Author Topic: struggling with what oil to use??  (Read 349 times)


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struggling with what oil to use??
« on: September 02, 2021, 18:15:04 »
So, thanks again to Pedro I have what I think is a pretty good source of information on what oil is "best" and what to use for my Pagoda.  I did a lot of research and reading and couldn't come to any definitive conclusions until now..  Here's the blog:

and here's his specific response to my question about old cars/engines - specifically ours..

540 RAT, I want to thank you for your science based blog and all the testing you have done to come to the conclusions you’ve come to.. I’ve been trying to find a reliable source on all of the new engine oils and confusing claims and I believe you have filled that need. All 5 of my vehicles will get changed to the new QS 5w/30. My one possible concern is our 1967 230SL Mercedes. It has either 90,000 miles or 190,000 miles on the original engine and I’d like to double check that you feel that the QS 5w/30 synthetic is the best choice. A compression test yielded PSI from 120 to 130 on all 6 cylinders and it puffs a little blue smoke at cold start which I assume is probably worn valve seals – they will be replaced shortly. Other than that it runs well and stays cool. Thanks – in advance for your response.


Hi Russell,

Welcome to my Blog.
For an old high mileage vehicle like that, you would be better served by using 5W30 Quaker State “High Mileage” Full Synthetic, API SP, in that one. The seal swell/seal conditioner additives in High Mileage motor oil, is intended to reduce oil leakage/oil consumption. So, it may help out with those issues.
I used to recommend “conventional” non-synthetic oil in old high mileage engines. Because conventional oil helps to reduce oil consumption in high mileage engines, better than synthetic oil does.

However, conventional oils are being phased out. And those still available, do not perform as well as today’s better synthetic oils. So, using a high performing High Mileage synthetic motor oil, is the best compromise.
If the suggested motor oil above doesn’t work out well enough for your needs, then the next step would be to move up to a thicker motor oil such as XW40.
Just so you know, compression testing is notoriously inaccurate. It was generally replaced decades ago by the much more accurate “Leak Down Test”. See my Tech Article #5, for the details on that.
I suspect that you likely have worn rings and cylinders that are major contributors to your blue smoke. That is a common condition with old worn engines.

Take care,

540 RAT