How safe is it to use synthetic motor oil in an older Opel?

We often get asked: “if it’s safe to use synthetic motor oil in an older Opel”? In actual fact many owners of older vehicles share this concern.

When is it safe to use synthetic motor oil in an older Opel?

Generally, the reference to synthetic oil for an engine means the lubricant is formulated with a polyalphaolefin (PAO) base oil. PAO, which is often called synthesized hydrocarbon, is pure and is compatible with mineral base oils.

These synthesized hydrocarbons, polyalphaolefins, diesters and other materials that form the base stocks of high quality name brand synthetics are fully compatible with petroleum oils which is why it’s safe to use synthetic motor oil in an older Opel. In the old days, some companies used untested materials that were not compatible, causing quality synlubes to suffer a bad reputation. Fortunately, those days are over.

However, before you decide whether it’s safe to use synthetic motor oil in an older Opel you need to find out if the oil contains polyalphaolefins because the PAO base oil does not dissolve additives effectively, it is usually formulated with an ester co-base (usually diester and/or polyolester). The additives are soluble with the ester, and the ester is soluble with the PAO.

Likewise, the PAO tends to cause seal shrinkage, and the ester causes seal swelling, so the effects are offset when both base oils are present. It is the ester that can cause problems when you change from mineral to synthetic.

Ester base oil used alongside PAO base oil in lubricant formulation is an excellent natural detergent. In other words, it will clean up varnish on component surfaces which were deposited as a result of thermal and oxidative degradation of the lubricant.

Now part of the oil additives function in a synthetic engine oil is to clean these deposits and when you switch from a typical mineral-based engine oil to a typical synthetic-based oil, the varnish layer will be removed by the ester in the synthetic lubricant and become suspended.

Depending on the build up, this suspended material could clog filters, block oil flow passageways and if left long enough, lead to component starvation. The same is true for gearboxes and other industrial machines.

How do I make sure it’s safe to use synthetic motor oil in an older Opel?

If you’re going to switch to synthetic engine oil on an engine that’s been operating for some time with mineral oils, it’s advisable to replace the oil and filter at a reduced mileage – just to remove the contaminants that have been cleaned off the working surfaces.


Although this is slightly off-topic; compatibility is something to bear in mind, whether using regular oil or synthetic oil. It is usually best to use the same oil for topping up as that you have been running in the engine. That is, it is preferable to not mix your oils. The reason for this is: the functions of additives blended for specific characteristics can be offset when oils with different additive packages are put together. For optimal performance, it is better not to have a mix of engine oil in the sump.

So to answer the question of whether it’s safe to use synthetic motor oil in an older Opel: Most definitely, and you’ll also enjoy all the benefits that synthetic motor oil provides over regular engine oil.

If you’re unsure whether it’s safe to use synthetic motor oil in an older Opel you need to call Habot Oil, a producer of high quality fully synthetic motor oil. The professionals at Habot Oil will give you advice on the best engine oil to use in your older Opel, or any older car for that matter.