How hot is HOT!?

[PToombs]

I would change the thermostat to the Cummins one and drive it then. I bet it's staying open and the water isn't getting cool enough before it goes back in.

I would think that it would run cooler in the lower gear because of less load? More RPM's equal more air flow. With my 5 speed it's true, especially with a load. Depending on speed, of course.

 

[JLEONARD]

I would think that it would run cooler in the lower gear because of less load?

I would agree with that.

 

[WCantrell]

I would think that it would run cooler in the lower gear because of less load?

I would agree with that.

That also agrees with my prior experience pulling loads in the mountains with gas engines.



Given that, what do you think would cause higher temps in a lower gear (higher RPM). Maybe the thermostat isn't metering the water flow correctly?

 

[cerberusiam]

That also agrees with my prior experience pulling loads in the mountains with gas engines.

Not a gas engine, don't work the same way.



Depending on how your fueling is setup, more rpm's equals more fuel which equals more heat to dissipate.



The question is how much fluctuation should there be? Given your cooling system is efficient you may or may not see a spike in temps with around stock fueling. Turn the fuel up and you get a temp rise at higher rpm's. Neither the turbo nor the cooling system can handle the extra load so temps rise a bit.

 

[JLEONARD]

more rpm's equals more fuel which equals more heat to dissipate

Not always. A diesel is pretty precise in that it will burn fuel based on horsepower being used.



That said, same speed in different gears will burn the same fuel, but the higher rpm will be circulating coolant faster, higher fan speed for cooling, and higher air flow thru the engine. That will cool the engine better and faster.

 

[cerberusiam]

more rpm's equals more fuel which equals more heat to dissipate

Not always. A diesel is pretty precise in that it will burn fuel based on horsepower being used.



That said, same speed in different gears will burn the same fuel, but the higher rpm will be circulating coolant faster, higher fan speed for cooling, and higher air flow thru the engine. That will cool the engine better and faster.

Across a narrow range of rpm's and gearing around BSFC that may hold true, not across a broad range of rpm's and huge jump in gearing from drive to OD.



The physics of that are impossible. HP is a function of rpm, the more rpm the more fuel it will take to reach the rpm UNLESS you change the load parameters. With a given load, BSFC will plateau across a narrow range of efficiency then ramp sharply upwards as rpm's increase. I guarantee there is a fuel consumption difference between 1900 and 2600 rpm's, which is about the equivalent of dropping from OD into drive.



If the cooling system is capable of handling the difference in heat there should be little or no change in the temp, but, lots of things will affect that. If the fan clutch locking up enough, is the water pump flowing adequately, is the radiator cooling adequately. All will impact the temp rise over time. As pointed out, increased water flow increased air flow, etc, will keep the temp down but that does not mean the heat was not generated. It means the cooling system is adequate for the conditions, variations of the parameters will yield different results.



Consider this also, the amount of fuel being injected may be more than the boost is capable of handling along with the advanced timing is going to jack EGT's somewhat. That will show in both heat in the oil being dumped to the cooling system and heat from combustion being dumped to cooling system. Now add a non-lockup TC that is spinning faster than normal and creating more heat which is also being dumped to the cooling system.



If the temp didn't rise some I would be suspicious. Its not about a rise in temp but rather about how much of a rise that needs to be watched.

 

[PToombs]

I agree with cerbs last line. The temp is going to rise, the question is, how much is too much?

And with his transmission mods and what he has said, I don't think heat sink from the trans is the problem.



WC, I think that's the problem, the thermostat metering the water flow. I know guys that wanted to cool their gassers more, so they pulled the thermostat. Guess what? The engine ran hotter yet. Reason, the water didn't stay in the radiator long enough to get cool. I think your thermostat is opening too soon or slightly stuck. Time and again on here guys use non-Cummins stats and have heating issues. 5 or 10 degrees difference on a stat makes a big difference on cooling in these engines.

 

[WCantrell]

Somehow I managed to post this to the wrong thread...



Thanks for all the input. I have learned much! Has anyone heard of changes in the design of aftermarket water pumps? The one I removed had a ring on the impellor. (maybe a restrictor?) The replacment did not. Fyi, the replacement came from NAPA.

__________________

 

[PToombs]

I've seen them either way also. It's been awhile so I can't remember which is new style and which is older.



Let us know if it helps!

 

[Mel Fuelling]

The ring, or shroud, on impeller fins is supposed to improve the efficiency of the water

pump.

 

[JHumphries]

On the down shifting topic:

If it takes 200 lb-ft to the driveshaft in OD to maintain speed, The engine would be putting out 273 lb-ft assuming a . 73 OD which is not correct for these transmissions.

However when you shift to direct-drive, 1:1, the engine only has to put out 200 lb-ft, therefor less load on the engine, combine that with more air and all of the afore mentioned increases in cooling, this is why we down shift to go up hills and keep EGTs down.

If I'm way off, someone speak up.

