I have been using Pennzoil High Mileage 5w-30/10w-30 in my 1991 3.0 for as long as I can remember. My truck doesn't leak oil at all. It gets a little wet around the valve covers when I used 5w-30 but I when I switched to 10w-30 it stopped. I've been thinking about switching to Mobile 1 high mileage 10w-30 but it is a full synthetic oil, so I would like to switch to using it. My question is will it cause leaks from being synthetic? And can I switch back to the pennzoil afterwards?

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1991 Ranger 3.0 5-Speed

I wouldn't recommend running a synthetic in your truck. That would be for like the first 5-10 thousand miles you put on your motor.

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*1992 XTRA CAB RANGER
*2WD
*4.0 5SPEED

Yeah you should stick with pennzoil, any minor leaks you may have now will just get worse. Besides pennzoil high mileage is great stuff and keeps your internals very clean.

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2011 Ford Ranger Sport
4.0L V6 2WD 4 Door
Silver Metallic

I agree with everything. It doesn't have any leaks except just that little on the valve cover when I run a lighter weight like 5w-30. When I run 10w-30 it for leak at all. I thought it doesn't make since to really make a high Mileage synthetic oil if high mileage cars are prone to leaks.

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1991 Ranger 3.0 5-Speed

Just get castrol synthetic blend. Good stuff.

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2010 Ranger XL Reg. Cab 4 cyl... 5 speed manual... W/reverse.

Mods: 5% tint on rear window, JVC KDHDR40 Headunit, Kicker KS-68 speakers, Kicker TCVT102 (10TCVT102) Sub, JVC DRVN KSAX3102 Amp, JVC DRVN KSAX3101D mono amp, Ford black rubber mat, White LED license plate lights. Added 6000k HID Fogs, 6000k Digital HID Heads.

This isn't gramhar skool so dont cry and whine about spelling.