Switching to full synthetic on a semi-old car

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1,451
Location
Dallas Texas Area
I had a 09 police vic same 4.6 V8

I would run Mobil 1 truck/SUV 5W20. I did a OCI using M1 truck/Suv right before I sold it and the cars performance improved A LOT running that oil


Dave
 
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29
Location
Detroit, MI
Hi, everyone. I recently purchased a 2007 Mercury Grand Marquis with the 4.6L V8 Triton/Modular engine. The car, as it sits right now, has 61,000 miles on it. To my knowledge, the car has only had dino oil ran in it all of these years. I've heard about switching to full synthetic on an older car can cause leaks around older gaskets. The car is completely dry underneath it, right now. No oil pan/valve cover seepage or signs of rear main leaking. Can I switch over to full synthetic on this car without worrying? I've been thinking about running a synthetic blend oil to try to slowly "break it in" for synthetic, so to speak. I don't know if that would make any difference. What do you guys think? TIA! :)
The OP has a older car which has been serviced with conventional oil all its life as far as we know, and has no oil leaks. The engine is relatively 'young' in mileage terms but the seals are surely as old as the car. The car is in warm climate and does not likely see cold winter and the engine is known to be easy on oil.
I think the main concern of OP is whether switching to synthetic could cause an oil leak? I don't think anyone here can predict that. More than likely switching to synthetic would not cause any issues. But if it causes a leak, then switching back to conventional may or may not stop it.

As a personal anecdote, I changed from conventional to synthetic on my 13 yr old 'completely dry' van 5 yrs ago. Oil leak started soon thereafter. Switched back soon conventional after that. Leak has slowed but still continues.

So with the known history, current application and climate, I personally would be inclined to just continue with what has worked so far. If the modern day conventional oil (is is really a blend for the last few years) is working fine and the engine is accustomed to it, I would just stay with it. Maybe reduce the OCI to 3000 miles if that makes him feel better. I don't see any pressing 'need' to change to synthetic.
 
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4,559
Location
Decatur AL USA
The OP has a older car which has been serviced with conventional oil all its life as far as we know, and has no oil leaks. The engine is relatively 'young' in mileage terms but the seals are surely as old as the car. The car is in warm climate and does not likely see cold winter and the engine is known to be easy on oil.
I think the main concern of OP is whether switching to synthetic could cause an oil leak? I don't think anyone here can predict that. More than likely switching to synthetic would not cause any issues. But if it causes a leak, then switching back to conventional may or may not stop it.

As a personal anecdote, I changed from conventional to synthetic on my 13 yr old 'completely dry' van 5 yrs ago. Oil leak started soon thereafter. Switched back soon conventional after that. Leak has slowed but still continues.

So with the known history, current application and climate, I personally would be inclined to just continue with what has worked so far. If the modern day conventional oil (is is really a blend for the last few years) is working fine and the engine is accustomed to it, I would just stay with it. Maybe reduce the OCI to 3000 miles if that makes him feel better. I don't see any pressing 'need' to change to synthetic.

Having been around a lot of 4.6 with their Teflon Main Seals I'm just not overly concerned that s switch from 60/40 GII/GIII oil like MC Blend or the PYB that might be 80/20 GII+/GIII+ to a straight GIII oil is going to make a difference. With synthetics less than a $1 a quart difference it's hard for me to justify the shorter OCI for a conventional/blend in today's market.

It's been pretty obvious that at times SOPUS has been dumping excess GIII+ GTL production into PYB so it's likely this car has had a pretty heavy dose of "Synthetic" at times.
 
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