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Old 08-13-2012, 09:12 PM   #1
cork1958
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Mid grade gas in 1966 Plymouth

Just bought a 1966 Plymouth Satelite that obviously is supposed to use regular LEADED gas.

Talking with my mechanic, he says you can use mid grade unleaded gas and NOT have to use the additive that is usually necessary.

Anybody know if that is true and has done such a thing?

Thank you

Last edited by cork1958; 08-13-2012 at 09:50 PM.
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Old 11-05-2012, 04:24 PM   #2
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Re: Mid grade gas in 1966 Plymouth

cork1958, I always use Marvel Mystery Oil in my old vehicles. So far so good.
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Old 11-05-2012, 07:07 PM   #3
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Re: Mid grade gas in 1966 Plymouth

89 octane has nothing to do with substituting lead additive, it only refers to octane, if the car is driven for short trips at moderate speeds you should be ok with no additive or Marvel, push it over longer distances I would use the prescribed synthetic lead additive, of course if this a 383 or other 10:1 compression engine from the day, 89 may not do it.
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Old 11-05-2012, 11:53 PM   #4
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Re: Mid grade gas in 1966 Plymouth

I use a lead additive with an octane booster in it, with my old junk. Lead replacements are cheap, new valve seats are not. Use the lead additive.

As for the fuel..... if you have an ear for detonation, listen for ping when using regular. If no ping, you should be fine. Otherwise, there's no harm in using mid-grade, to be safe.
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Old 11-07-2012, 09:25 AM   #5
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Re: Mid grade gas in 1966 Plymouth

Car has goof ball 361ci (5.9L)

I didn't think octane had much to do with it and HAVE been using Gunk lead additive since getting the car. Man, that crap isn't cheap!!

Forget exact compression but I think it's 9:1 or maybe 8:1, but doubtful.

Since adjusting timing and carb, there is no ping or hesitation or anything. Runs smooth as silk.

Sticking with adding Gunk and using 87 octane.

Hopefully, can either find a set of heads or during the winter, get my heads/valve seats done, so I can quit adding that Gunk junk!
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Old 11-18-2012, 10:44 PM   #6
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Re: Mid grade gas in 1966 Plymouth

Plymouths and other Mopars have always had hardened valve seats. This is one area that wears without the protection of lead. The only additive I use in my old Plymouths is Zinc and even that may not be needed but sinces it is realitively cheap, I use it as insurance. I belong to a Plymouth Owners Club and no one I know adds Lead Substitute to their cars. And no one has lost any valve performace either.
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Old 11-19-2012, 06:50 AM   #7
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Re: Mid grade gas in 1966 Plymouth

Quote:
Originally Posted by plymouthcranbrook View Post
Plymouths and other Mopars have always had hardened valve seats. This is one area that wears without the protection of lead. The only additive I use in my old Plymouths is Zinc and even that may not be needed but sinces it is realitively cheap, I use it as insurance. I belong to a Plymouth Owners Club and no one I know adds Lead Substitute to their cars. And no one has lost any valve performace either.
Don't know about that Plymouth Owners Club you belong to, but I will say this. Don't have a clue as to what you guys are smoking but you are nuttier than a fruit cake, if you think ALL Mopars have hardened valve seats. Nothing from 1970 and back, has them, as unleaded fuel wasn't even around yet, so NONE of them needed hardened valve seats!

I know several people in Mopar clubs from around this area, and not a single one of them will agree with you. The zinc additive you use is doing absolutley nothing, as far as anyone I asked about it.

Sure you can drive a car without hardened valve seats, or without adding a lead substitute, for up to around 30,000 miles, as ANY search will tell you, but after that, it WILL BE time to start looking at getting a valve job done.

Thanks for your reply, but I am totally disregarding that one!!
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Old 11-19-2012, 10:11 AM   #8
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Re: Mid grade gas in 1966 Plymouth

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Originally Posted by cork1958 View Post
Don't know about that Plymouth Owners Club you belong to, but I will say this. Don't have a clue as to what you guys are smoking but you are nuttier than a fruit cake, if you think ALL Mopars have hardened valve seats. Nothing from 1970 and back, has them, as unleaded fuel wasn't even around yet, so NONE of them needed hardened valve seats!

I know several people in Mopar clubs from around this area, and not a single one of them will agree with you. The zinc additive you use is doing absolutley nothing, as far as anyone I asked about it.

