5-30 synthetic oil
Posted: Mon Feb 26, 2024 1:16 pm
What ho, me dearios!
I need your advice. An abiding interest of mine is in reducing the fuel consumption of my 1963 1098cc Traveller which is typical in generally being in the upper thirties to the gallon and which with a little care I can stretch into the lower forties. My focus currently is reducing the internal friction of the engine by lowering the engine oil viscosity. Like most Minor owners, I suspect, I’m using an SAE 20-50 grade (using up the last of my Wilkinson store brand) but I’m thinking of moving to a 5-30 synthetic. Of course, there’s nothing wrong with 20-50 grades, indeed, I’ve used them since they became popular in the 1960s (especially the Duckham brand; see a history here https://www.duckhams.co.th/data_sheet/D ... y-Book.pdf). And further, my latest Workshop Manual (Publication Part No. AKD 530 (14thEdition)) recommends SAE 20-50 for all temperatures above minus12C. But I note that in my earliest Workshop Manual (Part No. AKD530B Issue 2 19997) SAE 30 & SAE 20/30 (Esso Extra) are recommended for the same temperature range, and if you scroll down in the Duckham history link above you’ll see on page 94 a Minor Lowlight(?) engine bay with a can of Duckham’s 10w/30 clipped to the firewall. So, my rationale for thinning down to SAE 5-30 synthetic is that originally SAE 30 was specified and then 20-30 included, and while these was overtaken by SAE 20-50, if the original design envisaged SAE 30 as the prime oil, then its superior modern equivalent should be even better.
If you scroll down to the graph shown here; https://www.widman.biz/English/Calculators/Graph.html you can see the difference at lower temperatures as well as the advantage when the oils reach the 50-60C mark. Quite how viscosity translates into friction I can’t find out, but the A Series engines are big for the power they deliver and so their internal friction is probably an important influence. Clearly, the graph shows that getting the oil above 60C helps a lot, but for me, this takes some brisk driving for some 25 miles or more on a hot day to get it. (Shielding the sump and heating the oil will be in a future thread.)
Of course, a lower viscosity oil will give lower oil pressure readings for any given engine speed and oil temperature, and for those with a gauge, high readings are generally considered “a good thing”. However, this thought needs care; the oil pump pressure relief valve opens at about 60psi and then short circuits some of the oil supply back to the sump. This means that if you’ve a gauge reading of 60psi or more a good deal of your oil is not going around the engine. (On a first start at below freezing my engine running at the raised idle given by the choke will show 70psi with a relief valve that opens at about 55psi.) Another reason, I think, for reduced viscosity at low temperatures.
A final point; at lower viscosities the oil flows more easily through the oil filter so there’s a reduced pressure across it. This is important ‘cos when the oil pressure across the filter rises (as it will do as it clogs) to about 3psi the filter bypass opens so unfiltered oil passes direct to the engine. (And I bet this is happening on cold starts.) Our Phil has suggested here viewtopic.php?t=77199 (at Mon Feb 12 2024 12.24 pm) how this bypass may be blocked but I fear that with a thick oil a high pressure may result across the filter raising the risk it might burst and dump its collected debris straight into the bearings. Another plus for a thinner oil.
So, all in all, I think my change to a SAE 5-30 synthetic is a good idea. What say you? Regards from MikeN.
I need your advice. An abiding interest of mine is in reducing the fuel consumption of my 1963 1098cc Traveller which is typical in generally being in the upper thirties to the gallon and which with a little care I can stretch into the lower forties. My focus currently is reducing the internal friction of the engine by lowering the engine oil viscosity. Like most Minor owners, I suspect, I’m using an SAE 20-50 grade (using up the last of my Wilkinson store brand) but I’m thinking of moving to a 5-30 synthetic. Of course, there’s nothing wrong with 20-50 grades, indeed, I’ve used them since they became popular in the 1960s (especially the Duckham brand; see a history here https://www.duckhams.co.th/data_sheet/D ... y-Book.pdf). And further, my latest Workshop Manual (Publication Part No. AKD 530 (14thEdition)) recommends SAE 20-50 for all temperatures above minus12C. But I note that in my earliest Workshop Manual (Part No. AKD530B Issue 2 19997) SAE 30 & SAE 20/30 (Esso Extra) are recommended for the same temperature range, and if you scroll down in the Duckham history link above you’ll see on page 94 a Minor Lowlight(?) engine bay with a can of Duckham’s 10w/30 clipped to the firewall. So, my rationale for thinning down to SAE 5-30 synthetic is that originally SAE 30 was specified and then 20-30 included, and while these was overtaken by SAE 20-50, if the original design envisaged SAE 30 as the prime oil, then its superior modern equivalent should be even better.
If you scroll down to the graph shown here; https://www.widman.biz/English/Calculators/Graph.html you can see the difference at lower temperatures as well as the advantage when the oils reach the 50-60C mark. Quite how viscosity translates into friction I can’t find out, but the A Series engines are big for the power they deliver and so their internal friction is probably an important influence. Clearly, the graph shows that getting the oil above 60C helps a lot, but for me, this takes some brisk driving for some 25 miles or more on a hot day to get it. (Shielding the sump and heating the oil will be in a future thread.)
Of course, a lower viscosity oil will give lower oil pressure readings for any given engine speed and oil temperature, and for those with a gauge, high readings are generally considered “a good thing”. However, this thought needs care; the oil pump pressure relief valve opens at about 60psi and then short circuits some of the oil supply back to the sump. This means that if you’ve a gauge reading of 60psi or more a good deal of your oil is not going around the engine. (On a first start at below freezing my engine running at the raised idle given by the choke will show 70psi with a relief valve that opens at about 55psi.) Another reason, I think, for reduced viscosity at low temperatures.
A final point; at lower viscosities the oil flows more easily through the oil filter so there’s a reduced pressure across it. This is important ‘cos when the oil pressure across the filter rises (as it will do as it clogs) to about 3psi the filter bypass opens so unfiltered oil passes direct to the engine. (And I bet this is happening on cold starts.) Our Phil has suggested here viewtopic.php?t=77199 (at Mon Feb 12 2024 12.24 pm) how this bypass may be blocked but I fear that with a thick oil a high pressure may result across the filter raising the risk it might burst and dump its collected debris straight into the bearings. Another plus for a thinner oil.
So, all in all, I think my change to a SAE 5-30 synthetic is a good idea. What say you? Regards from MikeN.