Well, not EXACTLY proof. Here is the story, then you decide. I've already made up my mind. I have heard that synthetic oils promote leaks, but kind of put it in the "old biker's never change" category. I have a 94 Evo softail that had 67,000 miles on it last summer. Right before going on a long trip of 4200 miles, I switched it to Harley Synthetic 20w50 as I wanted to go longer before oil changes. Well, although this bike had never dripped a single drop, within 3,000 miles I had developed the dreaded rear base gasket cylinder leak. Additionally, I had a leak at the base of the oil pressure plug.
Ended up doing a TOTAL top end build using cometic gaskets. The base gasket ok today, but that pesky leak at the oil pressure plug still persisted using synthetic (it is a very fine crack there). Also, slight misting at the rocker boxes. At the end of a day, I would put the bike away and in the morning WITHOUT fail I would have a 1" by 1" oil stain beneath the bike. After a couple of months, I thought, "What the hell, I'll just try old dinosaur oil again."

Leaks be gone!


So, not exactly proof, but worth filing away in the interesting things to know category.

 

Did you install the Hayden Enterprises "oil fix?" If you did, then you need not worry about base gasket leaks again.

 

When i was bracket racing my 69 firebird i asked all of the racers what they used for oil.
The reply from most all of them was a good motor oil and Lucas oil treatment.
so that being said I'm just gonna go with that setup.
I think the use of the Lucas stuff( or equivalent) should help with startups to protect the bearings etc.

 

Well, if you read enough oil threads and the all the pages dedicated to syn vs. dino, you'll pretty much be aware two things mentioned here (among others)

1. If you have a gasket or fitting that isn't real good, then synthetic may leak where dino oil doesn't. This is probably due to the molecule chains being generally longer in dino oil than synthetic as the main difference between dino and synthetic is that full synthetic is manufactured with shorter consistent molecule chains while the semi synthetics are dino oil that has the chains cracked to be more consistent but still have longer chains than dino.

A lot of times, a new motor will seep oil in a few places when changed to synthetic. I've seen where running dino for an oil change will stop the leak and then when switching back again to synthetic, the leak stays gone. Either way, as far as I'm concerned, if it seeps with synthetic, it might be time for a new gasket or a better fitting part.

2. The only real measurable advantage of synthetic oil is that it doesn't break down as fast as dino under heat. This fact is fairly well proven. As far as what a race motor is going to use, who cares that the oil won't break down as fast because it's not going to be in the motor very long anyways.

 

Can switching back and forth from Dino to synthetic cause any additional problems?

 

I'm a real beleiver that if the bike started from birth on synthetic oil it will last without the dread leaks but switching back and forth I think kind of follows what YJ is saying with if there's not a perfect seal the syn oil will find its way through.

 

When I was racing, the only ones that used synthetic oil was Hemi powered cars. Seemed like one of those scattered every race day and stopped racing for an hour to clean up the mess of synthetic oil and Mopar junk from the asphalt.

 

Oh no! You did not just dis. a Hemi engine! Game on!

 

I did. Sorry, GM to the bone.

 

I tried synthetic in the FXR and it did its damndest to get out of there from every possible place. Changed right back to dino...