Which engine oil, ATF and coolant should I put in my 1974 Datsun 260Z?

Question

Thank you in advance for taking your time in reviewing and answering my questions. I purchased a 1974 Datsun 260z 2+2 a little over a year ago. It's unfortunate but it has an automatic transmission with about 148,XXX miles. Since it's a Southern California car, there is nominal rust with the exception of the driver's side rear quarter panel (which I have to find a welder near me to replace a small 5" x 5" section). The tire shop replaced and balanced all 4 tires. I took it to the mechanic to replace the seized front brakes and the rear drum brakes appear to be fine. The car at that point became a running and "drive-able" project. There was a valve cover leak which I replaced the gasket but ended up leaking again about 2 months later. I checked the oil levels every 2 weeks but the oil levels on the dipstick always read high and I did not have to add any oil for 6-8 months (Probably because I only drive it once a week for about 10 miles). All the bushing and shocks are pretty much shot. The steering wheel has a little vibration and shakiness. So, I tried to replace the outer tie rods but failed due to a rusted bolt (I did not have a torch that could warm up the nut hot enough to loose it). I took it to a mechanic who replaced the value cover gasket again, ball joints, and outer tie rods. The mechanic recommended to replace the shocks and steering rack as well but things started to get expense (the labor cost of the mechanic was a little high due to the fact that they were the only ones willing to work on a vintage car near me). So, I am trying to work on the car myself as much as I can. I have three questions. (I have searched many Z forums but I value your opinion more than any one else.)

First, engine oil. In the Z forums, people were recommending to use an oil with high zinc content but everyone's opinion vary. Based on this I bought a Lucas Oil SAE 10W-30 High Zinc Hot Rod & Classic oil and wanted to know if this is a good choice or if I should return it and buy something else (better). I went through a lot of your videos but I don't recall a video about engine oils for vintage cars.

Second, transmission oil. There is a "thump" sound when I put the car in reverse. I was told the transmission oil was replaced and I forgot to ask for the old transmission oil. So a few weeks after I bought the car, I reached out to the seller who informed me that it has been discarded. The transmission doesn't seem like its slipping and even if I was told the transmission oil was changed, I want to just change it my self and have a peace of mind. (I had a bad experience at the Newport Beach Lexus dealer when I bought a used 2006 Lexus GS300 from them. The dealer claimed the engine oil and transmission oil were changed but ended up not being true. And to loot, they never filled up my gas tank.) The forum searches all vary with each other's opinion on the the better transmission oil. What is the best transmission oil I can use and should I add the "Lucas Transmission Fix"?

Third, what coolant can I use? (The sticker on the car says to use, Nissan Long life coolant (ethylene glycol-base) but there is a green and a blue one. If I recall the green one should be the right one but I am a little lost at this point because I have been reading too many opinions. I also have seen your videos about coolants but having too much information is confusing.

Thank you for your time!

Chuck Tobias · Accepted Answer

The Lucas High-Zinc oil (or any quality high-zinc oil) should be fine for that engine. Whether it's actually necessary in a stock engine is somewhat controversial, but being a performance car I'd say it's better to be safe.

Check your driveshaft universal joints, the clunk going into reverse might be a worn universal. Also check the transmission mount. Of course it could be almost anything on a 48-year-old car. In particular all rubber parts are suspect.

The automatic transmission is a Jatco 3N71B 3-speed unit. It was designed for Dexron automatic transmission fluid. Today the best match would be Dexron-III, frequently sold as Dex/Merc. That's an old specification no longer licensed by GM but it is still manufactured by leading brands such as Valvoline. (Dexron VI is the current standard and should be backward-compatible. I've been sticking with Dex/Merc for my older vehicles.)

Check condition of the fluid. If it is burnt and gritty the trans may well start slipping with fresh fluid. (Keep the old drained fluid just in case.) Unless the transmission is slipping and you're trying to get a few more miles out of it before rebuilding do not use any additives. Also do not flush the transmission, do a drain and fill. To replace most of the fluid you would do 3 or 4 drain and fill procedures, driving for a while in between.

I found a service manual for the 1976 280Z automatic trans, it should be substantially the same as yours:

http://pdf.textfiles.com/manuals/AUTOMOBILE/NISSAN/280z/1976/AT.pdf

In 1974 the factory coolant would have been what we call "plain green" antifreeze (Nissan branded), but there could be anything in there now. If you flush the cooling system to get rid of all the old coolant you can use whatever you like in it. Today's coolants will last longer and better protect the aluminum cylinder head, the head gasket, and cooling system. (Even the green stuff today is better than it was decades ago.)