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EFV-8 Club Forum / General Ford Discussion / 20W-50 vs 10W-30 Engine Oil

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Posted By Discussion Topic: 20W-50 vs 10W-30 Engine Oil     Classic1 08-08-2014 @ 3:14 PM reply profile send p.m. Member Posts: 27 Joined: Jun 2014 I've noticed a lot of recommendations for using 20W-50 in flathead V8s. It seems that the original spec was for 30 wt oil so I'm wondering about what effect the added viscosity has on performance and protection? Is there any danger in the more viscous oil providing more fatigue to the oil pump? Does it slow down the circulation through the engine or does it even matter? It's just that I haven't a clue but I do have a curious mind. Steve '39 DeLuxe Fordor Norm 08-08-2014 @ 6:00 PM reply profile send p.m. Member Posts: 85 Joined: Oct 2009 At the risk of calling fire on my own position, it has to do with operating temperatures. The multi-viscosity oils (like 20W-50 or 10W-40) do not change viscosity over a wide temperature range as dramatically as the single viscosity oils (30 wt.). That's why they were developed. When the flathead V-8s (and sixes) were produced, the multi-viscosity oils were not available, so the recommendation had to be a single viscosity - 30 wt. in most temperate climates. In the winter, you had to use 10 wt. because the 30 wt. was so stiff when it was cold that the engine didn't crank fast enough to start. Nowadays, the 20W-50 can be used year-round. It doesn't get as thin when it's hot nor as viscous when it's cold. 20W-50 is not more viscous than 30 wt. len47merc 08-09-2014 @ 5:44 AM reply profile send p.m. Senior Posts: 1165 Joined: Oct 2013 Similarly at the risk of calling fire on my own position, if you have a new, solid, lower mileage and well-maintained motor with tight tolerances 10W-30 will provide all the lubrication, protection and oil pressure you need year-round. On the other hand, if you are working with a higher mileage worn motor, running 20W-50 in the warmer months will better help to keep your oil pressure up and provide additional protection for the worn and wider/looser tolerances. Steve rotorwrench 08-09-2014 @ 7:36 AM reply profile send p.m. Member Posts: 59 Joined: Jul 2012 SAE 20W/50 is formulated for engines that are either air cooled or set up with looser tolerances as a lot of racing engines are. I remember the 20W/50 being marketed as "racing oil" when they first started marketing the polymer based stocks. The early Ford V8 engines had relatively tight tolerances when new and I remember using SAE 20/20W back in the day. We used SAE 30 for summer time. SAE 20W/50 will work but the friction of the higher viscosity as the polymers expand will slow the flow when the engine warms up to operating temperature so it could be hard on the bearings in colder weather start ups. As was previously mentioned 10W/30 is the best all around lubricant for the flathead V8s. It can be used year round with no worries at all. I used to be skeptical about polymers when the stuff was first produced but after I watched a guy drop a bale of the stuff in a mix up batch of oil stocks, I became a believer. Watching it expand under a microscope when it heats up is pretty interesting too. This message was edited by rotorwrench on 8-9-14 @ 7:42 AM Drbrown 08-09-2014 @ 8:00 PM reply profile send p.m. Senior Posts: 570 Joined: Nov 2013 I don't have the technical knowledge others here do but note I have used 10W-30 since my rebuild 35,000 miles ago and still have excellent oil pressure. As some have claimed, I also think it reduces gunk build-up. Norm 08-10-2014 @ 7:09 AM reply profile send p.m. Member Posts: 85 Joined: Oct 2009 The reduction in gunk build-up is the effect of using detergent oil, not viscosity. rstefani59 08-13-2014 @ 1:22 PM reply profile send p.m. Member Posts: 32 Joined: Mar 2010 Is it still recommended to use straight 30w for the breakin period? How long should the breakin period be? supereal 08-13-2014 @ 2:07 PM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 The original lube recommendations have long since been obsoleted. These old engines lived decades on bulk oil from many sources. Same is true of greases, such as "soda soap" types. Today's oils and greases are light years ahead of those of the past, regardless of application. Today, at our shop, we received a lengthy bulletin about sythetic oils and their traits. The newest are being made from natural gas, instead of petroleum. They have extraordinary qualities that may allow quite extended change intervals. Of course, it comes with a price. These new oils make the present price of premium synthetics look cheap! As to break in period, we use a special oil for that purpose that contains a high amount of ZDDP (zinc). After at least 500 miles, it can be drained and replaced with your customary type. The ZDDP coats and protects bearing and cam surfaces during the period after overhaul, but isn't necessary after, according to the info. We do use a special assembly lube for that purpose, as well. This message was edited by supereal on 8-13-14 @ 2:12 PM

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