Hello All,

I would like to change the oil on my 1966 Oldsmobile 98 this weekend. However, after reading the 1966 Chassis Service Manual I am only left with the ambiguous "intended for service MS" and "Meets General Motors Standard GM-4745M" statements with regard to the type of oil recommended.

Therefore, my questions are

1. What type (Conventional vs. Synthetic), brand (e.g. Amsoil, Royal Purple, etc.) and grade (e.g. 5W-30) of oil is suitable for this engine?
1a. Does anyone have any experience (positive or negative) with any specific brand/type?
2. Are any oil additives necessary to ensure peak performance?

Finally, are there any quirks that I should be aware of before attempting to change the oil? That is to say, is the procedure markedly different from the standard--warm engine, drain oil, install filter, add new oil?

Thank you for your thoughts.

 

The oil change procedure is as you described above. Oil recommended for older flat tappet cams needs to have a proper friction package and the newer oils for late model cars does not meet your requirements. There have been many discussions and threads on the proper oil with just as many opinions. I use Valvolene VR1 Racing oil as it is available at most parts stores. It's available in the following, 20w50, straight 50, 10w30, straight 30, straight 40, and straight 60. I use 20w50 in the summer and 10w 30 in the winter. There are 2 types one is street legal and the other is not. Use the street legal it's formulated for normal oil change intervals.

 

Z-ROD 20W-50 Synthetic Motor Oil
Modern Technology For Classic Cars


AMSOIL Z-ROD™ Synthetic Motor Oil is specially engineered for classic and high-performance vehicles. A high-zinc formulation to prevent wear on flat-tappet camshafts and other critical engine components, along with a proprietary blend of rust and corrosion inhibitors for added protection during long-term storage.

This is what I run in my '69 442. Great product and you need the zinc. Several years ago my son flattened the cam in his '75 Pontiac and he was using Mobil 1. Now that this problem has been identified that the lack of zinc in most oils caused these failures, most oils labeled "Racing" oils now contain the zinc need to protect these old flat tappet engines. I also use Amsoil gear lube in my 4 speed trans and in the differential.

 

I am starting to use this product.


Pat

 

MS was the highest grade oil available in 1966 when your car was new. As you can guess oils and the rating system have changed. Highest API oil grade now is SN but as stated above, these oils have had a lot of the anti-scuff and pressure additives taken out to satisfy the damn E P A. Plus with modern roller cam engines the extreme anti-scuff protection isn't really necessary.

I would use either straight 30 weight or 10W-30 in that engine, or alternately 20W-50 if you're not going to drive it in cooler temps. I don't think 5W-30 is suitable for it at all. Use a high-zinc content oil if you can find it.

Synthetic vs. conventional? That's a million dollar question. I'd stick with conventional meself simply because I'm still not convinced changing it to synthetic after a lot of miles won't create leakage problems.

I'm trying to remember if 1966 still had the recessed drain plug or one with hex head. If the oil plug appears "strange" (we get a lot of questions about them here) use a 1/2" drive ratchet to remove and install it. There's a special 8-point bit for the job but the ratchet will do it just as well.

 

I own a car with this exact same engine. A '67 Delta 88. I put in whatever name-brand motor oil is on sale at the local auto parts store of 10W-30 weight, which is what the chassis service manual calls for unless temperatures will be below 0 degrees F for any length of time. If it will be that cold, the book calls for using 5W-20. I also add a container of STP high-mileage oil treatment to make up for the missing ZDDP. That's it. I don't and never have used a synthetic. I don't use any oil with "purple" in the name. I've never used an oil with the words "high mileage" on the side of the container.

It is very to easy overthink this sort of thing. Everybody seems to think that these old engines need magical oils and potions that did not exist back in the day or the engine will somehow die an untimely death and float to the ceiling. Just put some oil in, put some STP in, drive the car, and don't worry about it. I don't, and I've had no problems in now more than five years of ownership of this car.


As far as the changing procedure, yes, it's the same as it's been on every engine for the last 10,000 years. Open drain plug. Collect oil. Close drain plug. Remove old filter. Screw on new filter. Clean up inevitable mess. Put in new oil. Drive Car.

 

AMSOIL 10w30 Z-Rod would be my choice. But you can run any 10w30 or 10w40 oil on the shelf if you want to. That cam and lifter set is mated and work hardened by now and the oil chemistry changes are not going to hurt it.

 

After reading numerous threads, it seems as if many people have had very positive experiences with AMSOIL. Thank you for your input.

Great information. I found this link quite useful as well.

I believe my engine currently uses conventional motor oil. After reading several threads/articles I anticipate switching to a synthetic blend or full synthetic oil in the near future. I appreciate your opinion.

I suppose you are right.

In today's age there is so much information at our disposal that seemingly trivial points (e.g. engine oil type) can become prodigious research efforts.