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Thread: Coolant temp fluctuates - thermostat or gauge?

  1. #1
    Registered User bfourman's Avatar
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    Default Coolant temp fluctuates - thermostat or gauge?

    I did the 98+ water pump upgrade recently on my 96, reused the single t'stat crossover with a AC Delco 195* thermostat. I also removed the radiator and flushed 14 years of farm dirt out. Since I did this, the operating temp seems to fluctuate between 185-195 on the gauge. I can watch the gauge move back and forth as I drive. It's not rapid, but it seems like the thermostat can't make up it's mind. I haven't checked the sensor to see if it's reading properly, but I didn't have a problem until I swapped t'stats.

    It hasn't gone over 195*, but it has been right at or below freezing here for a while.

    I used a Delco t'stat since I had read on here about the Stant having problems. Any ideas?
    1997 GMC K2500 Suburban SLT, VIN F, manual shift t'case, FSD in bumper, homemade TM, 4" DiamondEye exhaust, 2.25" crossover, boost & EGT gauges, ScanGaugeII, K47, PYOs w/ 265/75/16s, 3.73s, Kennedy fan clutch, Dodge flip-up tow mirrors. 223k. - Sold.

    1996 Chevy K2500 ECLB, VIN F, NV4500, 4.10s, KOJO tune, FSD in bumper, intercooler, homemade TM, 98+ WP w/ single t'stat, boost and EGT gauges and 4" Flo-Pro exhaust. 265/75/16 E range Treadwright A/Ts. - Will be missed.

    2004 Aerolite Cub 236 HTT.

  2. #2
    Registered User ak diesel driver's Avatar
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    might just be a really accurate guage. Takes alittle while for the water temps to stabilize especially if it's cold outside. also could be air in the system
    96 gmc k2500 4" exhaust, marine inj, #9 resistor, GL4, turbomaster, duraterms,-1.94 TDCO,FTB, remote pmd, isspro pillar gauges, lift pump relay added ,141 block, 2 1000 w block heaters, 2 150w glue on oilpan heaters, 2 150w glue on transpan heaters, 97 K47 air filter , IP replaced at 229k ,gear drive set awaiting install, Parts for intercooler waiting to be installed

    94 k1500 excab sb 6.5 plow truck. Fisher plow w/engine driven pump, F intake, h/m turbomaster, plowing chip by Buddy, remote PMD w#9 resistor, Duraterms

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  3. #3
    6.5 nut job/addict
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    x2 on the air in the system. I've never had any fiuctuation with the AC Delco thermostats. With other brands it was all over.
    Barry



    I am not on the Heath Bandwagon

  4. #4
    Registered User bfourman's Avatar
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    What is the best way to get the air out?
    1997 GMC K2500 Suburban SLT, VIN F, manual shift t'case, FSD in bumper, homemade TM, 4" DiamondEye exhaust, 2.25" crossover, boost & EGT gauges, ScanGaugeII, K47, PYOs w/ 265/75/16s, 3.73s, Kennedy fan clutch, Dodge flip-up tow mirrors. 223k. - Sold.

    1996 Chevy K2500 ECLB, VIN F, NV4500, 4.10s, KOJO tune, FSD in bumper, intercooler, homemade TM, 98+ WP w/ single t'stat, boost and EGT gauges and 4" Flo-Pro exhaust. 265/75/16 E range Treadwright A/Ts. - Will be missed.

    2004 Aerolite Cub 236 HTT.

  5. #5
    Registered User buddy's Avatar
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    It will work its way out over a couple days, you usually find that after it belches is out you are a half gallon low or something like that. If its been a few weeks then may not be it, check to make sure its full of water.

