91FirebirdFmla

I have an engine with about 200,000 miles on it with some valvetrain tapping and a little play in the crankshaft bearings, basically a well and evenly worn engine. It doesn't smoke and burn any oil. I started using 20 50 oil this summer with very positive results as far as valvetrain noise. I was wondering if for the winter, with temps in the negative single digits at times, it would be safe to continue using the 20-50, or would it be better to switch to 10-40. I'm not sure how much of an effect this would have, or if it even matters, but if anyone knows, that information would help. Thanks

Vader

Provided it isn't burning/leaking any oil, the obvious choice would be a 10W30 synthetic. Pumps and lubricates down to -71°F, and maintains viscosity to over 300°F. What more could you want?

Stick to the major synthetics, like Mobil 1 or Amsoil. I'd avaoid the wannabes like Castrol, Pennzoil, and Valvoline.

Fire"Dutch"Bird

iTrader: (1)

Please explain!!

Red Devil

IIRC, their base stock is not truly synthetic.

Stekman

Mobil 1 and AMSOIL seem to have the best overal ratings in viscosity index, flash point, and pour point.

Working off of what Vader said, AMSOIL goes to mid 70's below zero and Mobil 1 goes to mid 60's below zero. Both have a high flash point, AMSOIL being above 500, Mobil 1 being about 450. Their VI's are about the same, hovering at 160.

I don't think either AMSOIL or Mobil 1 use any viscosity improvers (polymers) in their 10w-30 oils. And the lower the number of polymers in an oil, the better. That leaves a smaller amount of things that can leave deposits.

91FirebirdFmla

With so much play in the bearings and all the valve noise, i would worry that 10w30 wouldn't provide enough protection to the engine. I don't use synthetic.

Maybe if i used 10w40 and drove the car only when it was at operating temperature in the winter, then the oil would be rated to protect at the coldest temperature the car may experience and it would protect the engine at operating temperature adaquately.

Does this make sense?

Vader

91,

Bear with me if you will. I'll try to keep this as short, concise, but accurtate as possible.

First, multi-viscosity mineral oils get their multi-viscosity rating through pour (Kinematic) testing at two temperature points. At the cold temperature, an oil must flow at a given rate to earn a low viscosity rating. SAE viscosity is rated based on ranges of Kinematic viscosities. In other words, an oil that just barely passes at the upper end of the "10W" range still gets a 10W cold rating, but may be considerably more viscous ("thicker") than another oil that has a 10W rating.

At the other end of the scale, oil that is heated to the upper test temperature must not flow faster than the minimum umber of second per sample size, again, within a range. Therefore, and oil that just barely passes the minimum hot flow test may be considerable less viscous ("thinner") than another oil that has a lot longer pour time, but still falls within the "SAE 40" range.

Keep in mind that mineral oils that pass these tests are made from base stocks that qualify for the lower, or cold test viscosity. Therefore, 10W-30 mineral oil and 10W-50 mineral oil are still both SAE 10W oil. The upper test numbers are achieved by adding polymers that maintain oil viscosity at higher temperatures. Unfortunately, these polymers are combustible, and create ash and deposits when they burn. They are also the first thing to "wear out" in a mineral oil with a multi-voscosity rating. Mineral oils with a "10W40" rating simply have more polymers than one rated "10W-30", which means the potential for more ahs and sludge formation. "10W50" has even more.

Therefore, incresing the viscosity range of your oil may not be providing the extra protection you presume.

Synthetics are a completely different animal. By their molecular nature, they are inherently more temperature stable without the need for added polymers. A synthetic that flows at a given rate in the cold test may continue to flow at or near that same rate at temperature well below that. The best comparisons for that are the pour point and pumping point ratings. Mobil 1 10W30 has a pour point of -71°F, and a pumping point of -48°F. Your 10W30 mineral oil likely won't pour below -35°, if you're even that lucky.

