Oil viscosity question (1 Viewer)

Joined
Aug 30, 2015
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San Carlos, CA
I just changed the oil in my FJ60 ('85, 160K miles) from it's regular 5W30 to 20W50. Not really for a particular reason, other than that according to the owner's manual 20W50 in the California summer is recommended. Both are conventional oils; the 5W30 always was a "high mileage" oil.
Not expecting any difference, I was surprised that:

1) idle RPM dropped from about 1100 RPM (I have never been able to get it any lower by adjusting the idle speed screw), to about 700 RPM
2) oil pressure is now constant at the second mark, independent from RPM, and even at idle. Before the pressure was a little below the second mark while driving, and quite a bit lower when idling (at 1100 RPM :) ).

I assume the lower idle and higher pressure at idle are caused by the higher viscosity of the 20W50 oil. Is this a good thing or not? Especially the lower idle, while a nice improvement :) , makes me think there is now more friction, which may have an effect on mileage (have yet to check this), or wear?

Any thoughts?
 

brownbear

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It's a good thing.

Hot weather and older engines like thicker oil. Probably won't leak as much too.

But if it gets colder out you may want to change it. Does it colder where you are?
 
Joined
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San Carlos, CA
Coldest it gets here is just about freezing, and then only for a few days each winter.
It would be great if the persistent leak from the rear main seal would also stop!
 

OSS

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I found that conventional (non synthetic) 20W-50 when used in the 2F:

  1. Decreased mileage
  2. Harder starting
  3. Decreased performance/power

For those reasons I refused to use it in the 2F.
There's way better oils to use than that old tech. An excellent alternative is Mobil-1 10W-40 High Mileage (synthetic) or Castrol Edge 5W-50 (synthetic). Or if you want to use conventional oil, try the diesel oils (Delo, Rotella).
My favorite I ran for 30 years and 290,000 miles was the Castrol Edge 5w-50.

Conventional dinosaur 20W-50 would be my very last choice, and my 2nd to last choice would be regular ole 5W-30 motor oil. Avoid using that stuff in the 2F whenever possible
 
Joined
Jan 17, 2005
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Southern Colorado
I lost 1 mpg when I ran 20w-50 in my '78 FJ40 - and noticed a lower idle speed. You might consider running a 'high mileage' oil to slow the leaks, and run 10w-30 or 10w-40.
 
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FYI synthetic oil and non synthetic oil are still made from the same petroleum. The process used to achieve the end product is different and while Synthetic is done in a lab type of process it isn’t grown from alpaca stem cells. Non synthetic oil is still evolving in performance and formulation and modern non synth oil is still ages better than stuff sold 10,20,30 years ago etc.

good overview for the brain

 

Spike Strip

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If you're gonna run a dino oil, you're better off with a 15w40 Diesel like Delo 400 or an oil made specifically for flat-lifter engines.

There's a lot of pressure on the solid, flat lifter surface and the cam lobe; that's where the excessive wear takes place when using low zddp oil, modern oil on a 2F and similar engine.

I've posted this like a 100 times now, but one more time: additives like zddp get consumed over the service life of the oil. 50% of it is gone at 3-5K miles depending on how you drive. An oil that just barely meets the requirement will not be sufficient after 3K miles (like Delo), so you really need an oil with sufficient zddp at the beginning of usage so it has sufficient levels over its entire service life.

The problem with additives is you have to get the concentration right and that will require you to know the initial level of zddp and then do some math for the concentration level. Too much zddp is as bad as too little.
 

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