we have had several discussions here about coolant temp here. i for one have had a problem keeping the temp up for quite a while. i have replaced t stats only to see them work for a short period. i finally replaced my radiator cap and that seemed to work. but about a month ago the same problem came back. i replaced the t stat again with one from napa. this one did nothing differant. on initial warm up the temp will go to 190 then drop down to about 165 and bounce around 165 and 175 in town or on the highway. it has been like that for a long time. i just installed my AD 165 and on initial start up it warms up to 190 and stays there just like it used to. what in the world would the ad install have to do with engine temp? i have got some road trips to make the next two weeks and will keep and eye on it. i havent seen 190 steady in a long time.

I wish I could keep mine running 190 as well, mine runs hotter than that constantly. Over the winter with temps 40 and under the truck would get to 190 within 5 miles and stay there with no winterfront. Didn't get much colder than 20 so I can't say how it would have been under that. Now with the temps up in the 60-70 range my temp has been running up around 210 or so just going down the highway where its level and no trailer behind it. I'm honestly considering taking the guts out of the t-stat for the summer.

Hmmm... I've never had a any issues with my cooling system I run between 193-197*F coolant temperature all the time. Even in the dead of winter with temperature as low as -25*F it still always made at least 193*F even without a winter front. Now hitch up the Jayco Travel Trailer and still pulling grades at 1,100*F EGT's I never get over 197*F...

My OEM thermostat runs rock solid, a needle width below the center mark. Towing heavy runs a needle width above the center line. 10 years, 56k on that OEM thermostat. I guess if I had problems with aftermarket thermostats, I'd go back to Cummins.

That's where I'm different I change thermostats every time I change coolant. I just don't skip that step and so far everything just works right. Fresh coolant, flush, and fresh thermostat every year.

I wish I could keep mine running 190 as well, mine runs hotter than that constantly. Over the winter with temps 40 and under the truck would get to 190 within 5 miles and stay there with no winterfront. Didn't get much colder than 20 so I can't say how it would have been under that. Now with the temps up in the 60-70 range my temp has been running up around 210 or so just going down the highway where its level and no trailer behind it. I'm honestly considering taking the guts out of the t-stat for the summer.

never had a problem with high temps. the first seven years the temps were always good and steady around 190. last three years its been a battle getting up any where near 190. dont need to gut mine.

--- Update to the previous post...

Hmmm... I've never had a any issues with my cooling system I run between 193-197*F coolant temperature all the time. Even in the dead of winter with temperature as low as -25*F it still always made at least 193*F even without a winter front. Now hitch up the Jayco Travel Trailer and still pulling grades at 1,100*F EGT's I never get over 197*F...

mine was like that for a long time but has always been a batttle lately. been rock solid the past two days though around 190.

--- Update to the previous post...

My OEM thermostat runs rock solid, a needle width below the center mark. Towing heavy runs a needle width above the center line. 10 years, 56k on that OEM thermostat. I guess if I had problems with aftermarket thermostats, I'd go back to Cummins.

my oe lasted about 7 years. started having temp issues about 2 or 3 years ago. i was foing to buy a cummings a couple of weeks ago and the freightliner dealer wanted 67 bucks for one plus he would have to order it. i decided against that.

i still cant figure out why it has been working right since the AD install. it floated around 165 to 175 the whole 1350 miles bavk from OK and around home the next few days. since the install one needle width to the left of 190 just like it used to.

I wish I could keep mine running 190 as well, mine runs hotter than that constantly. Over the winter with temps 40 and under the truck would get to 190 within 5 miles and stay there with no winterfront. Didn't get much colder than 20 so I can't say how it would have been under that. Now with the temps up in the 60-70 range my temp has been running up around 210 or so just going down the highway where its level and no trailer behind it. I'm honestly considering taking the guts out of the t-stat for the summer.

Have you checked the rad for gunk buildup on the fins?

Hmmm... I've never had a any issues with my cooling system I run between 193-197*F coolant temperature all the time. Even in the dead of winter with temperature as low as -25*F it still always made at least 193*F even without a winter front. Now hitch up the Jayco Travel Trailer and still pulling grades at 1,100*F EGT's I never get over 197*F...

What thermo are you running? I need to pull my rad out again and clean the gunk again. Still have the oem catch can. This time I will relocate it when the colling system gets cleaned this time.

What thermo are you running? I need to pull my rad out again and clean the gunk again. Still have the oem catch can. This time I will relocate it when the colling system gets cleaned this time.

Napa Thermostat... Cummins thermostat is just way too expensive just to have a name... You need to either build my custom crankcase vent or extend it down.

Napa Thermostat... Cummins thermostat is just way too expensive just to have a name... they quoted me $70. thats alota green for a tstat. You need to either build my custom crankcase vent or extend it down.

need to do this my self.

Are you going by the OEM temp gauge in the dash????? If so, these essentially are nothing but "glorified idiot lights"!!!! They tend not to be real accurate. If'n you're running an after-market temp gauge, I'd say your radiator is plugged up with the oily, slimy crap from the OEM crankcase breather. Mikes already mentioned that mod.Wait, I re-read your post:duh:..........you're having trouble maintaining temp??????? Is that correct???? It's gotta be thermostat related or else see my first paragraph here. That or you must do a lot of "low speed" driving. My 3rd gen even in hot weather will run at 190 if I'm doing low speed stuff. The cooling systems on our trucks are very, very, good. You've really gotta work'em to get the temp up!!

i know about the gauge, but it is all i have to work with. i am using the mark between the 140 and 190 as 165. since it was new the gauge read just below 190 very constant. really cold weather would bring it down some especially intown. 3 years ago it dropped to the 165 mark and would fluctuate up a couple of needle widths and back down. i have been thru 6 tstats and one radiator cap and got some results with them but it would always go back to the 165 mark. i pu in a new napa tstat 3 weeks ago and drove from Hooker OK to Hickory NC, 1350 in 27 hours, 45 to 85 mph. the gauge was sitting at 165 and slightly above the whole trip. i just installed my ADII and the temp is back up to just below 190 and stays ther just like new. drops or a little in town and idling just like new. I like the results but would love to know what the AD install did to bring the temp back to normal. the only other thing i did was to remove the relay and the wiring harness for the old intank pump. cant figure out what either one could have to do with the temp.

Is your fan working? Like locked up. That would be max airflow through the rad all the time.

the fan is not locked up. you can hear it come on and off. it is hardly ever on.

i just made a trip to and from Charleston SC. temp stayed just under the 190 mark the whole way. i dont know why it is working right now. iguess i will just be happy with it. hopefully she will h=not go back to her old ways.