My last oil change I switched to premiem blue extreme synthetic oil. I have heard once you go sythetic you should stick with it. Is this true? I was thinking that during the summer months I would use premiem blue 15-40 and winter use the 5-40 synthetic. It wont be due for an oil change till about april just want to find out now. You know its hard to make choices with all the rumors that I hear, but I know I will get some good info here.

 

I use 15-40 in the summer, and synthetic 5-40 winter with no problems. My brother has done this with his 97, 01, 03, and 06. He uses 0-40 syntnetic in winter.

 

5w40 synthetic can be used year round and if you want you can go back to 15w40 if you want to but why? I have noticed that when I changed over to the 5w40 synthetic my engine runs about 75-100 rpms lower then it did with 15w40 oil.

 

That magic synthetic oil must have changed your gear ratio too.

 

If the engine is running 75-100 RPM's lower with the synthetic, I would say it's because it is not lubing as well, which doesn't make sence. Did you mean 75-100 RPM increase.

 

I'am a maintenance nerd, if there is such a thing.

On my 1999 dodge cummins i would do maintenance even if it didn't need it. On my 2005 I changed all the fluids (engine, front and rear axle, transfer case, transmission) three times within 15,000 miles. Excessive, YES. Conpulsive, I have an addiction to maintenance. Enough, back on topic.

I changed engine oil on my 1999 dodge cummins more often than some people change underwear. I used every brand known, synthetic, non-synthetic back and forth my wife thought I bought stock in oil companies. Never hurt a thing. When I traded my 99 off it burned absolutely no oil and I towed and the engine/transmission was bombed with goodies. Changing oils never hurt a thing.

 

Like I said before I reduced/lowered my RPM’s between 75 and 10 RPM’s when I changed over to 5w40 synthetic oil. As I understand it, this means that the synthetic oil is doing a better job of lubing the engine then the dino 15w40 I had in it before the change over. With better and lighter oil the engine can run at lower RPM's to maintain the same speed. If the synthetic oil was not doing it's job of lubing the engine it would have to run at higher RPM’s to maintain the same speed at which I noticed a reduction at with the synthetic oil in the engine.

 

Ah, drain the oil out of your engine and then let it idle. Tell me if the rpm's will increase or decrease the longer the engine is run?

The same applies to synthetic or nonsynthetic oil in the properties that synthetic is suppose to lube better.

Now on a computer controled engine it shouldn't matter, as the computer will keep the engine at whatever predetermined speed it was calibrated for.

 

I will have to disagree with you and I don't recall ever talking about a computer controled engine. BTW what’s with this statement and I quote {“Ah, drain the oil out of your engine and then let it idle. Tell me if the rpm's will increase or decrease the longer the engine is run”} have to do with me seeing lower rpms from the use of Rotella 5w40 synthetic oil?

Also why would you think I should see higher rpm’s from the use of synthetic oil, as most people know that synthetic oil is better then conventional oil at reducing friction on metal to metal parts in a engine? FYI, I do not sell Rotella oil I buy it at Wall Mart. Any way with the use of the synthetic oil there is less friction in the engine and this in turn allows the engine to run at lower rpm’s.

FYI, my engine use to run at 2000 rpm’s @ 70 MPH and had done so for the past 10,254 miles. Now with the use of Rotella 5w40 synthetic it runs between 1900-1925 rpm’s @ 70 MPH. The only thing I had done to the engine was that I had my oil changed 20 minuets before I was on the Freeway when I first noticed the drop of between 75 and 100 rpm’s @ 70 mph.

Now this will be the last I have to say on this subject, as I’m not in the mood to argue with anyone.

 

unless the tire size, trans gears, or axle ring and pinions are changed, the only way for your cruising speed to change is for the speedo ,tach, or one of the senders are failing. not arguing, just stating fact....but what do I know?

 

DBLR,
Your first post said nothing about while driving or at any speed. I was trying to get accross that on a idleing engine and The slipperier the oil the less friction, the less friction would increase rpm's due to less resistance of moving parts.

If your talking road speed and rpm I don't care if your using synthetic, mineral based oil, vegetable oil, crisco, vaseline, or no oil at all. The rpm's for a given speed will not change.

If your seeing a rpm drop at road speed something else is going on.

 

I want some of what he is smoking!!!! Yes, synthetics allow for better efficiency, with reduced heat, friction, wear, BUT they WILL NOT LOWER the RPM of a DRIVETRAIN that is run by Gears!!! YOU MAY have to use less input on the throttle to stay at the same speed because the engine makes a little more power because of the lesser friction--------you will still however be running the same RPM NO MATTER WHAT!!!
---So in your theory, you are saying that an engine that is connected directly to a drive shaft (NO Transmission--No Differential Gearing-----straight 1 to 1 Ratio), that is turning a set of wheels at 2,000 rpm to aquire 70 mph,,,,,,,,, will actually be able to lower the rpm of that set-up just by using a synthetic oil???????????????????????????? Think about it and let us know what you come up with!!!!

 

DBLR,

There's no need to argue... You won't convince very many (if any) of us here that synthetic oil reduced your RPM's at 70mph.

I'd agree with you if you were right.

 

I do believe you forgot peanut oil, cod fish oil, **** ease and KY jelly.

 

LMAOROF, I though about the **** and KY jelly but I didn't want to deepen the discussion.