Again, at the other end of the scale, the flash point and breakdown points are good comparisons for high temperature protection. Mieral oils typically have a flash point near 360°F, which means they are basically vapor instead of liquid at that point. Synthetics fare a lot better.

The viscosity index is also an important indicator, which measures the ability of a lubricant to maintain its viscosity through a wide temperature range,and after prolonged use at higher temperatures. Again, this is an ares where synthetic stand markedly above mineral oils. As teh polymers in multi-viscosity mineral oils burn away (and create ash ans sludge) the oil no longer maintains its high temperature viscosity. Pretty soon, the oil is just dirty 10W and has no higher viscosity at higher temperatures. The primary reasons to change oil within 3,000 miles (if you are using mineral oil) are to remove the accumulated sludge caused by the oil, and to replace the failed oil with something that again provides a bit more temporary high temperature viscosity.

So, for the bearing clearance issues, cold protection and pumping, and wear protection, why would you suppose that mineral oil is better? With the superior cleaning properties of synthetics, and the lack of polymer sludges and ash in the sump, the switch might actually help quiet those valves and lifters by re-establishing the correct oil flow through passages that are now likely resitricted or clogged.

Did I clarify that any, or just confuse it more?

91FirebirdFmla

That is one of the best answers I have ever heard, much clearer. I would love to switch over to synthetic but I bought the car with 170,000 miles on it and I have no idea how the engine was treated and what sort of leaks synthetic might open up on it. I need the car to last a while. But based on your explanation of how they make multigrade dyno oil, I will be switching back to 10w30. Since that is what I was using originally. Do you synthetic is a realistic, no-risk option for an engine that old?

Fire"Dutch"Bird

iTrader: (1)

91,
Why are you assuming synthetic oil will cause leaks?
That may have been true about 20-30 years ago when synthetic came on the commercial market. Nowedays you can switch from dyno to synthetic and back as often as you like without (leaking) problems!
Altough the benefits from synthetic are far more superior than mineral oil in SOME cases.
There are plenty cases where dyno oil is the best choice, again Vader knows and will explain to you I'm sure, as a non American, my technical English is not that good.
In my case, owning 4 cars and 4 motorbikes, 4-stroke, 2- stroke, and from 1 to 8 cilinders, oil is very important, and I'm using Castrol products in all of them for many, many years without any problems.
The oil in my Pontiac right now is Castrol RS Racing Synthec 0W40, it's the oil used by the large teams in the German DTM races.
I switched from mineral Pennzoil GT 20W50 at about 100.000mls to Castrol RS 10W60 without problems.
Later Castrol added another Syntec, 0W40, so I changed again!

.

91FirebirdFmla

I'm not assuming that it will cause leaks, I'm just afraid of what will happen if it does. It's a lot of miles for an engine and I just think it's a little late in the game to switch. If there are leaks in the seals that have been filled with deposits from dyno oil, which are cleaned out after switching to synthetic and the engine starts leaking, I can't just switch back to dyno oil. I've just cleaned out 200,000 miles of accumulation. The engine doesn't burn oil, leak oil or anything for that matter, it runs fine now. I've heard "if it aint broke, don't fix it" on the boards a lot, so I'm following that as much as I can. I used to run 5w30 and probably still would be if my mechanic hadn't taken off the oil pan for some work and told me that the bearnings had some play. I figured I'd switch to a slightly heavier oil to ensure adaquate protection. I just don't want to run into cold start-up problems in the winter with such a heavy oil.

five7kid

iTrader: (14)

http://www.amsoil.com/products/pco.html

They call it "diesel", but it is SJ/SL rated as well (the "S" means "spark ignition" or gasoline engines - for the record, the "C" is for "compression ignition" or diesel engines). Lower pour point than the typical 10W petroleum oil, good high temp viscosity retention, petroleum/synthetic blend for reduced cost. It'll still tend to clean up the grung if there is any, but at a slow enough rate that if the grung is actually assisting your seals, it will soften the seals at the same time to preserve the sealing capability.