5W40 vs 10W40

bretttp1

I'm changing the oil in my car, the recommended oil to use by the owners hand book is 10W 40 semi synthetic but when I was buying the oil I was reading (off those flip charts in Hal fords) that for even better protection you can use fully synthetic, So I bought 5W 40 fully synthetic.

I know that this flows faster at low temperatures when starting the engine hence giving better protection but I was under the impression that the thinner the oil is the worse it is.

Any way (after all that waffle)

Is it OK to use fully synthetic oil when semi is recommended?

JHMEG

Stick with what was recommended. If your car has a few miles on it the thinner oils won't last in it anyway.

voxpop

What car have you got? There might be little or no benefit of moving to fully synthetic. I wouldnt be too keen trusting halfords over your owners manual either


Wouldnt worry about how many miles the car has done as regards to what oil to use. I use 5w30 and have 110k miles without problems

bretttp1

Thanks for the replies, the cars an alfa 147 1.9 JTD-M 16v with 35K on the clock.

SouperComputer

bretttp1 wrote: »

Thanks for the replies, the cars an alfa 147 1.9 JTD-M 16v with 35K on the clock.

10W is good enough for -25degC, so you are fine. The viscosity of 5w and 10W is pretty close when you are around freezing point, so I wouldnt worry too much, its a moot point. Obviously the viscosity at operating temperature is the same of course they are both rated at 40.

Both Oil thats too "thick" or thats too "thin" is a problem. Too thin and it doesnt provide enough pressure, especially bad on the bottom end too thick and it can cause high pressure, but also inadequate lube at the top end. Verymuch a sweeping generalisation (sp), but thats the jist of it.

Run with what the manufacturer's reccomendations, although, unless its a very old engine, id run fully synth. As the engine has higher miles put on it (100K+), maybe consider moving to an xW-50.

voxpop

Out of interest, why would you move to an xW-50 on 100k+. If the manufacturer says use XXX type of oil, is it not wise to stick with that ? I have the joy of having a VW and so have to wade through the reams of different oil specs :rolleyes:. Ive gone with the new spec for long life oil - which is basically 5W-30. I could use oil designed for interval servicing, which is 5W-40 - but according to the manufacturer 5W-30 and 5W-40 cannot be interchanged , ie you can you 5w-40 for long life servicing.

JHMEG

voxpop wrote: »

Out of interest, why would you move to an xW-50 on 100k+. If the manufacturer says use XXX type of oil, is it not wise to stick with that ? I have the joy of having a VW and so have to wade through the reams of different oil specs :rolleyes:. Ive gone with the new spec for long life oil - which is basically 5W-30. I could use oil designed for interval servicing, which is 5W-40 - but according to the manufacturer 5W-30 and 5W-40 cannot be interchanged , ie you can you 5w-40 for long life servicing.

What do you mean by interval servicing and long life servicing?

SouperComputer

voxpop wrote: »

Out of interest, why would you move to an xW-50 on 100k+. If the manufacturer says use XXX type of oil, is it not wise to stick with that ? I have the joy of having a VW and so have to wade through the reams of different oil specs :rolleyes:. Ive gone with the new spec for long life oil - which is basically 5W-30. I could use oil designed for interval servicing, which is 5W-40 - but according to the manufacturer 5W-30 and 5W-40 cannot be interchanged , ie you can you 5w-40 for long life servicing.

Built-in obsolecence

ZiabR

bretttp1 wrote: »

I'm changing the oil in my car, the recommended oil to use by the owners hand book is 10W 40 semi synthetic but when I was buying the oil I was reading (off those flip charts in Hal fords) that for even better protection you can use fully synthetic, So I bought 5W 40 fully synthetic.

I know that this flows faster at low temperatures when starting the engine hence giving better protection but I was under the impression that the thinner the oil is the worse it is.

Any way (after all that waffle)

Is it OK to use fully synthetic oil when semi is recommended?

5w-30 is the same as 5w-40 when cold, they are both rated as 5w.

When hot they are different.

The 30 (sae 30) is in fact 11cst at 100degC and the 40 (sae 40) is 14cst at 100degC i.e. slightly for viscous and will handle high oil temps better.

To explain in simplistic terms, they fall into two viscosities.

If you see an expression such as 10W-40, the oil is a multigrade.

This simply means that the oil falls into 2 viscosity grades, in this case 10W & 40.

This is made possible by the inclusion of a polymer, a component which slows down the rate of thinning as the oil warms up and slows down the rate of thickening as the oil cools down.

It was first developed some 50 years ago to avoid the routine of using a thinner oil in winter and a thicker oil in summer.

For a 10w-40 to attain the specification target a 10W ( W = winter) the oil must have a certain maximum viscosity at low temperature. The actual viscosity and the temperature vary with the viscosity grade but in all cases the lower the number, the thinner the oil, e.g. a 5W oil is thinner than a 10W oil at temperatures encountered in UK/IRL winter conditions.

This is important because a thinner oil will circulate faster on cold start, affording better engine protection.

For a 10w-40 to attain the other specification target a 40 oil must fall within certain limits at 100 degC. In this case the temperature target does not vary with the viscosity grade, if there is no "W", the measuring temperature is always 100degC. Again the lower the number the thinner the oil, a 30 oil is thinner than a 40 oil at 100 degC., which is typical of maximum bulk oil temperatures in an operating engine.

The engine makers are, of course, very well aware of this and specify oils according to engine design features, oil pump capacities, manufacturing tolerances, ambient temperature conditions etc. It is important to follow these guidelines, they are important and are an are stipulated for good reasons.

If the engine has been modified, the operating conditions may well be outside the original design envelope. The stress on the oil caused by increased maximum revs, power output and temperature may indicate that oil of a different type and viscosity grade would be beneficial.

So in essence, you are better off with a Fully Synth Oil. I am driving a Honda Integra DC5 Type R 2.0i Vtec and those engines do come under a lot of strain especially around a track and I did a lot of research into oils and how they work. You have chosen a super oil for two reasons, 1) it’s a Fully Synth Oil and 2) it’s a 5w-40.

Your car will thank you for it.

voxpop

JHMEG wrote: »

What do you mean by interval servicing and long life servicing?

interval = every 6000miles (i think) or based on time/mileage only

long life = up to 20000 miles (according to manufacturer) - so time/mileage + driving style. Basically the computer in the car works out your driving style, the type of journeys you do (short town driving vs long motorway) and there is also a sensor in the sump. The computer then tells you when to service.

In regards to oil - vw specify that only certain types of oil should be used for long life servicing and certain types for interval. Its ok to use the long life oil and service the car at intervals but not the other way around.


@logik - pretty interesting stuff. There must be more to oils than just viscosity though.Just taking VW again as an example - their long life spec oil is a different viscosity but there must be other aspects that make it different, ie make it long life ?