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Importance of Oil Viscosity

While the owner’s manual for my V-6 Toyota Tacoma and the oil filler cap both say to use 5W-30 oil, the dealer says that he puts 5W-20 in everything and that the difference between the two isn’t that important. Does he know what he’s talking about, or does he simply not want to stock more than one type of oil in bulk?

Never trust anyone who claims to know more about something than the people who made it.

The 5W-20 will be fine in the wintertime, but come summer, having 30 weight oil in there when it’s 95 degrees and you are doing 70 mph will work better…The penalty you pay for guessing wrong is called “Bearing Failure”

Just another good reason not to bring your car to a dealer for maintenance, unless they provide it for free. The other people you want to stay away from are chains especially the quick oil change places.

Local independent mechanics recommended by friends, neighbors, co workers etc. are usually the best bet.

without defending the dealership in question…perhaps this is their recommended winter oil and they switch to 5-30 in the summer?

Never trust anyone who claims to know more about something than the people who made it.

And remember the dealer did not make it. Toyota put a owner’s manual in the glove box. Do what it says.

Don’t believe the dealer, especially one that already has proven he has poor advice. Likely he is buying bulk oil to save him money.

Was it the service “advisor” at the counter that told you this?
Any mechanic that would just pump the same oil into any vehicle is IMHO derelict in his responsibilities. But the counter “advisor” often doesn’t have sufficient knowledge for his/her statements to be believed.

The good news is that there is truely little difference between 5W30 and 5W20. The first number is the “base weight” of the oil, its resistnace to flow at room ambient, also known as its viscosity. The second number is the oil’s ability to maintain its resistance to flow at elevated temperatures. It’s accomplished with “viscosity modifiers”, which are microscoping coiled polymers that uncoil as the oil heats up and make a “thickener”, then recoil as it cools down to allow the oil to return to its room temp viscosity. 5W30 has a little more additive than 5W20.

If you live in a hot climate you’ll want the 5W30. Your owner’s manual will probably recommend different weights for different operating environments, perhaps even a different mix than 5W30.

Either way, the difference between 5W20 and 5W30 will not be significant for your Tacoma engine. If you had a turbocharged hot rod it might be, but your engine will be fine.

Look at the engine family group. See if it’s currently approved for 20 grade oils. The time of manufacture may have been before validation of the engine for 20 weight oil.

There is very little difference between a 20 and most 30 weight oils. It’s an arbitrary line in the sand. That is, how much better do you feel @ 9.3 cSt (within the 30 range) or how much terror do you experience @ 9.20 cSt (within the 20 range)??

Does a Chevy pickup …fully loaded to 100% of design capacity and routinely climbing 6-8% grades, have a different recommendation for viscosity? Surely the oil temps are going to go up. What does GM say to do? They tell you to shorten the oil change interval, NOT go to heavier oil.

When is the last time you’ve heard of bearing failure in an engine? Even a track driven Corvette where oil temps can reach 290F+ with the OEM spec’d 5w-30 M1. Now before anyone comments on “yeah, but it’s a synthetic”, what does that have to do with viscosity? It may have something to do with HTHS, but not a darn thing to do with its sensible visc.

Now valve train wear may be a different story, but again you’re dealing with the size of the envelope. 99.44% of all usage fits well into 20 weight envelopes. It would only be the margins where any distinctions would be apparent.

These Oil Threads are always so much fun…While we are nit-picking, we could talk about the difference between 20 weight oil and 20W weight oil…They are NOT the same! 20 weight will not flow at 0 degrees…20W will…Isn’t that AMAZING??

Some times I think someone knocked over a can of oil over in and it spilled in here…

All the NEW Toyotas now recommend 5W20 in the manuals, and that’s what the dealers are stocking. My 2007 Corolla specifically calls for 5W30, but the last time I had the dealer change the oil (good price), they tried the 5W20 bit on me too.

Toyota also sent me a bulletin stating that the lastest 5W20 oils were OK in my car.

The underlying reason is likely that even Toyota now has difficulty meeting the CAFE fuel economy standards, and today’s 5W20 will get nearly all Toyotas past the warranty period without failing!

Yes, your warranty will be in effect if you burn out the engine crossing the Mojave Desert in July with a heavy load. Because you will be in the minority, and Toyota’s Risk Analysis has determinmed that avoiding CAFE penalties gains a lot more dollars than paying for a few burned out engines. Ford’s rationale is the same on this issue.

As mentioned, 5W20 will be OK in the winter with moderate driving, but it can be a killer in the summer. A good year round oil is 0W30 full synthetic; it will allow easy starts at -40F and also protect your engine in the summer in Arizona. In my wife’s car we use 5W30 Mobil 1, since the car is driven little and the oil has to be good for year round use.

“All the NEW Toyotas now recommend 5W20 in the manuals, and that’s what the dealers are stocking.”

Did that just start for the 2010 model year?

It actually stated in 2009 when I got the bulletin that mine and many other new Toyota models could use 5W20 oil.

The bullletin I received was EG018-06 and said 2006 and 2007 Toyota and Scion models could use ILSAC GF-4 oil in a 5W20 or or synthetic 0W20 configuration.

The reasons given was “superior fuel economy and engine protection”, and that ILSAC GF-4 (now the standard Toyota spec)can be used in all Toyota and Scion engines.

The 5W20, weight is for the following engines:

AZ series, GR series, JZ series, MZ series, NZ series, RZ serioes, UZ series, VZ series, 1ZZ-FE, 2TR-FE. It seems my Corolla would not be able to use the 0W20. No doubt because of too large clearances.

The 0W20 (synthetic) is for; 2AZ-FE Camry, 2AZ-FE Solara, 2AZ-FE HIghlander, 2AZ-FE RAV4 (ACA3#)

Hope that helps.

“All the NEW Toyotas now recommend 5W20 in the manuals, and that’s what the dealers are stocking.”

Actually, the 2010 Tacoma owner’s manual specifies 5W-20 for the 4 cylinder engine but 5W-30 for the V6 1GR-FE engine. Given that they differentiate between the two engines, I gotta think there is a reason. I have written to Toyota for a clarification, and it will be interesting to see what they have to say.

Thanks for the additional info. The 1GR in the truck must have large enough clearances that under heavy load it will use oil and possibly damage the bearings. I found the same type of info in a Ford Explorer book; one engine uses 5W20 and the other 5W30.

The bulletin I received from Toyota was printed in 2006, and Toyota may have found since that using 5W20 in a truck is a bad idea.

Having said all that, my Toyota dealer pushes 5W20 for everything.

This discussion seems to confirm the fact that the 5W20 is driven by CAFE mileage requirements. Even a fraction of a mile per gallon multiplied by several million vehicles is worth a lot; Ford was fined $40 million a few years back for not meeting the CAFE mileage standards for their fleets.

If you have a chance to visit any country without CAFE standards, check the oil viscosity the sevice stations sell there and what the owner’s manuals say. You may be surprised they put 20W50 in those same cars in tropical countries.