What is the difference between Full Synthetic and Semi Synthetic Oil

I am assuming, maybe incorrectly that Full Synthetic is better and offers more protection.

But what's its Secret, what does it have that Semi Synthetic doesn't have and is it really worth the extra money.

Does anyone still use Mineral Oil in their XJS.

How often should you Change your Oil.

 

There is way more to this answer than you think.

Please visit Bob Is The Oil Guy website (or bitog for short). You'll read more about oil there than you'd ever care to know.

I use Mobil1 synthetic so I can extend the drain period to 7,500 miles or about 6 months.

If I were to use regular oil, I'd change it every 3,000 miles.

People will have differing opinions so be prepared. Ultimately you can send in a used oil sample to a place like Blackstone Laboratories and they'll tell you if your oil has more life in it or not. That should give you much better feedback than anyone, including me, on this forum.... Or BITOG's!

 

Fully synthetic gives you the full "Feel good" sensation when you use it.
Semi-synthetic gives you a semi "Feel good" sensation when you use it.




Cheers
DD

 

The difference between them is quite hard to state...But here is my answer
Synthetic blends offer protection for somewhat heavier loads and higher temperatures. They don’t evaporate as readily as conventional oils. They are a good choice for drivers who put heavy loads on the engine such as towing or off-roading. Semi-synthetics offer many of the same benefits of full synthetics, but at a fraction of the cost.

 

The only definitive way to know when to change oil is by doing oil analysis. At a previous employer I was involved with packaging large industrial engines, and on these the oil change interval is generally specified in terms of properties of the used oil in relation to new oil; plus a few hard limits, like TBN no less than XXX.

As an example at one customers site the oil change interval was 100 hours. At another it was 9,000 hours. Same engine model, the difference was fuel gas quality.

Another engine had a "deep sump" option, which basically doubled the oil capacity. Not surprisingly, the oil change interval also doubled.

On V12's with their large sumps I suspect that 3,000 mile changes are shorter than they need to be, but again analysis is the only way to tell for the way you drive your car.

 

I'm thinking it may be cheaper to just buy Synthetic and Change the Oil every 6 months (I only use the Car six months of the year) than it would be to get an analysis, although I see where you are coming from.

 

Thanks, that's very useful to know and you are right about the Cost, Synthetic seems way more expensive for some reason (probably a good reason)

 

I think I'll just change it every 6 months, as I only do around 5,000 Miles a year

Thanks for your help.

 

That Site just blinds me with Science, so many different opinions, that I think I would rather take the advice of practical users on here.

 

Hi Doug

I guess that's one way of putting it lol

 

hmm ... an oil thread that didn't go off the rails

must be a full moon or something

 

That is why I didn't include the subject of Viscosity!

 

Hasn't this been debated the odd time here before?

I just change it every 5000 km, no matter what. Mineral, semi or synthetic hasn't seemed to make much difference to me. if it is the right grade and the right price I use it.

 

I'll see your 5000km and raise another 5000km!

Of course, on mine the capacity using the 'silverstone fill'
is about 9 US quarts. Lots more volume to float contaminants.

 

It's still early, give it time.

 

The cost for synthetic is down. Check Walmart or Amazon for Mobil1. A 5 quart jug for $26?

http://www.amazon.com/gp/aw/d/B00HG7...IrZkPE6pL&ref=

At that price, why not go with synthetic?

 

Amazon UK (Mobile 1) £35-94

I would have preferred Magnatec 10/40

 

Oooh, I did not see that you were from the UK.


I also own a very high mileage (186k) 2000 Ford Taurus which I have used regular oil every 3,000 miles since it was brand new. (Was a company car that I kept) It equated to an oil change every 2-3 months.


It was my daily driver and I never had any issues with it. When I bought the XJS back in 2010, the miles I put on the Taurus dropped dramatically. To the point that I only needed to change the oil once a year. (I only put 3,000 miles a year on it now) I switched from regular 5w20 to semi-synthetic 5w20 because I believe that the "semi" part of the oil helped maintain the integrity of the oil over the longer time interval.


I recently had to take the cam cover off of it to replace the gaskets. The engine, at 180k miles looked absolutely wonderful. I plan on sending an oil sample to Blackstone next time I change it to make sure I'm doing the right thing.


Since the last change, I bought Quaker State Full Synthetic, since the local parts store was selling 5 quarts of that plus a filter for $20. Had it not been that cheap, I probably would have stayed with the Motorcraft semisynthetic I had been using before.


To make a long story short, I switched to synthetic (or blend) to increase the amount of time between oil changes. For the Jag, it means I extend the mileage (I wait until 7,500 miles), for the Taurus it means I feel comfortable keeping the same oil in it for a year, even though the miles are low.


If I stuck to a standard 3,000 miles/3 month schedule, I would keep running standard oil.

 

Just don't mention the price of Petrol/compared to what you have to pay on your side of the pond.

I just found some Magnetec Semi 10/40 for £20 for 4 litres, so it looks like I will need 3 cans of the stuff.

Mind you, they sometimes have deals around Easter, so I'll have to live in hope.

 

An analysis isn't that expensive, you really only have to get it done once to know where you stand.

The oil is the garbage pit of the engine, the reason for changing oil is it gets contaminated, rather than wearing out. At a certain contamination level it can't protect the metal parts from wear, and it's time to change. Always nice to know where that point is.

Although if you only use the car a few times a year, change it before it goes into storage for the winter.

Make sure the oil comes up to temperature as well, don't do lots of short trips and that will extend the life of the oil. Ideal oil temperature is between 170-190F (77-88C). Colder and it won't drive off the condensation that causes acid formation, and hotter causes oxidation and breakdown.