Sure you can drive a car without hardened valve seats, or without adding a lead substitute, for up to around 30,000 miles, as ANY search will tell you, but after that, it WILL BE time to start looking at getting a valve job done.

Thanks for your reply, but I am totally disregarding that one!!
Cork, if you disagree with cranbrook, do so, but don't call him nutty. Thats not in keeping with the friendly spirit of cooperation we have around here at AF.

I have never heard of Plymouths always having hardened valve seats before 1971. They might, but just in case they don't, use the lead substitute.

I will say that the Plymouth Cranbrook had the old Chrysler flathead six, which had lower compression, lower valve spring rates and lower revs than an OHV V8. I am sure a flathead six, driven occasionally will last many years without valve trouble. But an OHV 361 has higher reves and stiffer valve springs and subsequent increased stress on the valve seats. So, use the additive imo.
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Old 11-19-2012, 11:13 AM   #9
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Re: Mid grade gas in 1966 Plymouth

The 331 Chrysler Hemi had hardened exhaust seats, if you have a parts book for the cars in question you will see replacement valve seats, exhaust only, which are steel not cast. Every engine design and varying driving habits will dictate whether one would get away with no lead, combustion temps being the big issue here.
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Old 11-20-2012, 05:47 AM   #10
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Re: Mid grade gas in 1966 Plymouth

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Cork, if you disagree with cranbrook, do so, but don't call him nutty. Thats not in keeping with the friendly spirit of cooperation we have around here at AF.

I have never heard of Plymouths always having hardened valve seats before 1971. They might, but just in case they don't, use the lead substitute.

I will say that the Plymouth Cranbrook had the old Chrysler flathead six, which had lower compression, lower valve spring rates and lower revs than an OHV V8. I am sure a flathead six, driven occasionally will last many years without valve trouble. But an OHV 361 has higher reves and stiffer valve springs and subsequent increased stress on the valve seats. So, use the additive imo.
Sorry about the nuttier than a fruit cake comment and DID NOT mean it in any way as an insult, but more of a totally astonished comment! I have NEVER heard anyone say anything even remotely close to that line of bull though and I would suggest that plymouthcranbrook check his car and the facts, before driving his vehicle much more and relying on the other members of that club he belongs to.

I am now considering this topic closed and will not reply to it again. Besides, the info I've received from the other 2 Mopar forums I've joined is much better, with much faster replies and definitely more accurate replies!! In fact, I had forgotten I had even joined this forum until I received the automatic e-mail for having subscribed to this topic. I mean, crap, it took almost 3 months to get the first reply!! Sheesh!!
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Old 11-20-2012, 09:36 PM   #11
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Re: Mid grade gas in 1966 Plymouth

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Originally Posted by cork1958 View Post
Sorry about the nuttier than a fruit cake comment and DID NOT mean it in any way as an insult, but more of a totally astonished comment! I have NEVER heard anyone say anything even remotely close to that line of bull though and I would suggest that plymouthcranbrook check his car and the facts, before driving his vehicle much more and relying on the other members of that club he belongs to.

I am now considering this topic closed and will not reply to it again. Besides, the info I've received from the other 2 Mopar forums I've joined is much better, with much faster replies and definitely more accurate replies!! In fact, I had forgotten I had even joined this forum until I received the automatic e-mail for having subscribed to this topic. I mean, crap, it took almost 3 months to get the first reply!! Sheesh!!
Thank you for the follow up. This forum is a 'general purpose' forum for auto enthusiasts. I like this place because I am interested in just about all automotive brands and everything automotive.
Special purpose forums, like the Mopar one are fine and perhaps more helpful, if your interests really are that narrow. AF's beauty is its broad, diversified nature, something which no Mopar forum could ever be.

Hope to see you here again soon
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Old 05-14-2013, 09:35 PM   #12
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Re: Mid grade gas in 1966 Plymouth

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Originally Posted by Kathter View Post
your mechanic is right, i just did so.
I know you can and not harm anything doing it occasionally and most searches will tell you that you can get away it for around 30,000 miles, as did most of the guys in the hot rod club around here.

My concern was the fact I had no clue how many of those 30,000 miles had already been used up even though the guy I got car from and who had it for the last 15 years, used it regularly. That's still almost 30 years I don't know how it was driven before.

Does not matter any more as have had a complete head job done over the winter and even replaced cam with a slightly upgraded one and threw in a new timing chain and fuel pump. Have also converted front drum brakes over to disc brakes.

Car is set to cruise!!
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