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One way to tell if a t-stat is stuck open is to start the vehicle cold and let it run at idle. If the upper radiator hose at the radiator slowly warms up until it is hot the t-stat is stuck open.. With a normal operating t-stat the hose will stay cold then when the t-stat opens it is hot, no slow warm up. 

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Do yourself the favor and just change the thermostat. Please don't go the Cummins / Mopar route being Cummins and Mopar do not manufacture thermostats and currently Cummins  and Mopar is using a Robertshaw 320 high flow thermostat which is produced by Mr. Gasket. Very poor quality thermostat that will separate and drop the bypass shutter in the block because of the junk design. 

 

Suggestion: NAPA thermostats have been working awesome for years here. 

20190815_112742.jpg20191108_164624.jpg

Edited by Mopar1973Man
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If the heater blows hot I would lean more towards a coolant temp sensor than a thermostat. Do you have any way to verify temp? IR gun? IBMobile’s suggestion is a good one. 
 

 

As far as the thermostat, I’ll go against what moparmans says. You couldn’t pay me to run a NAPA thermostat (or anything), I quit buying NAPA garbage many years ago for good reason. They sell cheap crap... but you overpay for it. 
 

I will recommend not buying a thermostat from MOPAR thou, as they are generally rebadged and overpriced Cummins parts. Try to get it directly from Cummins. 

A thermostat is a wear item and needs to be changed more often than many people thing. Often you can’t see it failing on the dash gauge until it’s too late. Big temp swings and late opening are a good sign it’s time for replacement. 

 

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Lets say I've never had a NAPA fail yet, in my truck and hundreds of customers I've do work on, including all makes Dodge, Ram, Chevy, or Ford yet. Remember I'm counting all my customers and vehicles I've worked on or serviced.

 

Now Cummins thermostat I replaced plenty of them so far. Short life span, physical failed as I've documented (attachments above) etc. Also Cummins has changed providers several times being I've documented several different designs and manufactures sold by Cummins. Like example Robertshaw, Mr. Gasket, Motorrad, etc. Very unsettling when Cummins has to change manufactures over 4 different times. 

 

As for Robertshaw and Mr. Gasket failures they cover all name brands Dodge, Chevy and Ford...

 

Image result for robertshaw thermostat failures

 

Related image

 

As for Mr. Gasket...

image.jpeg

 

So being Cummins is currently using Mr. Gasket since Robertshaw no long manufactures engine thermostats. I've already called Robertshaw and and asked for more info.

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I, like Mike, have always used napa. I see people recommending cummins only and it makes me mental. I went to cummins for a 190* for my 98 24v and they wanted $90. I went to napa and got one for $22 and it worked great. My 2012 came with a 200* and after I deleted it I used a 190* from napa with zero issues. 24v t-stat is so easy to change that if they do fail, I could do 3-4 napa and still be cheaper than cummins

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Posted (edited)

Pay triple the price for a thermostat... Again I'll repeat again "Cummins and Mopar do NOT manufacture thermostats". Both of these vendors Mopar and Cummins buy from the CHEAPEST source they can and triple the price because the thermostat box has a Cummins logo or Mopar logo. Being that Mopar and Cummins both have no control on what the manufacture is going to produce.

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Cummins and Mopar are not the only companies that have others manufacturing for them. It is fairly common practice. The manufacturers get specifications to build by from their customers. If Cummins or whoever decides just to accept what they get without any quality checks of their own, then they are giving up control. To say they have no control over a product with their name on it is a bit misleading. 

 

I have used a Cummins and a Mopar. They did not work any better or worse than the other brands out there so I choose to save the money. Just another personal opinion.

Edited by dripley
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Posted (edited)

The only spec for a thermostat is opening temp. Nothing else can be changed. As for them falling apart that is a quality issue and nothing is being done about it being that Robertshaw / Mr. Gasket design is failing for all makes Ford, Dodge, and Chevy.

 

Just think Carter fuel pumps have been junk from the start but Dodge still sells them and so does Cummins. They don't hold up period. Never met the minimum standards then and still don't.

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Just like Mopar oil filter and Fram are the same... 

