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Hey guys, just reaching out before I start spending some money. I have a 2nd gen dodge 5speed 3.73 gears with mild build. I recently bought a 37’ toy hauler that weighs close to 9,000lbs empty. I live in Colorado and when I tow this thing is usually over some pretty serious passes. As summer is here I’m struggling keeping my engine temps under control. I do have a high flow water pump, new oem replacement radiator and 190* thermostat. While pulling up RIO with my RZR in the trailer I got a little out of control on my temps. Probably 225*. My EGTs were getting a little hot at about 1250. My truck was getting hotter sooner with my antifreeze/water ration about 70/30. I took some advice from my father who ran heavy duty diesels for 20plus years and am running 25/75. As he said it will still get hot but not as quick. He was right. Anyone done anything to their truck to keep the temps down that actually worked while pulling heavy? I’m guessimg my truck and trailer combo was close to 24,000lbs when loaded. 

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Posted (edited)

What tires?     did you regear? 3.73 is not a stock ratio. 3.54 or 4.10.  what rpm are you towing at? 

 

I spend a lot of time towing over i70 and other passes like that as well.   as long as coolant stablizes at 225* I am not worried personally.  

 

 

coolant does not do near as good of a job of transfering heat compared to Water to the higher water mix does help.  

Edited by Me78569
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Hey sorry about that misinformation it has 3.54 gears. I pull on 4th usually around 2200 rpm. That’s where my truck usually seems happiest. I have 35s on it now for tires while in a way helps me stay around 60-65 in 4th without spending too much time in high RPMs. I wasn’t too worried about it getting to 225. But I also would like to keep it a little cooler lol 

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Drop your EGT's to about 1000-1100*F it will hang at about 205-208*F coolant. I got several steep grades here in Idaho and have no issues with cooling or engine temperature. Now if I was to push 1,200 to 1,250*F it can go to 220-225*F engine coolant temperature. 

 

Image result for mopar1973man 16% grade

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225° is the most Cummins wants to see with a 190° thermostat. 

 

225° coolant also puts your oil temp around 245°, which is very close to the oil temp limit of 248°.

 

You're running 25% coolant? You need to run at least 44% coolant to get corrosion and water pump cavitation protection. 

 

Water does dissipate heat better than coolant, but you have to maintain a good percentage of coolant. 50/50 is the best of everything, if you can survive with the freeze point. 

 

Do you hear the fan operating? I would suspect it's not moving enough air when it cycles. 

 

Exhaust manifold wrap/blankets will also help with overall underhood temps, especially when you have 2 turbines. 

 

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mopar1973man- first thing I want to say thank you for your site!! This has helped me more then anything. Plus your 3cyl high idle switch is the BEST!!! I made a janky set up a few years back but swapped it with yours to cut back the amount of toggle switches I have haha also I modified it to fit my POD on my pillar looks clean!

-back to the topic. I figured my egts and engine temp were corralated to some extent. Im going to swap back to 100HP injectors to calm my egts and if that doesn't help Ill get my hands on some water/meth. It sucks to have an engine load of 41% and not be able to use the rest! 

 

~AH64ID Im running about 30% coolant with come conklin Coolant lube. Im trying to find the bottle but basically its "supposed" to supplement all the lubricants in antifreeze so you can run water. I also didn't have a choice due to time line. That was my quick fix.

I do hear my fan operating in 1st and 2nd gear. Nothing past that. I heard that it doesn't operate past that speed due to ram air being more efficient. Please correct me if that is wrong. I due have some heat wrap/ turbo blankets to do everything but haven't had the time. 

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I know on my 3rd gen the fan makes a HUGE difference, and 4th gen's too. 

 

Before I had UDC Pro with fan control my fan wouldn't cycle until 215°+, and then only barely. I now have my fan set to cycle at 208°, 1° above full open on the 190° thermostat, and the hottest I've seen my coolant is 211° and that was only for a couple seconds before it dropped back below 207°. I run about 400 rwhp and tow up to 22-23K GCW on some steep/hot hill. 

 

When the fan is working properly it makes a big difference even at 60 mph. 

 

2nd gen fans aren't electronically controlled so the temp coming off the radiator has to be enough to engage it, but I would think sustained coolant at 225° is enough to do that. 

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See I wish my fan was close to the same size as a 3rd gen. I also wish I could control mine. On a previous 2nd gen I had dual electric fans and the sucked for heavy pulling, that option is out the window. It came on it when I bought it. But it would be nice to hear the fan roar. I have only heard it come alive a few times in the 8 years I’ve owned it and all at very low speeds 

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Mine comes anytime I am towing and load the engine up good on a grade. Maybe something wrong with the fan clutch? Mine sounds like a turboprop trying to pass me when it comes on.

