I have a 94 300Tdi and need to top my oil up. The engine has conventional oil in at present, but the question is, would there be any vile reaction if I were to top it up with semi-synthetic oil. I picked it up off the shelf some time ago without looking at it properly and didn't notice semi-synthetic oil on the label. I was just looking for 15-40 and was in a hurry so picked it up.
i done the same thing not so long ago its still in there no problems yet but did get a good bollocking off the missus for useing her oil
Thanks robint. Thats just dandy. I'm not one to waste things so its saved me having to dispose of it. It also means I don't have to stare at my mistake every day for the next few years I can now use it with confidence. Anyhow I'm not sure what difference there is between semi-synthetic and ordinary oil when it comes to the car anyway
discool
Well-Known Member
Anyhow I'm not sure what difference there is between semi-synthetic and ordinary oil when it comes to the car anyway
There's loads of info on the web, if you want some new bed time reading, so you can put the Haynes Manual down
There's loads of info on the web, if you want some new bed time reading, so you can put the Haynes Manual down
Ok ta very much. I'm off surfing then!!
discool
Well-Known Member
One to start u off What oil for your car? | Used Car Expert
What oil for your car? | Used Car ExpertWell the first article I found was from The Engine Oil Bible and here it is.
Mixing Mineral and Synthetic oils - the old and busted concepts
For the longest time, I had this to say about mixing mineral and synthetic oils:
That's the thing with progress - stuff becomes out-of-date. Fortunately for you, dear reader, the web is a great place to keep things up-to-date, so here's the current thinking on the subject of mixing mineral and synthetic oils. This information is based on the answer to a technical question posed on the Shell Oil website.
There is no scientific data to support the idea that mixing mineral and synthetic oils will damage your engine. When switching from a mineral oil to a synthetic, or vice versa, you will potentially leave a small amount of residual oil in the engine. That's perfectly okay because synthetic oil and mineral-based motor oil are, for the most part, compatible with each other. (The exception is pure synthetics. Polyglycols don't mix with normal mineral oils.)
There is also no problem with switching back and forth between synthetic and mineral based oils. In fact, people who are "in the know" and who operate engines in areas where temperature fluctuations can be especially extreme, switch from mineral oil to synthetic oil for the colder months. They then switch back to mineral oil during the warmer months.
There was a time, years ago, when switching between synthetic oils and mineral oils was not recommended if you had used one product or the other for a long period of time. People experienced problems with seals leaking and high oil consumption but changes in additive chemistry and seal material have taken care of those issues. And that's an important caveat. New seal technology is great, but if you're still driving around in a car from the 80's with its original seals, then this argument becomes a bit of a moot point - your seals are still going to be subject to the old leakage problems no matter what newfangled additives the oil companies are putting in their products.
Wonderful thing the web.
Mixing Mineral and Synthetic oils - the old and busted concepts
For the longest time, I had this to say about mixing mineral and synthetic oils:
- If you've been driving around with mineral oil in your engine for years, don't switch to synthetic oil without preparation. Synthetic oils have been known to dislodge the baked-on deposits from mineral oils and leave them floating around your engine - not good. It's wise to use a flushing oil first.
- If you do decide to change, only go up the scale. If you've been running around on synthetic, don't change down to a mineral-based oil - your engine might not be able to cope with the degradation in lubrication. Consequently, if you've been using mineral oil, try a semi or a full synthetic oil. By degradation, I'm speaking of the wear tolerances that an engine develops based on the oil that it's using. Thicker mineral oils mean thicker layers of oil coating the moving parts (by microns though). Switching to a thinner synthetic oil can cause piston rings to leak and in some very rare cases, piston slap or crank vibration.
- Gaskets and seals! With the makeup of synthetic oils being different from mineral oils, mineral-oil-soaked gaskets and seals have been known to leak when exposed to synthetic oils. Perhaps not that common an occurrence, but worth bearing in mind nevertheless.
That's the thing with progress - stuff becomes out-of-date. Fortunately for you, dear reader, the web is a great place to keep things up-to-date, so here's the current thinking on the subject of mixing mineral and synthetic oils. This information is based on the answer to a technical question posed on the Shell Oil website.
There is no scientific data to support the idea that mixing mineral and synthetic oils will damage your engine. When switching from a mineral oil to a synthetic, or vice versa, you will potentially leave a small amount of residual oil in the engine. That's perfectly okay because synthetic oil and mineral-based motor oil are, for the most part, compatible with each other. (The exception is pure synthetics. Polyglycols don't mix with normal mineral oils.)
There is also no problem with switching back and forth between synthetic and mineral based oils. In fact, people who are "in the know" and who operate engines in areas where temperature fluctuations can be especially extreme, switch from mineral oil to synthetic oil for the colder months. They then switch back to mineral oil during the warmer months.
There was a time, years ago, when switching between synthetic oils and mineral oils was not recommended if you had used one product or the other for a long period of time. People experienced problems with seals leaking and high oil consumption but changes in additive chemistry and seal material have taken care of those issues. And that's an important caveat. New seal technology is great, but if you're still driving around in a car from the 80's with its original seals, then this argument becomes a bit of a moot point - your seals are still going to be subject to the old leakage problems no matter what newfangled additives the oil companies are putting in their products.
Wonderful thing the web.
There's a higher detergent level in synthetics, and diesel synthetics have even more.
Glad to see someone has finally debunked the old myths about dislodging lumps of old crud and damaging engines, I've never seen that in any engine.
We've used Shell Helix in our V8 since the rebuild, and after 8500 miles it is still clear although going brown, possibly some of that is the remains of old oil deposits in the heads and rocker gear.
We will be changing the oil in the next week or so, as soon as it stops raining!
Peter
Glad to see someone has finally debunked the old myths about dislodging lumps of old crud and damaging engines, I've never seen that in any engine.
We've used Shell Helix in our V8 since the rebuild, and after 8500 miles it is still clear although going brown, possibly some of that is the remains of old oil deposits in the heads and rocker gear.
We will be changing the oil in the next week or so, as soon as it stops raining!
Peter
