Hello all I am new to this forum and hoping to find some insight. I have a 98.5 with the following mods,Edge juice with attitude, turbo modified by Gillette diesel, 275 RV injectors AFE intake and 4" turbo back.What i am seeing is some weird temp issues. Truck unloaded sitting at a stop light will start building temp for no reason starts at 180 and sometimes will go up to 190 or higher, ambient temp plays no factor will do it on a 55 deg morning or a 90 deg day. Differnt from one stop light to the next. Took to my local shop that helps me out strapped down to dyno duplicated problem but here is where it gets weird, one pull the truck wont break 190 with a 60% load applied via the dyno next pull truck truck hits 230 easily and once in a great while the truck will puff a tiny cloud of white then right back to black out of the exhaust. Fan clutch cycles normally, coolant shows no signs of combustion contamination not a 53 series block water pump looked great and truck uses absolutley no coolant. Radiator is five years old was clean externaly and passed flow test at the radiator shop earlier today. T-stat is probably 4 years old and this is the 3rd one but last time i replaced it the sympotoms were not like this. Engine has 102k on it and probably gets 3 to 5 k a year on it? i would really appreciate some feedbackThanks in advace

I have had some interesting temp issues this spring. However, most of my issues were lower temps. Wouldn't get to 190 unless I was on the road for and hour or more.Even when I had my winter front still on the system would never seem to get to normal operating temp like I was used to seeing.But every now and then the temp would shoot up above 220.Checked every thing I could think of. Had it in the shop for testing but never found a specific reason for the strange behavior. Never acts up when it's in the shop!I had put in a new thermostat last summer because I was seeing some higher temps on my drive to work so I kept discounting the thinking that I could have a thermostat acting up and causing the temp swings I was seeing. When I replaced the thermostat last summer I bought one at Schuck's Auto. Paid something like $18 for it.Frustrated this late spring, I went to NAPA and bought a new one and got the expensive one and paid $32 I think. Well my problem was solved. Have not experienced any more slow or non normal operating temps and haven't seen any unexplained high temps either.It was simply a bad acting thermostat. I will only replace the thermostat with the higher dollar version as I have seen the poor quality and life of the low dollar one.

Since the miles are so low are you the original owner? If so was stop leak or anything else used in the cooling system to your knowledge, did you do a good flush of the motor Im wondering if some of your coolant flow ports are clogged. Also are you running gauges? If so when this is happening what are EGTs? Have you tried replacing the temp sensor it could be malfunction and giving you false readings.-Jordan-

I second the napa thermostat. It sounds like yours is sticking. Get a 180 degree one from Napa. Make sure it is Napa.

I 3ed the t-stat. A cheapo thermostat, 4yrs old, get it out of there. If everything else is good what's left. A temp sensor will either open circuit or short circuit and the CEL would come on.

you got a bad stat , i see it here all the time, customer,s op for the cheaper stat,s and run into trouble

Thanks for the input guys in response to some of the replies the temps have been verified via laser temp gun so i dont think its a bad sending unit and the very first stat i replaced years ago i put a carquest in and pulled it out a month later and installed a factory chrysler stat and that has always been what i have used

I agree with everyone on the tstat... Go to the local Cummins shop and pick one up, cheaper than Mopar. Thermostats fail at a higher rate on these motors than other rigs due to the huge cooling capacity. It take a lot of load to get the thermostat to hit full open and stay there so its always modulating. It's not uncommon to see a 15° swing while towing, or even driving around a city on a hot day. The 180° thermostat cracks at 180°, but isn't full open until 198°.

