Gentlemen,
Looking for a little guidance on a problem with a 2001 Dodge Ram 1500- 5.9 overcooling. This started when I replaced my Plenum seal gasket. Since then, my truck does not want to get to proper operating temp. I have replaced the heater core, the fan clutch, the radiator, 7 new thermostats, all tested with a thermometer in a slowly heated up pot of water, and the current opens between 195-199. new temp sensor. Purged coolant system multiple times and flushed entire block twice now. I'm out of ideas. I can watch the gauge raise, drop when the thermostat opens, and see it fluctuate while driving. Scan tool reads between 181 and 177 depending how cold it is. But I haven't had it out in 5 degree weather yet, just around 25-35. before I did any work, the truck use to run around 195-198 and have great heat. Even if sitting and idling while waiting on someone in a snow storm. I now get heat up to the point the thermos opens then its luke warm. No where near what it use to be, no slushing or air sounds in the heater core, and currently running a super stant that tested really good, thought it was going to be the cure. Like I said, I have replaced the thermostat 7 times, buying the stats from different stores, in 2 different states to eliminate a bad one, my work has me traveling a lot so getting a thermostat from another state to try is not a problem. The Fan Clutch is not frozen and free spins when cold and I shut off the engine. I even now have a section of the radiator blocked and it really doesn't help much, I don't want to block it all off, as I would like to get the truck back to the proper operating temp the correct way, I have had this truck 17 years now and am stuck with this problem. I doubt that I have repaired this engine so well it produces so little friction that it runs cold. (imagine how much that would be worth if I did) Any help, ideas would be greatly appreciated.

 

Are you sure the block is not cracked somewhere internally, possibly leaking coolant where it shouldn't internally? How about your water pump, is it a hi-flow? Maybe flowing too much? I'm just throwing these questions out there trying to help.

 

also, the temp sensor reads shy of the 2 on the 210 mark, reflecting the scan tool pretty well.

 

Zen, thanks for jumping in. oil looks new, has about 3000 miles on it, coolant looks great, no boiling or any symptoms that a block or head gasket would cause. drove 500 miles this Christmas with no problems except the temp. also, did check the oil during travel to monitor if water was getting where it shouldn't be. never seem to have to add water either.

 

to add, this truck went to the west coast from the east coast 2 times with this problem, I'm just sick of not having hot heat in the winter, reckon I'm getting old.

 

new water pump, got the recommended from AutoZone. the old pump started leaking, thought the same, so I ensured I bought the one recommended and not a high flow or anything fancy like that.

 

What about the heater core? Could it have blockage or possible leaking into the cockpit and you just don't know it or haven't seen it. If the engine is running fine and you are getting no heat, I'd bet it's the heater core under the dashboard.

 

I would agree if the engine was getting at proper temp, as it stands, I had a mechanic tell me the heater core was blocked and causing hot water to back up and keep the thermo open. OK, so I removed the dash, installed a new heater core, and nothing new. I left the dash loose after running the truck for a day, letting it heat then cool over and over, checked the floors and box, all dry. I wanted to ensure no leaks before reassembly of the dash. Put everything back together, no antifreeze smell anywhere. the heat gets hot when the engine is around 181, but when the temp gauge drops to around 177 or slightly below, the heat drops to luke warm.

 

Okay, I can honestly say you have me stumped!!!!

The only other thing I can think of, is were the head originally cast iron and replaced with aluminum ones? That's all I got, sorry I couldn't solve your issue.

 

Zen,
All engine parts are as they were from original build. No new heads. I appreciate your suggestions, I even have the dealer stumped, even bought a thermostat off him, to no avail. I personally feel its a thermostat, but after 7, I got to pause and step back to evaluate. With all new parts, I even pulled the hoses to ensure nothing was blocking a hose. I ordered a quality sending unit, hoping that if its reading wrong, and sending BS to the computer, possibly adjusting my fuel to a mixture that is allowing a cooling condition, it would be worth a try, but now I think you can see that I am reaching. once it gets here, I'm still going to put it in. All my short and long term readings are well within standards, no codes and no DTC warnings or alerts to possible failures, unless I reset the computer, but after about 150 miles, all is green. The dealer said they can look at it, but if I have them stumped on a diagnostic inspection, how much will it cost for them to do all I did, and if they are still stumped, I would still end up paying them. It is a stumper, isn't it.