Engine Oil Discussion

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SlantedMark4

'74 Valiant 225 /6
FABO Gold Member
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I am sorry for bringing this up again but the more I'm reading about it the more I get confused.
I have a high mileage 225 Slant Six which seems to burn and/or loose a bit of oil. I also seems to be never rebuilt. The oil pan is a bit wet but it doesn't seem to be the only issue.
Anyways, I am planning to change the engine oil since the level is low and I don't know what the previous owner had filled in.
In some forums, they said they put in synthetic 10W30 or 10W40 into the Slants while some other say synthetic stuff isn't good, just like what my father said who used to be a mechanic (and ownes some old Volvos) . Some zinc stuff is also required, some people said. My user manual says "no straight mineral oil".
An oil company here in Switzerland makes special oil for old cars. I have found one with extra zinc, based on mineral oil and SAE 50. I now don't know if this will be fine for my Slant... I have read about the Chevron Delo but I would have to import it from the States.


My question now is what oil is not good for the slant, and what do I have to check before I fill in the oil.

My Slant was built in early 1974 with a 3 speed auto, in a 4 door Valiant.
 
The factory recommended oil is 10-30 non synthetic., and that is what I use in all my slants. The only thing wrong with synthetic, is it will have a tendency to leak more, and is more expensive. I wouldn't worry about using added zinc, unless you have a fresh rebuilt engine. I would not use a straight grade oil, and definitely not SAE 50. If your engine needs SAE 50, it is time for a rebuild.
 
The factory recommended oil is 10-30 non synthetic., and that is what I use in all my slants. The only thing wrong with synthetic, is it will have a tendency to leak more, and is more expensive. I wouldn't worry about using added zinc, unless you have a fresh rebuilt engine. I would not use a straight grade oil, and definitely not SAE 50. If your engine needs SAE 50, it is time for a rebuild.
The "problem" with synthetics is also because it will damage seals/gaskets, right? I've heard synthetics will clean the engine better than conventional oil which causes the engine leaking, because of "missing impurities", which "sealed" the engine, but I don't know what's true about that.
The brand, Motorex (a Swiss brand), produces special oil for old cars. One of those oils has extra zinc, as I've read worn out/not rebuilt engines actually require zinc, so I was thinking about that kind of oil. It is also available in 10W30 or 15W30.

So, a non synthetic oil is "better", but my user manual said i shouldn't add straight mineral oil. This part still confuses me a bit...
 
The brand, Motorex (a Swiss brand), produces special oil for old cars. One of those oils has extra zinc, as I've read worn out/not rebuilt engines actually require zinc, so I was thinking about that kind of oil. It is also available in 10W30 or 15W30.
I'd stick with the Motorex 10w30.JMO
 
With or without the added zinc? There are like 5 different versions of this oil.
 
With or without the added zinc? There are like 5 different versions of this oil.
 
In the US I always run Valvoline Racing 20w50. You can also run a straight Valvoline 30 racing oil. 20w50 will solve a lot of oil burning. Not sure what all translates to what is available to you. All the above oils have zinc and are non synthetic. My cars get their oil changed every 3,000 miles and have up to 300,000 miles on them and still run like new.
 
Don't change grade (weight) trying to control oil burning. It's not a good idea. Synthetic oils are great. Their only "drawback" with older engines that have leaks is, synthetic oil will tend to leak more, or "find" a leak where there may not be one, due to its excellent flow characteristics. It flows THAT good. Synthetics are made more for engines with modern rubber type seals for all of the gaskets and modern one piece rear main seals that have much less chances to leak. As already mentioned, your engine is probably ready for a rebuild if you're having these issues.
 
I used to have an article from I believe consumer reports or Popular mechanics, honestly can't recall. Anyways, they had tested a whole bunch of NY city taxi cabs using several different mineral oils and several synthetics plus a couple using additives such as "slick 50" which was a silicone additive and quite a big deal back then ( I believe the article was from the 90's). Anyways, they changed the oil every 6,000 miles...yes, 6,000 miles on a taxi that sat in traffic going nowhere half its life. Then at 200,000 miles they tore them all down and measured wear. Guess what? There was no significant difference in wear between any of them. Based on this, I changed the oil on my 2003 Saturn Vue whenever the computer told me it was required which averaged a little over 10,000 miles. At 240,000 miles I traded it in and it consumed about 1/2 quart in 10,000 miles which is pretty respectable. The oil never smelled oxidized. If your oil has that horrible smell to it, it has oxidized and that is bad as it will act as a catalyst to oxidize the replacement oil quicker and if that happens your going to be forced to change it more frequently.

