I have a 1999 5.9L 4WD, K&N Filter with CAI, Cat-back magnaflow exhaust, with approximately 140,000 miles. About two weeks ago, after driving about 75 miles, I noticed the engine temp rose to about 220 while driving on the freeway, then rising to about 230-240 after getting into regular city stop and go traffic. I immediately became worried since I know too well the dangers of overheating the magnum engine. I immediately checked the coolant level, which was perfect, and examined the engine for any leaks. Nothing obvious. In any case, it didn't rise any further, and went back down to 210-220 once back on the freeway.

I looked through my manual and this forum for any other obvious hints, but nothing jumped out. It continued this pattern the next couple of days and I figured maybe the thermostat was failing or something, so the next day I changed to my "summer" 180* thermostat (I infrequently swap them depending on the season). Well, the overall engine temp went down, but now it is still running hotter than it should, approximately 215 during the afternoon. Seems that it runs cooler if the ambient temperature is lower (190ish if less than 65 degrees outside, and up to 210-230ish if over 75 degrees outside). I also noticed that once it gets past 210, the idle will jump up to about 900rpms, as well. The truck seems to run fine, with no obvious loss of power or missing, but I am concerned about the higher than normal temps. I would say it is running about 30-40 degrees higher with both thermostats. Fan clutch seems ok, coolant level is fine, cleaned any debris from radiator/AC unit, etc., etc., so I am out of ideas. I did change the spark plugs over a month ago, from the Champion Truck plugs (RC12LC4) to the AutoLite 3923's just for comparison, but the truck was running fine for weeks after that swap. I also installed a new water pump about 4 months ago, as well. My next idea is to change the coolant temp sensor, but does anyone have any ideas what else it could be? I will include a picture I took yesterday while driving, after approximately driving 40 freeway miles, with an ambient temperature of 75*.

 

Could be a clog in the radiator or maybe the waterpump not pumping well. I wouldn't overlook the possibility of the temperature sensor being bad either.

 

Thanks for the reply. I put new water pump on the truck just a couple of months ago, so I am doubting that is the issue, for now. It seems to be extremely temperature related in some way. Since I wrote the post, I have had a couple of 150+ mile round trips, with temperatures between 60 and 90 degrees. It seems that the hotter it is outside, the hotter the truck will run. It will stay about 190 until about 70 degrees, and will get to about 235 when the temperature was at 85-90 degrees. I have only been in the "hotter" weather for about 20 minutes at a time, in fact, living here on the coast of California, the temperature dropped nearly 25 degrees in approximately 10 minutes. I may just change the coolant temp sensor since it is an inexpensive fix, and probably due, at 15 years old and 150k+ miles. Coolant seems to flow, well, but I will take it to a shop today after driving it around today and have them put an IR thermo on the radiator to see if it is a clog.

 

I had a overheating problem w/ my 2000 Dodge Durango 4.7. I changed the radiator, waterpump , temparature sensor and thermostat. It was still doing it. It was suggested to try Blue Devil. Best thing I ever did. Stays at 180 degrees, not 220-240. Make sure you follow directions on bottle. I hope this helps.

 

Let us know how the test with the temp gun goes.

 

Just a thought, but a bad head gasket can cause overheating that all the new thermostats and water pumps in the world wont help.

 

Well, IR temperature scan wasn't as helpful as I had first hoped. Apparently, the tech couldn't get to enough specific points of the radiator to determine "if' there was a clog. After driving around town for about 30 minutes, and idling at the shop in the cool 65 degree weather, the temperature never rose above 180 degrees. I doubt I have head gasket issues, since the coolant level hasn't changed one bit, and the coolant looks as fresh as the 3 months it should be (when I put on a new water pump). I may end up flushing the system just in case there is some strange clog in the water jackets or something, but I will plan a coolant temp sensor first, even though I don't think that is the issue, either. I will update as info becomes available, but still not smoking gun as to why it runs significantly hotter than it should in warmer weather.

 

What are the obvious ways to tell of a head gasket? I've been losing coolant and can't seem to find a leak. I don't think I see any water in the oil on the dipstick, but still wonder. When i was a kid, my mom would blow the head gasket on the old station wagon all the time and the sound was obvious (pssh, pssh, pssh). Don't mean to hijack...

 

Loosing coolant can be a sign, sometimes air bubbles puffing out the fill hole, white smoke out of the tailpipe, a sweet smell to the exhaust are all things that can indicate a bad head gasket. These indicators can all be very subtle if the leak is small.

 

I don't understand how he couldn't "get enough points" to check the radiator. They guy sounds like a moron if you ask me. Flushing out the system might help some.