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Posted (edited)
3 hours ago, Akaiser21 said:

Hey sorry about that misinformation it has 3.54 gears. I pull on 4th usually around 2200 rpm. That’s where my truck usually seems happiest. I have 35s on it now for tires while in a way helps me stay around 60-65 in 4th without spending too much time in high RPMs. I wasn’t too worried about it getting to 225. But I also would like to keep it a little cooler lol 

 

Actually, it's your tires. The 35" tires change your final gear ratio way too low in the 3.1x to 3.2x realm. This adds huge amount of load on the engine typically creates way more heat both coolant and EGT's. Now if the axles where regeared for 4.10 this topic wouldn't happen. Most people choke when they hear the price of regearing the axle to keep their pretty 35 to 37 inch tires.

 

Fuzzy math. 35" tire with 3.55 gears in the axle has a final ratio of 3.14:1

 

Like on my truck I'm running 235's with 3.55 gears. Now if I switch over to 245/75 R16 that will change the final gear ratio to 3.7x or so. This would improve my torque output to the ground and allow more pulling power with more speed. Way too many people look at the cool factor but forget about the science of the gears. Tires are just a smooth gear and when you increase tire size you increase engine load because the gear ratio went too low. 

 

Optimal towing ratio is right at 3.73. 

Edited by Mopar1973Man
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I would be looking at your fan clutch if it is not locking at 225*f.  I only ever saw prolonged 225*f was pulling from silverthorn to the top of the tunnel and the fan locked and it was obvious.

 

 

Good info as always @AH64ID

 

Given 3.55's and 35" tires you might need to stick to 3rd when pulling big hills.

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2 hours ago, Akaiser21 said:

I do hear my fan operating in 1st and 2nd gear. Nothing past that. I heard that it doesn't operate past that speed due to ram air being more efficient

Yes "ram air" starts to become greater than fan air above 35mph but, when towing an 8K LB 5th wheel, I've also heard the fan clutch cycle on and off while going up long 6% grades while locked up in 3ed.   Exhaust temps will climb to 1200°F+ if left in 4th (over drive), in 3ed I can keep it below 1000°F 

 

Truck has 245/75-16 tires with a 4:10 rear end

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First off, I can guarantee that your 37' toy hauler is heavier than 9000 lbs.  Probably more like 11k - 12k unloaded...and then add a couple more thousand pounds for all your stuff/water.

 

I cant speak for the high flow water pump, but given that the Cummins cooling system is already pretty aggressive as coolant pressure can builds upwards over 70+ psi at the back of the block at upper rpms, I cant see where a high flow water pump would offer any benefit other than to create more coolant flow problems.  Not sure...

 

And as Mike pointed out, EGT's play a huge role in engine temps.  If you hold the EGT's around 1000* - 1100* then the engine temp will stay well within the normal range.  But push EGT's over 1100* and your engine temperature will definitely climb to uncomfortable levels.

 

Lastly, yes, your tire size isnt helping with a trailer that heavy.  Oh, and are you absolutely positive the radiator is clean?

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I missed the high flow water pump...

 

The 6.7 has a higher flow water pump and IIRC it's not an uncommon mod for deleted 6.7's to go back to the 5.9 water pump. The high flow pump is needed for the EGR cooler, but without it the 6.7 doesn't seem to cool as well as with the lower flow 5.9 pump. 

 

If the coolant moves too fast thru the radiator it's not cooling off, and it will cause temperature problems.  

Who makes the high flow water pump? 

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6 hours ago, Mopar1973Man said:

 

Actually, it's your tires. The 35" tires change your final gear ratio way too low in the 3.1x to 3.2x realm. This adds huge amount of load on the engine typically creates way more heat both coolant and EGT's. Now if the axles where regeared for 4.10 this topic wouldn't happen. Most people choke when they hear the price of regearing the axle to keep their pretty 35 to 37 inch tires.

 

Fuzzy math. 35" tire with 3.55 gears in the axle has a final ratio of 3.14:1

 

Like on my truck I'm running 235's with 3.55 gears. Now if I switch over to 245/75 R16 that will change the final gear ratio to 3.7x or so. This would improve my torque output to the ground and allow more pulling power with more speed. Way too many people look at the cool factor but forget about the science of the gears. Tires are just a smooth gear and when you increase tire size you increase engine load because the gear ratio went too low. 

 

Optimal towing ratio is right at 3.73. 

 

I will Be looking into swapping to a 285 tire here soon as possible. It would help me I'm sure. I only get hot when pulling long grades and when on flat or mild ground with the trailer on I only see about 28% engine load 2 190* (quadzilla PV2). I do understand what you are saying for sure. I never pull in over drive due to how weak 5th gear is and like I said my truck seems pretty content at 2-2200 rpm. I have my old stocker wheels on the other truck of mine. Ill swap back and see how it does.

5 hours ago, Me78569 said:

I would be looking at your fan clutch if it is not locking at 225*f.  I only ever saw prolonged 225*f was pulling from silverthorn to the top of the tunnel and the fan locked and it was obvious.

 

 

Good info as always @AH64ID

 

Given 3.55's and 35" tires you might need to stick to 3rd when pulling big hills.

