Engine/Transmission (1998.5 - 2002) What Is Causing This

[DIESELWRKS]

my trucks thermostat needle is bouncing from approx 160-195 degrees. not constant but at freeway cruising will not stay at 190 degrees then would move and couple of minutes later would move back. . I recently changed the thermostat it was a 190 degree stat. I know that temp has dropped outside and much colder now and does take some time to warm up. but winter shouldnt matter I guess just expose a bad thermostat. so is it possible this 5 month old thermostat just went bad. . or if the needle was acting irratic what could I do to troubleshoot the gauge/needle... any help will be helpful.....





2002 HO 6-SPD LB 4X4 QC HTT 62/14 SB-FE SMARTY TST PM3 MACH 4'S, RINGED AND STUDS, AFE/2 "SILVERLINE D/PRICOL PYRO,BOOST,FUEL FASS 150, VULCAN 1/2 DRAW-STRAW, VULCAN 3/8 FUEL LINE AND FITTINGS, DSS 03 TRAC-BAR DSS BOX TURN-OVER BALL, RIDE RITE AIR BAGS. SUPPORT 17'' KMC BLACK HOSS, 315/70/17 MICKTHOM BMTZ'S 6" RCD LONG ARM LIFT AND DE-BADGED FOR FUEL MILEAGE. :-laf

 

[DCreed]

possible bad stat, also sender or ground. if the temp rises/falls smoothly or slowly probably a stat. if its quick ,jerky ,eratic then suspect sender/ground. also check for a dirty radiator.

 

[PSoffe]

Mine did this as well. It wan't until I replaced the t-stat and flushed the radiator and installed fresh 50/50 that it stopped. Not sure why but happy to have one more thing off the list.

 

[DIESELWRKS]

thanks probley the stat 5-6 months ago I did the head and studs and I flushed the radiator. I will check the stat

 

[paulb]

First temp fluctuations in cold weather are common. The water in the radiator is so cold (and there is so much of it in our trucks) that by the time it circulates clear through the block (tstat is on the exit), the water temp has dropped. Using a winter cover helps prevent this. Having said that, I have seen some aftermarket tstats that responded slowly to temp changes. I spend the extra bucks and get a Cummins tstat.



Hope this helps...

Paul

 

[DIESELWRKS]

Paulb, thanks. . I will have to call rip he put the new one in when he did the head. find out if it was a cummins stat or a chuck it out schucks. thanks I really didnt realize the cold weather would do this to the temp of the coolant since I got out of the Marines this is the first winter that I will wear pants and not shorts... ha. thanks

 

[WrenchRat]

DW, changing the 'stat will likely solve the problem. You are experiencing 'cycling'. Cycling is defined just as PaulB did above. And yes, a winter cover will help, especially if you are running empty or light.

Even with the new thermostat, you may occasionally experience the temperature fluctuation. It will not harm the engine but is quite annoying to operators (most folks never notice). It is simply a function of the very large radiator (sized for maximum heat rejection when the Cummins is working hard) and the thermostat barely cracking open (also opens the bypass valve a tad) once heat builds enough to expand the wax/copper mix in the 'wax motor'. It then allows a volume of colder water into the block to replace the exiting hotter water. -And the 'stat obliges when it sees the cooler water and closes or nearly so. This cycle will repeat itself, more or less, until load or ambient changes.

The Cummins stat, which is made by Standard Thomson will be your best bet in solving this as the performance standards are fairly stringent. (I used to work for a T'stat mfr. We had the 'B' account prior to Std-T)

Rather than pay the big buckos at the Cummins counter, NAPA is stocking the Standard Thomson 190 stats. P/N 375190. IIRC, the last one I bought was ~$25. Do not hesitate, get the good one, as it is specifically designed for our B. It has a bypass valve built into the thermostat and will include a new O-ring gasket. Some after market stats don't do this. The by-pass valve function is very important.

 

[DodgeWarlock]

I'll second that on the thermostat. Had several customers with Cummins when I sold auto parts. Had trouble finding the correct thermostat with the bypass controll at my last place of employment. Finally had to send customers to Napa(at least theirs had the bypass). If it doesn't have the bypass control the cooling system won't flow right. The same goes for the cold weather cycling, I've seen that in old six cylinder gas trucks if you put a big 4-row in them. You can watch the thermostat open and close on the temp guage. The radiator will outcool the motor under light load and high airflow in cold weather. The correct Cummins design helps even this out better than any other I've seen. Actually it's a pretty sweet set-up if you study the way it works.

 

[DIESELWRKS]

Stat

Thanks for your help. this weekend I will pull it out and find out what is going on. and go see Napa.