mile. When I got home, I pulled out the code reader and it displayed "P1281: engine too cold for too long". It was 80 degrees, 10 degrees less than normal for this time of day/year/location, and the A/C was on. Temp gauge maybe a little below normal, upper radiator hose very hot to touch. No leaks, coolant tank at normal level.

This is the first time the CEL has come on since I did engine work -- water pump, 180 degree thermostat, hoses, timing chain, intake/plenum gaskets, distrib cap, rotor button, wires, etc -- in May. The coolant temp sensor was replaced at that time because it was broken.

Could the coolant sensor be defective, cheapest but not easiest to replace, or thermostat stuck open, even more difficult to change? Other ideas? Will drive it tomorrow though I don't have anywhere I need to go.

 

Sounds like the thermostat may be sticking open. Unless the engine has been heavily modified, I'd purchase a good quality 192 degree Stant Superstat and install that on your engine.

 

From what I gathered the code sets when the coolant temp does not reach 176F within 20 minutes. Between tolerances in the sensor and the thermostat I could see this happening. If your scanner has live data check what the temperature the PCM sees.

 

Cool and rainy Saturday last weekend. Returning home from activity of the day, I noticed temp gauge didn't get much above cold mark. Dove into the engine bay, bad thermostat. Parts store warrantied it. Normal again.


new on left, less than 600 miles on right

 

Coolant nasty too, nearly as filthy as when I did engine work back in May. Flushed it out and refilled with fresh coolant.

 

Another thermostat failure Tuesday October 25, this one lasted 270 miles. Removed it Friday afternoon and went back to NAPA for another "lifetime warranty" replacement. The guy behind the counter said the THM SS1800072 Safe-T-Stat's were (expletive). Said he worked at local Dodge dealer for 12 years, and they would sometimes fail as soon as the engine was started after replacement. He recommended the THM 170, also with a "lifetime warranty", for nearly half the price. So far, so good.

 

Update: Miles farther, still good.