Gang,

When I bought my used 1999 xk8 (75,000 miles), the guy wanted to impress me by doing an oil change the day before.

I previously asked him if there were any oil leaks before I went to look at it, and he said it's as "dry as a bone". And it was dry as a bone when I looked at it, and the engine wasn't all that clean (dusty), so I truly believe him.

So...he did an oil change using synthetic oil (for the first time), and within several days, I'm getting some smoke from oil leaking from each valve cover gasket.

I have always heard that if you want to use synthetic oil, you shouldn't have too many miles on it, as leaks will occur.

My question from anyone with this experience is...If I change the oil back to regular oil, will the leaks persist or will they stop?

I'm not aksing for 'absolutes'...just good educated guesses or past-histories.

Thanks in advance!

 

Tom,

You are truly and properly being entertained by your new toy!

I do not have an engineering degree but simply cannot see any way that an oil change would suddenly cause the valve covers to leak. Had the tensioners been changed recently? Disturbing a 10 year old gasket could cause a leak.

Consider the Lincoln LS parts in the FAQ for significant savings.

I have had my covers off twice without changing the gaskets and have had no leaks.

 

OK, here is the deal. You need to go Google it up after I give you this very quick explanation.

Regular oil has molecules of all different sizes, think basketballs to marbles. Synthetic oil has molecules of all the same size, think baseballs. If all of the molecules are the same size, you get more contact, better heat dispersion and several other positive factors. Unfortunately, when the baseball sized molecules push the basketball sized molecules out of the way, there is leakage.

That is the very quick version, I will let you go and do your own research.

 

I would say replace the gaskets and move on! Changing the oil to synthetic is not what I would have done but it was done for you and now you do not need to make the decision to make that change.

 

I would return to a non-Synthetic oil. For just one oil change I'd use one of the "high - higher mileage" dyno oil. They add a few more chemicals that will soften up and swell your gaskets a little.

I've found with a new car that if I start out with the first oil change using synthetic oil I don't have any leaks but if I start with dyno oil and later on when there are 50K or so miles on the engine and I switch to Synthetic oil I find leaks.

My Vette was used when I bought it and it had 40K miles. The other owner used dyno oil and I switched to Mobil 1 and ended up with valve cover leaks (both sides) and an oil pan leak. I switch to Mobil's high mileage oil for 3000 miles then went to stright dyno 5W30 and the leaks stopped.

I've since had the engine rebuilt (crank shaft broke between cyl 5 & 6). I've had this engine "built" (ported & polished, cam, roller lifters, Procharger, super ram, headers, etc. etc.) and use Valvoline 20W50 racing oil without any problems. I send in every other oil sample to Blackstone Labs and they tell me if things are going okay inside the engine. I do the same with the Jag and my truck's oil too.

You can return to dyno oil from synthetic oil, they are both compatable. Synthetic oil is dyno based. As Kevin D says, do your little research. Log onto Blackstone Labs and read their info on their tests and you can see what the result sheet looks like.

 

Prediction:

Changing your oil is not going to stop your oil leak.

 

My Rav4 has 254,500mi on it and synthetic oil was used from day 1 and it has no evidence of oil leaks. I recently changed my 99xk8 to synthetic oil and it has no leaks. And I agree with Tom (TestPoint) !

 

The urban legend that synth oil causes leaks is rooted in the early days of synthetics when the ester balances were off and they did cause some leaks. This was fixed 20 years ago but some folks still dredge it up. Synthetic does not cause leaks....just use the correct weight and fix any leaks, they are from something else. The gaskets on these engines do get leaks, it is not ususual, but is fairly easy to fix. Be sure you don't have a plugged full or part-load breather, this can pressurize the engine and cause oil leaks. The aprt load breather has a pin-hole and can get plugged if the oil gets goopy. Keep in mind that synthetic oils are not slipperier and do not go through gaskets easier than conventional oils, they are just more stable at high temps.

 

Hmmm, I've heard alot over the years about going both ways (with oil) and the size of the molecules at gaskets, etc.

I want in on this poll. My prediction - going back to dino oil within a few hundred miles of the synthetic change, will stop the leak.

Who else wants in?

 

I'm taking the meaning of "leak" is just a wet gasket area, not droplets of oil that roll onto the floor of your garage.

 

Here, as I said, do some research and decide for yourself. It seems to me, as others have said, that it is risky to change to synthetic oil on a high mileage engine that has always used regular oil. One form of logic would say that it is better to put the best oil that you can in a high mileage engine, but, it may just be that synthetic oil may not be the "best oil" for such an engine.

http://www.aircooled.net/gnrlsite/re...s/synthoil.htm

Myth #2 debunked
Synthetic oil causing oil leaks is another commonly spread myth. The truth of the matter is that if all your engine seals and gaskets are in good condition, synthetic oil will NOT leak in your engine. The myth started because on occasion, an engine will leak with synthetic oil, but not dino oil. The reason for this is that the smaller molecules of the synthetic are able to get past very small crevices, where the larger molecules of dino oil cannot. But this does not mean that the synthetic oil has caused the leak, it simply has "discovered" an infant leak, and regardless of what oil you are running, this infant leak will eventually grow to a size that will allow dino oil to occupy and pass also. Synthetic oil has not been shown to deteriorate engine seals or gaskets. It is not some evil solvent that will break down sealant, or anything like that. Like was said earlier, it is just a man-made base stock, that is uniform and smaller in molecule size than dino oil. Nothing more, nothing less.