Hey guys, I have been running castrol gtx 10w 30 for a year or so in my 327sb. I do not know the history/miles in this motor (but am assuming it's high milage)and have been considering moving up to a thicker oil. I live in SoCal by the coast so cold starts are a non issue for me. I also have a small leak I was thinking a thicker oil might remedy. Is this a good place for thicker 20 50? Also, I am assuming it has oe flattappitcam so what oil do you recommend or zinc additive I can add to regular gtx?
Any input would be greatly appreciated!
Do NOT assume using a high zinc oil is the best choice for a flat tappet cam. I've extensively tested over 130 different motor oils for their load carrying capacity which shows how well they prevent wear. I found that high zinc oils rank between number 4 and number 133, which VERY CLEARLY shows that simply having a high level of zinc is no guarantee of superior wear protection. If a high level of zinc was a guarantee of superior wear protection, then all high zinc oils would rank at the top of the list. But, that simply is NOT the case.
And if that itsn't bad enough, my testing clearly showed that adding aftermarket zinc additives actually makes an oil worse, NOT better. Many wiped flat tappet lobes COULD HAVE BEEN AVOIDED, including at break-in, if people had not blindly believed that all high zinc oils provide all the wear protection they need. Because nothing could be further from the truth. That whole line of thinking that you need high zinc oils for adequate wear protection has been completely debunked by Engineering tests, and is nothing more than an old wive's tale. See my Oil Testing Blog link below to see what oils really provide the best wear protection.
As for viscosity to use, 20W50 is way too thick. Consider the benefits of using thinner oil:
• Thinner oil flows quicker at cold start-up to begin lubricating critical engine components much more quickly than thicker oil can. Most engine wear takes place during cold start-up before oil flow can reach all the components. So, quicker flowing thinner oil will help reduce start-up engine wear, which is actually reducing wear overall.
• The more free flowing thinner oil at cold start-up, is also much less likely to cause the oil filter bypass to open up, compared to thicker oil. Of course if the bypass opened up, that would allow unfiltered oil to be pumped through the engine. The colder the ambient temperature, and the more rpm used when the engine is cold, the more important this becomes.
• Thinner oil also flows more at normal operating temperatures. And oil FLOW is lubrication, but oil pressure is NOT lubrication. Oil pressure is only a measurement of resistance to flow. Running thicker oil just to up the oil pressure is the wrong thing to do, because that only reduces oil flow/lubrication. Oil pressure in and of itself, is NOT what we are after.
• The more free flowing thinner oil will also drain back to the oil pan quicker than thicker oil. So, thinner oil can help maintain a higher oil level in the oil pan during operation, which keeps the oil pump pickup from possibly sucking air during braking and cornering.
• The old rule of thumb that we should have at least 10 psi for every 1,000 rpm is perfectly fine. Running thicker oil to achieve more pressure than that, will simply reduce oil flow for no good reason. It is best to run the thinnest oil we can, that will still maintain at least the rule of thumb oil pressure. And one of the benefits of running a high volume oil pump, is that it will allow us to enjoy all the benefits of running thinner oil, while still maintaining sufficient oil pressure. A high volume oil pump/thinner oil combo is preferred over running a standard volume oil pump/thicker oil combo. Because oil “flow” is our goal for ideal oiling, NOT simply high oil pressure.
• Oil flow is what carries heat away from internal engine components. Those engine components are DIRECTLY oil cooled, but only INdirectly water cooled. And better flowing thinner oil will keep critical engine components cooler because it carries heat away faster. If you run thicker oil than needed, you will drive up engine component temps. For example: Plain bearings, such as rod and main bearings are lubricated by oil flow, not by oil pressure. Oil pressure is NOT what keeps these parts separated. Oil pressure serves only to supply the oil to this interface. The parts are kept apart by the incompressible hydrodynamic liquid oil wedge that is formed as the liquid oil is pulled in between the spinning parts. As long as sufficient oil is supplied, no wear can occur. In addition to this, the flow of oil through the bearings is what cools them. Here are some comparison numbers from an 830 HP road race engine on the track:
15W50 oil = 80 psi = 265* oil sump temperature
5W20 oil = 65 psi = 240* oil sump temperature
Here you can see how the thicker oil flowed more slowly through the bearings, thus getting hotter, driving up bearing temperatures and increasing sump temperatures. And the thinner oil flowed more freely and quickly through the bearings, thus cooling and lubricating them better than thicker oil, while also reducing sump temperatures. If an engine is running hot, use a thinner oil to increase flow, increase internal component cooling, and help keep sump temperatures down. Keeping oil temps down is important to help keep oil below the threshold of thermal breakdown.
• Thinner oil will typically increase HP because of less viscous drag and reduced pumping losses, compared to thicker oils. That is why very serious Race efforts will generally use watery thin oils in their engines. But, an exception to this increase in HP would be in high rpm hydraulic lifter engines, where thinner oil can allow the lifters to malfunction at very high rpm. In everyday street vehicles, where fuel consumption is a consideration, thinner oils will also typically increase fuel economy. The majority of new cars sold in the U.S. now call for 5W20 specifically for increased fuel economy. And now Diesel trucks are increasingly calling for 5W30, also for fuel economy improvement.
• With the exception of high rpm hydraulic lifter engines, almost no engine should ever need to run oil thicker than a multi-viscosity 30 weight. The lower the first number cold viscosity rating, the better the cold flow. For example, 0W30 flows WAY better cold than 20W50. And 0W30 flows WAY better cold than straight 30wt, which is horrible for cold start-up flow and should be avoided at all cost. And the lower the second number hot viscosity rating, the better the hot flow. For example, 0W30 flows WAY better hot than 20W50.
• Thicker oil DOES NOT automatically provide better wear protection than thinner oils. Extensive “dynamic wear testing under load” of over 100 motor oils, has shown that the base oil and its additive package “as a whole”, is what determines an oil’s wear protection capability, NOT its viscosity. For example, some 5W20 oils have proven to provide OUTSTANDING wear protection, while some 15W50 oils have only been able to provide MODEST wear protection. So, do not run thicker oil under the false assumption that it can provide better wear protection for our engines.
• BOTTOM LINE: Thinner oils are better for most engine lubrication needs.
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To see my entire 130+ motor oil “Wear Protection Ranking List”, along with additional motor oil tech FACTS (with over 40,000 “views” worldwide), here’s a link: