Selecting Engine Oil Wt vs Outside Temps 3

[lowtechgrad]

Checked thread 89-62555, but I don't think it quite answered my question. If it did, just give me the ref, and accept my apologies.

I’m just a shade-tree mechanic- after oil & filter changes, maybe a battery or thermostat, today’s auto maintenance is beyond me. About 15 years ago, I encountered a very unique Texaco Customer Hotline: 1- They actually answered the phone, and 2- I spoke with an engineer!! (Alas, 6 months later, the line was answered by a ‘customer rep’ who either knew, or would commit to – nothing.) btw- I checked thread 89-62555, but I don't think it quite answered my question. If it did, just give me the ref, and accept my apologies.

On that lucky occasion I spoke with the engineer, he sheepishly admitted (“I’m probably not suppose to say this”) that auto manufacturers were recommending the thinnest possible oils, to get better mileage, but with minimum consideration to engine life. As I keep my cars for about 100,000 or more miles, I’d like to know if he was right. In the warmer temps of South Florida, I always insisted on 10-40, rather than the 5-30 dealers tried to sell. Now I live in Arizona. I might go 5-30 for a winter start in Flagstaff, but when I have to drive in Phoenix in August, I'd like to know if the engineer's admission is still valid. Seems to me, the ideal oil would be 5-60!
Thanks in advance, sorry to be so wordy. Rich

Comments?

 

[25362]

Thread71-99132 may help.

 

[TheBlacksmith]

Multi-vicosity oils do not thicken, they just don't thin as much. A 5w-30 has the same approxiamate viscosity as a straight 5 weight at low temperatures (if I remember right 0 F) and the same approximate viscosity as a 30 weight at high temperatures (I think around 200 F). The 5 weight would be like water at 200 F! In the bearings of an engine, the oil is sheared between the fixed and moving parts and a thicker oil can actually make the bearing run hotter as it takes more energy to shear the oil. So, yes thinner oils can increase the mpg, but also can make the bearings run cooler. Also thinner oils pump up quicker during a cold start and may run through the engine quicker, carrying away more heat from the combustion area in the process. Film strength, which is what protects your bearings, is not directly related to viscosity. So, lower viscosity oil may be better, may be worse. Unless you designed the engine and/or the oil, I recommend you stick to the manufacturer's recommended grades with a quality name brand oil.

 

[lowtechgrad]

<<< Unless you designed the engine and/or the oil, I recommend you stick to the manufacturer's recommended grades with a quality name brand oil. >>>


Just to be clear- you believe I should stay with manufacturer’s 5-30 recommendation, in slow traffic, with OATs above 110F ?

I keep (cynically wondering if passenger auto manufactures, pressed with higher MPG requirements, might be ‘recommending’ more toward mileage, than getting the engine well beyond 100,000 miles.

Thanks again,



Rich

 

[TheBlacksmith]

Yep. I run 5W-30 in all my vehicles, in stop and go rush hour traffic in Norfolk Va ~ 100 in summer to Upstate NY ~ 0 in winter, including 9 hour trips between same with a full load in the pickup bed. My F150 has over 123,000 miles on it and is still quiet, powerful and gets better than its EPA rated mpg. If its going to fall apart at 100, 000 miles, I guess it better hurry up! BTW, I do use synthetic 5W-30.

 

[lowtechgrad]

Can't beat that testimonial. Thanks.





Rich

 

[evelrod]

Here's one more, Rich. My wife's Lincoln LS V6 has been dealer serviced since new in March 2001 and has always been on 5W-20 summer and winter (well as 'winter' as we get here in Socal). Lots of summer days of over 100f around here.
Oh, yeah. I forgot to mention, the car is just over 146,000 miles and still gets it's usual 21/22 mpg and uses no oil between changes...still on the OEM sparkplugs...just passed it's first California smog test...What more can I say?

PS: I don't use these 'light weights' on most of my vintage cars...either 15W-50 Mobil 1 or 20W-50 Castrol in the older cars and my diesel. After all, we are in Socal where it never (usually) gets colder than 40f !

Rod

 

[lowtechgrad]

<<< . . . PS: I don't use these 'light weights' on most of my vintage cars...either 15W-50 Mobil 1 or 20W-50 Castrol in the older cars . . . >>

If the 5w20 did so well for the newer car, why the heavier wts for the viintage ones?



Rich

 

[evelrod]

Bearing clearance in older cars is generally a bit loose for the ultra light oils. Newer cars have really tightened up the clearances, partly for NVH reasons and largely for fuel economy of operation. Something machining technology did not allow in my older cars. EG, main bearing clearance on my Metropolitan are set at 0.0025"/0.003" and the 2001 Lincoln specs are as low as 0.0005"! Piston clearance can be as low as 0.001" on new cars and as much as 0.007" on some older engines. Lighter wt lube could contribute to a rather noisy engine, particularly when cold. The lighter wt oil would still most likely be servicable...it's difficult to teach an old dog new tricks.

Rod

 

[lowtechgrad]

Ahhhh- makes perfect sense.

Not trying to plug the forum, but I''ve asked my initial thread question to numerous mechaniics & service managers, for 10+ years. The answer was always a shrug and ''that's what the manual says'

This has really helped- both in testimonials & explanations.

Thanks again, guys.




Rich

 

[bigmo460]

Having worked in the OEM industry I saw a lot of engines torn down that ran tests on both 5W-30 and 10W-30. I noticed a slight bit more wear on the thinner oil. I'm talking immeasurable wear only visual marks. All the engines passed all testing. And your right the thinner oil is for improved fuel econ. I personally like the 10W just because of the increased wear I saw. I suspect you might only see a slight difference in very high mileage. I just like to error on the safe side.