How to lower Cummins ISL 400 operational temps?

[Nomad Al]

The Cummins ISL 400 in my four-month old Allegro Bus usually shows 190-205 degrees on the temp gauge when running at 65-70 mph on the "straight and level"� with the Allison 3000 transmission in "6-6"� (sixth gear overdrive). I've never previously manually downshifted on the road, leaving the selection of the proper gear to the "computer."�

However, during a recent trip from Little Rock to Branson, pulling a Honda CR-V, with the ambient air exceeding 100 degrees, the Cummins engine temp spiked to 220, and I got a warning message on the dash info panel: "Approaching thermal limits of engine"�!

By manually downshifting to 6-4, I increased engine revs to 1800-2200 rpm. The temp gauge dropped to 210 and the warning message went away. When climbing hills during the rest of the trip, I drove with my right hand on the steering wheel and my left hand on Allison transmission panel, fingers dancing between the downshift and upshift buttons, to keep engine revs in the 1800-2000 range, and the temp gauge below 220. If I let the transmission decide its own downshift points, the engine would lug down and the temperature would again spike.

After returning home, I took my motorhome to the local Cummins engine service center. They had never heard of the "thermal limit"� warning message. They checked the recorded engine fault codes and found an inactive, unexplained #2964 "Intake Manifold Temperature High."� They referred me to the local Freightliner service center for an operational check of the side radiator fan.

At my local Freightliner service center, the tech phoned Gaffney and learned that the "thermal warning"� message was intended to alert the driver to manually downshift. If I had not downshifted, the engine temperature would have continued to increase, ultimately throwing a "Check Engine"� code, and shutting back power to a "Limp Home"� mode! Gaffney also told the tech the only way they knew to check the operation of the radiator fan was with an old-fashioned, strobe light. The local service center is having to order the light.

I'll soon be driving my new Allegro Bus, again towing the Honda CR-V, to the West Coast. I'm concerned that if a short summertime drive in the Ozark hills caused the Cummins ISL 400 to flush and go red in the face, the high temps of the desert SW and long climbs through real mountains will cause the engine heat stroke, leaving me stranded alongside the road!

I'd appreciate suggestions on how to keep the Cummins ISL 400 below the thermal limit, short of playing Chopin, with the left hand, on the transmission panel!

[Nomad Al]

The Cummins ISL 400 in my four-month old Allegro Bus usually shows 190-205 degrees on the temp gauge when running at 65-70 mph on the "straight and level"� with the Allison 3000 transmission in "6-6"� (sixth gear overdrive). I've never previously manually downshifted on the road, leaving the selection of the proper gear to the "computer."�

However, during a recent trip from Little Rock to Branson, pulling a Honda CR-V, with the ambient air exceeding 100 degrees, the Cummins engine temp spiked to 220, and I got a warning message on the dash info panel: "Approaching thermal limits of engine"�!

By manually downshifting to 6-4, I increased engine revs to 1800-2200 rpm. The temp gauge dropped to 210 and the warning message went away. When climbing hills during the rest of the trip, I drove with my right hand on the steering wheel and my left hand on Allison transmission panel, fingers dancing between the downshift and upshift buttons, to keep engine revs in the 1800-2000 range, and the temp gauge below 220. If I let the transmission decide its own downshift points, the engine would lug down and the temperature would again spike.

After returning home, I took my motorhome to the local Cummins engine service center. They had never heard of the "thermal limit"� warning message. They checked the recorded engine fault codes and found an inactive, unexplained #2964 "Intake Manifold Temperature High."� They referred me to the local Freightliner service center for an operational check of the side radiator fan.

At my local Freightliner service center, the tech phoned Gaffney and learned that the "thermal warning"� message was intended to alert the driver to manually downshift. If I had not downshifted, the engine temperature would have continued to increase, ultimately throwing a "Check Engine"� code, and shutting back power to a "Limp Home"� mode! Gaffney also told the tech the only way they knew to check the operation of the radiator fan was with an old-fashioned, strobe light. The local service center is having to order the light.

I'll soon be driving my new Allegro Bus, again towing the Honda CR-V, to the West Coast. I'm concerned that if a short summertime drive in the Ozark hills caused the Cummins ISL 400 to flush and go red in the face, the high temps of the desert SW and long climbs through real mountains will cause the engine heat stroke, leaving me stranded alongside the road!

I'd appreciate suggestions on how to keep the Cummins ISL 400 below the thermal limit, short of playing Chopin, with the left hand, on the transmission panel!

[Cruzer]

Hi Al,

I too, have typical temps as you've mentioned on the straight and level.

I also do lots of mountain climbing out west and get into some hot temps, high altitudes, and serious grades that just don't quit so I can relate to what you are saying.

First of all, the Freightliner XC chassis uses a 1,050 sq in radiator that stacks everything in series. According to Cummins' recommendations, this is minimal for the 400 ISL. FL has a had a number of recalls to try to correct this. The first was a fan speed reprogramming and the second was a bunch of baffles to try to help redirect the airflow better and shield the heat. They also replaced the Dexron hydraulic fluid that drives the side radiator fan motor with 15W-40 motor oil because they felt that the Dexron thinned out too much when it got hot and the fan speed suffered. There is a new recall that just hit where they want to replace your hydraulic oil cooler. Now it seems that the thicker engine oil blows out the oil coolers so they have a new heavier duty one.

Spartan, on the other hand, stacks their components vertically so that they all get clean, cool air. They also use a 1,326 sq in radiator and don't have these issues.

Okay, all that history aside, the FL chassis is capable of not overheating on extreme grades. It gets close, but generally isn't an issue.

