Hey guys. I took my 99 discovery 2 to firestone to get an oil change (this was against my better judgement but I was in a bind at the time). Anyway, I told the guy to put in 5w30 conventional and when I left I thought everything was ok. However, I went to check the level about a week later I noticed that the oil was a little lighter than I usually have. Needless to say they put a synthetic blend in my car. The truck has 123000 miles on it and I have always used conventional and still want to use it in the future. That being said, can I, now that I have time, simply just drain the sythetic out, replace the filter and put conventional back in. I have heard that once you go synthetic you cant go back. Is this true? Also, since the oil change I have noticed that there is significant knocking upon start up. After about 15 sec this goes away and doesnt come back, but it sounds terrible. Could this be because of the oil itself or the filter that they put in? Thanks i advance

 

Ohh, and the knocking only happens if the car is allowed to sit for a long period of time (overnite for instance)

 

I don't think there are any laws that say you can't switch back. I wouldn't worry about it. Maybe you ought to stick with synthetic since it's a better lubricant anyway (albiet more expensive)?? I use Mobil 1 in my Seville.

As far as the knock goes,most likelythe filter they useddoes not have an anti-drainback valve (or it isn't doing it's job) andsome oil is seeping out of the filter as it sits. Takes a couple seconds to build back oil pressure once you start it.Try replacingthe filter with a better one.

Mark G

 

The knock is a cheap oil filter.

You can change back a forth with the oil the only time you may
not want to do that is you have not changed the oil regularly
and have build up in the motor.
If so you will end up with more oil leaks.

 

Ohh well thats great news. Can I replace the filter now without changing the oil. It been about 500 miles since the change and I would rather wait a little while before doing a full change. I would have to add more oil after I take out the filter though right. Also should if I do do this should I wait till the car has sit for a while so that the oil drains out of the filter. Thanks alot

 

I would think a good flush and then change back to your preference. But you may wait for DiscoMike for a more experienced opinion.

-Ugly

 

Change the oil filter ASAP, cause every morning that noise you are getting is because the oil has drained from your oil filter so your engine starts with "NO" oil pressure.
Go pick either a Mobil 1 oil filter or a K&N 3001. Use these only in the future. As for the engine flush, this would be a great Idea, so let me know before your next oil change and I'll walk you thru it.
As for the using a synthetic Blens, good for them, this was a treat for your engine and I would recommend you continuing with it.

 

For what it's worth, synthetic oils, blends and non-synthetic oils are compatible with each other by design. The additive packages are all very similar and the only meaningful difference is the base stocks. Synthetic base stocks are simply more uniform at the molecular level than mineral base stocks but the chemical compounds are the same- hydrocarbon chains.

Interestingly, Castrol Syntecand Syntec Blendactually use a mineral base stock that they put through a special hydrocracking process, so even it isn't a "real" synthetic. Whoever told you that once you go synthetic you can't go back is incorrect.

Dave