R.White

What oil to use?

Recommended Posts

I have now finished the rebuild of my '26 4 cyl engine.  What do you guys think would be the best oil to use; synthetic or mineral?  

 

and what grade would suit my engine?

 

Ray.

Share this post


Link to post
Share on other sites

Grade: 5W-30 or perhaps 5W-40. Perhaps a single grade initially (not non-detergent though) for running in, but I haven't read anything authoritative about that so would research first.

 

Most synthetic oils are better at minimising wear than ALL mineral oils.

 

Some say one needs a mineral break-in oil for a few hundred miles before going to synthetic. Others say no, just go straight in with the synthetic. I haven't read about that so would need to find authoritative writing about it. Someone posted a Skinned Knuckles article in a thread about oil recently in this thread:

 

Edited by Spinneyhill (see edit history)

Share this post


Link to post
Share on other sites

Thanks Spinneyhill.  Lots of reading material there.  Although I have cleaned the engine as thoroughly as I can, one cannot be absolutely certain.  I have put a magnet in the filter tube just in case (despite my best efforts) there is any loose material left over from the rebore.  I think I will go for a basic 30 grade mineral oil to start with and change it sooner rather than later.  I was interested to see the comments about zink in oil helping to bed in a rebuilt engine.  Also, the notion that diesel engine oil can be used to good effect!

 

Ray.

 

 

Share this post


Link to post
Share on other sites

Hi Ray

 

I've used Penrite Shelsley Medium - it appears to tick all the boxes for vintage splash lubrication.  See their website for more details.

 

Tony

Share this post


Link to post
Share on other sites

Thanks Tony.  I am on to it now.  Never had a problem with Penrite stuff.

 

Ray.

Share this post


Link to post
Share on other sites

I have used several different synthetics for decades. The best I can find these days is Amsoil Z Rod. With a 10W/30 and a 20W/50 , it can be blended according to need and conditions. Right amount of Zinc and Phosphorus. Engineered for , along with other  parameters, engines which spend significant time without being run. (Long term corrosion protection - cheap insurance against stuck valves). You will probably run the 10W/30 after break in. Amsoil also make a Synthetic (!!!!!!) break in oil. These products seem to be current state of the art for our engines. A bit more expensive , but for me the best is NONE too good for my expensive engines. My ancient cars are not driven ten or thirty thousand miles a year , etc. so the cost of an oil change is not a significant cumulative factor. I have absolutely no affiliation with Amsoil whatsoever. (Although independent dealerships are available for energetic individuals). I have been using Synthetic lubricants for a very long time. Amsoil has been a leader in their development for a very long time. Some people rationalize using less than the best  eg: "The worst oil today is better than the best oil 90 years ago". Hey ! How about going out to find the cheapest "El Cheapo" Dinosaur lard derived goo you can find ? "Still better than the best .........." . So far no one , not even one person has tried to rationalize against using synthetic grease. Use it also. I sure hope you will be accumulating many trouble free miles soon !  - Carl

Edited by C Carl
Clean up (see edit history)

Share this post


Link to post
Share on other sites

Thanks Carl.  Now I am spoilt for choice.  

My only worry is that as my engine has quite generous crankshaft clearances ( explained elsewhere)  and hit and miss "splash" fed bearings a synthetic oil may be too thin.  On the other hand whilst a molly additive might give me a useful coating, the last thing I want is glazed cylinder bores and rusted piston rings which such products can cause.    

Share this post


Link to post
Share on other sites

I run a straight 30 wt non detergent ( that's what recommended in the manual) in my 25 with no problems

  • Like 1

Share this post


Link to post
Share on other sites

Splash lubrication will be better with thinner oil. More oil will be scooped up and flow around the  bearings. You already know that non-detergent oil is a very poor choice.

Share this post


Link to post
Share on other sites

It seems that there are very different, yet strongly held positions about which is the optimum choice of oil for our cars.  I have no desire to open up old wounds and am happy to accept all recommendations given in good faith.  I still have some concerns about using a detergent oil with no effective filter ( I only have a simple gauze strainer ) because it seems to me that all the impurities are held in suspension and fed to the bearings instead of settling in the pan.  An oil change every year ( or more frequently ) is not very cost effective given the added expense of synthetic oil which I gather has been developed for modern, properly filtered engines.

 

Ray.

