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Oil and ZDDP

Technical issues not related to a DLOC car marque, eg tyres, ethanol, other car makes, etc. and legal, political and insurance
Chris_R
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Re: Oil and ZDDP

Post by Chris_R »

Andy, it may indicate a small amount of wear, this could be supported by the fact you only see 45psi when hot instead of the manufacturer stated 55psi but I don't think there is anything serious there. The fact you have a healthy positive pressure means there is a good flow occuring.
Despite the crankshaft journal to bearing gap being of the order of 0.0010", under load from the downforce of the pistons the crankshaft is pushed downwards in the bearings but due to the rotation of the crankshaft its running position is normally at about the 7 o'clock to 8 o'clock position in the space. Oil enters the cavity between the journal and the bearing and is dragged round that cavity and is squeezed into a reduced space due to the offset running position creating a wedge of oil and an instantaneous pressure of many thousands of pounds per square inch. It is that instantaneous very high pressure wedge that sustains the running gap between bearing and journal. Provided you have a sufficient flow of oil into the bearing cavity this wedge will always be created, the higher the rotation speed of the crankshaft, the greater flow of oil that is needed. The pressure that you are measuring is the resistance to that flow of oil. Not all of the oil is squeezed into the wedge, by design a lot of it simply leaks out of the sides of the bearings to just drop down inside the engine taking heat away from the crankshaft and to be replaced by freshly pumped oil. What I theorise about your slight increase in perceived pressure on deceleration is that with the downward load on the crankshaft relieved the crankshaft has returned to a more central location leaving less space for the oil to enter the bearing and there is slightly more resistance to the flow.
Increasing the weight of your oil from say a -40 to a -50 or from a -50 to a -60 would quite possible improve your running oil pressure from 45 to something a bit higher but that is unlikely to mean you are actually getting any more oil into the bearings, simply that the oil you have is not flowing so easily around the system and it takes more effort, hence more pressure to get the same quantity of oil through. I think people worry too much about high pressure in the belief that high pressure is good. It ain't necessarily so.

Phillmore
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Re: Oil and ZDDP

Post by Phillmore »

Ok so what is the importance/interpretation of VI in determining a suitable oil? Morris Golden film is 130 and Penrite 20/60 is 134.
Andy

1954 Conquest Mk1, 1956 Conquest Mk2, 1957 Conquest Century Mk2, 1955 Austin A90 Westminster

Chris_R
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Re: Oil and ZDDP

Post by Chris_R »

Reproduced from the Oil Engineering article I published in The Driving Member
Viscosity Index
The Viscosity Index is a value that represents the change of viscosity with temperature. The higher the index the more stable will be the oil. In other words, the less change in viscosity (thinning and thickening), the higher the index will be. High numbers good, low numbers bad. Oils are made from different types of base stocks that are classified into 5 distinct groups. Groups 1, 2 and 3 are mineral petroleum based oils and usually have an index of less than 140 as they tend to thicken more at the colder temperatures. Groups 4 and 5 are fully synthetic oils (only group 4 are used for motor oils) and due to their manufacture have viscosity indexes of more than 150. Because they have been manufactured from uniform molecules with no paraffin they make no use of Viscosity Improver additives but are still able to pass the multi-grade viscosity tests as a straight weight! So by contrast, a 10W-40 mineral based oil is a thin SAE 10 oil with Viscosity Improvers that make it seem like a SAE 40 oil when hot, a synthetic oil of the same multi-grade i.e. a 10W-40 is an SAE 40 oil that behaves like a SAE 10 oil when cold. Quite the reverse concept.

timmartin
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Re: Oil and ZDDP

Post by timmartin »

Thank you Chris for the information and clarity of both your September 2015 DM article and your many posts.

I too am trying to find the ideal oil for my engine and my type of use. My engine condition is probably about average for a Dart (I have never had an overheating experience); my driving is boringly gentle but very seldom less than an hour return trip, and mostly an hour or more one way.

I believe that I should be looking for an oil that gives a tolerable oil pressure at 650rpm tick over after (say) an hour of driving (and therefore a thorough heat soak), and as thin a 40degree viscosity as I can afford.

This seems to suggest semi or even full synthetics; but will my type of use keep me clear of, or lead me towards, the possible problems in an elderly engine (e.g. "sticky deposits, particularly in the piston rings")?

Which brings me to thinking about real oil temperatures. I notice without surprise that it takes 5 or 10 times as long for the oil temperature to peak (as indicated by dropping tick over oil pressure) than for the water temperature to stabilise (as indicated by the gauge).
I was surprised that you said in your article that oil temperature could be expected to be 10 or 15 deg. above water temperature. I had expected rather more. I also expected the real water temperature to be well above thermostat temperature (perhaps at 105deg). So I expected peak oil temperature to be 120 deg, or quite a bit higher.
Particularly if this was correct, it occurred to me that different but nominally similar oils might behave significantly differently to each other after time at temperatures well above the 100 deg at which their viscosity is rated and tested.
So I found myself wondering whether the higher performance (i.e. more synthetic) oil I used, the better my heat soaked tick over oil pressure might be.

Or expressing it differently using Mobil 40 grade products as an example, might the tickover pressure with the oil at the maximum normal temperature (well over 100deg) -
- when using Mobil 1 ESP be higher than when using Mobil Super 3000,
- when using Mobil Super 3000 be higher than when using Mobil Super 2000,
even though the nominal 100deg viscosities suggest quite the opposite?