    Which ACDelco stat did you use, because they have a 195 and a 190 degree for the same application.
    94 6.5TD C1500 ECLB w/ 50 gallon aux tank/box; 235/75R17 tires on Alloy wheels; 3.42 gears; A-Team Turbo; 4" Aero Turbine 4040 muffler to 5" Aero Turbine 5050XL muffler to 6" tip before rear axle; FSD heatsink, marine injectors; "F" intake; SynBlend 10W-30 oil; Walbro FRB-5 w/ 12 micron prefilter; Feed The Beast; WMI and Propane fumigation; OPS extension & relay; 110K original miles; Engh GMTDScanTech
    Near Future: Battery relocation, Amsoil Nanofilter behind headlight, and stereo upgrades
    Veterans of America Club, member #18

  6. #6
    Registered User bfourman's Avatar
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    Quote Originally Posted by buddy View Post
    It will work its way out over a couple days, you usually find that after it belches is out you are a half gallon low or something like that. If its been a few weeks then may not be it, check to make sure its full of water.

    Which ACDelco stat did you use, because they have a 195 and a 190 degree for the same application.
    It's been several weeks. The reservoir is full to the line. I don't know exactly which one I put in, I called the local GM dealer we have an account with and got the stock replacement for my 96.
    1997 GMC K2500 Suburban SLT, VIN F, manual shift t'case, FSD in bumper, homemade TM, 4" DiamondEye exhaust, 2.25" crossover, boost & EGT gauges, ScanGaugeII, K47, PYOs w/ 265/75/16s, 3.73s, Kennedy fan clutch, Dodge flip-up tow mirrors. 223k. - Sold.

    1996 Chevy K2500 ECLB, VIN F, NV4500, 4.10s, KOJO tune, FSD in bumper, intercooler, homemade TM, 98+ WP w/ single t'stat, boost and EGT gauges and 4" Flo-Pro exhaust. 265/75/16 E range Treadwright A/Ts. - Will be missed.

    2004 Aerolite Cub 236 HTT.

  7. #7
    Registered User NVW's Avatar
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    There is a little air bleed screw on top of the T stat housing, the air should have bled out on it's own by now though.
    Leo
    * 95 GMC 3500 4x4 dually, VIN "F", 4.10 gears, 4L80/E trans, 405,000km, 3" downpipe, 4" exhaust, FSD mounted on heat sink in bumper, #9 resistor, 3 pillar gauge's, High Idle kit, Bosch marine injectors, Bosch Duraterm glow plugs, Leroy's ATT chip, ATT, GP overide, K47 airbox, FTB, Racor fuel filter, fuel pressure gauge
    * 98 Chev. 1500 4x4 VIN "S", 3.73 gears 250,000 km, (needs work)
    * 97 GMC C3500 VIN "F", 4.10 gears, 5 spd manual, 324,000 k (parts)
    * 04 Yukon Denali, 6.0, 196,000 km.
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  8. #8
    Registered User bfourman's Avatar
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    Would a slight fluctuation like this cause any problems, or should I just not worry about it? I'll probably flush and fill the system in the spring to prepare for camping season, I'll try and get all the air out and see what happens.
    1997 GMC K2500 Suburban SLT, VIN F, manual shift t'case, FSD in bumper, homemade TM, 4" DiamondEye exhaust, 2.25" crossover, boost & EGT gauges, ScanGaugeII, K47, PYOs w/ 265/75/16s, 3.73s, Kennedy fan clutch, Dodge flip-up tow mirrors. 223k. - Sold.

    1996 Chevy K2500 ECLB, VIN F, NV4500, 4.10s, KOJO tune, FSD in bumper, intercooler, homemade TM, 98+ WP w/ single t'stat, boost and EGT gauges and 4" Flo-Pro exhaust. 265/75/16 E range Treadwright A/Ts. - Will be missed.

