Changing out the coolant on the NHC250

[WillWagner]

ELC is bad juju for old engines. Rubber parts WILL be compromised. Stick with a low silicate, normal glycol antifreeze.

 

[acme66]

Turns out it ate No 3 piston. From underneath the rest all look near perfect with no scoring. Going to pull the piston and liner Friday. If the liner shows signs of pitting then I am going to drop in a used liner, piston, rings, wristpin, o-rings and rod bearings from the motor we are rebuilding, the best of whatever I have left and limp it up to the shop as having it towed is $1000 to $1500. It only has to make it 90 miles and it can do that pissing water and burning oil. I will then pull it and replace with the fresh rebuild we are doing on the last one to take a dump. We can go through this one in the fall.

If I pull the liner and it shows no signs of pitting and instead shows injector failure then I am going to hone the best liner from our rebuild and do the exact same thing but with new o-rings, piston rings, bearings and then just run the dang thing.

Be very interesting to what the liner looks like. More info and update maybe Friday night or Saturday.

Ken

 

[71DeuceAK]

Keep us posted!

 

[acme66]

Liner is out and looks brand new 100% no pitting. O-rings are a gummy mess and a large chunk was missing from the top one though it did not put water in the oil for over 48 hours while it sat. Injector tip looks fine. I am at a total loss as to what would cause this motor to eat a liner after sitting all winter. Update videos over on the NelsonStudios youtube channel, click videos tab and you can see for yourself. Antifreeze was SCA Precharged meeting Cummins 14603 spec, ie the recommended stuff. I don't see how the antifreeze could eat the o-rings of one liner and not another which look brand new so I think the gummy might be heat damage. Going to cook a set in the toaster oven later and see if they get soft.

Ken


videos:


https://www.youtube.com/user/acme663ryo

 

[Csm Davis]

ELC is bad juju for old engines. Rubber parts WILL be compromised. Stick with a low silicate, normal glycol antifreeze.

This is why I fuss about guys changing to fluids that have never been used in these trucks, some of you folks over think this stuff. These trucks were designed before most of us were born, (KISS) keep it simple stupid is the thing to remember. If it was good enough for 50 years of military use it should be good for us to use, I am not saying not to put the newest latest greatest junk in but be prepared for what might happen if it is incompatible with 50 year old rubber.

Sent from my SM-G930V using Tapatalk

 

[71DeuceAK]

Keep us posted Ken! I saw your latest 4 updates on YouTube, great videos! Re: the 50 year old rubber, the 939's are more like only 25-25 years old, but yeah, I know what you mean. Still before some of us younger enthusiasts (like myself) were even born...

 

[Csm Davis]

Keep us posted Ken! I saw your latest 4 updates on YouTube, great videos! Re: the 50 year old rubber, the 939's are more like only 25-25 years old, but yeah, I know what you mean. Still before some of us younger enthusiasts (like myself) were even born...

Okay whipper snapper little educational information the M939 came from a long line of great trucks that started in 1951 with the M39 trucks then the M809 trucks in 1969, then the M939 in 1982. And each of the newer series got the first trucks made from the older series trucks so I don't know if this actually happened but you could have possibly have a M939 made from a M39! Doubt that ever happened but I have seen stranger things. So it is very possible to have a 48 year old 250 Cummins in a M939. Supposed to have been 11,000 M809s upgraded M939 so I bet there are some old motors running around still.



Sent from my SM-G930V using Tapatalk

 

[71DeuceAK]

Interesting information! So, say, could an '82 or '83 M923 be on an M813 frame/chassis?

 

[snowtrac nome]

my experience with the upgraded trucks is that when they upgrade the old trucks the old power plants were pulled and new ones were installed. even if you had a 40 year old engine it would have been upgraded to have the same stock number as the 900 series is supposed to have. remember uncle sam doesn't deal in long blocks they deal with complete engines. that said when those trucks were fielded and right up to 10 years ago we still ran green glycol. even in the m1114's, were all other gm products were using dexacool antifreeze. I understand that dexacool will play havoc on seals and gaskets intended for green glycol, but I have never experienced it the other way around. the red stuff gets drained here once the warranty is up, and green is put back in, so the fleet runs the same antifreeze. usually by the time is up, our coolant is murky brown because the drivers cant pay attention to what fluids their trucks are supposed to have anyway. I just change coolant on a regular basis and have had no problems.

 

[Jakelc15]

View attachment 3300963A.pdf

It's a pdf download. I hosted it here but it still makes you download it.

