oil bargain at Asda

Castrol GTX has been around for many a year, and its spec (API, etc) changed many times. You need to make sure this one is to the spec (or better) needed for your car.

Well the 10W40 or 15W-40 spec is fine. As for more detailed specs, I have no idea.

However I would feel confident it's a better oil than that included in a KwikFit £30 oil change.

Buying oil in bulk is far cheaper per litre than in retail packaging. You could likely find out the spec of the oil Kwik fit use.

Castrol GTX is about the cheapest oil Castrol supply.

I thought this looked reasonable value, and the API specs are listed

At least you know what it is. The GTX 'brand' has been around for 40-50 years. It was at one time the premium name Castrol used. But not now. And of course the formula has changed dramatically over the years. It's the same with say Mobil 1. Unless you read the spec it could be anything. And these things are priced to what the market will stand.

As said elsewhere, it depends on the destined vehicle. Unless the car is quite old, API specs are largely irrelevant for European cars used with European fuels in Europe, which should be run with oils to the manufacturer recommendations.

The ACEA is a European working group of European vehicle manufacturers that specify the quality of oils used in their engines to meet emissions legislation. They then give their own classification over and above the minimum ACEA spec.

API specs are not set by the vehicle maunfacturers alone, but that of around 400 companies in N. America where practically anyone can vote on the oil specification. This often leads to the lowest common denominator winning the day.

David

I'm pretty sure that GTX is what you'd get from Kwik Fit.

Not necessarily as they would not like to be discovered using the incorrect oil which destroyed a motor. Most modern vehicles use full synthetic oils and have done so for several years.

GTX, I don't think, is a full synthetic oil, just going by the price alone.

I have no faith in GTX and that goes back to the early 1970's when it was released. (oil pressures varied too much compared to XL.)

Anyone know where's the cheapest for 5W-40 fully synth at the moment?

Seemed to come out as clean as it went in, not good.