Amsoil Recommendations For 1968 GTO 400 H.O.

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propuckstopper

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Happy New Year. After many years of sitting, I am getting back to working on my 1968 Pontiac GTO 400 H.O. Convertible. We are freshening the original engine (rings, bearings, heads) and I have already chosen Amsoil Z-Rod 10W-30 for the engine.

I will also be changing out the automatic transmission fluid (Turbo 400) and am wondering if I should go with the Amsoil Multi-Vehicle ATF or the lighter viscosity offering? The owner's manual requires a Dexron III fluid.

Also, looking to find out your opinions on a gear oil for the original Positraction 3:23 rear end. In a 75W-90 viscosity, do you think I should go with the Severe Gear offering, or the regular Amsoil?

As a restored car, this GTO will be driven only on nice days and fairly gently.
 
Originally Posted By: propuckstopper
I have already chosen Amsoil Z-Rod 10W-30 for the engine.



I would have chosen this:

Quote:
Z-ROD 20W-50 Synthetic Motor Oil
 
I certainly did consider the Z-Rod 20W-50, but I was concerned that it may be too thick for a new engine. We are going 100% original on the rebuild with new rings and bearings. Back in 1968, Pontiac actually recommended 10W-30 (I have the reprinted orginal shop manual). So, I naturally figured with a "new" engine I would go back to what the factory recommended.
 
Originally Posted By: Merkava_4
I would have chosen this:

Quote:
Z-ROD 20W-50 Synthetic Motor Oil


^^2nd
 
Originally Posted By: propuckstopper
We are going 100% original on the rebuild with new rings and bearings.


In that case I'd drive it for 300 miles on conventional SAE30 and then switch to 20W-50 Amsoil.
 
I would mix the two. I'm not a fan of 20W for Canada climate. You should be around 15W-40 with a 50:50 cocktail. Although I would choose to go with more of the 30 weight if you do mostly up to 16 miles trips. If you go over that but still don't push it then a 50:50 mix would suffice.
Another excellent choice would be the 10W-40 Premium Protection.

Sever gear should be your choice for the diff. 90w split a few years ago because of the very wide span (Check the latest J306). Now we have 110W and 90w replacing the old 90 span. I would go with the top end 90 which today translates in 75W-110 Severe Gear.
I can't comment on the atf.
 
As an owner and dedicated drag racer I have had many Pontiacs.

If the engine is new and tight the oil selected (Zrod 10-30) is an EXCELLENT choice!
 
Originally Posted By: hounddog
10w30. 20w50 is awful thick.


It may be thicker than 10W-30, but Cadillac 425's love 20W-50. Pontiac 400's would probably like it too.
 
Originally Posted By: propuckstopper
Happy New Year. After many years of sitting, I am getting back to working on my 1968 Pontiac GTO 400 H.O. Convertible. We are freshening the original engine (rings, bearings, heads) and I have already chosen Amsoil Z-Rod 10W-30 for the engine.

I will also be changing out the automatic transmission fluid (Turbo 400) and am wondering if I should go with the Amsoil Multi-Vehicle ATF or the lighter viscosity offering? The owner's manual requires a Dexron III fluid.

Also, looking to find out your opinions on a gear oil for the original Positraction 3:23 rear end. In a 75W-90 viscosity, do you think I should go with the Severe Gear offering, or the regular Amsoil?

As a restored car, this GTO will be driven only on nice days and fairly gently.


As described the 10W-30 is fine.

Use the synthetic ATF, NOT the lighter ATL.

Not 75W-90 - use 75W-110 Severe gear. The 110 is closest to the original OEM recommendation. The SAE specification changed.
 
When I bought my 68GTO in October 1967 I used Valvoline 10w-30. Since this an freshening with stock replacement parts I believe your choice is fine.
No 50 anything please. Mine was black over red with3:08 in the back. Not a racer but a fine highway car once I replaced the US Royal redline tires which seperated at the redline. Two sets replaced and then to GoodYear Polyglass which were like driving on four cement blocks when cold.
 
I agree with the 10w30 AMSOil.

In your freshening, are you changing the cam and lifters? If so, then I recommend running a break-in oil.
 
The 10W30 Amsoil ZRod oil is a good choice for your 68 GTO.
We use Amsoils HDD 5W30 in our 68 GTO with the HO engine and it has been excellent. Like the ZRod 10W30 it also has high
ZDDP ( 1380 vs 1440 ) and a 3.5 HTHS. It's viscosity is a bit higher ( 169 vs 157 ) and it's 40 degree viscosity is 67.8
vs 72.5 so we prefer it for cold starts. We use the Amsoil HDD
5W30 in several of our 60's era muscle cars.

There is absolutely no need to go to anything higher than
a 10W30 oil in this engine for the use you describe.

The Amsoil 75W110 would also be fine for the Positraction,
Just be sure to add GM's Positraction additive also.

Enjoy your car...it's one of the "Great" ones !
 
I think the 10w 30 will be perfect for this engine also as will the regular Amsoil ATF for the Turbo 400.

These GM engines really benefited from a better oil pump, they did then and still do. Now would be a good time to swap it anyway.
Check out the Mellings 54F or butler BPI-M54-PRO.
 
Originally Posted By: Pablo
Originally Posted By: propuckstopper
Happy New Year. After many years of sitting, I am getting back to working on my 1968 Pontiac GTO 400 H.O. Convertible. We are freshening the original engine (rings, bearings, heads) and I have already chosen Amsoil Z-Rod 10W-30 for the engine.

I will also be changing out the automatic transmission fluid (Turbo 400) and am wondering if I should go with the Amsoil Multi-Vehicle ATF or the lighter viscosity offering? The owner's manual requires a Dexron III fluid.

Also, looking to find out your opinions on a gear oil for the original Positraction 3:23 rear end. In a 75W-90 viscosity, do you think I should go with the Severe Gear offering, or the regular Amsoil?

As a restored car, this GTO will be driven only on nice days and fairly gently.


As described the 10W-30 is fine.

Use the synthetic ATF, NOT the lighter ATL.

Not 75W-90 - use 75W-110 Severe gear. The 110 is closest to the original OEM recommendation. The SAE specification changed.


Hi Pablo. I went with the Severe Gear 75W-110 as you recommended, and also picked up a bottle of the Anti-Slip additive (just in case of chatter). I also ordered the Synthetic ATF as per your recommendation.

I am pleased about the many people in this thread coming to my defence regarding my choice of the 10W-30. I see no reason why I would need the heavier 20W-50 offering in a fresh engine that was designed to run 10W-30 originally.

If this engine was a high mileage unit, I would be the first to use 20W-50. In fact, we had an old 1978 Ford Motorhome (460 C.I.) that we ran 20W-50 in all the time. This engine, however, was a high miler and we towed a race car with the motorhome in sometimes very hot weather. But for this fresh GTO engine, I firmly believe 10W-30 is the ticket.

Everything else aside, I must confess that I am a wee bit nervous about using a "Universal" ATF fluid. I have used almost every other available Amsoil product in my lifetime, but I have never ordered their transmission fluid. I understand why and how a given engine oil could be "Universal" to all engines, but it is also my understanding that automatic transmissions are much more fussy about their fluids. With so many different transmission fluid specifications on the market, I don't see how a company can "nail them all" with a single formulation. However, I have always had good luck with Amsoil products so I decided to take the plunge.

We will see what happens. Thanks for all the replies, fellas.
 
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