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NHC250 blows?

319cssb

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I keep coming across videos and posts from people with blown engines due to pitted liners?Is that an issue with these engines? What could the cause be?
One guy had 3blown engines , I think he said. is it the coolant? I drained mine, and ran with dish detergent and flushed it a million times. First flush, I thought I had accidentally opened the engine oil pan drain plug.
the end was light brown... like a light tea sorta look.
I got the old style green coolant and mixed with filtered water.
 

Elijah95

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Tee in a coolant filter on your heater core supply and return, you’ll be amazed at what you’ll catch even after flushing 5+ times. I did it to my 8.3 when I rebuilt the top end and was appalled.
 

sandcobra164

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Well perhaps it does in limited observation. My current 5 ton has one of these engines and the Cummins NHC-250 started serving the military with the introduction of the XM809 series in the late 1960's. It was a Commercial Off The Shelf drop in that met the requirements. The Military doesn't design engines or trucks. My truck was built in 1984 and never went through any type of rebuild and the NHC-250 is running strong as ever. I had to replace the injection pump 2 years into my ownership due to a failed 20 plus year old seal in the pump. That wasn't a deal breaker. If you'd like newer running stock, the later 5 tons had late 80's early 90's 8.3's which are rock solid as well. We're dealing with 20 to 30 year old trucks in this forum, they fail from time to time. We reach out on here to find answers to how to fix them... At least that's my approach. Your mileage may vary.
 

simp5782

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He was blowing motors cause he wasn't running green coolant low glycol. The ELC eats rubber in the new stuff and it was his driving after watching his video. He was lugging the motor way to much. 1825 to 1850rpms is a shift point to keep her happy on hills.
 

74M35A2

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Yeah, the 250 motor blows. Ha, just kidding, but onto the good stuff:

If the SCA level in the coolant is not maintained, corrosion and cavitation can occur, both of which cause pitting to the outside of the cylinder liners, to the point it is weakened and punches through.
 

319cssb

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Tee in a coolant filter on your heater core supply and return, you’ll be amazed at what you’ll catch even after flushing 5+ times. I did it to my 8.3 when I rebuilt the top end and was appalled.
got a link for that coolant filter you used?
 

Ajax MD

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I keep coming across videos and posts from people with blown engines due to pitted liners?Is that an issue with these engines? What could the cause be?
One guy had 3blown engines , I think he said. is it the coolant? I drained mine, and ran with dish detergent and flushed it a million times. First flush, I thought I had accidentally opened the engine oil pan drain plug.
the end was light brown... like a light tea sorta look.
I got the old style green coolant and mixed with filtered water.
I went through the same hyperventilation about this stuff when I bought my truck.

It's true, you don't know if the military bothered testing the coolant and keeping up with the diesel coolant additive that is supposed to prevent cavitation. Might be a ticking time bomb, might not. Probably not.
The military at least (probably) used the proper, green coolant and not the ELC (Extended Life Coolant).

While the truck is in your care, check the coolant with test strips periodically. Add DCA if test strips indicate. You'll achieve a more uniform mix if you just buy coolant "pre-charged" with diesel coolant additive. Saves you from mixing it in manually.

I also had sludge drain out of my radiator and nearly panicked, thinking of blown head gaskets and other apocalyptic visions. It turns out that the sludge is iron from the block, suspended in the coolant.
You did the right thing. Flush it with detergent, add a filter if you like.

As Simp says, don't lug the engine. My internet reading seems to indicate that these engines have a rather narrow power band. They redline at 2100-2200 but the shift point is around 1850 so you're going to be shifting frequently to keep the RPMs within that band.

Fun stuff!
 

simp5782

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I went through the same hyperventilation about this stuff when I bought my truck.

It's true, you don't know if the military bothered testing the coolant and keeping up with the diesel coolant additive that is supposed to prevent cavitation. Might be a ticking time bomb, might not. Probably not.
The military at least (probably) used the proper, green coolant and not the ELC (Extended Life Coolant).

While the truck is in your care, check the coolant with test strips periodically. Add DCA if test strips indicate. You'll achieve a more uniform mix if you just buy coolant "pre-charged" with diesel coolant additive. Saves you from mixing it in manually.

I also had sludge drain out of my radiator and nearly panicked, thinking of blown head gaskets and other apocalyptic visions. It turns out that the sludge is iron from the block, suspended in the coolant.
You did the right thing. Flush it with detergent, add a filter if you like.

As Simp says, don't lug the engine. My internet reading seems to indicate that these engines have a rather narrow power band. They redline at 2100-2200 but the shift point is around 1850 so you're going to be shifting frequently to keep the RPMs within that band.

Fun stuff!
I can honestly say in 3yrs and 220,000 miles I never checked the SCAs.

And. Precharged SCA in green coolant is pretty hard to come by only in valvoline Xerox. so you need the additive as Walmart coolant is alot cheaper at 5 gallons of concentrate and 5 gallons of distilled
 

Ajax MD

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I found a Peak coolant that is not ELC but is also pre-charged with SCA. It's not green, it's pink but their own website says that the color is only for identification purposes.
The jug doesn't say "ELC" on it like other products I've seen.

This is what I used: https://www.peakhd.com/product/fleet-charge/sca-precharged-coolant-antifreeze/

I only added a few gallons and it's only been in there for about a month. I can drain and replace it if it's considered ELC. What do you think?
 

Scrounger

Active member
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Southern, Maryland
There are several things to keep in mind on this topic.
When these engines were designed the antifreeze/ coolant was the old-style green stuff. That is what they were designed for and that is what the military put in them. The new ELC stuff has a completely different chemistry. While I haven’t torn down an engine and inspected what effects ELC does to these older engines, I can say that ELC has caused issues with engines in cars and lite trucks that came from the factory with the old green stuff.

Unlike gasoline engines, diesel engines have a very narrow power band. Most diesel engines have what is referred to as a 400-rpm split. As an example, 1300-1700 rpm or 1400-1800 rpm. When accelerating go up to the next gear at 1700 and the engine should fall into gear and start pulling at around 1300. If the engine rpm drops to 1300 it is time to down shift.

Normal diesel ignition causes a shock pulse on the wet liners. If the coolant doesn’t have SCA the coolant will cavitate and produce bubbles on the liners. Those bubbles remove the normal oxidation from the liners. Then a new oxidation layer will form. Then bubbles will remove the new layer. Eventually pin holes will develop in the liners.

Lugging an engine, running it below its power band, causes harder shock pulses on the liners. So, it is important not only for power, but for the life of the engine to keep it in its power band.
 

319cssb

Well-known member
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The green stuff doesn't have that SCA in it , i guess. Thats why its supplemental.
Ill have to get test strips , test thr ph , then add this SCA and live a happy carefree life ever after.
 

Ajax MD

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Sigh...although I can't find any evidence that the Peak Fleetcharge I used is ELC, I think I'm going to drain and replace it with green coolant and manually add the SCA.
 

Ajax MD

Well-known member
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Location
Mayo, MD
Hmmm...check this out: https://www.amazon.com/Miles-Everco...eeze-Gallon/dp/B00YUL3N72#feature-bullets-btf

Green, does not say anything about "extended life", comes precharged with SCA, but you do have to add water.
EDIT: Nope, I was wrong. It does say "extended life" but doesn't really explain how or why.

Geeze, I think 319cssb has probably found the best stuff. The description clearly states "conventional" and "for older vehicles" as well as "light duty diesel applications."
All of the coolants I found on Wal-Mart's pages are ELC.
 
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