Use a good quality 10w30 oil in your 300 I-6. 20w50 is like taffy, much too thick, unless you are burning oil / haze of blue smoke out of the tailpipe when fully warmed up? If so, 20w50, 10w40 is your choice.

Today's oils are designed to run in much hotter running engines. Using high viscosity oils is dated thinking, back in the 60s, 70s when some oils would begin to break down in hot engines / towing conditions ect. People would switch to high viscosity oils to combat the breakdown.

The 300 I-6, if tight, will run beautifully on 10w30 oil. Let's see: Immediate cold start-up lubrication to camshaft and upper valve train areas of the engine. Crankshaft, bottom end, spins much easier, without overcoming internal friction present in any high viscosity oil. Peak gasoline efficiently through all temperature cycles as the engines warms up to normal operating temperature. Sludge / varnish formation is nearly eliminated in a 10w30 oil as compared to 20w50.

Sure, an engine will start and run on 20w50. However, it's nowhere near the best oil t choose in a normal, tight, 300 Ford I-6 engine. Ford never used 20w50 as a new oil, so why use it now? Ford does not know what an engine needs as far as lubrication is concerned?

I don't think so. Good luck, the 300 I-6 is a great engine.

 

This is just the kind of information I've been trying to find. I have a 1992 F150 300 I6 with 170,000 miles on it which I recently acquired. Not knowing what kind of oil would be best for this engine, I've been trying to determine if there is really any difference in all the oils at the store or if I should just get the cheapest 10w30 and a common filter.

Does it really matter?

 

Probably not. The I-6 in that application is not revving high or working particularly hard. In the old Camry (200,000 miles) it gets the PepBoys $10 special. Last time that was Formula Shell, and a ProLine (by Purolator).

Jim

 

If it was me, I would make sure the 10w30 oil is API certified, for a conventional oil. Many house brand oils carry this certification (Super-Tech at Wal-Mart, ect.) so if you see it, you are good to go.

Plus, you can get many brand name oils as "oil change specials" for $15 or less, (as stated by Jim) that's a bargain and clearly the "budget" way to go for your 300 I-6 engine.

Ed
(PS I have a friend in northeast Ohio who says he swears by the 300 I-6 in a 4X4 Ford truck used to plow snow, over some bigger V8's! The 300 provides better grunt, and properly maintained, can plow just as much snow and do it for much less gasoline consumption. Over a winter, those savings add up significantly!)