Thanks again all i will report back when i get everything back together. Radiator and intercooler will be back this morning. New stat is on the way! Its weird to me though that these stats fail so much. This will be my fifth stat the other ones failed in a manner that the truck just started running hotter, replaced stat and bingo fixed. This time it was hit and miss. Truck has always ran right at 180 -182 according to the attitude monitor and i migfht hit 188-190 when towing when evrything was what i consider to be normal but my experiance is that there is nothing normal on these trucks. Maybe i need to drive it more and exercise the t-stat. There are times that the truck will sit 2 weeks without being started

You have to drive it more with a big load to fully exercise the stat. I watch my coolant temps via OBDII and this year about 60% of my miles were towing and I bet I only went full open on the thermostat 10 times, if that. It takes a lot of heat!

You have to drive it more with a big load to fully exercise the stat. I watch my coolant temps via OBDII and this year about 60% of my miles were towing and I bet I only went full open on the thermostat 10 times, if that. It takes a lot of heat!

Thermostat doesn't get full open till like 208-210*F... AH64ID is right they need to be worked...

i have used tstat from advance, auto zone,oriellys,rock auto, and the high dollar one from napa. al have had the same results. i run cold most of the time. mine will swing form 165 to 185. you can watch the temp gauge and watch it climb up and down.when towing the temp will be about 5* warmer but still sways around like empty, just alittle warmer. i have replaced it withdifferant ones 3 times this year. the latest one from oriellys. labled Murray Plus+ no differance than the others. says made in isreal on the box but says germany on the stat. the $70 cummins is the only one i have not tried. read a long thread on CF about this a few weeks ago with folks having the same problem. most had just started living with it. i would like to find a solution. i believe the cummins is next.

The only thing is the Cummins Stat are really expensive and still have the wild swing problem too.

I was having weird stat problems an the only way I was able to resolve my problems was to go with an original Cummins tstat!!! Sent from my DROIDX using Tapatalk

So would a crappy thermo explain the temp rising at a stop light for no reason sometimes and not others and the differnt temps seen on the dyno?

The only thing is the Cummins Stat are really expensive and still have the wild swing problem too.

that was discussed in the thread on CF and supposedly cummins had a new part and part# that was supposed to fix that. i have got both numbers somewhere, just cant put my hands on it now. gonna check it ou be cause i am tired of watching the gauge move so much. $70 from cummins +tax

--- Update to the previous post...

So would a crappy thermo explain the temp rising at a stop light for no reason sometimes and not others and the differnt temps seen on the dyno?

it could they can stick open or closed. they can just hang up little also mine just cant decide how far to close. yours might be having a hard time decideing when to open.

Thermostat doesn't get full open till like 208-210*F... AH64ID is right they need to be worked...

180°'s go full open at 198°, max allowed operating temp is 212° 190°'s go full open at 207°, max allowed operating temp is 225° What's your engine serial number?

56853981 it says engine no. model no. dont see aline with serial noumber.

56853981 it says engine no. model no. dont see aline with serial noumber.

Your motor was built on my wife's 19th birthday.

My guess is the thermostat is the same, but its represented a little different here.. instead of the crack/full open numbers in other places.

[TABLE=class: box]

[TR]

[TD]Coolant Capacity (engine only)[/TD]

[TD]9.0 liters [9.5 qt][/TD]

[/TR]

[TR]

[TD]Standard Modulating Thermostat - Range[/TD]

[TD]84 to 91°C [184 to 195°F][/TD]

[/TR]

[TR]

[TD]Maximum Allowed Operating Temperature[/TD]

[TD]100°C [212°F][/TD]

[/TR]

[TR]

[TD]Minimum Recommended Operating Temperature[/TD]

[TD]71°C [160°F][/TD]

[/TR]

[TR]

[TD]Minimum Recommended Pressure Cap[/TD]

[TD]48 kPa [7 psi][/TD]

[/TR]

[/TABLE]

i take the chart pretains to the cummins tstat. wher did you go to get the info with the serial number?

I've towed a little bit with my trucks and the only time my thermostat swings is when its bad or was purchased somewhere other than Napa. My temp stays firmly on 190 when towing unless it is going uphill for a long time. I run the 180 degree tstat. The cummins tstat is a waste of $70 in my opinion. I also change my tstat every 30 to 40k miles.