Another NP200 heat thread!

[Kaiserjeeps]

Does the 205 and 200 share the same gear pitch? Or are they different?

[TxRider]

How many trucks over the preceding decades ran 80W90 or higher in their tcase and manual trans and lived for lots and lots of miles...

I'm not sure, but then again how many old flathead engines spun the gears in these old 40's style boxes up to more than 2500 RPM? It seems higher modern RPM's are the issue.

Not saying 50W is a bad or good idea...just wondering why it has taken well over 50 years for this to come to light.

I couldn't say why, I was only born in '59.. I'm just looking at a problem I am likely to have and seeing someone else's solution is to go to 50wt HD motor oil, and I figured since guys here are the only ones testing NP200's with temp gauges and fighting this problem more than anyone, who better to try it?

I was half expecting someone to answer "been there done that, use the search noob!", but it doesn't look like that's the case.

Here's another data point from a Tom Bauer who runs M35 deuces up to highway speeds, and is using (and producing) a custom OD gear set for the spicer 3053 transmissions in .71 and .69 ratios... Speaking of the duece's transfer case....

don't forget that you will have problems with the transfer when you turn it that fast. over 65 mph or so you will need to go to 50 wt oil. when i ran mine at 70 + the 90 wt would foam and come out all the seals (new) i was turning the drive shafts at 4600 rpm

Just wondering if anyone had tried the 50wt, as it appeared everyone seems to be working the other direction, to higher viscosity higher pressure oils. Could the oil viscosity itself cause heat when spinning a gear faster in it?

Kaiser, the gear angles look the same in the drawings I can see, not having the two side by side I don't know. I've been in my 200, never seen inside a 205.

[chicklin]

I'm definitely willing to try the 50wt oil. I've already caused a leak due to overheating, so I'm getting ready to put new seals in. I think I will try the NP205 seals and the 50wt motor oil and see what happens.

[brute4c]

Anything that will let the stock case live AND drive at 60 MPH...I am all for it...even though I have a 205 out in the shop.

[chicklin]

Anything that will let the stock case live AND drive at 60 MPH...I am all for it...even though I have a 205 out in the shop.

No kidding. Obviously, the 205 is the best solution at this point. But for those of us with stock trucks and limited tools/fab skills (maybe that's just me ), another solution would be wonderful.

[brute4c]

It isnt just you...I could well be the worst fabricator here...

[TxRider]

I'll be trying it in mine in a couple or three months with a good HD 50wt synthetic I believe, and I have a little battery powered digital oil temp sender/gauge setup I've had lying around for years now and I'll thread it in the drain plug so I can monitor it.

The guys who have done that here have been the most helpful information I've seen on this issue, the only real hard temp vs RPM data I've seen yet.

In my mind until someone tries 50wt or maybe even 30wt and monitors heat with a gauge for direct comparison it'll still be a foggy issue... Not to mention the safety factor of monitoring the heat when trying something like this. Could it heat up even worse? Is foaming an issue, and does motor oil foam less and handle higher temps better?

For all I know 50wt motor oil might be so close to 70wt gear oil that there will be no temp difference at all. But I figured I would throw out what I've seen about it, the more shared info the better i say.

[chicklin]

Anybody got the NP205 seal part numbers handy? Should be a direct replacement, right?

[randyscycle]

I have a transmission temp gauge installed in the bottom of the sump of the transfer case, and it runs around 180 degrees here in VA in the winter using 80-90 synthetic gear oil. In the warmer months it will easily run up to 220 degrees after a run of about 10-12 miles at 50MPH+. If I continue to push it, it will climb up even more to around 280 degrees. Push a bit more, and it will then send the needle off the scale at 320 degrees very quickly. Sticking around 45MPH will keep the heat at 220 on a 90 degree day pretty much all day long.

I may just try the 50wt to see what happens. Couldn't hurt, and the idea of 90W retaining heat may be a valid one.

[Mikel]

Push a bit more, and it will then send the needle off the scale at 320 degrees very quickly.