Image result for mopar1973man fuel filters

 

Yes the is the gasoline side but there is no special specification for this is there... Nope just the cheapest filter repainted with Mopar label. These are a few reason why I will not pay trip price for a junk product and still continues today. 

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Posted (edited)
22 hours ago, Mopar1973Man said:

The only spec for a thermostat is opening temp. Nothing else can be changed. 


Ha. 
 

Other specs have been discussed many times, in threads you belong to. 
 

I suppose flow and full open temps aren’t part of the specs :lmao2:

 

You keep using the word specification, but I do not think it means what you think. 
 

There absolutely is a “special” specification for oil filters. MOPAR will always use the cheapest manufacturer for their part, and I’ve never seen them triple the price. In fact when I changed the oil on my Jeep, since were taking gas now I guess, I a MOPAR as it was cheaper. That was only for a couple thousand miles thou, I ditched that baby for a better filter. But the point is that the cheapest filter still has to meet the minimum vehicle specific specs. 
 

I also don’t think you’ll ever find a Cummins MOPAR oil filter with Fram guts... they are in fact made by Fleetguard and not bad for a OE filter.. must be that special spec. 
 

As far as thermostats.. NAPA doesn’t make them either. Cheapest bidder. Maybe they learned their lesson on bad reputation and have stepped it up some. Don’t know, won’t try it. NAPA burned their bridge with me many years ago. Other options have worked far better, so why go back to giving NAPA any of my money?? 
 

NAPA fuel filters are another POS item, hell they don’t even meet that “special” spec for 3rd gens. 

Edited by AH64ID
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14 minutes ago, AH64ID said:

I suppose flow and full open temps aren’t part of the specs :lmao2:

Being that Cummins is using 4 different thermostats I guess not being they went all over the map. Being Motorad was a small neck and low flow, then my OEM was a different as well, etc. We can compare all kind of OEM themostats and they are all different but one thing... Opening temperature. 

 

Still there is only a few companies that produce thermostats. Sure not worth $65 bucks for... 

 

14 minutes ago, AH64ID said:

There absolutely is a “special” specification for oil filters. MOPAR will always use the cheapest manufacturer for their part, and I’ve never seen them triple the price.

Bingo... LOL... I got charged $80 dollars for a Mopar OEM Fuel filter. Why I told the dealer to stuff it. I can buy Fleetguard for $13 dollars. Just like buying a $65 dollar thermostat from Cummins that splits apart in under 100 miles. 

 

16 minutes ago, AH64ID said:

As far as thermostats.. NAPA doesn’t make them either.

True. But they have been very stable and failure free in my usage. Remember I service more than just Dodge. Ford and Chevy as well as foreign cars too. Subaru, etc. Remember I speak for wider range than just a 3rd Gen Cummins. 

 

18 minutes ago, AH64ID said:

NAPA fuel filters are another POS item, hell they don’t even meet that “special” spec for 3rd gens. 

There is much bigger world than just a 3rd Gen Cummins... Again I service a very wider range a of vehicles.

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I’ve never experienced any variation in Cummins OE thermostats over 13 years... maybe it’s the application. Maybe they haven’t failed often enough to look at more frequently. 
 

Dealer is the operative word, not MOPAR. Of course you’re going to overpay at the dealer.. that’s vehicle servicing 101! So let’s not compare dealer prices to real world prices. 
 

The point isn’t just about a 3rd gen Cummins, it’s the fact the NAPA/Wix knowingly fail to meet publish minimum specs, period... I could point  to multiple instances, but they aren’t relative to this forum. Why would you ever consider them quality when they don’t care if they meet spec or not? That’s the bigger issue... they are putting their bottom line above yours. Not worth the time or money to shop there if they don’t care about the consumer. 
 


 

 

 

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Posted (edited)

Yeah I know I've changed a few of those and they are a PITA to do. Deleted truck are like the old school days for sure. Free revving the engine is not a valid test. The timing is too retard for a free revving event. You have to drive the truck to test.

 

 

Edited by Mopar1973Man
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On 1/13/2020 at 9:26 AM, kzimmer said:

I've had good results with Gates thermostats.

 

Last Gates 200*F I bought didn't last 1 week. Very wild up and down swings in temperature. Down as low as 168*F and the way up to 220*F on open.

 

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