 

[Jakelc15]

http://www.knowyourparts.com/technical-resources/diesel-engines/diesel-engine-coolant-maintenance/

A good read about coolant and additives. Too much or incorrect additive can cause oring failure

 

[acme66]

Truck is back up and running. Used liner, piston, wristpin, rings and we reused the rod bearings that came out of it. Started instantly and after smoking for a bit burning the grease off now idles with no hint of white, black or blue smoke. Rolls a little dark grey when reved up, more than I remember it doing before. Has a bit of blow-by (one would expect that with a mix-n-match set of used rings) but less than the motor we are currently rebuilding did in its prime. If I had just inspected the motor for the first time with that puff of blowby I wouldn't have given it a second thought. Ordering in another full kit then driving it as is up to the shop (80 miles) to put the inframe in. Working on dumpster picked sheets of plywood in the dirt isn't fun. Also going to put a full injector set in. We will time it as per the manuals but then take it to a trusted heavy truck shop to have them run the full top end. Motor runs so smooth I can't think the timing is off far enough to eat pistons but at this point I am checking off boxes. I really, really expected to see pitted liners, almost kind of wish I had... Since everything we found in this motor was brand new (or nearly so) I am going to save it and dump it into the very first truck to die under us. Maybe I get away with just buying a gasket set. If these things are just going to randomly explode then why have it randomly explode with $2000 worth of new parts inside?

Back to the coolant:

Motor has a build date of 1985 as per serial number check with Cummings. Scrap motor I just bought from a 70's 808 truck had a build date of... 1987. I have a chunk of gasket in undiluted coolant, one in mineral spirits and a chunk in lacquer thinner. If those two solvents don't touch it then we will know it wasn't the coolant but I have the control test anyway. Also plan to cook some to see if heat makes them gummy. Some truth to the old motor, old fluid argument but then it isn't an old motor and there is a iron clad reason why a 100,000 mile motor when I was a kid was about done for and today it means only 30-40% of the expected lifetime. There is a reason why million mile heavy OTR motors are no longer a few and far between event and have become, maybe not expected but very, very plausible in even moderate maintenance situations despite much higher HP and boost. Modern fluids and filtering. Period. What I am using is the exact spec (or one of anyway) recommended by the manufacturer for that motor with that build date. But something keeps shooting the horses out from under me. At this point I am trying to eliminate the coolant. Finding 100% spotless liners in that truck wasn't what I expected to see. I expected pitting. I know for a fact pitting was in the other two but this looks spotless... so why did it fail? Gummy spots in the o-rings on this one were located at 90 degrees to the crankshaft. That is where the liners wear the most and the location one would assume heat might build. I don't remember where the gummy spots were on the other motor by my father is quite sure they were also at 90 degrees to the crank. It is like the 5 ton towbar thing, I am sick of what if's and guesswork so I plan to systematically torture those little rubber rings until I know why they failed and if they were the cause of all my grief or tragic victims in some other set of circumstances... and then I will tell you what I found.

Ken

 

[BigDawg41]

Figures I would be reading this post now. 2 years and over 2000 miles ago,I flushed my cooling system for days because it was so dirty and rust colored with the old green coolant in it. I switched over to using Mopar 5 year extended life coolant because I get it free from the dealer I work at. I would save the leftovers from jobs I do in the shop. This past week I had enough saved up again so I decided it's time for another flush before the busy season. Again it came out pretty dirty I'm sure due to more stuff loosening up. I suppose at this point after running it 2 years with no problems I might as well keep on running it. My 250 has a 1990 rebuild tag so the o-rings I'm sure aren't original. I will be refilling it next week after I install a new thermostat. If I have any problems I will be sure to let you guys know.

 

[acme66]

I will know in a few weeks if it was something attacking the rubber.

Ken

 

[someoldmoose]

Some hard won advice :

NEVER, NEVER, NEVER flush any system unless there has been a catastrophic failure with contamination of the involved fluid(s) -- Head gasket blows and oil and coolant try to mate. If the coolant is dirty, DRAIN what you can then refill with whatever coolant you choose. If it is used in the manner directed it makes no difference which coolant you choose. The rubber degrades with time and heat. No coolant on the market will "attack" the o-rings. Change the coolant when you get the vehicle and keep it clean ( filter or change per TM ) and it will do what it's supposed to. Sad to hear that someone had that many failures with such coincidental timing but I would be hard pressed to believe the coolant was at fault. NOT saying it can't happen, just that it would be VERY unusual.

Electrolytic corrosion CAN happen, READ THE FLEET-RITE pdf, but this is not the coolant's fault either. Coolant is a solution capable of carrying a charge, not the cause. Dissimilar metals and bad grounds are the two biggies. Keep the coolant clean and problems disappear. Anodes can be added if the electrolysis cause can't be found but look for the problem first.

There is ABSOLUTELY NO NEED to add any additive to any modern coolant. Even the cheapest out there has to meet standards. If the anti-corrosion package is depleted, change the coolant. Additives are just that, additional revenue for the companies putting them out there. Have used them all and have seen absolutely ZERO difference when maintenance is done like it SHOULD be. Clean coolant is ALL that is needed.