Share this post


Link to post
Share on other sites

The stuff in the oil is extremely fine. You need a microscope to see the particles. Big stuff settles out. Metal particles will settle out. The fines are mainly combustion products like carbon and so on. If you have particles in the oil that will damage the bearings it is too late anyway.

 

Anyway, the choice is whether to keep it in the oil and drain most of it out at oil change time, or leave it everywhere in the engine (including in the bearings!) every time you shut down and gradually build up a layer of crud everywhere.

 

There was a photo posted recently of a Rolls Royce crankshaft. It showed a worm of muck being pushed out of the oil way in the shaft. Clearly, oil flow to the bearings was compromised.

  • Like 1

Share this post


Link to post
Share on other sites

It looks like synthetic is the way to go.  Thanks.

 

Looking at the different brands on offer, something has occurred to me.  There are synthetic oils marketed for motorcycle engines.  Is this the same stuff in different bottles?

 

Ray.

Share this post


Link to post
Share on other sites

If the API rating is the same (e.g. SM) then they pass the same API standard.

 

I have just been reading an article about it in Motor Cycle News (albeit quite old - they discussed API SG oils). Motorcycle oils claim the earth and deliver far less. The article said the 300+% price difference was a rip-off. They tested two m/c oils vs three auto oils; the m/c oils were least good at retaining viscosity after use.

 

Viscosity retention is one of the major reasons we should NEVER use "non-detergent" oils. Viscosity retention is delivered by additives, the so called "detergent". Oil becomes thinner with use and synthetic oils thin least.

Edited by Spinneyhill (see edit history)

Share this post


Link to post
Share on other sites

Any recommendations for transitioning from detergent to non-detergent oil?

Share this post


Link to post
Share on other sites
On July 6, 2017 at 0:34 PM, RickBrinker said:

I run a straight 30 wt non detergent ( that's what recommended in the manual) in my 25 with no problems

 

Living testimonial to the "Worst today is better than the best oil 90 years ago" , truism. As I have said many times , I treat my expensive engines to the very best I can find. The margin of protection one has in , as high a flashpoint or shear strength possible , is cheap insurance. Add the overwhelming amount of research done to engineer lubricants for OUR cars , used and stored as WE do , and the logic of using such products (Z Rod) , becomes clear and irrefutable. Ray , you have some conflicting parameters (eg. wide mains vs. re bore , new rings) , which mitigate towards wide spectrum capabilities in a motor oil. Perhaps a 50/50 mix of the two Z Rod viscosities ? The result would be a 15W/40. Break in your new cyl walls on the Synthetic break in oil Amsoil makes. You need all the lubrication capability you can buy. DO NOT SECOND GUESS ADDITIVES YOU CONJURE UP WITHOUT TECH SUPPPORT FROM OIL MANUFACTURER !! I TOTALLY reject the theory that 93 year old petroleum engineering would remain the  be all and end all , dogmatic solution for old engines used a century after manufacture. Would you lubricate any of your bearings or articulations with hog lard just because the manual written in 1898 says to do so ? We've come a long way , ..................   - Carl

 

P.S. : Is Amsoil available in U.K. ?  - CC

Share this post


Link to post
Share on other sites
6 minutes ago, FreFord said:

Any recommendations for transitioning from detergent to non-detergent oil?

 

You bet ! In a word : DON'T.  - Carl

Share this post


Link to post
Share on other sites

One exception to the sage advice given here must be that a detergent oil should not be used if an engine has been run for years on straight mineral.  A dirty engine needs to be dismantled and  properly cleaned rather than relying on detergent oil to do the job in service. As I see it, a clean engine gives one the opportunity to choose a different method of lubrication taking advantage of the advances that have been made over the years.

 

Carl. The cost of the European version of Amsoil is way out of line with other fully synthetic oils available.  Unless someone can give me a very good reason not to choose a more competitive equivalent for use in such a basic engine, in a car which will probably be moved on anyway, I will probably go for a different brand.

Ray.

Share this post


Link to post
Share on other sites
7 hours ago, R.White said:

One exception to the sage advice given here must be that a detergent oil should not be used if an engine has been run for years on straight mineral. 

 

That is not what I have read. The main thing is to remove and clean out the sump first, clean as much muck out of the bottom of the block as you can, make sure the oil pump pickup and pipe-work is clean, then reinstall and fill with the oil with additives. Expect another change in a few hundred miles. The oil with additives will not clean the engine out in a hurry, but will have an some effect long term. It won't clean it out completely though.

