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So recently I’ve been noticing when i leave in the mornings for work after letting my truck warm up, my coolant temp is never past 165. No matter how long I let it warm up. I Was hauling my horse trailer this morning it was 34° And the coolant temp never reached 190. Maybe touched it once on an uphill but otherwise no. Is this a problem? Stuck thermostat? 

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These engine do not produce alot of heat idling especially from a cold start in 30* weather. I can let idle for 30 minutes or 2 hours and not see  any difference in temp until I drive it. I have never found any benefit by letting run in the morning more than a couple minutesI.  am sitting idleing after driving to work and only at near 175*. But if you have a 190* t stat it should come up near 190 and hold while your driving. Might just be starting to fail. They are not expensive and easy to replace.

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Cummins states no more than 3-5 minutes at idle and anything over 10 minutes is considered excessive. Best bet in those mild temps is a short idle for oil pressure to build and then drive her easy until she is at operating temp. 

 

How long is your drive? It's possible the thermostat isn't fully closing and not allowing the block to get to operating temp. 

 

What year truck? Do you know what temp thermostat is in it?

 

 

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13 minutes ago, AH64ID said:

Cummins states no more than 3-5 minutes at idle and anything over 10 minutes is considered excessive. Best bet in those mild temps is a short idle for oil pressure to build and then drive her easy until she is at operating temp. 

 

How long is your drive? It's possible the thermostat isn't fully closing and not allowing the block to get to operating temp. 

 

What year truck? Do you know what temp thermostat is in it?

 

 

About an hour drive, it’s a 2001. I have no idea what temp Thermo it is. I know I hve never seen it go over 190 unless I’m going up something steep with my horse trailer. Even then just barely. Maybe 195

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52 minutes ago, ColoradoColt said:

About an hour drive, it’s a 2001. I have no idea what temp Thermo it is. I know I hve never seen it go over 190 unless I’m going up something steep with my horse trailer. Even then just barely. Maybe 195

 

If it's an hour drive and you're not getting to 190° unless loaded then you likely have a stuck thermostat. 

 

I would start by replacing the thermostat... not going to start another thermostat brand war... with a 190° thermostat and see if that helps. 

 

It is possible that a previous owner put a 165° thermostat in as that's a marine option, but not very likely. 

 

The 190° thermostat should crack at 187°-193°, run around 191°-193° cruising, go full open at 207° and not exceed 225°. Depending on load, speed, and ambient temp you might see up to 215°-217° pulling a steep grade. 

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My truck had a 180 in it,  heater was useless and it never really got warm, backflushed the heater and used Cat cooling system cleaner and fitted a 190 thermo..... just right now, never really goes over 190 to 195 ish

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I put a 200 degree in mine and that sucker will put out some serious heat during the winter.  I have a regular cab and it's not long before I start thinking about cracking a window.

 

OP...I can hit 200 with a cold engine on a cold day in about 12-15 mins of driving so I would guess that your thermostat is stuck in a slightly open position.  Of course I'm on the gulf coast so our definition of 'cold day' may differ slightly. 

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3 hours ago, Bullet said:

I put a 200 degree in mine and that sucker will put out some serious heat during the winter.

 

I tried a 200 a couple years ago and holy F you're right, it was hot as hell. I'm back to a 180 and still a satisfactory amount of heat in -35°C on the highway. Just enough.

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48 minutes ago, kzimmer said:

 

I tried a 200 a couple years ago and holy F you're right, it was hot as hell.

Hahaha...I don't know how hot hell is...yet.:evilgrin:  But the cab becomes a sauna in a hurry!

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It does not take much to tighten those bolts. I usually do mine with a 1/4" drive socket wrench and snug them down. Never has leaked.Nothing wrong with torquing though.

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9 hours ago, 98whitelightnin said:

Mpg will suffer at 160

Is there a documented experiment to support this? Just curious. I like learning facts like this, but only if they're substantiated.

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4 minutes ago, kzimmer said:

Is there a documented experiment to support this? Just curious. I like learning facts like this, but only if they're substantiated.


There are a few good articles on the subject. Compression ignition always benefits from higher coolant temps. It’s one of the reasons that Cummins went to a 200° thermostat on the early 4th gen 6.7. 

I suspect that oil temp is why they went back to a 190° thermostat. That’s nothing but an opinion based on what I’ve seen with oil temp in these motors. 

