Help with oil type and weight selection

Joined
May 9, 2022
Messages
2
Hello all,

First off, long time reader, first time poster. I have read many in depth posts and explanations over the years and for a while I though I had a good grasp on what oil I wanted for my car (depending on application). Recently I've come back to the table only to feel lost again. I am hoping that by posting here, I will get some better feedback which is a bit more specific to my situation.

The car is a 1991 Nissan 300ZX twin turbo. It has been completely rebuilt, iron block bored out for oversized forged pistons, forged rods, upgraded turbos, cams, Haltech ecu, the works....

FSM specification calls for 10w40 oil to 20w50 for my climate (south Georgia). I have always thought that 0w40 oil would be a good choice because it's the same weight as 10w40, just with better cold startup viscosity but I could never bring myself to make the swap from my 10w40. Since it didn't really exist in 1991, would Nissan have recommended a 0w40 over 10w40 if the exact same car was made today?

Another thing I go back and forth on is synthetic vs conventional. Yes, I get synthetic is hands down better in basically every aspect, but this is not a daily driver. I have put maybe 5,000 on the car in 5 years... My thought has always been to buy the cheap stuff (Havoline 10w40 conventional) and just change it every 6 months or so. Is a 5 month old synthetic oil with say 1,000 miles on it actually better for my engine than a 5 month old conventional oil with only 1,000 miles on it?

With the amount of blowby my engine has (forged pistons in an iron block with 2 turbos, 8.5:1 compression) I have recently began to wonder if the synthetic oils would actually perform better than conventional even with the frequent oil changes simply because the synthetic oil would resist breakdown from heat and gasoline in the oil much better.

When I do take the car out, I drive hard. I started looking at Amsoil race oils and while they seem good, I don't think it is a good fit for my car with an iron engine block due to lower anti corrosion additives. Which lead me to Amsoil signature series oils, which lead me to wondering if any synthetic oil would be my best bet and full circle though loop again.... lol

Fwiw, I did use Lucas break-in oil for the first 1,000 miles last year after the rebuild. Can anyone out there shed some light on my situation?

Maybe to sum up here:

(1) 10w40 vs 0w40 (do they offer the same protection at operating temp?, is the only difference the first few min on a cold start?)

(2) conventional vs synthetic (do they offer essentially equal performance out of the box? Is the main draw on synthetic it's ability to retain its viscosity and lubrication after 3,000 or 5,000 or 10,000 miles? Ie: conventional is just as good with pil changes every 2,000 miles?)

Thanks in advance to anyone who provides some input.
 

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FCD

Joined
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Very cool car.
I would definitely not run 10w40 conventional oil in a highly stressed twin turbo engine, if it were my car i would run Mobil 1 5W-50 or 15W-50 in it and sleep well, either of those oils will protect your engine well no matter how heavy your right foot is.
 
Joined
Jul 30, 2003
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Look at the HTHS of the two oils you're comparing. For all we know, the 0W40 could be thicker at op temp than the 10W40.
 

Cliffe5

Thread starter
Joined
May 9, 2022
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2
Thanks for all the replies already coming in! I'm wondering if anyone has made an excel sheet with all the popular oils on the market and their differences in performance metrics? It would be nice to have a quick reference without having to search different sites and labels for info. Anyone know of something like this already exists?
 
Joined
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Thanks for all the replies already coming in! I'm wondering if anyone has made an excel sheet with all the popular oils on the market and their differences in performance metrics? It would be nice to have a quick reference without having to search different sites and labels for info. Anyone know of something like this already exists?


That would be difficult because of all the oils plus the oil companies are constantly reformulating their products.

What would that information tell you about a particular oil?
 
Joined
Dec 26, 2005
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Thanks for all the replies already coming in! I'm wondering if anyone has made an excel sheet with all the popular oils on the market and their differences in performance metrics? It would be nice to have a quick reference without having to search different sites and labels for info. Anyone know of something like this already exists?
What “performance metrics” are you looking for?
 
Joined
Jan 20, 2022
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If not stock. I would probably stick with the castrol 30 wt. Or depending how I'm gonna be driving the car; Maybe some Redline 5w-20
 
Joined
Jan 25, 2022
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for your car and climate 20w50 would be best but of course it needs to be changed more often because its conventional. I usually recommend 0w40 but not in your case as you state its not a daily drive, its would be more expensive and not necessarily better.
 
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