I have a 65 f-250 with a T-18 tranny. The shop manual says to use 50w oil.
Can i use 80w-90 with out any problems?

 

Use the 50w, the 80w90 will make it very hard to shift... already found that out the hard way!

 

thanks for the heads up...

 

I use 80w-90 in my t-98. It shifts just fine. My understand is the t-18 is only slightly different.

 

I have the T18, and it is pretty much the same as the T98, The T18 as I understand it replaced the T98. The ford factory repair manual suggest using only the 50w which I have in mine now, but I can understand using the heavier 80w 90 in the trans too, mostly though if it has leaking seals, as it will slow down the leak rate. The down side is, like any oil product a heavier weight reduces efficiency slightly as it is harder to push through, not that is would make a big difference, but every little bit helps with HP and MPG. I have noticed with mine , and also on my Mustang GT that the 80w 90 makes the shifting a little bit less smooth, the lighter 50w hasn't that problem. Now in my RX-7 it is the opposite, the lighter weight gear oil, and it will barely shift. My thinking is, if Ford had a reason for the lighter oil, I will trust their judgement, after all they built the darned thing. I don't try to recreate the wheel!

 

50wt is fine if you can find it, if not just use a 15w40 oil and you will be fine. But DO NOT use gear oil like 80w90 in the trans the sulfur content of GL-5 is very high and will eat and destroy yellow metals.

 

Funny that you mention that I was just reading that in an article about the gear oil choices, the high sulfur content eating the yellow metals aka Copper and Brass, another reason to avoid the Hypoid gear oils. It is fine in the newer Transmissions, which use steel, and aluminum, but it is a no no in the older gal's like we drive

Kudos 390 Gas Hog!

 

Puchased GL-5 Hypoid 85-90 gear oil w/ the limited slip additive for rear end and according to sales person it would be okay to for the T18; ended using it and then decided to posted question in the 'oil & lube' forum and received response from 'jimandmandy', posting response below; needless to say I have since replaced w/ GL-4 Hypoid 85-90 gear oil. Obviously not knowledgeable when it comes to oil's and lubes, see where 'jetcopilot' mentions article concerning Hypoid oils, anyhow not sure if GL-4 is available in non Hypoid flavor but may be food for thought

(Comments by 'jimandmandy'
Limited slip additive is not a good thing in a sychromesh transmission, can cause grinding. I would suggest Stalube GL-4 instead. That is what I use in older manual transmissions and transaxles that dont specify ATF. GL-5 can cause corrosion of brass or bronze parts in some of these older gearboxes. GL-4 uses less of the stinky, corrosive sulphur-based EP additives not needed for transmission and transfer case gears..

Product Description
GL-4 Hypoid Gear Oil has low pour points and high temp properties to provide lubrication over a wide temperature range. This versatile lubricant contains anti-rust and anti-wear EP additives to provide the corrosion protection in drives and hypoid gears.

Product Specifications
Applications Auto, truck and bus standard transmissions and differentials requiring API/GL-3 and GL-4 oils
Unit Package Description 1 Quart Bottle
Brand Sta-Lube
Generic Description 1 Multi Purpose Gear Oil SAE 85W90
Net Fill 32 Fl Oz
UPC Code 072213242294

 

50w motor oil is same viscosity as 90w gear oil. I use Lucas 80w-90w in all my old manual tranny's, NP435 and three speeds, Also in My Dana 20 transfer case and front and rear diff's. It is GL3,4,5 and LS compliant.

 

The GL Rating is tied to the Sulfur content, And EP rating. Any Sulfur content in long term use on yellow metals can be very corrosive, in such places as Pilot bearings bushings, and guides. The corrosion can cause catastrophic failure. As for the NP435 , I am not sure if it has any Copper or brass in it works, but I know that the T18 does, and therefore GL rated Gear oils are not to be used in that type of Manual trans, I would assume that the T98 being an earlier version of the T18 would also contain the Yellow metal parts. This is the reason that Ford repair manuals advise the use of 50w.


Here is a good read for those that want to use the right stuff in their Slick--

Gear oils [SubsTech]

 

so where can you find non-detergent 50w?

 

I got it at Autozone for about 3 bucks per quart!
as I recall it take about 2.2 quarts or something like that, for a complete change!

 

Do you recall the brand? Thanks for the help..

 

Mobil 50 wt.!

 

well i can find a 50w oil but not a non-detergent 50w. Will the 50w with the detergent have additives that can damage my t-18?