 

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Like myself I running a 190*F thermostat. Typically with winter temperatures I run about 160*F to 170*F in oil temperature. 

 

2nd Gen vs. 4th gen for oil coolers are way different layouts on how the coolant flow is routed over the oil cooler and 4th gens have a much better coolant flow over the oil cooler and can easily run a 200*F year round. 2nd gen isn't as good but still very functional system. 

 

Anything below 180*F is going to suffer for sure. I've done my own testing with coolant temps. Being you need heat to make the fuel change from liquid to vapor and then ignite and burn completely. So between coolant and IAT these two numbers will either improve the ignition quality or not.

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180*F alternate cooler thermostat. I tried it as a test its fine in the summer time but doesn't work very well in the winter time gets too cool.

 

190*F is the stock temp. 

 

You can install 6.7L 200*F thermostat and it will fit just fine and produce serious vent temperatures in the cab. It will strip the ice from a windshield rather quickly. 

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6 hours ago, ColoradoColt said:

Thanks guys, put in a 190°. Sitting at just under 190 now. Seemed to warm up faster this morning as well. I’m happy about that 

 

Good news!!

 

7 hours ago, Mopar1973Man said:

Like myself I running a 190*F thermostat. Typically with winter temperatures I run about 160*F to 170*F in oil temperature. 

 

I didn't realize you put a oil temp gauge in. Where did you put the sender? You run a lot colder oil than I did in the 05. 

 

My 05 would run coolant temp to coolant +5-10° in the winter without towing. Summer or towing in winter it ran coolant +15-20° unless I was on a long hard pull then it could get to coolant + 25-30°. 

 

7 hours ago, Mopar1973Man said:

 

2nd Gen vs. 4th gen for oil coolers are way different layouts on how the coolant flow is routed over the oil cooler and 4th gens have a much better coolant flow over the oil cooler and can easily run a 200*F year round. 2nd gen isn't as good but still very functional system. 

 

The design of my 05 5.9 and 18 6.7 coolers looks very similar, thou they don't share the same core part numbers. The block holds less coolant on a 6.7 than a 5.9 and I do see that effect on warm-up and cool-down times, they also fluctuate temps a lot faster. 

 

I don't run a oil temp gauge on the 18 and the one on the dash is fake, but it really mirrors what I saw on the 05 in nearly all situations. 

 

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6 hours ago, ColoradoColt said:

Thanks guys, put in a 190°. Sitting at just under 190 now. Seemed to warm up faster this morning as well. I’m happy about that 

Congrats...glad you got her fixed up! :thumbup2:

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12 hours ago, kzimmer said:

Is there a documented experiment to support this? Just curious. I like learning facts like this, but only if they're substantiated.

I had one of Mikes or Ryan’s high idle boxes about 10 years ago and for some reason the truck ran 160* with it hooked up. I drove around for a month at 160* and getting 13.5. Finally figured out it was the high idle box And when I removed it, Temps went back up to 190* and mpg jumped back up to 16.5

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14 hours ago, Mopar1973Man said:

Like myself I running a 190*F thermostat. Typically with winter temperatures I run about 160*F to 170*F in oil temperature. 

 

It blows my mind that your oil temp could be colder than coolant temp. I'm not sure that's possible.

 

2 hours ago, 98whitelightnin said:

I had one of Mikes or Ryan’s high idle boxes about 10 years ago and for some reason the truck ran 160* with it hooked up. I drove around for a month at 160* and getting 13.5. Finally figured out it was the high idle box And when I removed it, Temps went back up to 190* and mpg jumped back up to 16.5

 

 

Perhaps the high idle box was fooling coolant temp, and you weren't actually at 160, just displaying 160.

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8 hours ago, kzimmer said:

It blows my mind that your oil temp could be colder than coolant temp. I'm not sure that's possible.

 

Efficiency... Less heat lost the more power to the ground. All about the Quadzilla timing. 

 

14 hours ago, AH64ID said:

didn't realize you put a oil temp gauge in. Where did you put the sender? You run a lot colder oil than I did in the 05.

 

 Oil cooler port on the oil filter housing. Extra temp sender comes with the Quad which is labeled Trans Temp but I know it Engine oil temp. I'm running about 20* at 2k RPMs. 

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