I recently picked up an 1990 F150 with the 5.8 351. The truck has about 170k miles. Is 10-30 or 10-40 the correct oil for this engine? Also I'm assuming the rear differential takes 80-90? Thanks

 

I believe 10w-30 would be the stock recommended oil. 10w-40 wouldn't hurt since it's an old engine.

 

best oil for these trucks in my opinion is the Rotella T 15w-40 Diesel. has alot of ZINC which is great for high mileage engines. alot of people use Rotella in there daily driver passenger cars as well. you can get lighter weights if you get blend or full synthetic

 

X2 on both earlier replies. That engine has a flat tappet cam, and could use the extra zinc. May want to shoot for the Rotella 10w-30 blend now. 15w-40 is fine, I just don't use it when the temp dips below 20's at night, unless I have a block heater installed.

Quaker State has a new blend called Defy, with extra Zinc and Phosporous. It's synthetic blend and is cheaper than most higher name brand oils on the market. I've used it in my rebuilt 302 with flat tappet cam, my 300, with 128K miles and flat tappet cam, and the wife's 2000 Expedition with 200K miles.

I used 75w-90 in the rear and 80w-90 in the front. The wife's Expedition has 75w-140 synthetic in the rear, and that was filled at the factory, and it's suppose to be service free, unless rear axle has been submerged in water.

 

+1 on Rotella. I've been using 5w40 in the truck, crown vic, and the impala.

75w140 is what's specified for the 8.8 rear in my F150.

 

Yes, Rotella diesel oil is also a good choice. The zinc in it will help your engine last.

 

what about CAT 15w-40 diesel oil in a 5.8?

 

Would probably do okay as well

 

Thanks for the replies. After asking I found a sticker under the hood that states 10-30. I will be going with Valvoline conventional 10-40 and a Motorcraft filter.

 

I know a lot of people here have used diesel oil (Rotella is usually what's mentioned) in gas engines with good results. Not to take anything away from their first-hand experience, but I have one second-hand experience that didn't work out so well.

This was back in the mid 80's. A guy who maintained a fleet of vehicles for the city had a Pontiac Sunbird 2.0L four cylinder with about 15K miles and a completely wiped out camshaft. He had been using the same oil that he bouth in bulk for the city's medium duty diesel dump trucks and the heavy duty diesel frontend loaders etc. That matchup didn't work out well at all.

So that was oil purchased by a city manager (probably the cheapest stuff he could find) intended for medium- to heavy-duty diesels that didn't work in a 4-cyl OHC engine.

How does that compare to high-quality oil made for light duty diesels being used in gas V8 push-rod engines? I don't know. And again, a lot of people here have used Rotella in gas engines with good results. But personally I'm going to keep using oil recommended for gas engines in my gas engines.

 

Don't blame you. Whatever works for you and keeps your engine in good shape is good enough. There are so many different oil options.

 

I too run Diesel engine oil on mine, it clearly states it's formulated for gas engines too so it's fine by me, I've run it for about 5-6 changes now without any noticeable problems.

 

That likely had far more to do with the viscosity than the HDEO add pack.

 

The only problem with diesel oil is that it wipes your gaskets clean from the inside out... Which makes it leak a bit more

 

Never heard that one before. Why would it leak any more than other oil? Rotella says it's also suited for gasoline engines. What properties would make it do that?