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tom41 · 06-30-2006, 06:20 PM

I was reading an other post about the rpms an downshifting of diesel large engines on long pulls to keep down high temps . I have a 36 ft 230 turbo cummins 6 sd allison, an have a problem with higher temps on long grades 6% or more in 80 degree an higher summer temps. Doesnt happen in cool weather or even raining it will run considerable cooler. Anyone have any ideas as to my engine as to what rpms should be maintained on long grades ? thanks

tom41 · 06-30-2006, 06:20 PM

I was reading an other post about the rpms an downshifting of diesel large engines on long pulls to keep down high temps . I have a 36 ft 230 turbo cummins 6 sd allison, an have a problem with higher temps on long grades 6% or more in 80 degree an higher summer temps. Doesnt happen in cool weather or even raining it will run considerable cooler. Anyone have any ideas as to my engine as to what rpms should be maintained on long grades ? thanks

John_Canfield · 06-30-2006, 08:10 PM

Tom - sometimes I need to run my ISL 400 HP at 2000 rpms to pull a long grade to keep the temperature in the low 200s (200-210.) I have the side radiator with a variable speed fan that doesn't kick in until about 210 degrees and it won't spin at full rpm until the engine is at 1700 rpm.

Gary RVRoamer · 07-01-2006, 03:47 AM

There is no simple answer. Higher RPMs generate more heat but also run the cooling fans at higher speeds and circulate more water through the cooling system. You have to experiment to find the spot that works best for your particular engine and cooling system.

tom41 · 07-01-2006, 03:57 AM

Thanks John An Gary for the replies, I'm also in the process of cleaning the radiator an aftercooler, an hopefully that will help also. thanks again,

Kiwi · 07-01-2006, 01:38 PM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by RV Roamer:
There is no simple answer. Higher RPMs generate more heat but also run the cooling fans at higher speeds and circulate more water through the cooling system. You have to experiment to find the spot that works best for your particular engine and cooling system. </div></BLOCKQUOTE>Gary, can you always say that higher RPM = higher temp? If the engine is lugging, downshifting puts the work in the powerband where it can more easily be done, this normally lowers engine temp. I think heat is more directly proportional to load than RPM.
Walt

Gary RVRoamer · 07-02-2006, 04:24 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">can you always say that higher RPM = higher temp? </div></BLOCKQUOTE>

What I said was that higher RPMS = more heat , which may be different than "higher temp". Engine heat comes from the detonations of the fuel in the cylinders and more RPMS generate more detonations per second and thus more heat. Whether more generated heat results in a higher engine temperature depends on the efficiency of the cooling system at any giver RPMS.

Lugging doesn't make the engine produce more heat. However it does reduce the effectiveness of the cooling system, which often results in higher engine temperatures. That's why I said that higher RPMs can also be beneficial and that you need to find the spot where heat generation and heat removal are in optimum balance. This is generally neither very high nor very low RPM and is typically near the peak of the horsepower or torque curve becasue the systemns are designed to run well togeher at that point.

However, if the cooling system is clogged with sediment or the air flow through the radiator is inhibited for some reason, it may be lower or higher. Sometimes higher RPMS will overcome cooling system problems through greater water pumping or fan airflow, but in other cases it merely generates more heat that is not carried away.

Kiwi · 07-02-2006, 09:03 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by RV Roamer:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">can you always say that higher RPM = higher temp? </div></BLOCKQUOTE>

What I said was that higher RPMS = more heat , which may be different than "higher temp". </div></BLOCKQUOTE>

Good clarification, thanks. I understand better now.
Walt

Ed-Deb · 07-02-2006, 09:22 PM

My experience with my Dodge p/u with Cummins ISB diesel engine is not necessarily as others explained.

While pulling a hill if the engine RPMs are low 1500-2000 rpms then the exhaust gas temperatures (EGT) are very high (1100-1200 degrees plus). This temperature increase correlates to the fuel being burned at low rpm but within the max torque range. This equates to higher engine temperatures but due to the low RPM there is less cooling effiency. Therefore, the engine temperature will increase.

When I down shift and increase the RPMs to about 2300-2600 then the EGTs drop dramatically (800-1050 degrees) which corresponds with a lower engine temp (180-190).

I have not driven my MH enough yet to see if this holds true but it should as the diesel engine works the same. The difference will be with the Allison 6 speed auto.

Kiwi · 07-03-2006, 04:36 AM

Thanks Ed-Deb,
That raises a question in my mind. I agree with RV-Romer that more RPM's equal more detonations. But is the same amount of fuel delivered at each detonation? Is the fuel delivery proportional to load? If that is true, then more fuel would equal more heat. And it would be possible for a slower turning engine that is lugging to be generating more heat than a faster turning one running in the power band.

Not trying to be nit-picky here but want to understand my engine.

Walt

jlb77399 · 07-03-2006, 01:45 PM

My experience is the same as Ed-Deb. I have a 2001 PSD Ford and pull a 16,000lb 5th. If I try to pull a hill and lug the engine (1600-1900 rpm's) I will have my EGT go to 1250-1300 degrees, if I down shift and get the engine to 2400 rpm's the boost will go up and the egt's will go down. I have the Ford chipped and have all the gauges and big exhaust.

Now on the M/H, it has a 300 Cat and I see the same thing. If I try and let the Allison decide what gear I pull the hill in, it usually will be in one gear to high., thus I down shift and get the CAT to over 2000, sometimes 22-2300 rpms and the water temps do not get as high.

So, if it were I, just down shift and keep the RPM's up.

Jim

HarveyP · 07-03-2006, 02:35 PM

I have a 1994 Cummins 230 hp 5.9 liter engine. Where is the redline for this sort of engine? What is the max rpm any of you would feel good about? Thanks, Harvey

RKL2 · 07-07-2006, 05:36 PM

Tom41...on my previous 94 Vectra with the 230 cummins I had to run at 2100-2200 RPMs to pull long grades on hot days.....It could pull all day at those rpms but below 2000 rpm it always heated up and up....Did the Rockies without a problem after a trucker told me at what rpm to run those grades....I run my 330 cat at 2000 on the same grades and no heat problems to date...On the 230 the increased rpms spun the fan faster and that was what was needed with the small 230 radiator.....good luck RKL

Lug_Nut · 07-08-2006, 08:47 AM

HarveyP, I believe your question is, what is the red line" not what should you operate it at as RKL has pointed out. The red line, is the governed RPM the engine will power up to, in gear or not. The ISB is governed at 2800 RPM. For engine braking such as an exhaust brake if so equipped, you should be good for at least 10% over governed RPM. I hope this answers your question.