Pat’s Perspective – Oil

Every week I get oil questions like, the guy who changes my oil says I should be using thicker oil in my car. I trust him, but I don’t know about this advice. What should I do? It seems far too many people who change oil know more than the engineers who design engines. These morons keep telling drivers to use thicker oil for better protection. But, better protection doesn’t come from thicker or thinner oil. It comes from the right oil the engine was designed to use.

Don’t be a moron and do it because two morons don’t make a genius. Changing oil, no matter how many times anyone does it, won’t magically morph them from oil changer to oil engineer or chemist. Nor will changing oil teach anyone the steps used in a refinery to change crude oil or synthetics into something that can protect the parts inside your engine. This means protection during cold starts, blazing hot days in traffic, and every situation in between. Sadly, changing oil will not make a tech into a metallurgist that can study the amount of expansion of engine parts as it heats up. Nope, changing oil or even repairing engines won’t give anyone the knowledge necessary to make recommendations to switch from the oil recommended by the manufacturer to something not recommended by the manufacturer.

The primary job of oil in an engine is to keep moving parts from touching one another. This is done by means of a thin film of oil in gaps between parts that keep them from touching. But, heres the rub, as engines have become more precise due to sophisticated computer controlled machining….the space or gap for this film of oil has become smaller.This means these engines need thinner oil to pass through those smaller gaps and still provide the film of oil necessary to keep parts from touching. Also, nearly all engines these days have variable valve timing which works off oil pressure. Changing to a thicker oil changes the pressure needed to move oil through the engine. That increase in oil pressure can confuse the car’s computer…which controls the variable valve timing leading to lowered performance, lower gas mileage, or in some cases even a check engine light. Bottom line, changing oil or repairing cars does not give anyone (myself included) the knowledge to determine if a change in oil thickness will be good/bad/indifferent for an engine.

In other words, don’t reinvent the wheel. The manufacturer has spent millions in testing and engineering to determine the right oil for your car. Did the person changing your oil spend millions of dollars to develop their suggestion or is it just mental fantasy or outdated wacko bull? Unless the vehicle manufacturer issues a bulletin telling you to do something different, always use the oil recommended in your owner’s manual. Very few people are smarter than the engineers who designed the engine and typically they won’t be changing your oil.

Drive Gently
-Pat Goss


Bryan B said:

May 5, 2018 at 11:36 am

One episode you had mentioned a oil vapor separator. I have a prius that drinks oil if I use the more aggressive regen (speeds up the gas engine for better braking). Have you been able to prove your hunch regarding problems with buildup on intake valves?
I’m thinking that it should help my case significantly, but trying to figure out which hoses to insert this part into, not that easy.

Marcy said:

May 8, 2018 at 9:57 am


Thanks for watching! Proving this is like proving cars have wheels, there really isn’t anything to prove as it is well known within the auto repair industry. The “Catch Can” is simply inserted into the crankcase breather tube between the engine and intake manifold. Please keep in mind, this will not reduce oil consumption, it will simply reduce valve deposits and related performance issues.


Reggie Davis said:

May 24, 2018 at 8:17 am

I changed the oil recently in my Ford v10 engine. The manufacturer says to use 5W-20, but I used 5W-30 beacause that formulation had been tested and proven to resist viscosity breakdown better than the leading synthetic. Would it be likely to cause problems or should I remove the oil and replace it? The motorhome has not been driven yet.

Marcy said:

May 24, 2018 at 11:18 am

Hi Reggie:

I doubt it would make sense to drain and refill again. If it were a car I would say yes change it but because this is a motorhome where the engine will be working harder I think the 5W30 would be okay. In a motorhome the engine has to do more work to move all the extra weight and more work means more heat which would tend to affect the oil’s viscosity. The one thing that worries me is your statement “proven to resist viscosity breakdown better than the leading synthetic” which would lead me to believe you went with conventional oil instead of synthetic. If that is the case and you based your decision solely on viscosity stability I would disagree. There is a lot more to oil than viscosity stability and high quality synthetics beat conventional oils in nearly every aspect, better flow, much higher shear strength, etc., etc. So if you are talking about synthetic as opposed to conventional I would have to vote for synthetic. But in the end that’s only my opinion and the one person on the planet that has to be happy is you.

Pat Goss

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