Temperature swing question

[paccool]

OK guys, need a little help. Today I pulled some small hills, was empty. The temp gauge has 4 marks on the center section. Lets call these cold, warm, warmer, and hot. Normal for my truck is the warm or second one. Pulling the hill today, the needle went to warmer or the third one. Then would go back down after the hill leveled out. Is this the thermistat swing I keep hearing about? The pyro never went above about 750 degrees.



If it is a radiator problem, I guess I'll find out this week end when I pull the travel trailer.

 

[Matt S]

This is what I see on my gauge. I usually run on the first third of the gauge in cooler weather but in the summer pulling a trailer I see mid-gauge. I've recently noticed with the temps strating to change that mine will move around the first third mark.

 

[NuttyMopar]

swinging

Mine use to swing like a Big Band dancer until I replaced with a newer one. Now it mostly stays put at the 2nd mark sometimes going up to the 3rd when I go up a 10 % - 11 % grade with my foot well into the pedal. This is empty not pulling anything. If I let up on the throttle, it quiets right back down to normal again.

 

[RamAZ]

The thermostat on my truck used to swing quite a bit. Cold towards the first mark and sometimes with the camper on it would get up to the middle but never over to the third mark.



Had new thermostat put in and now it stays just this side of the second mark and may get right on the second mark. The new thermostat seems to keep the temperature real stable.



In the next couple of weeks I'm going to change the radiator and at the same time the thermostat. Will let you know how the temperature is when this is done.



Jim

 

[paccool]

Thanks guys

Sounds like a new thermastat is in my future. hope thats all it is. don't want to buy a new radiator or recore.



Keep us informed RamAZ.



Stan

 

[drives mopars]

mine

mine stays at 1/2 b4 the 1st and w/ load goes at most to half on gauge.



blow the dirt out of rad fins, does fan clutch



feel real tight, can you hear fan come on



also put some water wetter in rad

bill

 

[ERMiles]

I just did a trip from Maine to Virginia and back via North Central Pennsylvania hauling a horse trailer (with 2 horses) - MUCHO BIG hills! My temp guage was normally on the line that's left of 12:00 and on the hills it went up to the next line to the right of 12:00. At that point the fan kicked in and it sat on the line until I was over the hill. The last day the air temps were in the low 80's and the needle went a bit past that. I figured this is normal for a long pull but maybe I need a new thermostat, too?

 

[paccool]

Smiles, mine was a little higher than that but it sounds like our trucks are behaving similar. I haven't had a chance to change it yet.

 

[dan_gilson]

What I was seeing on my '96 12V was a

swing from 140 to 190 and back to 140 in

typically 2 minutes and 5 seconds.



This normally happened when I was unloaded

and it was in the 50 to 60 temperatures.



Oh, and I did not buy for a minute when

Dodge told me that it was normal and OK. At the

time Cummins customer support told me

what was causing the problem and they were

redesigning the thrmostat to correct this.

Dodge could not even bother to call to verify

this.

 

[ERMiles]

Correction !

I was referring to the needle relative to the 12:00 position based on my memory (hah!) As you all probably realized I'm upside down. My heat guage has an arc with 4 markers - one at each end and two evenly spaced between. normally I'm at the second marker with little or no fluctuatio when I'm hauling the horses up a really steep or long hill it goes to the next marker (to the right of center) and sits there - that's when the fan kicks in. Does this sound normal? I haven't lost any coolant. Also I wonder about the exhaust temp - I have a Banks Blower with guages but I don't have the exhaust temp sensor (still trying to get it from the former owner).

 

[paccool]

Smiles,



I would get the EGT gauge installed. You need to keep an eye on this when towing.



BTW, what is your boost with the banks unit installed?

 

[GOODE11]

Same Problem but worse!

I have the same problem on my 92 1 ton. But it gets really bad when pulling our hay trailers. It will peg the guage, if I let it. I posted on the 2nd gen 12v forum about a topic on a "jiggle pin" that may be the problem. Do 1st gens have these?



I really don't have an answer for the temp swing b/c I still haven't fixed it.



Here's what I've done to it w/o results: new water pump, t-stat, fan clutch, bypassed the heater core (heater doesn't work worth a darn?), and rodded out the radiator. Anyone know what else can/should be done?

 

[paccool]

Goode11, sounds like you have already done the stuff I have been thinking about. I don't know what a "jiggle pin" is, have not heard that term before. sure hope someone comes up with a reason for the swing-has been discussed in the past but the thermastat was the most frequent cause.

 

[ERMiles]

Stan;

My boost at full throttle is around 18. I was getting up to 20 plus before I put in new Bosch injectors - I would have expected it to go up, not down - go figure.

 

[Gary - K7GLD]

Aftermarket, non-Cummins thermostats are NOTORIOUS for rapid fluctuations in temp readings - sometimes they settle down after a week or so use - usually not...



I finally went direct to the nearest Cummins dealer for the RIGHT thermostat, and IMMEDIATELY, no more fluctuating temps!



My temp runs slightly below the second mark empty and around town, and will go up to about 2/3 scale up steep grades towing our 24 ft fiver, then quickly return to normal after the hill is topped.



The "jiggle pins" are small rivet-like pins fitted loosely in the thermostat flapper valve that allow air bubbles or vapor to pass thru the thermostat rather than creating a vapor bubble or trap that prevents proper operation of the thermostat - the thermostat temp sensing pellet MUST be immersed in coolent to operate properly, and a vapor/air bubble will prevent the thermostat from opening as it must for proper operation. I see that later Cummins thermostat housings actually have a small diameter hose that essentially seems to bypass the thermostat - and I suspect this is used in later engines to eliminate the too common tendency for improper thermostat operation due to trapped vapor ahead of the thermostat - especially when non-Cummins thermostats are being used...

 

[BushWakr - RIP]

The "Jiggle Pin" is there to slightly disrupt the water flow past the thermostat when it is in the closed position. (There is a tiny bypass hole in the thermostat housing) It creates a kind of swirling flow rather than a steady contiunuos stream of water. It apparently has something to do with allowing a modest amount of water exchange in the block to reduce hotspots before the thermostat opens up fully. TWIW, Toyota's have em too.



Regards, Bob

 

[GOODE11]

Well I guess that throws the jiggle pin out the window for my strange temp fluctuations. As my post above stated, I've done everything to the cooling system w/ little if no real results. Still have the same problem. Anybody have any thing else I can check?



Thanks for the info guys!

 

[paccool]

Just went to the FAQ sectin and found some stuff on the swing problem. There is details in issue's 5, 6, 12, and 13. Will try to look these up tonight. Apparently there is a new thermostat out that is supposed to stop the swings.



Cummins P/N 3934373



Mopar P/N 05014568AA