How do you decide what viscosity of oil to use? I'm talking about 10-30 vs 20-50. We know that new engines have closer tolerances in the bearings requiring thinner oil ie.. 5-30 or 10-30.

But at what point would you use a thicker oil, 0.001-0.002 or more? Lets assume we are operating at moderate temperatures and driving around town.

Not sure about any of that, but I use 10-30 year round (northen california).

Actually, I believe it is more a choice of how you are planning on driving the car than what the engine clearances might be.

Especially when you are comparing todays multi-viscosity oils with the straight grade of old.

I've seen engines that were filled with 20w-50 run from their first oil change to over 160,000 using the same grade of oil with absolutely amazing results.

So the choices between 10w-30, 20-50, 5-30 etc are really more a matter of preference, useage, and sometimes geographical location more than any other reason.

Howdy,

I use synthetic in all my cars. Not because I am a expert on engine oil but I know enough engine builders to be convinced that synthetic is the way to go. The only time I would not use synthetic is if your car uses a lot of oil, because synthetic is more expensive. I choose to go with 10w-40 for all my cars ('99 Honda Odyssey, '90 Honda Civic, '71 240Z L28, '79 Ford F250) because it is in the middle of the road and I buy it by the gallon! If you are in colder climates and have difficulty starting your car you may want to go with a thinner oil during winter months and if you race you may want to consider a single grade thicker oil.

Hope it helps!

The synthetic argument is pretty compelling. But there is an 'old wives tale' about not switching in an (older) car that has been 'raised' on petrol-based. Any truth in that?

I also met someone the other day who "changes his synthetic every 3000." This is the first time I have heard that. Any benefit? Everyone else I have met uses the 3-5000/filter, 10-20,000 oil method. Comments?

steve77

Steve77,

Your old wives tale has some truth. The problem occured in years past when non detergent oils were popular. When some well meaning soul put a detergent oil in an old horse that had been raised on non detergent, The s__t would literally hit the fan. The detergent would loosen up the gooky stuff left over from old non detergent and it would start floating around and sometimes plug things up. They used to try and keep the oils from getting mixed up by putting a blue color band on the top of non detergent cans, and a red band on the detergent.

However, all current detergent petroilum oils are compatible with synthetics. Not sure about the old Castrol R "bean" oil though. I ran that stuff back in the early seventys in a H-Prod Bugeye just cause I liked the way it smelled.

Also, I too change synthetic oil every 2500 to 3000 mi. The oil is still perfectly good, but dirt, fuel contaminants, carbon, and other nasty stuff can not all be removed by the filter. Thats why it turns brown or black. Clean oil means life to your engine. I've been building mostly racing (and aircraft) engines for nearly thirty years,

and have found clean oil to be the best insurance an engine can have for a long life.

One last thing. Choosing a brand or wt. of oil is like having sex.

Everybody has there own preference on how to go about it. But they all seam to get the job done ok.

Phred

Phred,

Wow, an H-Prod Bugeye -- didn't you need an extra quart or two of oil piped in from the cockpit during a race? :classic: (Sorry, just giving you a load -- those are quite beautiful cars)

My crew chief has been a professional mechanic for several decades and has a personal friend who is an engineer at Mobil Oil. His recommendation, for my Z race engine at least, is to run non-synthetic 20w50. We change it after each race weekend -- totals four 30 minute sessions -- or about 125 miles -- mostly at 6500rpm. I know a lot of guys that run Redline and other high performance lubricants but I know I can't justify the cost. Our engine shows no sign of wear after eight weekends.

I run 10w40 non-synthetic Valvoline in all my street vehicles.

I am now using 20 w 50 .. I have run a couple of different brands. I am now running Castrol... Seems to work fine..

I used to run 10-40 in the winter and 20-50 in the summer in Sacramento, but now that I live on the coast, I just run 20-50 all the time. Castrol. But seriouly comtemplating the synth thing...

steve77

So, bearing clearances has nothing to do with what type of oil to use? That's the message I'm getting. Seems like personal preferance and weather conditions is the deciding factor. I always thought that the older the engine the thicker the oil.

Rick Hanson:

No, I did'nt need to carry any extra oil, But I did carry a set of points, and a coil. "Charles Lucas-Father of darkness" is not a myth.

Phred

I think the idea of thicker oil in older engines, is a way to prevent engines that leak oil from leaking as much. If your engine does not leak oil, adding oil that is the correct viscosity for the driving and weather conditions.

To me weather is a really factor. I lived in North Dakota for a while, and on a cold winter morning (i.e. -10 degrees F), the last think you wanted in your car was thick oil. Starting a car with "frozen" oil is not a good way to lubricate anything.

I am not really sure... I used to build hot SAAB engines , and the guy I bought my parts from was a long term race builder... I asked him once about running the thinner synthetics. He did not recomend it for his race engines. His claim was that the thicker oils protected the engine better... His quote was something like the thicker oil keeps the parts from beating themselves to death... I don't know if I conpletely buy this idea, but who knows. I have read the info on the synthecic oils, and they sure sound superior. But I think that if you keep clean reasonably good quality oil in your car, you may have a hard time proving any difference. If your car will last 200,000 to 300,000 miles either way. And a Z will,, what's the difference... I will want to rebuild before then anyway..