What is the biggest performance difference between synthetic and mineral oil? Two things and they both have to do with temperature. Synthetics will maintain a better viscosity index, meaning viscosity will change less over temperature. Translated that means they will flow better in extreme cold and not thin out as much in extreme heat. The second is that at extreme heat, they will not break down as quickly and oxidize or evaporate. This makes synthetics much better for heavy duty use in extreme heat (like pulling a 5th wheel through the desert for example). What others have said about synthetics leaking more is also true. If it were me, I would use a 10w-40 with zinc or add zinc if it doesn't have it. The zinc replaces lead which is no longer put in gasoline. The zinc is a lubricant for the valves on older cars designed for leaded gas. With a modern rebuilt engine it is usually not required but you will need to confirm this with the engine rebuilder.
 
I used to have an article from I believe consumer reports or Popular mechanics, honestly can't recall. Anyways, they had tested a whole bunch of NY city taxi cabs using several different mineral oils and several synthetics plus a couple using additives such as "slick 50" which was a silicone additive and quite a big deal back then ( I believe the article was from the 90's). Anyways, they changed the oil every 6,000 miles...yes, 6,000 miles on a taxi that sat in traffic going nowhere half its life. Then at 200,000 miles they tore them all down and measured wear. Guess what? There was no significant difference in wear between any of them. Based on this, I changed the oil on my 2003 Saturn Vue whenever the computer told me it was required which averaged a little over 10,000 miles. At 240,000 miles I traded it in and it consumed about 1/2 quart in 10,000 miles which is pretty respectable. The oil never smelled oxidized. If your oil has that horrible smell to it, it has oxidized and that is bad as it will act as a catalyst to oxidize the replacement oil quicker and if that happens your going to be forced to change it more frequently.

What is the biggest performance difference between synthetic and mineral oil? Two things and they both have to do with temperature. Synthetics will maintain a better viscosity index, meaning viscosity will change less over temperature. Translated that means they will flow better in extreme cold and not thin out as much in extreme heat. The second is that at extreme heat, they will not break down as quickly and oxidize or evaporate. This makes synthetics much better for heavy duty use in extreme heat (like pulling a 5th wheel through the desert for example). What others have said about synthetics leaking more is also true. If it were me, I would use a 10w-40 with zinc or add zinc if it doesn't have it. The zinc replaces lead which is no longer put in gasoline. The zinc is a lubricant for the valves on older cars designed for leaded gas. With a modern rebuilt engine it is usually not required but you will need to confirm this with the engine rebuilder.


Slick 50 was Teflon not silicone.

Its 2023. Not using a synthetic oil is just nonsense.
 
this will do the job
Olio Hot Rod & Classic 10W/30 10679 - Promorally

the zinc has nothing to do with leaded petrol or lack of lead in unleaded petrol

Zinc dithiophosphate


its a a compound that chemically bonds to iron surfaces so it acts a a chemical barrier between the cam lobe and the cam lifter in addition to the oil.

i.e it helps avoid disasterously quick ware and damage when metal to metal contact could occur (i.e it doesn't occur when ZDDP has bonded to the surfaces)

don't just put 10w30 from your local mobil/bp/shell/chevron/texico filling station
the zinc compound is not included in great enough quantities in modern oil, used in modern cars, because it isn't necessary with roller lifter/cams and it probably damages catalytic converters.


mineral or synthetic oil?
Up to you, one costs a lot more and i'd save that expense for my rebuilt engine

keep in mind oil technology has changed dramatically over the 50 years your car has existed

so the 10w30 you buy today will be much better at its job than the 10W30 the first owner purchased back in 1974 and they would probably not be using synthetic oil in a Valiant back then.

change the oil filter as well

Dave
 
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@S'cuder is an oil tech.
Thanks, Steve.

A few facts:
Slant six engines are easy on engine oils. Open valve spring pressure is relatively low, especially on an engine with high mileage. High valve spring pressure can cause the metal to metal contact between camshaft and lifters. ZDDP in the oil is sacrificed to prevent this.

Modern engine oils have lower amounts of ZDDP, but certainly not none. Some are limited to about 2/3 of the amount present before it was reduced a couple decades ago. In a non-high performance application like a slant six that hasn't been modified, a quality modern oil will contain enough to give good service.

Quality engine oils from a known producer will contain other anti-wear additives to supplement the ZDDP.

Mineral base oil will do well in your application. To meet modern specifications however, most have at least some synthetic base oil blended in. Finding an oil with no synthetic base may prove virtually impossible, and not really worth the effort.

Many European auto producers require oils to be of very high quality, so good oil should be easy for you to find.

My recommendation is to find an oil from a well known company in the grade you like, probably a xxW-30 or xxW-40. If you can find a high mileage product, it will contain seal conditioners which may be helpful. Use it without additional additive and don't worry, it will perform well in your application.
 
