www.iFourWinns.com

Use synthetic if you want, but I agree on an old engine you could get leaks. I use normal oil now, but when my '07 volvo penta turns into a 15 year old engine, I'm going to switch to high mileage oil. It has worked wonders in my truck so far. Its supposed to have additives to help the seals and burn less. I thought it might be snake oil when I bought it, but it really seems to be helping in my truck. I had a very slow oil leak that it has nearly sealed up in only a few months. My truck also used to burn 2 qts per 5000 miles or so. It seems to be consuming less now.

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2007 FW Horizon 200 5.0GXi/SX-A

Your 07 should be good forever. The new technology in the gaskets will or should insure that. There not like the old cork or felt type

I used to train Mechanics and Retailers on Automotive Oils, so I know of a wife's tale when I hear one (or read one on the internet! )
Synthetic oils are simply a more hydrocracked (processed) mineral oil, consisting of predominantly Group 2,3 and 4 base stocks.
Back in the day (where most old wife's tales originated), there were cases of people experiencing oil leaks with synthetics, as they could only make lighter viscosities.
Try run your SBC on a 10w30 synthetic that will shear to a 0w10 after 2000 miles! I'm confident that minor weeps will now become more prominent.
What other changes have been made to gaskets to make them "safe for synthetic oils"?!

p.s. Mobil had hurt the public's perception on synthetic oils due to their Mobil 1 product shearing so fast.
Technology has moved in leaps & bounds and shear stability allows manufacturers such as Mercedes to offer 30,000km service intervals for certain applications.

Use the highest API spec' synthetic of the correct viscosity and your engine will love you for it.

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2011 Four Winns H180 SS.
Aussie built Mustang 2800.
SOLD - 1997 Four Winns Horizon RS

No disrespect intended, but I've seen it. And I disagree that it's an issue of old seal technology. When oils used to cook off (not as much of a problem now) the vapor formed sludge buildup on the seal surfaces. The sludge, over time, prevented any fresh oil from keeping the seals lubricated. The sludge itself would be the main thing preventing leaks. Now, switch to synthetic which doesn't cook off, doesn't form sludge, and is great at cleaning away the old sludge... hello leak. Most of those leaks were above the oil pan - valve cover gaskets, timing covers, etc. Those who don't believe it will never be convinced, but I've seen it. So I'm the opposite.

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Mike
2005 Four Winns 230/240
VP 5.7GXi/DP
1998 F-150 XLT
Boat Pic

Agree with you 100%, Mike.
Oils have had sludge cleaning detergents in them for quite some time now and if you used a newer style oil (post API SF - 1980 grade from memory), you will run a higher risk of leakage.
Remember that newer oils turn black quickly because of their detergents suspending the carbon.

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2011 Four Winns H180 SS.
Aussie built Mustang 2800.
SOLD - 1997 Four Winns Horizon RS