 

[cerberusiam]

On the down shifting topic:

If it takes 200 lb-ft to the driveshaft in OD to maintain speed, The engine would be putting out 273 lb-ft assuming a . 73 OD which is not correct for these transmissions.

However when you shift to direct-drive, 1:1, the engine only has to put out 200 lb-ft, therefor less load on the engine, combine that with more air and all of the afore mentioned increases in cooling, this is why we down shift to go up hills and keep EGTs down.

If I'm way off, someone speak up.

Good try but you need to compare apples to apples for it to make sense. TQ and HP are 2 different animals, one is a rate of acceleration while the other is a measure of work performed. Your trying to apply TQ to speed and its not applicable, only as calculation of HP.



Its not about how fast we get to speed, its how much force it takes to maintain the speed that that determines HP and ultimately the amount of heat generated to do so.



Think more HP is more heat, and, more rpms is more HP.

 

[DValentine]

Cerb touched on this... Adding fuel to a diesel makes heat. Over fueling makes lots of heat= high egts,

On a gas engine it is the reverse Fuel, or excess fuel creates a cooling effect.

There is another post ongoing, about high water temps( in second gen) where a guy was not running a thermostat. As previously mentioned in this post without the thermostat there is no flow control.

 

[JHumphries]

Higher RPM doesn't necessarily mean more fuel does it?

Downshifting puts less load on the engine, and the driver lifts off of the pedal a little bit. The end result is an engine making less power due to gearing at a higher rpm, probably using less fuel.

 

[JLEONARD]

Higher RPM doesn't necessarily mean more fuel does it?

Downshifting puts less load on the engine, and the driver lifts off of the pedal a little bit. The end result is an engine making less power due to gearing at a higher rpm, probably using less fuel.

You are essentially correct. A diesel uses fuel based on horsepower in use, not on rpm like a gasser.

 

[cerberusiam]

Higher RPM doesn't necessarily mean more fuel does it?

Downshifting puts less load on the engine, and the driver lifts off of the pedal a little bit. The end result is an engine making less power due to gearing at a higher rpm, probably using less fuel.

From a physical movement stand point think about it for a minute.



Downshift a gear and hold the throttle steady and what happens to your speed? It drops of course, it can't help but do so.



Lets consider this without a fluid coupling and the accompnaying TQ multiplication that happens in a TC, locked TC or clutch:



X rpm's at Y gear ratio result in Z speed, right?



Now lower the gear ratio and maintain Z: X must change to make the equation work, right? You have to give it more throttle to maintain speed.



Then consider this, how does a diesel make more rpm's? More fuel is the only way to spin it up, thats a given.



Therefore the hypothesis more rpm MUST equal more fuel holds true both mathematically and in observed phebomena.

You are essentially correct. A diesel uses fuel based on horsepower in use, not on rpm like a gasser.

Here is where Jay and I part ways in agreement. Conceptually the statement is true, technically it is incorrect and only applicable in a very narrow sense.



Technically it should read: A diesel uses fuel based on load. Subtle distinction but it makes all the difference. HP required is a function of load, not the other way around. Load is a bugger because it is not static, its not just the weight you are moving its the friction to overcome at different speeds, its the leverage generated by different gear ratios at different speeds, its the aerodynamics, etc. Load changes across speed, atmospheric conditions, terrain, temp, etc. HP is a constant of weight time over distance, load is variable across all dimensions and that is what ultimately determines how much fuel it takes.



The concept of raising rpm and using less fuel CAN be true, but, only in a very narrow range of rpm change AND minimal load change. You may get better fuel efficiency by changing rpm's slightly when BSFC is realtively flat across the rpm range, but, that will NEVER happen with 4, 5 or even a 6 speed transmission. The jumps we have to deal with fall outside of the narrow range that would make it true, it just can't happen in what we deal with.



We still come back to more rpm equals more fuel in daily application.

 

[WCantrell]

Finally got the truck out for a run today 170 miles round trip. Here' the Tally:



Pulling 3 horse slant with Dressing room (20 ft) with 1000 lb junk. (no I would not do that to a horse!)

Ambient Air temp: 112

Running 65 on the flats: 215-220

5 mile grade (a couple of these): Up to just under 240 cooled back to 210 on the downside of the pass

Back to town ambient Air 103: 200-205.

transmission temp stayed at 165-170 execpt for the second 5 mi pass in second gear @ 210



I also had to replace the radiator... I guess my flush was a little agressive, and it sprung a leak. O' well better find that out in my driveway rather than the road.



Thanks for all the info an helpfull advice! I'm a bit more comfortable managing the engine temp now.

 

[PToombs]

WC, from that it sounds like it's not the trans for sure. Seems the truck just runs hot. I don't get those temps here, so I can't compare. I don't think it should run that hot, but those ambient temps... ...

 

[cerberusiam]

transmission temp stayed at 165-170 execpt for the second 5 mi pass in second gear @ 210

Where are you measuring trans temp?

 

[WCantrell]

Where are you measuring trans temp?

On a tee off of the OD temp sensor on the way to the cooler.