Cycling temp gauge

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Cycling temp gauge

Postby theoldmanW350 » Mon Aug 26, 2013 12:05 pm

Hello all. Just completed the KDP/KCB fix on my 1990 CTD. While I was there I installed a new t-stat (Gates from Genos). I took the radiator out to do the fix and backflushed it then flushed it from the top. The water looked fine a bit brown but nothing I worried about. Anyway prior to the fix my temp gauge was cycling from "normal" (mid-way) down to just above the lowest tic in the temp range. Then it would repeat this cycle. Thought the t-stat and new coolant would solve this but it continues to behave this way. It creeps up to about midway then sharply drops down to above the lowest tic. I'd expect the gauge to read a constant temp instead of cycling this way. I feel I filled him up correctly but could it just be air in the coolant? I installed the t-stat in the correct position (jiggle pin on top). How can I bleed the air out? Thanks for any suggestions.
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Re: Cycling temp gauge

Postby ellis93 » Mon Aug 26, 2013 12:16 pm

You my friend need a genuine Cummins thermostat,the rest is junk.
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Re: Cycling temp gauge

Postby PToombs » Mon Aug 26, 2013 5:20 pm

From what I have read some of these trucks cycle the gauge up and down and some read pretty steady. Mine reads steady. Try to park it with the nose uphill and let it run a bit when it's warm. It should be all bled out by now but if not, this should burp the bubbles out. Other than that, there's not really any bleeding to it.
If that doesn't cure it and it bothers you, try a Cummins stat like Ellis said.
pete

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Re: Cycling temp gauge

Postby theoldmanW350 » Wed Aug 28, 2013 12:05 am

Thanks for the replies. The t-stat I removed had four jiggle pins surrounding the t-stat spring so I assume it could've been the oem t-stat. Like I said it was behaving this way before I switched it out. I'm a member on other cummins forums and from what I've read some trucks do it, others don't. Some expressed concern about cracking a head over the long haul which is what I was thinking. Not sure if that has actually happened to any owners. PToombs, I'll try your recommendation. I gotta use my ramps at some point. Cheers.
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Re: Cycling temp gauge

Postby RumbleFish » Wed Aug 28, 2013 4:37 am

The awesome Dodge "best guess" gauges might have something to do with it as well. Id consider tossing in a temporary aftermarket gauge if you have access to one and see what its really doing, by reading real numbers instead of lines!
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Re: Cycling temp gauge

Postby Remps » Wed Aug 28, 2013 12:10 pm

X2 on the cummins thermostat. My w250 cycled the gauge like yours with a non oem thermostat. Switched it to a cummins thermostat and now it stays steady around the 1/3 mark on the gauge.
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'96 2500 S/C L/B,2wd,NV5600,3.54 L/S,cai,egt,pacbrake,mbrp exhaust,10 plate.
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Re: Cycling temp gauge

Postby Arnold Layne » Wed Aug 28, 2013 9:04 pm

Where does a person find the Cummins part number for a t-stat?
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Re: Cycling temp gauge

Postby PToombs » Thu Aug 29, 2013 5:09 pm

I found one in the part numbers sticky. Try 3802968. It's 83*c, what ever that is in American temps. :lol:
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Re: Cycling temp gauge

Postby theoldmanW350 » Sat Jun 27, 2015 6:11 pm

Revival time! Well it's been some time since the last post but I changed out the genos t-stat to an OEM cummins part# 5292738. It matched up with the engine number. Anyway jiggle pins at 12 and 6 and it still climbs up to about 3/4 then it dropped to 1/4 then 1/2 then back to just above 1/4. I'm moving to Redding in about a month which is why I got off my butt and did the switch. Hotter than hell there. I suppose I just live with it?
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Re: Cycling temp gauge

Postby CumminsPower59 » Thu Sep 10, 2015 12:28 pm

When I rebuilt my 91, I did the same, swapped in a Cummins thermostat with two jigglers...same thing, swinging temp gauge. A few years ago at SOP 8 or 9 I got a Cummins thermostat with three jigglers, it worked as they should with no swinging coolant temps in my old 92. Unfortunately, I tossed the box with the part numbers on it and I have yet to find the number again. FWIW, the old thermostat I removed from my 91 was one I installed in 2004, and it was not a Cummins unit, just an aftermarket one. I am half tepted to swap in another Gates or Stant unit and see the difference. One thing that can be done is cut the jigglers out, allowing some flow all the time. This kept the swinging to a minimum on my 91, but it takes a bit longer to get it up to operating temperature in the colder months.
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Re: Cycling temp gauge

Postby Douglas » Mon Sep 14, 2015 11:31 am

Both mine do it. never had them apart, so what is in there is unknown. Damps itself out as it warms up; the gage movement is about a needle's breadth after a haff an hour. First rise when it is cold takes the longest to crack and is highest( about 2/3 of gage travel ).
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