The 400 ISL has lots of guts so you don't tend to rev it that much when climbing grades. However, the load is increased upon the engine, which increases the heat it needs to get rid of. Unfortunately, a slow revving engine is turning a water pump that is also turning slow and water pumps pump more water at higher speeds than at low speeds. BY manually downshifting you will increase the engine revs, which does two things. First, it decreases the heat load upon the engine because more intake air is coming in at higher RPMs, which helps cool the engine as well as reduce the load placed upon it by "lugging" it. Second, the water pump spins faster, transferring the hot engine water to the radiator where it can be cooled faster.

I've seen the "Warm Engine Temps" (or whatever it says) light come on a few times when climbing out west. This is set at somewhere under 220 degrees. Then, when I manually kick it down a gear it'll hold it's temperature or reduce it, depending upon how steep and how long the grade is. If it's extreme grade, such as 9-11%, I'll generally drop it down to 4th gear soon enough as the speed scrubs off. I also push the snowflake button on the dash air if it's running to kick out the dash air conditioning compressor because that too adds heat to the radiator because it's right in front of it.

Your cooling system is pressurized. It shouldn't boil until you get to around 235 degrees. Therefore the initial warning light is just that - a warning. I think of it as a wake up call to monitor the temps and perform some manual input. On extreme cases you'll see the temps climb a bit more but you should be able to keep them within tolerance so that they don't get into the 225-230 range. At 235 you will get an alarm and the Check Engine light and then you'll be pulling over and letting it cool. However, I've climbed over 11,000' in hot temps as high as 106 in places like the Beartooth Mountains, Mount Evans, Crater Lake/Diamond Lake, and the infamous US-14A over the Bighorns without having any serious issues. You will have to do the piano thing though because the Allison can't automate well enough to regulate engine temps.

[Nomad Al]

Hello Mark!

Thanks for info on why my new Allegro Bus/Freightliner XC/Cummins ISL 400 operates on a thermal razor's edge under heavy loads in hot weather.

After reading your post, I crawled under the back of my Bus and studied Freightliner's side radiator arrangement. You're right, the relatively small surface area, AC compressor/radiator sandwich cooled by a single, multi-speed fan has got to be an over-achiever to keep up with the heat load thrown off by the Cummins 400!

It seems to me that the "normal"� operating temp range of the Cummins 400 is designed (too) high primarily to control/burn off pollution emissions and could be reduced to improve performance and reliability. Do you know of any single or combination of feasible, after-market mods like an increased-flow intake system, "straight-through"� muffler, larger core radiator, multiple electric cooling fans, dash-controlled ECM chip, synthetic lubricants, coolant additives, etc. that would enable the Cummins 400 to keep a "cool head"� when others are "seeing red"�?

[Cruzer]

I recently discussed this with someone who was a cooling system engineer (ironically, he now works for Spartan chassis ). He agreed that all of the airflow fixes will only yield a few degrees at best. The problem really isn't that the radiator doesn't have adequate airflow, it's just that it's too small. It's the coolant side of things that needs help. The coolant absorbs the heat from the engine and delivers it to the radiator. The heat transfers from the "wet" molecules to the air molecules flowing through the radiator via conduction in the radiator tubes and fins. There really needs to be more tubes and fins. Besides, at high altitudes the air density is less so you are going to have less heat transfer - just when you need it the most, unfortunately.

Synthetic lubes are nice but not the answer. Your Allison is already filled with Transynd but it's not real cost effective to run synthetic oil in the engine, although it is great stuff. The big benefit with synthetics is not that they run cooler, but that the hold up better in extreme conditions (and heat) so that they do a better job of lubricating. That really won't help with this problem though.

I did pick up a few degrees by switching coolant to the Fleetguard ES Compleat coolant. It's the best that Fleetguard (a subsidiary of Cummins) makes for that engine. I forget the big difference (other than it's blue) but it was something to do with Boron additives in the coolant. The Fleetguard website will give you details if you want. Still, it's only a few degrees and you'll still have to shift manually on the big grades.

I have heard of a "Desert Cooler", which is some sort of a water spray system that cools the radiator down. I don't have any details on it though, nor do I know how effective it is. I remember that someone on the TiffinRVnetwork recently posted that they went with that so maybe they could help if you are interested in it.

[Nomad Al]

It's very frustrating to have paid for a 10-ton gorilla engine that may pass out from heat exhaustion because it can't sweat!

Next time around I'm going with Spartan!

[Cruzer]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Nomad Al:
......

Next time around I'm going with Spartan! </div></BLOCKQUOTE>

I hear you. Check out This Link to see one that I'm looking at on Monday.

[rebelsbeach]

GO ahead and get that thing Mark!!!

You have to tell yourself you aren't getting any younger and you deserve to have your toys now...

[Cruzer]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by rebelsbeach:
.......
You have to tell yourself you aren't getting any younger.......... </div></BLOCKQUOTE>

Speak for yourself. As for me, I don't ever plan on growing up.

[Teach]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Cruzer:
Speak for yourself. As for me, I don't ever plan on growing up. </div></BLOCKQUOTE>

Me either...

[Ed-Deb]

Cruzer,

Very nicely done review.

Your not getting older...just wiser! And remember...He who has the most toys wins!

[Cruzer]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Ed-Deb:
Cruzer,

Very nicely done review.

Your not getting older...just wiser! And remember...He who has the most toys wins! </div></BLOCKQUOTE>

Yeah, but you can't take them with you. That's why you have to enjoy them while you're still here. The Bible says that the streets of heaven are paved with gold. Does anyone know if they'll be on the "Street Atlas Heaven" version?

Oh wait, Street Atlas runs on Windows and I don't think we'll have to put up with Windows in heaven because everything will be perfect.