There is no benefit to using extended life coolant in a vehicle that sits most of the time. El Cheapo green ethylene glycol mixed properly for the lowest temperature encountered is all you need. If you are using your truck every day then there is some benefit (better anti-wear package) to extended life or "permanent" OTR truck coolants. Parentheses indicating that NOTHING is permanent, follow the coolant manufacturer's change schedule.

Keep her clean and full and Happy Motoring !

 

[acme66]

I will know in a few weeks if it was something attacking the rubber.

Ken

 

[Bandit02]

I just did a coolant drain & refill on mine. I added a Baldwin coolant filter and a block heater.

I bought generic non-sca green concentrated coolant. Poured a gallon into a clean tub, poured a gallon of distilled water and added 2.5 UPG (units per gallon) of Donaldson DCA4 additive. The filter is just for maintenance, it won't maintain the sca charge in that much coolant I put in (8 gallons or so without DCA4)

2 gallons of the 50/50 mix = 5 Units per batch.

I haven't tested it yet but I believe 2.5-3 UPG is what Cummins calls for or Donaldson on their pdf site about DCA4.

 

[WillWagner]

We will time it as per the manuals but then take it to a trusted heavy truck shop to have them run the full top end.

Cummings.
Ken

Dude, if you have the tools and can time it WHY would you take it to a shop to set the overhead?

And it is Cummins.

Cummings, she was a **** star, Carol Cummings. http://www.imdb.com/name/nm0191860/

 

[simp5782]

Dude, if you have the tools and can time it WHY would you take it to a shop to set the overhead?

And it is Cummins.

Cummings, she was a **** star, Carol Cummings. http://www.imdb.com/name/nm0191860/

Whitney Cummings is a pretty good comedian too

 

[red]

Truck is back up and running. Used liner, piston, wristpin, rings and we reused the rod bearings that came out of it. Started instantly and after smoking for a bit burning the grease off now idles with no hint of white, black or blue smoke. Rolls a little dark grey when reved up, more than I remember it doing before. Has a bit of blow-by (one would expect that with a mix-n-match set of used rings) but less than the motor we are currently rebuilding did in its prime. If I had just inspected the motor for the first time with that puff of blowby I wouldn't have given it a second thought. Ordering in another full kit then driving it as is up to the shop (80 miles) to put the inframe in. Working on dumpster picked sheets of plywood in the dirt isn't fun. Also going to put a full injector set in. We will time it as per the manuals but then take it to a trusted heavy truck shop to have them run the full top end. Motor runs so smooth I can't think the timing is off far enough to eat pistons but at this point I am checking off boxes. I really, really expected to see pitted liners, almost kind of wish I had... Since everything we found in this motor was brand new (or nearly so) I am going to save it and dump it into the very first truck to die under us. Maybe I get away with just buying a gasket set. If these things are just going to randomly explode then why have it randomly explode with $2000 worth of new parts inside?

Back to the coolant:

Motor has a build date of 1985 as per serial number check with Cummings. Scrap motor I just bought from a 70's 808 truck had a build date of... 1987. I have a chunk of gasket in undiluted coolant, one in mineral spirits and a chunk in lacquer thinner. If those two solvents don't touch it then we will know it wasn't the coolant but I have the control test anyway. Also plan to cook some to see if heat makes them gummy. Some truth to the old motor, old fluid argument but then it isn't an old motor and there is a iron clad reason why a 100,000 mile motor when I was a kid was about done for and today it means only 30-40% of the expected lifetime. There is a reason why million mile heavy OTR motors are no longer a few and far between event and have become, maybe not expected but very, very plausible in even moderate maintenance situations despite much higher HP and boost. Modern fluids and filtering. Period. What I am using is the exact spec (or one of anyway) recommended by the manufacturer for that motor with that build date. But something keeps shooting the horses out from under me. At this point I am trying to eliminate the coolant. Finding 100% spotless liners in that truck wasn't what I expected to see. I expected pitting. I know for a fact pitting was in the other two but this looks spotless... so why did it fail? Gummy spots in the o-rings on this one were located at 90 degrees to the crankshaft. That is where the liners wear the most and the location one would assume heat might build. I don't remember where the gummy spots were on the other motor by my father is quite sure they were also at 90 degrees to the crank. It is like the 5 ton towbar thing, I am sick of what if's and guesswork so I plan to systematically torture those little rubber rings until I know why they failed and if they were the cause of all my grief or tragic victims in some other set of circumstances... and then I will tell you what I found.

Ken

Out of curiosity, what are your EGT's at and for how long?

Since these engines have been around in the 60's and 70's million miles has not been uncommon, including the small cam 250's. Military often neglects maintenance and abuses the vehicles which shortens the lifespan of mechanical components.

Pretty sure it's either a temperature issue or chemical reaction from the coolant. From a fresh rebuild the coolant type usually doesn't matter, changing partway through the engine's lifespan tends to create problems. Owners of GM vehicles experienced similar problems going from 'Dexcool' (red) to typical green. Rubber components in the cooling system going out early and (when some Dexcool had remained) severe reactions to the metal components.