Reader Question: Ultralight-Weight Oil and Uncle?

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Here’s the latest reader question, along with my reply!

Larry asks: Here is another piece of lunacy, under the religion of the EPA’s CAFE holy grail. I recently bought a 2018 Tundra 5.7L V8; in the owner’s manual is the phrase: “recommended” use of 0W-20 or 5W-20 in the engine for “better, more efficient start ups, better fuel economy” – right in the manual! No mention of using – or not using – heavier weight oils. They – the auto manufacturers – can eek out another 0.25 to 0.5 MPG, is what I have found in my research. It supposedly reduces engine drag caused by the heavier weights of oil that used to be recommended; 5W-30 was recommended primarily by Toyota engines prior to 2008. What I cannot find out for certain is if I can still use 5W-30 – I think I can. Can you help here? Many peeps on two Toyota forums say their Tundra’s rings were cooked because of the lighter oil – and more oil burning as a result. Thanks to Google search, I am sure I cannot get valid information. Same holds for a 2009 Corolla recommending 5W-20; it burns oil – which is part of the design I believe. Either way, it’s asinine!

My reply: The car companies are, indeed, desperate to squeeze out even fractional increases in gas mileage as well as fractional reductions in emissions, which these very lighter weight oils help them to achieve. They facilitate quicker starts and faster warm-ups as well as decrease drag, as you note. But they are also very . .  light, relative to what was usual 15 or 20 years ago. Which is part of the reason they’re also usually synthetic. The synthetics offer more protection in extremes (heat/cold, high load, etc.). But you pay extra for them, a hidden cost of the “savings” on gas.

Can you use a different (heavier) viscosity oil? Yes – and probably it won’t cause any problems. But, it might. If the engine has a variable valve/cam timing system, for instance – as many Toyotas do. These systems use oil pressure and oil pressure can be affected by heavier oil, especially during initial warm up. It may not cause any problems at all. But if it does, and the oil is thicker than what the manufacturer specifies, any warranty claim might be disallowed on that basis.

Given the huge buy-in cost (and repair costs) of modern vehicles, I’d err on the side of conservatism and use the heaviest recommended grade (i.e., 5W-20 for the Tundra) and abide by the “severe use” changeout schedule or once a year, regardless of miles.

I will also put in a call to an engineer friend of mine and get his thoughts, under the table, about this as well.

. . .

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  1. A lot of the question depends mainly on two things. What is the oil pump designed to pump, and what was the discharge side of the oil pump (oil passages, bearing clearances, relief valve orifice sizes, etc.) designed for? I have been hearing rumors of recent redesigns of both in existing automotive engine designs to take advantage of high-spec synthetic oil and lower viscosities. I have also hears rumors of mere re-specifying of the lubricant to make Uncle happy. I will be very interested in hearing what Eric’s engineering contact has to say.

    Here’s an example from the past. Two engines designed around the same time, with similar loadings, neither really designed as a performance engine, but with two very different lube requirements. MoPar Slant Six and BMC B-Series in the MGB. The Slant Six has generously sized oil passages (.50 caliber size), and somewhat larger bearing clearances, and a lower-pressure design target (say 20 psi hot idle). The B-Series has much smaller oil passages (like .30 caliber rifle bores or smaller), tighter bearing clearances, and a relief valve set to 55 psi. It runs more or less 45 psi hot idle. The Slant Six was designed for SAE 30, or 10W30 if mutigrade, and low pressure/high volume oiling. The B-Series was designed for 20W50, and high pressure/low volume oiling. So, the design and the viscosity go together.

  2. Though he may see 0W-20 in the engine bay, there may be a chart in the manual showing the different grades of oil that can be used, and at what temperatures. My Honda Helix owner’s manual had a horizontal bar graph chart that would show the various grades of oil that could be used, and at what temps they would cover. Perhaps digging in to the owner’s manual would help?

  3. It might depend on where you live as well. Up here the lighter weight helps when it gets down into the single digits, southern states not so much.

  4. The wife’s 2012 Honda has a little over 90k on it. I’ve been changing the oil myself since it was new. Perhaps stupidly, never even looked at the manual, and always used 5w 30 oil, just like most of the other cars I’ve had. Well, a few months ago I was looking at the manual for something else, and I find that Honda says I should use only 0w20! Oh well, it runs fine, doesn’t burn any oil. Think I’ll just keep doing what I’ve been doing.

    • Well, assuming you’re in FL (via your handle) the higher ambient temps via the weather would okay the use of heavier oil. Also could be the 0w20 is one viscosity for all the Hondas in the US, to include like the ones that live in Wisconsin. YMMV, of course


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