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M923a1 failure, need input.

TXFirefighter

Member
Steel Soldiers Supporter
90
1
6
Location
Tomball, TX.
The above issues don't necessitate an engine replacement. These are Heavy Duty engines and built to be over hauled multiple times. The failures noted are from age and lack of maintenance and fall under routine maintenance/ repairs for engines of this age. Because of this is why I have been staying away from the NTC engines. Parts are lots heavier and torques much higher than when dealing with the 8.3L's.
After my department spent over $5000 each for 3 trucks to have radiators removed and replaced, we educated ourselves on cooling system maintenance.
The coolant test strips mentioned by Droprat are an essential tool for caring for our trucks. Heck, they are a must have for any diesel engine! NAPA has them too and if you make the switch to extended life coolant, it requires its own type of test strip because you are testing for different chemicals.
With green diesel engine coolant, NAPA has pint bottles of SCA additive to quickly adjust and correct cooling system levels. It is part # 4056.
We switched over all of our trucks to the 50/50 pre-mix Shell Rotella ELC coolant. first reason is ease of maintenance and life of coolant. Second, we use the 50/50 pre-mix so we don't have firemen adding tap water and contaminating the system. We have real dirty water here and getting/ keeping distilled water in stations is a real PITA.
With the ELC, we run it for 3 years (testing each months) then add 1 pint of system conditioner and run for another 3 years and drain, flush and re-fill with new. Every 6 year coolant replacement we replace all the system hoses. Our cooling system issues are a thing of the past now and I have 12 years of track records to prove it.
 

74M35A2

Well-known member
4,145
334
83
Location
Livonia, MI
I hate to drop more fear here, but coolant (ethylene glycol) eats the coating off of engine bearings like an acid, and leaves them with a rough surface. If it is just milky oil, maybe OK, but if you see any green on the dipstick, you can almost count on it that engine bearings have been eaten away (crank/rods/cam/others).
 

Ironman97459

New member
10
0
1
Location
oregon
Just went thru this with my newly purchased 250. Within twenty miles I destroyed the complete block and crank. Number one liner leaked coolant into the pan and then spun bearings. That destroyed the thrust bearings which destroyed the block. Great way to start ownership.
 

jarhead1086

Member
112
2
16
Location
Farr West, UT
When all my nasty brown stop leak fluid blew out on my recovery I luckily had a friend who knew about this and answered his phone. I was clueless, but he said I had to get Fleet SCA precharged. I just followed directions and glad I did after reading these stories. Mine is made by Peak, bought it at OReilleys, and it has a long list of specs it meets on the back. I will watch how it does with the strips. Thanks for the education. Looks like you get a big cam replacement Ironman97459. Hope you can get a smile in the end.
 

elkhtr

Member
502
12
18
Location
Stanwood, Wa.
M923 engine replacement options?

Searched the site and couldn't find the discussion that I was looking for, so here goes.
If you had to, or wanted to replace an Nhc 250 what would be your choice and why?
I am looking for all the pro's and con's, cost, fitment issues, etc, of the available choices.
The only criteria at this point is that it mates to the existing Allison transmission.
Would a 6bt be strong enough?
Big cam 400 too much for the trans?
Update to the 6cta?
Or rebuild the "hard to find/expensive parts, underpowered, fuel guzzling 250"
Let the games begin!
 

doghead

4 Star General /Moderator
Staff member
Super Moderator
Steel Soldiers Supporter
26,246
1,179
113
Location
NY
Depends on what is needed to rebuild the motor.

What is wrong with it?
 

doghead

4 Star General /Moderator
Staff member
Super Moderator
Steel Soldiers Supporter
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1,179
113
Location
NY
Might be just an oil cooler.

I would not consider replacement until you diagnose the problem.
 

elkhtr

Member
502
12
18
Location
Stanwood, Wa.
Below is copied from another thread regarding this issue, gives a little more detail.
The fan was functioning properly.


Went to take the girls for the once a month spin down to the ice cream store.
Pre flight checks were good.
About three miles down the road I notice the temp gage at a little over 200 deg.
This truck has never ran that hot before.
Another half mile or so and it's at 210.
I plan for a landing strip at the local church parking lot, and we make it there safely.
I shut the truck down and open the hood to see what is going on.
Nothing abnormal except slight smell of coolant.
I restart the engine to see if the fan is working and I get a steam sauna shooting from the crank case vent tube coming out of the valve cover.
Shut her down, pull the filler cap, and see milky white goo.
Pull the dip stick, water in oil.
After the wrecker got me home I had to start it briefly to get her parked, started normally and ran fine.
At this point I am feeling a little gut punched.
Oil cooler? worse?
Anybody else had this happen.
And I will apologize in advance, I havent searched yet, just looking to share my misery.
 

Artisan

Well-known member
2,761
227
63
Location
CDA Idaho
If I had to replace my NHC250 I think I would consider
an NHC250 w/ turbo built by a pro.
Why, cause more power is mo betta!
 

elkhtr

Member
502
12
18
Location
Stanwood, Wa.
If I had to replace my NHC250 I think I would consider
an NHC250 w/ turbo built by a pro.
Why, cause more power is mo betta!
Hi Artisan,do you mean a turbo built by a pro, or the whole package?
Might be outside the scope of the cash I can drop.
As much as it concerns me buying the unknown, I did find a "good running" 6cta for under 3500.00
I have never priced a heavy diesel overhaul, I am new to this world.
 

Artisan

Well-known member
2,761
227
63
Location
CDA Idaho
elk FIND a local engine rebuilder* who is versed in turbo
and ask them the hard questions. Every NHC250 in an M939
Series truck, to the best of my knowledge, is already set up
for a turbo, but adding one is a double edge sword an only
a pro can advise you correctly of the ramifications of doing
such a mod, like IS YOUR TRANNY GOING TO HOLD UP?

*Or from afar and you do the swap

BE CAREFUL about who you listen to on these forum, Moi' inclusive.
 

zxmedic

New member
157
2
0
Location
Canada
I've been researching the mechanical N14 it's essentialy a 855 a bolt in I would probably run a 15 speed behind it and the T138 case. I am no expert. With your own research you can find the right info .
 
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