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After draining, flushing and replacing water pump and t-stat I'm having some really weird temp issues. While sitting at a stoplight it reads 180, when I start driving it climbs to around 190 and then cools off again at the next light is it possible there is air trapped somewhere in the system. I followed the instructions in the article by moparman filling the block before installing the t-stat then filling the system via the radiator filler neck. How can I get it to burp the air out if that's the case. 

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That sounds just fine to me.  Mine will do exactly the same except I have a 200° stat...so mine sits at 190ish and goes up to 200 then back to 190.  It's a self purging system so it will eventually remove any air by itself. 

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Ok, does it eventually settle back down, ive owned this rig for 9 years and ive always had it flushed by a machine at a shop but i figured since I needed to do the wp and t-stat I would do it myself. But it's always been pretty steady temp wise untill now.

I'm used to my power wagon gassed fill it and forget it lol

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There was quite the discussion about thermostats on here a while ago. A number of guys having wild temp swings as more and more name brand parts are being made in China. Yours sounds normal to me too. Mine will usually go to 200-202 and then open up and fall back to 188 and then kind of stabilize around 190-198. A 10 degree swing isn't bad. Just curious, what brand stat did you get? 

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Been running only NAPA thermostats no issues. Typically doing 75k miles and do coolant flush and fresh thermostat.

 

Matter of fact I found my last Cummins thermostat I changed for a customer being it fell apart. Ill post a photo when I get home.

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Be careful I just replaced mine with a Napa unit and they gave me one for the 12 valve. It caused really wide temp swings and would not settle down. I went back and asked for one like I took out and they could not find one as per their pictures. I had the same problem 3 years ago and they finally found one but the store was bought out and all of the old employees left. I ended up getting one at Advance auto that was a Stant. Here is a comparison with the 12 valve on the right. 1229370990_thermostat2.jpg.caf7008423910126782a7752ec3da69d.jpg2144731974_thermostat1.jpg.d18722330a692f708a3434a72feda2bf.jpg 

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Well at this point the swings are only 6-9 degrees. And mine does look like the one on the left. The thing I found weird is that it would cool while sitting and heat up 6 to 9 degrees while driving then go up and down while on the freeway.  When it's normally the opposite way. Fortunately the old one is still in good shape just replaced it since i haven't before just kinda wondering if the sender is funky

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Posted (edited)

I have changed my sender 3 times over the years with no difference. T stats seem to make some diffetence. Had both shown in the pictures and they act similar. Funny though for the first 5 years the needle was like it was glued to the gauge almost. But since then I see a lot swings no matter what t stat I put in. I dont give it second thought anymore.

Edited by dripley

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Posted (edited)
1 hour ago, dripley said:

I have changed my sender 3 times over the years with no difference. T stats seem to make some diffetence. Had both shown in the pictures and they act similar. Funny though for the first 5 years the needle was like it was glued to the gauge almost. But since then I see a lot swings no matter what t stat I put in. I dont give it second thought anymore.

Mine was the same way till about a year ago stuck on 180. So I thought it might be weak when it started fluctuating . So the Chinese are just screwing with us by making inferior products and giving us something to talk about on our forums. So it's a car ona virus LOL. 

Edited by Dave f
Omission
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Posted (edited)
On 6/22/2020 at 6:13 PM, Dave f said:

Ok, does it eventually settle back down, ive owned this rig for 9 years and ive always had it flushed by a machine at a shop but i figured since I needed to do the wp and t-stat I would do it myself. But it's always been pretty steady temp wise untill now.

I'm used to my power wagon gassed fill it and forget it lol

 

You have owned the truck for 9 years with the temps fine until now. If your Napa t-stat looks like the one on the right in Bobs picture, I would get rid of it and find one like the t-stat on the left. Note the different type bypass sealing surface on the bottom of the t-stat. My '01 will not work right with a Napa stat. 

Edited by NIsaacs

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So mine does look the same as per the top view of the one on the left. Are you referring to the rounded bottom so it sits in the kind of beveled portion of the block casting. If so never thought of looking at that not sure the one I pulled out looked like that. Need to check that out tonight 

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Posted (edited)

The right is the new style NAPA which I'm using currently. The one on the left is the previous model napa which I've used in the past.

 

Here is the junk Cummins T-stat... Be aware that Cummins DOES NOT manufacture any thermostats. This design started by Reobertshaw which no longer produces thermostats and then handed this off to Mr. Gasket. So you Cummins thermostats is not Cummins Design at all. The original design was produced by MotorRad back in 1998.5 to 2002 and you can no longer by that thermostat.

post-11421-138698198982_thumb.jpg

 

Another member with Cummins thermostat that seperated...

OEM & Aftermarket - Page 2 - General Conversations ...

