Recommendation for a high mileage engine

Joined
Apr 5, 2020
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CA
So I've been looking through a the forums and haven't really found a clear answer. I have a 1985 Toyota Celica Supra with 240k miles never rebuilt still running fine with minor oil leaks. I'm planning to do my first oil change since I bought it and am not sure what type of oil the previous owner used. I've had a few people tell me to be sure to use an oil with zddp added. After doing some research it sounds like I should be using a high mileage version of oil. But most of the high mileage oils seem to be synthetic? I though switching to synthetic in such an old engine would cause more leaks? I'm thinking of M1 high mileage, Valvoline MaxLife or maybe Royal Purple HMX? The only concern I have is that these are all full synthetic. My question is what oil would you guys recommend thats for high mileage engines with zddp added? 10w-40 range.
 
Joined
Sep 27, 2015
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Alabama
Different answers all the way around lol Op, use which ever of those oils you want. They will all do the job.
 
Joined
Aug 1, 2017
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WA
I would use conventional 10W40 and change it more often. May also try syn-blend and see how it does. In CA, I would stick with 10Wx. Could also try 10W30. I haven't had a good luck with full syn or even syn-blend in old cars. Maybe just a coincidence ... idk
 
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Oct 22, 2009
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Wet side WA
I would try some Valvoline Maxlife that's what I'm using in my stepdaughters 94 Mazda with 265K miles on it.
 
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Joined
Feb 12, 2008
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PA
Just use a HM conventional. From personal experience synthetics will exacerbate a leak. Especially a RMS leak. Have had it happen on several SBCs and 4.0 I6s with high miles and minor leaks .
 
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Jul 14, 2020
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What kind of bad luck with synthetic?
I would use conventional 10W40 and change it more often. May also try syn-blend and see how it does. In CA, I would stick with 10Wx. Could also try 10W30. I haven't had a good luck with full syn or even syn-blend in old cars. Maybe just a coincidence ... idk
I have switched every vehicle I've owned to synthetic and never noticed a difference (positive or negative). Vehicles included 87 Oldsmobile (110k-200k), 86 Caprice (130k-150k), 87 Caprice (120k-170k), 83 Delta 88 (1 winter - can't remember mileage), 89 caprice (291k-332k miles), 83 Caprice (160-240k miles), 76 350 Olds (from junkyard unknown miles put 110k miles on it in 14 years). No issues with synthetic or difference between conventional on any of them. These don't include my ex girlfriends vehicles (94 grand Prix, 99 grand am with 240k, 99 Lumina.
 
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