 

The main thing is to run clean from then on, not continue to fill it up with muck. Remember also the oil is much more stable in terms of holding its viscosity over time and not turning to sludge (which is what the old oil started to do from the moment the engine was started with clean oil).

 

 

Share this post


Link to post
Share on other sites
8 hours ago, FreFord said:

Any recommendations for transitioning from detergent to non-detergent oil?

 

Agree with Carl. That would be a serious retrograde step. Any thinking you might have read or picked up that it is the right stuff is, well, rubbish, misinformed, uninformed.

Share this post


Link to post
Share on other sites

I think a little caution should be exercised when selecting a synthetic oil for engines with no effective filter.  Up to 25% of the oil consists of additives such as detergents and these can have a scouring effect with disastrous results should an oil jet be blocked by a lump of carbon/gum lifted and carried by the oil which is only doing what it is designed to do.  This is why you should not change from mineral to synthetic oil without thoroughly cleaning the engine first.  

 

Another, equally serious consideration is the build up of metallic ash in the combustion chamber.  Synthetic oils have been designed for modern engines with close tolerances.  If you have an oil burner then synthetic oil will cause a build up of metallic ash causing detonation, or "pinking".

 

We have had synthetics for some 25 years now and over that time there have beed considerable changes.  Modern cars have catalytic converters which are affected by zinc.  There has been a relentless decrease in the zinc/phosphorus additive  which is bad news for our type of engine.  I am not saying mineral is better; it plainly is not but what I am saying is that care has to be taken in choosing the right synthetic with the correct ZDDP formulation or stick with mineral.  

 

 

Share this post


Link to post
Share on other sites
1 hour ago, R.White said:

 Up to 25% of the oil consists of additives such as detergents and these can have a scouring effect with disastrous results should an oil jet be blocked by a lump of carbon/gum lifted and carried by the oil which is only doing what it is designed to do. 

 

Another, equally serious consideration is the build up of metallic ash in the combustion chamber.  Synthetic oils have been designed for modern engines with close tolerances.  If you have an oil burner then synthetic oil will cause a build up of metallic ash causing detonation, or "pinking".

 

I haven't read of those effects. Can you point us to the references for those statements? Thank you.

 

It is my understanding the additive oils will not lift lumps of anything unless they dislodge it by hydraulic force (i.e. caused by speed of flow past the blockage). They carry minute particles and might pick them up, particularly in areas of turbulence.

Share this post


Link to post
Share on other sites

You don't want much do you???

 

I read about the effects of detergent oil on the "Austin Seven Friends" forum some time ago.  That reminds me.  Did you know that you shouldn't use synthetic oil or molly additives in motors with ball/roller mounted crankshafts which can be Austin Sevens or Bugattis!  Apparently you can have oil that is too slippery!  It appears that a ball or roller race needs a certain amount of traction to work properly.  If the oil is too slippery the balls don't rotate and you can end up with flat spots. 

 

There are lots of things to consider which is why I raised the question.  It has been interesting to see there is a strong following for fully synthetic oil but mineral still has a following.

 

Ray..

Edited by R.White (see edit history)

Share this post


Link to post
Share on other sites

Thank you.

 

Just reading an article from Truck Trends. It appears diesel oil API standard CJ-4 (promulgated in 2007?) included a low ash requirement to protect catalytic converters. This went hand in hand with low sulphur diesel.

 

It is interesting that Wikipedia gives this as a benefit of synthetic engine oil:

"Superior protection against "ash" and other deposit formation in engine hot spots (in particular in turbochargers and superchargers) for less oil burnoff and reduced chances of damaging oil passageway clogging.[8 "

The reference is "Synthetic oil vs. conventional oil | Mobil™ Motor Oils". mobiloil.com. Retrieved 2017-03-24.

Edited by Spinneyhill (see edit history)

Share this post


Link to post
Share on other sites

It could be that fully synthetic Diesel oil may be a cheaper option for our cars.  As Diesel engines are much dirtier than petrol the oil has to work that bit harder so it needs to be pretty good stuff.  Personally (and I have nothing against Diesel owners!) I can't stand Diesels.  I understand the need for it in trucks etc. but there are enough particulates floating about in the air without cars adding to it.  I see the USA Diesel owners have won compo from VW/ Audi over the emissions scandal.  No such luck over here unfortunately.:(

 

Ray. 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now