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Probe SE Member
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15 Posts
Discussion Starter #1
i recently (last oil change) switched oil from regular castrol GTX to castrol syntec blend. i've heard from a few people that its not good to switch to synthetic on an engine that has a lot of miles with regular oil. (mine has 94,000) now i've noticed leaking around some of the gaskets. is it too late to switch back, or have i just screwed everything up?
 

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PT Owner - SCPOC Prez
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681 Posts
don't sweat it.

i switched to synth when my car had nearly 80k miles and i haven't had any problems aside from the normal change of the valve cover gaskets. other than that, which i needed anyway, there haven't been any problems.

i would recommend using mobil 1 5w-30. castrol synthetic is not synthetic, just highly refined petroleum.
 

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Big Daddy
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357 Posts
Yep.. my car had about 71,000 on it whne i changed over to sythn.. i also recomend 5W-30 is what i'm running Mobile one.. i had the problem with my VCG's before the switch.. so i needed it anyways..
 

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Mod/SCPOC/Probe LX Member
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276 Posts
im running 10w30 synthetic blend on an engine with 152,000 miles and it runs great.

shouldnt leak because its synthetic. did you use a lower viscosity?
 

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Probe SE Member
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15 Posts
Discussion Starter #5
i'm using the same viscosity as my old oil. my valve cover gaskets leaked a little bit before, but seems to have gotten worse since i switched oil.
 

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Crazed Wodka Drinker
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67 Posts
Which is normal. The VCG's are a day's job for an inexperienced mech. Do it and go full synthetic. I use Mobil1 5w-30 with a Motorcraft filter and the motor purrs like a kitten at 79k and counting. I first changed over at 67k. And just did the VCGs 'cos we had the IM off anyway for some other stuff.
 

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Registered
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9 Posts
I have less than 70K on a 95PGT and switched from castrol syntec 5W-30 to complete synthetic 5W-30. No problems or leaks at first, after about 2K I started noticing I was burning oil, somehow. It was not leaking out anywhere. So I went back to part synthetic with no problems.
 

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Honda Who?
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56 Posts
I think whoever told you that is toking on something. Synthetic oil conditions seals that are old and worn. It is also easier on the engine that way. dont use a higher viscosity though b/c our HLA's dont' like it too well. I use 5-30 in mine Mobil 1 full synthetic. I go through about 1.5 quarts per 5000 miles. But I have a oil leak in my 2nd cylinder due to the bad VCG.
Switch to synthetic and enjoy a longer living engine.
 

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Honda Who?
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56 Posts
BTW: my car has 138000 miles on it and I use it. Been using it since my car hit 100k.
 

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Crazed Wodka Drinker
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67 Posts
Use the Mazda filter! Best one yet that I've seen after experimenting with a lot of them
 

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Registered
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6 Posts
I have heard that on high mileage cars Synthetic will leak through old gaskets.

I used to have a suzuki sidekick, and it started leaking when I switched.
I went back to good ol' castrol organic.
 

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Registered
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9 Posts
I totally agree with you, read my post above...........
 
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