Synthetic Oil
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Joined: Mar 2010
Posts: 609
Likes: 6
From: Apopka, FL
Synthetic Oil
What is your opinion on using synthetic oil over dino oil?
The reason I am asking, I am considering changing over to sythetic in my 7.3 Ex with 309,000 miles.
What are the opinions? good or bad?
I dont have any history on the EX. I purchased it about 1.5 years ago with 285,000 miles and change the oil every 5,000 miles.
Thanks for the ideas.
The reason I am asking, I am considering changing over to sythetic in my 7.3 Ex with 309,000 miles.
What are the opinions? good or bad?
I dont have any history on the EX. I purchased it about 1.5 years ago with 285,000 miles and change the oil every 5,000 miles.
Thanks for the ideas.
Post Fiend
Joined: Jun 2001
Posts: 5,228
Likes: 5
From: Running Springs CA
In Florida, there is probably no reason to switch to synthetic for a diesel, especially an older one. Any name brand 15W-40 will serve you well. Is an Amsoil dealer trying to make a sale? If you are considering Rotella T6 5W-40 syn I would still question the benefits due to the lack of cold weather starting issues where you operate.
Post Fiend
Joined: Jun 2001
Posts: 5,228
Likes: 5
From: Running Springs CA
Unless you drop down to a 0W-30 (not recommended), negligible. Without short trips in freezing weather, what controls motor oil's contribution to internal drag is the HTHS viscosity. That varies with SAE grade, not chemistry of base stock. Engine oils approved for diesels do not contain the friction modifiers of "For Gasoline Engines" oils. Again this has nothing to do with conventional, synthetic or blend.
Senior User
Joined: Oct 2011
Posts: 207
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From: Willard
Using synthetic oil on a vehicle with high milage will likely make it start leaking. I have seen this over and over in older vehicles with higher milage. I believe it is due to the fine nature of synthetic oil.
Good Luck!
Good Luck!
Logistics Pro
Joined: May 2011
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From: Maine
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Post Fiend
Joined: Jun 2001
Posts: 5,228
Likes: 5
From: Running Springs CA
There is some truth to it. There are two very different possible causes.
The first has pretty much been solved. Polyalphaolefin (PAO, Group IV) does shrink and harden seals. However, all modern finished PAO-based oils have an additive to conteract that tendency.
The second cause is not that synthetic causes leaks, but can make existing seeps and leaks worse. While synthetic is exactly the same viscosity as dino oil at operating temperatre, it does flow better cold. A cold engine, especially a worn one, has greater clearance between parts and seals are shrunk and less pliable, like rear main and intake valve stem seals. These factors can lead to smoke or drips where they were not noticed before.
The first has pretty much been solved. Polyalphaolefin (PAO, Group IV) does shrink and harden seals. However, all modern finished PAO-based oils have an additive to conteract that tendency.
The second cause is not that synthetic causes leaks, but can make existing seeps and leaks worse. While synthetic is exactly the same viscosity as dino oil at operating temperatre, it does flow better cold. A cold engine, especially a worn one, has greater clearance between parts and seals are shrunk and less pliable, like rear main and intake valve stem seals. These factors can lead to smoke or drips where they were not noticed before.
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Hotshot
Joined: Mar 2007
Posts: 10,101
Likes: 40
From: Pa
In Florida, there is probably no reason to switch to synthetic for a diesel, especially an older one. Any name brand 15W-40 will serve you well.
When I bought my 74' some years ago the all original 302 was somewhat gunky from sitting and using dino oils. No oil additive helped and I tried several. Switching to a full synthetic 10w-30 cleaned the engine out nicely and made the engine run better with less noise and got rid of the majority of the lazy lifter clank at startup. Switching from dino to full synthetic didn't change consumption any nor cause more leaks despite still having 30 year old antiquated seals keeping the oil in. The engine was not a high mile engine though. I just thought the full synth oil did a nice job.
Logistics Pro
Joined: May 2011
Posts: 4,832
Likes: 668
From: Maine
I ran synthetic oil in my 73 mustang, 70 dart swinger, a 81 Suzy GS850, and a 84 Honda Magna and never had an issue with leaks.
Post Fiend
Joined: Jun 2001
Posts: 5,228
Likes: 5
From: Running Springs CA
The OP stated that he was interested because of mileage. His engine already has 309k on it, so dino has served it well. Low temps are not an issue in FL and 15W-40's are extremely robust at high temperatures. Look at flash point and HTHS specs for Delo 400, Rotella T, etc.