I haven't ever gotten my truck that hot until that day. It was about 80 degrees out and I was pulling pretty hard. I evened up in 3rd towards the top. Good to know that you have hear your fan at higher speeds. I will be swapping mine out just to give it a go. 

4 hours ago, KATOOM said:

First off, I can guarantee that your 37' toy hauler is heavier than 9000 lbs.  Probably more like 11k - 12k unloaded...and then add a couple more thousand pounds for all your stuff/water.

 

I cant speak for the high flow water pump, but given that the Cummins cooling system is already pretty aggressive as coolant pressure can builds upwards over 70+ psi at the back of the block at upper rpms, I cant see where a high flow water pump would offer any benefit other than to create more coolant flow problems.  Not sure...

 

And as Mike pointed out, EGT's play a huge role in engine temps.  If you hold the EGT's around 1000* - 1100* then the engine temp will stay well within the normal range.  But push EGT's over 1100* and your engine temperature will definitely climb to uncomfortable levels.

 

Lastly, yes, your tire size isnt helping with a trailer that heavy.  Oh, and are you absolutely positive the radiator is clean?

 

Im sure it weighs way more with it loaded. It claims to be 9,000 lbs "dry." With everything loaded Im guessing to be around 13k. I bought this water pump from my local cummins dealer. Its calmed to be on their heavy equipment version of the 5.9. I honestly don't know if I'm flowing too fast. I have had this pump on for close to a year and haven't had any difference in performance. Engine temps always normal and never over cooling/ over heating... until I pulled heavy lol... I know my egts were getting a touch far and am planning on taking control of that . 

My radiator looks as good as new. I relocated my breather tube to dump back behind the motor. Sick of the mess! Also no dirt or other debris caked on. 

Thank you everyone on their input. My plan is to reduce my injector size to 100Hp over stock, change fan clutch for the sake of doing it, run with smaller tires and do myself some heat wraps. I'll give that a go and let everyone know what the difference is. If I still have the issues I might looking into a mishimoto radiator. 

 

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Posted (edited)
6 hours ago, Akaiser21 said:

I never pull in over drive due to how weak 5th gear

 

If your tires were not so big you could. I tow all the time in 5th gear and never lost the 5th gear nut. Oversized tires do kill transmissions because of the excessive low final ratio.

6 hours ago, Akaiser21 said:

I will Be looking into swapping to a 285 tire here soon as possible.

 

With 3.55 gear you should look into the 245's for a tire size that would get the final ratio right. Either that or regear to 4.10 gear so you can keep your larger tires. Looking cool comes at a price.

 

315/75 R16 (35") tires with 4.10 gear would give you a final ratio of 3.75:1.

285/75 R16 (33") tires with 3.55 gears would give you a final ratio of 3.42:1 rather low for towing.

245/75 R16 (30") tires with 3.55 gears would give you a final ratio of 3.69:1 ratio close to the 3.73 range. Optimal towing and highway runner.

6 hours ago, Akaiser21 said:

It claims to be 9,000 lbs "dry.

Skip the dry weight... Use the GVWR weight always! 

 

Like my Jayco claims a 6,588 pounds dry weight. (when pigs fly). GVWR is 8,500 pounds. Actual weight it typically around 8,000 pounds.

 

Image result for mopar1973man scales

Edited by Mopar1973Man

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Posted (edited)

Good chance your fan clutch took a crap. I had similar problems in Montana pulling 10-12k enclosed 28' camper over some serious passes. Don't buy a Chinese fan clutch.. napa $55 HD or Mopar one from genos for 150$ is money well spent. I had a fan go into my radiator with a made in China one from AutoZone. Napa one looked identical but said made in the USA. Maybe the nut was a different color. Chinese one sheared off at the nut. My experiences with camper weight is dead on what moparman said. Verified at the scales

Edited by rogerash0
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Agreed, the aftermarket clutch fans have seemingly been unreliable for members.  Kinda hit and miss, whereas the OEM units you can get at places like Geno's work best.

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1 minute ago, Akaiser21 said:

I’ll probably just get a napa fan clutch since I don’t have all the choices where I live lol. Has anyone tried out the plastic fan similar to the 3rd gen? https://www.genosgarage.com/product/dodge-ram-cummins-replacement-cooling-fan-fan9402/fan-clutch

 

Not cheap, but 39% airflow improvement is HUGE!!

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Its been years since I remember where the information came from, but the OEM engine fan on the Cummins ISB is supposed to pull 10,000 CFM at 2000 rpm.  Thats a lot...!  And towing my 5th wheel up the mountain grades in triple digit summer heat, the fan noise and power loss would support that CFM estimate.  So I guess I'm not sure what another 30% of CFM would do...if its even necessary.  Might just load the engine so much that the cooling capacity gained is offset by the increase in EGT's just trying to move the fan.

 

That said, yes, the OEM fan is no longer available but there's a thread where someone found another fan that is almost exactly the same and its bolt on.  I'll have to look for the thread.

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