The origin of many of the stories regarding seal failure and leakage was specific to the first synthetic motor oils on the market.
There are a number of resources you can investigate if you want more in depth of what is called a 'synthetic'.
IMO Richard Widman's paper is one of the best summaries in plain language.
Here's English version Classic_car_oil

Whether to go for a -30 or a -40 depends on what you observe during long drives. If when the engine is fully hot, it seems to burn more oil and perhaps runs a bit lower in oil pressure (if your model has a gage) at highway speed, then a -40 might help a little. Otherwise 10W-30. And if its leaking a lot, no point in spending a lot more money for some specialty oil.
 
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Slick 50 was Teflon not silicone.

Its 2023. Not using a synthetic oil is just nonsense.
What synthetic would you recommend with enough ZDDP for a flat tappet?
 
Thanks, Steve.

A few facts:
Slant six engines are easy on engine oils. Open valve spring pressure is relatively low, especially on an engine with high mileage. High valve spring pressure can cause the metal to metal contact between camshaft and lifters. ZDDP in the oil is sacrificed to prevent this.

Modern engine oils have lower amounts of ZDDP, but certainly not none. Some are limited to about 2/3 of the amount present before it was reduced a couple decades ago. In a non-high performance application like a slant six that hasn't been modified, a quality modern oil will contain enough to give good service.

Quality engine oils from a known producer will contain other anti-wear additives to supplement the ZDDP.

Mineral base oil will do well in your application. To meet modern specifications however, most have at least some synthetic base oil blended in. Finding an oil with no synthetic base may prove virtually impossible, and not really worth the effort.

Many European auto producers require oils to be of very high quality, so good oil should be easy for you to find.

My recommendation is to find an oil from a well known company in the grade you like, probably a xxW-30 or xxW-40. If you can find a high mileage product, it will contain seal conditioners which may be helpful. Use it without additional additive and don't worry, it will perform well in your application.
I tell you what. I recently changed Vixen's oil over to Motorcraft synthetic blend 5w20 and I can actually FEEL a difference in power and how more quickly the engine revs. I wouldda never thought it, but I can. I also mixed in some Rislone ZDDP additive just to be safe. I'm sold on it now, though.
 
On my car that has a flat tappet cam I like to use Mobil1 0W-40. The spec on the engine calls for 10W-30 and it has a ton of miles on it, so I figure I'm fine with a XW-40 oil. Mobil1 says that oil is designed for European vehicles so you should be able to find it pretty easily. They actually publish the information we want to know, so there's no guessing or need to put additives in your oil: 1000 ppm phosphorus and 1100 zinc, which should be enough for a stock slant 6.

https://www.mobil.com/lubricants/-/...w-us-1/files/mobil-1-product-guide-rev-31.pdf
 

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On my car that has a flat tappet cam I like to use Mobil1 0W-40. The spec on the engine calls for 10W-30 and it has a ton of miles on it, so I figure I'm fine with a XW-40 oil. Mobil1 says that oil is designed for European vehicles so you should be able to find it pretty easily. They actually publish the information we want to know, so there's no guessing or need to put additives in your oil: 1000 ppm phosphorus and 1100 zinc, which should be enough for a stock slant 6.

https://www.mobil.com/lubricants/-/...w-us-1/files/mobil-1-product-guide-rev-31.pdf
Good stuff at a great price. Probably the best value in a widely available oil that is a good match for our V8 Mopars.
 
What synthetic would you recommend with enough ZDDP for a flat tappet?
Mobil1 FS 0W-40.

I tell you what. I recently changed Vixen's oil over to Motorcraft synthetic blend 5w20 and I can actually FEEL a difference in power and how more quickly the engine revs. I wouldda never thought it, but I can. I also mixed in some Rislone ZDDP additive just to be safe. I'm sold on it now, though.
I believe that. My daily driver is my wife's old car, a '09 Pontiac Vibe. It calls for 0W-20, which I used when I got it for free. That source dried up when I retired, so I started using 5W-30 synthetic I have from an old stash . I swear that thicker oil slowed down that little POS. It went from peppy to doggy with that oil change. But free is free, right?
 
Mobil1 FS 0W-40.


I believe that. My daily driver is my wife's old car, a '09 Pontiac Vibe. It calls for 0W-20, which I used when I got it for free. That source dried up when I retired, so I started using 5W-30 synthetic I have from an old stash . I swear that thicker oil slowed down that little POS. It went from peppy to doggy with that oil change. But free is free, right?
I reckon so.....but if it makes a change for the worse, it ain't really worth it, right? lol
 
Do you know of those are Group III oils?
The FS 0W-40 is about 25% Group IV, the balance Group III. It meets Porsche A-40 and BMW LL-01 specs, so really good anti-wear, volatility, anti-oxidation and viscosity index. I'd use it up to 500 HP all day long. If I had more money in an engine than 500 HP worth, I'd go to Red Line.
 
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