    2004 Aerolite Cub 236 HTT.

  9. #9
    Registered User NVW's Avatar
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    As long as it doesn't get high I wouldn't worry, it just might be a sensitive gauge.
    Leo
    * 95 GMC 3500 4x4 dually, VIN "F", 4.10 gears, 4L80/E trans, 405,000km, 3" downpipe, 4" exhaust, FSD mounted on heat sink in bumper, #9 resistor, 3 pillar gauge's, High Idle kit, Bosch marine injectors, Bosch Duraterm glow plugs, Leroy's ATT chip, ATT, GP overide, K47 airbox, FTB, Racor fuel filter, fuel pressure gauge
    * 98 Chev. 1500 4x4 VIN "S", 3.73 gears 250,000 km, (needs work)
    * 97 GMC C3500 VIN "F", 4.10 gears, 5 spd manual, 324,000 k (parts)
    * 04 Yukon Denali, 6.0, 196,000 km.
    * GMTD ScanTech
    * CarCode

  10. #10
    9 11 Never Forget Brooklyn Tow's Avatar
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    Maybe you got a skechy T Stat......I like the Robert Shaw 180*- JMO
    Louis

    96 3500HD Dynamic Wrecker....3" DP to 4" Exhaust....Severe Duty Fan Clutch....D Max 21" Fan Blade.

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    I would say X3 on the sensitive gauge. On my gasser rebuilts (Range rovers) I always use autometer senders and gauge. You actually will see the T stat working. The temp will reach the tstat open temp , it will get a few degrees hotter and then you see the tstat fully open as the temp decreases, slowly building up temp again. Normal ops.

  12. #12
    Registered User Big T's Avatar
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    Did the Heath cooling mods on the '95, but it has the dual crossover with AC Delco 195 T-stats. The temp moves around just as you described. That never happened when I had the 180 t-stats in it. With the 195 t-stats you're running it in the most efficient temp zone, but it's also right there where the fan clutch kicks in. So you bump up against the fan clutch kicking in and it knocks the temp back down. It's the constant back and forth, ying and yang with the 195 t-stats. If you don't like it, then go with the 180. I honestly have never seen any mpg difference between the 180s and the 195s. It must be a very slight difference, or really it's that the 195s were the optimal range for emissions which I really don't give a hoot about.
    1999 Chevy Suburban K2500 4x4 w/ 6.5TD 190K miles. 4L80E and 3.73 rear gears. HD lift pump, ATT, Heath HO injectors, 4" Diamond Eye Turbo Back exhaust, Warpspeed x-over, deleted soot trap , D-Tech pmd behind bumper, Heath programming for ATT, Pillar mounted gauges: EGT, Boost, Tranny Temp. Replaced IP at 130K. HID light conversion with All-4-On-Hi. Forged Alcoa wheels.

    My son's 1994 GMC Suburban K2500 4x4 w/ 6.5TD 243K miles. 4L80E and 4.10 rear gears. Buddy 4 position tune. Rebuilt Bosch injectors and new Duraterm glows. HO water pump with Dmax fan, HD fan clutch and new AC Delco 195 T-stats. Diamond Eye 3" Downpipe and 4" exhaust, deleted soot trap. Warp speed 2.5" mandrel bent crossover. D-Tech PMD mounted behind the bumper. Pillar mounted gauges: EGT, Boost, Tranny Temp. Rancho 9000 shocks. Rebuilt front end and steering box tightened. Forged Alcoa wheels.

  13. #13
    Registered User bfourman's Avatar
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    For winter time I'll keep the 195, probably switch to 180 for towing season.
    1997 GMC K2500 Suburban SLT, VIN F, manual shift t'case, FSD in bumper, homemade TM, 4" DiamondEye exhaust, 2.25" crossover, boost & EGT gauges, ScanGaugeII, K47, PYOs w/ 265/75/16s, 3.73s, Kennedy fan clutch, Dodge flip-up tow mirrors. 223k. - Sold.

    1996 Chevy K2500 ECLB, VIN F, NV4500, 4.10s, KOJO tune, FSD in bumper, intercooler, homemade TM, 98+ WP w/ single t'stat, boost and EGT gauges and 4" Flo-Pro exhaust. 265/75/16 E range Treadwright A/Ts. - Will be missed.

    2004 Aerolite Cub 236 HTT.

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