1989 F-150 4x4 - Diff Fluid

[NewGuy]

I would appreciate some thoughts on what type of gear oil I should use in a 1989 F-150 4x4. It was my Dad's old truck and I have started driving it. It has 122K miles, but looks great and runs great. I am using it here on my farm .... just like my Dad used it.

The manual suggests a Hypoid gear oil for the front and rear differentials. It lists a Ford Part #, but doesn't give a weight or even a range of weights. I have only used Amsoil products 1x in my life, but I purchased some Amsoil SVG (Severe Gear Oil) for my 2004 Tahoe. I thought it was a great product and might use it again. I will need about 3 quarts.

Question: What product would you guys suggest for this old Ford? I would like to keep it running as long as possible. My young boys love riding in it. I will use it to pull a trailer and haul hay, so it will be a work truck.

Thnks.

 

[Food Scientist]

I would worry about the GL rating. If it is recommended that GL-4 is used, then you cannot use GL-5 oil as it is not backwards compatible except for a few oils.

 

[daman]

If the trucks going to be farmed used the Amsoil would be my first choice.

it'll go many years/miles with that fill SVG is great oil.

 

[SuperDave456]

I expected to be able to look up what your vehicle would take on the Amsoil website.

It gives several reccommendations. As a matter of fact it looks like you can use just about any gear oil Amsoil carries.

I have put Amsoil in all the Differentials I have on my small home fleet just because I know it is a great product that will last. I like to do it once with a quality product and leave it for a very long time.

 

[Jim Allen]

You can run a high dollar syn like the SVG in it if you want (a 75W90 would be fine). It's a great oil, no question, but I don't think it passes a cost vs benefit analysis for a seldom used truck. At least for this tightwad farmer. The 8.8 axle in your old Ford will do nicely with a mineral 80W90, for which is was designed. Any name brand oil is safe and, frankly, there is little to choose between them. I don't trust store "house" brands or "no-name" oils as much, but many of them are good too.

If you want to discuss the oil in service, I have two trucks on my farm used just the way you outlined. Towing a grain or hay wagon at the legal farm speed of 25 mph is no real strain... even with my half-ton... as evidenced by relatively low oil temps (I have diff temp gauges on my trucks), even with 30-35 tons behind them. Going up hills, or at faster speeds, raises the temp a bit, but I don't have far to go and presume you don't either. Plus, here in Ohio, you are only allowed to go 25 miles from home with a SMV placard anyway. I have satisfied myself that a good mineral oil will do the job. If I had to pick some mineral brands, I'd look at Chevron, Shell and Valvoline.

 

[Gene K]

Unless the 31 Spline 8.8 in the Trucks have a different Diff Cover than the 31 Spline 8.8 in the 2005+ Mustangs, 2 Qt + Friction Modifier (If it has a Limited Slip) is about all that will fit.

New 8.8 Diffs come from the factory with Synthetic. In the case of the Mustang 75W140 GL5. Im not sure if the trucks get the same weight.

In a heavy truck we have to change non-synthetic every 50,000 miles and only have a 250,000 mile warranty if we use it. If we run synthetic we can go 500,000 miles and have a 750,000 mile warranty. This makes me think Synthetic is well worth it in that application.

The Motorcraft Fluids are very good if you can get them at a reasonable price. We have an independent local Authorized Motorcraft Dealer where we can get them at around 50% of Retail.

Dollar for Dollar Chevron RPM (Group III) 75W90 which carries both GL4 and GL5 Approvals is very hard to beat if thats what your axle calls for. It meets 500,000 mile Change and 750,000 warranty requirements in Heavy Trucks but is a lot cheaper than GIV PAO based lubes. If you need friction modifier for a limited slip then nothing aftermarket seems to work as well as the factory Motorcraft XL-3 ($4.63 for 4 oz at my Motorcraft dealer).

PS Dont overfill... Its not supposed to come all the way up to the fill hole.

 

[NewGuy]

Thanks for all of the good advice. I just spent the last 2 days on/off a tractor putting up hay. I have decided I am taking on any more difficult chores until the temperature gets down to 90 degrees!!

I do need to look at the cost vs. benefit of the different options. I have no idea what Amsoil SVG, synthetic 75W90 or mineral oil 80w90 costs these days. My '04 Tahoe required a synthetic diff fluid, so that was my introduction to the SVG. That Chevron RPM gear oil is interesting. I may try to find it. I have some time to research the issue and price some materials before I get time to change the diff fluid. These are good projects for those rainy days when you can back the truck in the barn and do maintenance and have a few cold beverages.

Thanks again for all the advice.

 

[01rangerxl]

The diffs in that truck are not all that picky about fluid. Any 80W90 would be perfectly fine. If it were my truck, I'd probably go with something like Mobil 1 75W140.

 

[marc1]

Originally Posted By: 01rangerxl
The diffs in that truck are not all that picky about fluid. Any 80W90 would be perfectly fine.


Exactly. I personally use Castrol Hypoy 80w90 in everything I own that needs a GL5 fluid.