Engine/Transmission (1994 - 1998) How hot is too hot? Trip report on first tow...

[CStansbury]

I returned yesterday evening from WV towing a 16' trailer with my 404 Unimog on it. We came across some pretty good mountain passes on the way here (pales in comparison to you Rockies folk I'm sure). The trailer and Mog weigh about 8600 lbs. The steepest grade slowed me down to around 55mph in 5th and then 60 in 4th. When in 5th or 4th, the EGTs hung right around 1200-1250 with the pedal matted. After several minutes like that, the factory engine temp gauge would climb as high as 220 and stay there until I crested the hill and then cool off pretty quickly coasting down the other side.



Questions are: Am I pushing the temps up by staying in 5th too long and keeping the rpm's low? Would running the big hills in 4th from the bottom help by spinning the rpm's up and moving more air/coolant? Am I doing any harm by running it that hot?



I was very pleased with the Optix gauges on the trip. They seemed to respond very quickly to temp/boost changes.



I'm guessing with temps maxing out at 1250 and 31 psi matted pulling 8600, that I have 215 injectors and a boost fitting with a stock plate. It'll work good for now. I do plan on getting a bigger trailer, about a 20' gooseneck, so that should push my weight up to about 9600. I'll prolly be looking for more power then

 

[Matthug]

1250 is completely safe, you can leave it to the floor all day at that temp. 220 on the coolant is on the warmer side but still OK, just make sure you have a proper 50/50 mix and not too lean on the antifreeze to keep your boiling temps proper. With a 50/50 your coolant shouldn't boil until 260.

 

[Vaughn MacKenzie]

I disagree. . . you're really flirting with the danger zone at 1250 on a 12-valve. Better hope the gauge is accurate, I know of at least 2-3 cases of 24-valves melting down at 1250. You're a bit safer there on a 24-valve HO and 1250 is pretty OK on the 600 series 3rd Gen but I would definitely keep it under 1200 if you want your Cummins to live a relatively long life. I usually keep mine at 1150 tops but have let it get to 1200 briefly.

 

[CStansbury]

I'd say 1250 was the absolute peak and it probably didn't stay there for more than 20 secs. Most of the time it was between 1150 and 1200 until the steepest part of the grade. I hadn't heard of any meltdowns at 1250. Thanks for the heads up Vaughn.



I'll double check my coolant mix before the next haul Matt.

 

[moparguy]

With a load, I'd rather drop a gear and turn a few more rpm. Nothing wrong with humming along at 23/2400 rpm, all day if necessary.

 

[Matthug]

I disagree. . . you're really flirting with the danger zone at 1250 on a 12-valve. Better hope the gauge is accurate, I know of at least 2-3 cases of 24-valves melting down at 1250. You're a bit safer there on a 24-valve HO and 1250 is pretty OK on the 600 series 3rd Gen but I would definitely keep it under 1200 if you want your Cummins to live a relatively long life. I usually keep mine at 1150 tops but have let it get to 1200 briefly.

Cummins specifies that 1280 is max sustained temp, and temps up to 1400 are OK but should not be sustained for more than 20 seconds.

 

[DWeik]

Have traveled back and forth between Virginia and Dunmore WV several times a month, sometimes with a 24' trailer weighing in at as high as 15,000 lbs. I found the problem not to be with the long grades but rather the steep grades along with the twisting, winding, hairpin curves. Exhaust temps are generally in the 1100 range while climbing with short spikes to 1200 / 1250. Water temp though stays below 190 to 200 degrees. If you are traveling route US 33 for this trip, I have found this to be the most brutal route. I prefer crossing the Appillation divide either further north or to the South via Rt. 220/250.

 

[Vaughn MacKenzie]

I'd say 1250 was the absolute peak and it probably didn't stay there for more than 20 secs. Most of the time it was between 1150 and 1200 until the steepest part of the grade. I hadn't heard of any meltdowns at 1250. Thanks for the heads up Vaughn.

Well you probably didn't hurt it CStansbury. I know about those W. Virginia hills

So how are you liking your new ride, still ?



Matthug where did you hear 1280 from? The main thing is giving yourself a little margin of safety incase your gauge isn't exactly on. JNutter burned up his '01 on a grade a few years ago at a little under 1250 and someone else on the 24v forum fried #6 at around 1250 last year. So it basically boils down to whether or not you want to play with fire

 

[Howard Durand]

We trust those guages as if they were telling the gospel truth but I doubt if they are any better than 5% accurate. If so, at 1250* the actual temperature could be as high as 1310 or as low as 1190.

 

[CStansbury]

Vaughn, I am definitely still I am loving the truck and for the most part on the trip back I was blown away on how it could haul. I am looking forward to towing again because it was so much fun. The fuel bill I could do without though



Howard, good point on gauge accuracy. Certainly is something to keep in mind when pushing the limits of EGTs.



My next big project is the TST KDP kit. After that I want to get my pump timing bumped to around 16* which should help me run a little cooler and hopefully kick my MPG up a bit too.



After that it will be time for more fuel, maybe a TST #5, and Rip's 4" straight pipe kit.



DWeik, yep, the steep twisties are tough. I was really glad to have the Turnpike instead of having to run Rt 60 from Gauley Bridge to White Sulpher :-laf

 

[DWeik]

I wouldn't trade these mountains or these roads for any others. You just learn to deal with it under your right foot!

 

[Matthug]

Matthug where did you hear 1280 from? The main thing is giving yourself a little margin of safety incase your gauge isn't exactly on. JNutter burned up his '01 on a grade a few years ago at a little under 1250 and someone else on the 24v forum fried #6 at around 1250 last year. So it basically boils down to whether or not you want to play with fire

From a guy that worked at cummins on B models everyday! But I do agree gauges are not always accurate nor immediately responsive so a margin of safety would be wise. Say, keep it under 1200 sustained and it should be plenty good.

 

[Vaughn MacKenzie]

OK I'll give you that Matt

Seemed I'd heard 1100 or 1200 from Cummins, didn't remember 1280. Was he referring to the 12 valve or newer engines? As each generation progresses with higher HP and EGTs they are designed to handle more. A 600 series can take a lot more than the first gens.



Vaughn

 

[therabbittree]

big question is your pyro pre turbo or post turbo. . makes a big difference in the egt 300 degrees or so and slower response if post. turbo. .

later

Deo

 

[CStansbury]

If I was post-turbo I would have had a meltdown already seeing that the pre-turbo temps would have been about 1550*.

 

[Matthug]

OK I'll give you that Matt

Seemed I'd heard 1100 or 1200 from Cummins, didn't remember 1280. Was he referring to the 12 valve or newer engines? As each generation progresses with higher HP and EGTs they are designed to handle more. A 600 series can take a lot more than the first gens.



Vaughn

You know at the time I didn't own a cummins so I was referring to my bro's 02' 24 valve while talking to him. There's the difference i suppose. Well you learn something new everyday huh?