Have I got it completely wrong, or only a bit?
Tim
Blue 1964 SP250 in Berkshire

Chris_R
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Re: Oil and ZDDP

Post by Chris_R »

Tim, I think your assumption on water temperature is not correct. Instantaneous water temperatures on the surfaces that are in contact with the cylinder walls or in contact with walls in the head may well be in excess of thermostat temperature and may be in excess of 100c but that water is moved away very rapidly by the water flow from the pump to transfer its heat to cooler water and also be replaced by cooler water that has not been in contact with the surfaces yet. This is a continuous cycle. The average temperature therefore is around thermostat temperature. Engine cooling is a whole different science. The reason for the specifications at 100c is that is the expected condition during normal operating conditions.
But to answer your question, oil thins as temperature increases. Figures aren't quoted above 100c as the table I included in the article shows.

JT7196
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Re: Oil and ZDDP

Post by JT7196 »

Hi, Chris, have read most of this discussion on Oil's and found it very interesting, I do have a question that perhaps many of us owners of Pre-War cars would appreciate your opinion of, as to what Oil would be most beneficial to use in "Our" engines?
I have very recently completely overhauled the engine in my 1937 Lanchester Eleven, and at the moment, am running it using Castrol XXL SAE 40 Grade, and having read the many and varied opinions on Oil types, would it be sensible to use a Multigrade 'say 20/60 such as Pennrite, or one of the modern Synthetic oils, which had been discussed, as having the ability to maintain it's Molecular structure at the higher temperatures, plus having a greater "Flowability" is that a real word ? at the lower ones?
Your educated opinion would be greatly appreciated.

Best wishes, A'l :D :D

JT7196
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Re: Oil and ZDDP

Post by JT7196 »

Hi Chris, having just re-read all the threads again, it would seem that your recommendation was:-
Quote:-
I like Mobil oils and would choose either Mobil Super 3000 5W-40, Mobil Super 2000 10W-40m, Mobil 1 5W-50 or Mobil 1 10W-60 depending on what I needed. All of these have about 950 - 1,000ppm of ZDDP.
So in my own particular case, which would be the "Best" for me to use?

Best wishes, A'l :D :D

Phillmore
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Re: Oil and ZDDP

Post by Phillmore »

Another question would be - what are the disadvantages (if any) of using a semi synthetic oil in cars designed to use a monograde? Ie affect on seals etc.
Andy

1954 Conquest Mk1, 1956 Conquest Mk2, 1957 Conquest Century Mk2, 1955 Austin A90 Westminster

Chris_R
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Re: Oil and ZDDP

Post by Chris_R »

Al
The point I am trying to make is that all of "our" engines were designed at a time when the available oil was either SAE20 or SAE30 and we shouldn't need much more than that. I do say "shouldn't" because as I have described, wear factors do also have a part to play. If the engine is worn then an SAE30 would not have the strength to support the bearings increased gaps and you would get metal to metal contact.
The thinner oil you can get on the W rating, the better it will be at startup. You can see the differences in that chart I included in the article in DM. Those differences are less marked when you get up to operating temperature.
Now, you see the thing is, you are running on a single grade oil. As we all know, the most damage occurs to an engine in the first few minutes after starting and so that is when we want to get the maximum protection as soon as possible. To the engine, when you start it up an SAE40 oil is like treacle. Hard to pump and relatively slow to move round the engine. Look on that graph at where an SAE20 oil is at lower temperatures and then imagine where an SAE40 grade oil will be. It will be off the scale. I really fail to understand why the single grade oils get recommended these days. Multigrades are always superior to single grade oils. If you are running an SAE40 single grade you certainly don't want to be using anything with a -50 or -60, they will be much thicker than your SAE40 and un-necessary.
If you want to use mineral oil, a 15W-40 multigrade would be an improvement over the single grade, if you want to spend more money, a 10W-40 or even a 5W-40 (which only come as synthetic or semi-synthetic) would be a further improvement. All of them will give the same performance when hot but all of them will give you superior lubrication performance when you start the engine and it's cold.
Today's quality (e.g. Mobil, Shell, Castrol) mineral multigrade oils are far far superior to anything that was available when our cars were new and the synthetics even better but the synthetics are much more expensive and you may not feel the cost is justified.
Hope that helps.

Chris_R
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Re: Oil and ZDDP

Post by Chris_R »

Phillmore wrote: Thu Jun 08, 2017 12:14 pm Another question would be - what are the disadvantages (if any) of using a semi synthetic oil in cars designed to use a monograde? Ie affect on seals etc.
As far as I know, there shouldn't be any. There are plenty of anecdotes that people who have switched to using synthetics and the like suddenly get oil leaks but this is more often to do with deteriorated seals and the various modern detergents cleaning out gunge that had built up in the seal leading to a leak.
Remember, they were only designed to use a monograde because there was nothing else available. Multigrades did not begin until the early to mid 1950s. Daimler recommendations in the 1950s and 1960s in the owners handbooks of the time would recommend both monograde oils and multigrade oils. Usually the multigrade recommendation was for a 10W-30. Some owners books would still quote summer and winter grades.

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