When to switch to synthetic on recently-rebuilt 1982 280zx engine?...

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Apr 21, 2003
San Diego
At what mileage can I switch to synthetic oil in my newly-rebuilt engine, and what weight synthetic should I use?

Everyone I've consulted has told me that I need to let the engine break in for between 3-5K miles before putting synthetic in.


I have a 1982 280zx non-turbo (straight 6 2.8 liter).

I had to have the engine rebuilt at 160K miles because the previous owner's mechanic left the bolt on the crankshaft pulley loose and the resulting vibration destroyed the end of the crankshaft.

I had the engine rebuilt by a very reputable Z car specialty shop. The mechanic who worked on it has rebuilt about 80-90 of these engines. So I imagine the rebuild was about as good as they come.

Anyway, they insisted on starting the car on Valvoline's standard 20w-50. I've put about 3,000 miles on the engine changing the oil at 100, 500, and 1000 miles after the rebuild. I've kept Valvoline 20w-50 in it because I couldn't get anyone to say it was necessarily a bad idea. I've used Mobil1 and now AMSOIL oil filters.
Redline Oil lists on their bottles not to use synthetic until 3000 miles on a new or rebuilt motor, thus I would trust their opinion and use it after 3000 miles. You gotta respect their advice when a synthetic oil company tells you not to use it before 3000 miles. So you are good to go if you so wish as Patman states.


[ April 22, 2003, 08:55 PM: Message edited by: Idrinkmotoroil ]
Thanks for the responses.

I haven't noticed any oil consumption in the first 3,000 miles.

I don't know why they recommend 20w-50 for these engines. The Amsoil tech I spoke to recommended 0w-30. Does that sound good?
good, no oil consumption, sounds like they did it correctly.

Yes, the 0W30 (or Mobil 1 10W30) for the first 30,000, then Amsoil 10W30 ATM for the next 30,000. And stay with 10W30 until you see increased consumption. Then go to a 0W40 or 5W40.
You are the first person who has recommended that. Why do you suggest raising the viscosity like that?

Does anyone disagree with this?
your car will start to consume more oil as it ages. some cars don't but most likely you will have increased consumption as your car gets older. In my car, I find Amsoil being a bit heavier works better to decrease oil consumption.

Originally posted by Lee280zx:
You are the first person who has recommended that. Why do you suggest raising the viscosity like that?

Does anyone disagree with this?

Sounds like a good plan to me, as engine tolerances open up with miles added, a thicker oil can help in several ways, makes sense. There is a crowd out there that believes sticking to the same viscosity all the time, but i don't subscribe to that philosophy, I see nothing wrong with changing viscosities as needed.
I prefer a something like a Pennzoil 5W30 or 10W30 for run-in, but if that's what the mechanics recommended.....

A good indication that the engine rings and liner are sealing properly is when the oil consumption drops to almost zero.
... and if the oil consumption never drops to nearly zero even early in this engine's life. It means the rings aren't sealing properly and this rebuilder's skill probably does not match his reputation ... unless you are broke it in wrong (early trips to redline).

I have 5 quarts of Valvoline All-Climate 20W50 sitting on my shelf in our shop. Virgin oil analysis shows this oil to be VERY light in most additives (anti-wear as well as detergents). I'd probably give the stuff away if someone asked me for it.

After the break-in period, I don't see why you'd need to be using a 50 weight oil in a freshly rebuilt motor.

10W30 or 10W40 should be fine unless this guy builds them 'loose' and he shouldn't unless specifically instructed to do so (for a specialty racing condition).

As with the others, I'd guess you are fine switching to synthetic now. I think this idea is oversold anyway.

--- Bror Jace
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