Another NP200 heat thread!

[Mikel]

Right now my M715's NP200 is in my '63 J300. I'm getting ready to fire it up, so I went to fill up the TC with gear oil. The old gear oil came out brownish, but very clean. I put my finger inside the drain hole and I noticed about 1/8" of a muddish substance.

I have filled the 200 with gasoline to hopefully dissolve the residue and plan on flushing it numerous times before I put gear oil in it.

I wonder if this may be a factor in the overheating issues these things suffer.

Mikel

[chicklin]

I am certainly no expert, but I wouldn't think it would contribute to the heat issues. If the entire inside was coated that way, maybe it would act as a sort of insulation, trapping the heat. But since it's just the bottom of the case...

The build-up probably causes the gear oil to break down faster, which I suppose could amount to more heat in the long run, but I think people have said the NP200 overheats with brand new gear oil, anyway.

[randyscycle]

My NP200 has been thoroughly cleaned, overhauled with new bearings and seals, and correct preload, and it still makes noise at anything over 40 MPH and gets hot at any extended running over 50 MPH.

It takes about 30-40 minutes of steady highway speed and it will get up to around 190 degrees (read on a temp guage installed in my transfer case) on a warm day. Driving further on for another 20 minutes or so it will climb to 220 degrees. After that, it doesn't take long for it to shoot up to the end of the scale if you keep pushing it.

Running synthetic or conventional gear oil makes no difference in temperature either. They are just an antiquated design, plainly put.

[Barrman]

90% or so of the NP200's in M715's will not handle more than 30-45 minutes at 2500 drive shaft rpm or more. That is just a fact of life for these trucks.

Replace it, drive slower, change axle ratios or get bigger tires

[Mikel]

Well, I have 3.08's in my truck, so the NP200 will be seeing almost half of the RPM's compared to an M715.

[Barrman]

The funny thing about the NP200 is non M715 peopel want them. The guy I bought my NP205 from really wanted to do a flat trade for the 200. He drag races SD Ford's and goes through a lot of parts. He thought at the time that a 200 would be the best he could get.

MR.Positive expressed some interest in a M715 200 compared to a "lighter and weaker" M37 version of a 200.

Then you have the monter truck guys that want a 200 because you can clock it almost 90 degrees down for more lift with less drive shaft angle.

Yet, we all want to get rid of them and feel good to get $5.00 from one that is good. Go figure?

[randyscycle]

I'd gladly give mine away as soon as I find a suitable replacement 205.....

[george walker]

I always have to say something when this subject comes up. I have owned my truck for 13 yrs now, many yrs ago I lived in Wash DC, and I attented the MVPA national convention in Memphis Tenn. I think that was around 2000. I drove my truck there (the convention is at the height of summer). I took my time going 50 mph mostly on the flat streches, however the convention center where the show was held was a/c'ed and they didnt want to open it up until the last hour of the show sunday, many of us needed to go much sooner to get home. They relented and let us out sat eve., however we only got the nashville that night and had to be home in DC sunday night. I drove my truck at fully 55mph non stop from Nashville to DC, I wasnt sure it would do it but I pushed and made in in like 13 hrs. the truck and the transfer case made that hot summer drive w/o any problems, (nor adding any oil)and today at 40000 miles that same case still runs fine even in the 116 heat of the desert summers,(it is starting to whine now but i'll reset it someday) the 200 has shortcomings but is a capeable gearbox.

[TxRider]

New guy here,

I'm not a 715 owner, maybe someday, but an M-37 owner with an NP200 transfer case, re powering with a 4bt and OD trans.

I've searched here a bit, looked elsewhere a bit and looked for all the NP200 heat issues I can after many overheat warnings and there are a few things I haven't seen, and some I just haven't seen here.

It looks like this is only an issue when the T-case is spun up over 2500 going up through 3000 it gets too hot..

What I haven't seen suggested is that maybe the gears when spinning that fast are either cavitating in the oil and not picking it up and oiling the bearings etc. or that it's slinging enough oil around the case so fast as to lower the level enough to starve?

My curiosity also got peaked when I also looked at the recommendation for an NP205 case, and saw that 50wt motor oil is specified as an alternative. The recommendation says 30wt as an alternative for below 32 degrees.

This fits with recommendation for many older transmissions as well that use 50wt motor oil or some even ATM fluid, as well as some other gear T-cases that use motor oil.

I've also seen some M37 folks using 50wt in the NP200 and running highway speeds, has anyone of you with a temp gauge in the T-case tried to run 50wt motor oil to see a difference? I wasn't able to find it in the search if so.

[Kaiserman]

Interesting thread. I'm still on the hunt (but think I have one cornered) for an NP200 for my 63 J300. It's going to be seeing 45 mph somewhat regularly. Be interesting to see how ot does. From what I've read (here and elseware) some of the 200's have heat issues bad and some don't.