 

Robertshaw 330 - Called and verified no long manufacturing...

https://www.flowkoolerwaterpumps.com/products/robertshaw-330-160-degree-thermostat

 

Then Mr. Gasket. Which is now products by Holley... Current manufacture.

https://www.holley.com/products/cooling/thermostats/parts/4365

 

Edited by Mopar1973Man

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Posted (edited)
19 hours ago, Dave f said:

Well at this point the swings are only 6-9 degrees. The thing I found weird is that it would cool while sitting and heat up 6 to 9 degrees while driving then go up and down while on the freeway.  When it's normally the opposite way.

My gas motors will act the normal way that you're talking about...but my diesel is different the same as yours is.  Mine will not reach thermostat temp unless I'm driving it.  Even if I just let it idle after I've been driving it will cool low enough to not open my 200° thermostat until I start driving again.  Diesels just idle cooler than gas motors do. 

 

Another thing I've noticed is that the fluctuations lessen substantially the longer I've been driving it.  If the coolant in the radiator is closer to ambient temp I'll get the biggest fluctuations.  If the rad coolant is warmer from being driven and circulated through the motor for a while I'll get more stability. 

Edited by Bullet

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 Just my $.02 but while idling the clutch fan is engaged and pulling as much air as possible. Have you seen the size of that thing. The fan is huge and moves a chit ton of air at idle and with very little fuel being burnt at that time there isn't a lot of heat being created either. Now if you had just pulled over after a long hard pull uphill and let her idle she would cool down for you. The reason behind the fan design on a diesel. 

 Again, just my thoughts after pondering it a minute.

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That surely could have an effect on it in keeping ambient heat from loitering under the hood around the block.  All my gas motors idle hotter than my diesel does...they will keep the thermostat open at idle while my diesel will keep it shut.

 

My sport car will open the thermostat from a cold start just idling in the garage in just 3 minutes...crazy fast.  But maintains that temp just fine after open and with the electric fans ripping. 

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Ok gentlemen, been to all the local part stored and No one has one with the beveled part or nipple on it and dodge has discontinued it in 2013 . This is rather frustrating also the one I have in the truck now is a 190 everyone states is oem and the one I pulled out is a 180 WHAT THE @#$$#@ LOL sorry for the explative

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My clutch fan does not lock till it at least 220*F coolant temp. Mine remains unlocked for 90% of my driving. My idle temps can drop as low as 188*F in the winter being my heater core performance can suck the heat out of the coolant. Running temps I typically hover about 195 to 197*F. I never idle warm my truck, well lets say the only amount of time I'll give it is till it reaches about 80 to 100*F and hit the highway. In the winter I'll warm it slightly to get oil spread out in the engine. Then I get rolling instantly. I make more heat rolling than idling. 

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Ok @Mopar1973Man, explain this to me because I may have been wrong in my previous post.

 Are the fans on these trucks not like on a gasser where as the clutch engages to spin the fan at low rpm and releases it at higher rpm when there should be air flowing as road speed increases?

 I know on the "big rigs" they are controlled by a temp sensor and an air activated clutch but these are not, I have not noticed any electrical going to the hub either (but then wasn't looking for it).

 Not questioning your comments, just wanting to learn, I may have misspoke earlier. Thanks.

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To me degrees is pretty much just a personal preference...you're not gonna harm your truck with either.  I've also heard that 190° is stock on our trucks...which is pretty much the temps I got before I changed.  Also heard that the hotter they run the more efficiently they run...so I slapped in a 200°.  I haven't noticed any difference in mpgs but the heater sure does work more efficiently.  And since all the 6.7's run 200° I figured if it's good enough for them...

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Ok, so what would be the reason it would have a 180 in it. But the 190 one is the one I'm having issues with its like it's constantly opening and closing. My truck runs ice cold in the winter. I never idle warm it or It would take forever in winter I have a 15 mi commute in witch it doesent hit 180 till mile 15 in winter even after using the block heater when it's below 40 degrees in the morning. It's always been steady when it hits 180 never straying much more that a few degrees wether it's 30 or 105 why such weird swings now it will jump to 190 degrees after driving a block then dropping to 183 degrees two blocks later. Im confused 

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The reason that the larger tstat causes wild temp swings is that my 190 degree will not open at anything below about 198 and then temp is so high that it opens all the way dumping a large slug of cold coolant through the motor and cant close fast enough to keep it at temp. This happened with both tstats installed 3 years apart. The way it acted makes me think that when running down the road the flow pressure might be so great that it does not allow the large tstat to open when it should and when it generates enough force it slams fully open because temp has gone to high. When I was a owner/operator I was taught back in the 80 that it was not good to heat cycle a engine and dumping a slug of ambient  coolant that fast has to cause a fair amount of stress and will shorten your engine life.

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