Slant-6 and unleaded fuel

MoPar Man

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Jun 23, 2012, 7:22:07 PM6/23/12

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A friend of mine (who lives on a farm) bought a Massey Fergusen combine
that was made in 1974. This thing is powered by a Chrysler Slant-6 (225
cid) engine.

My first car (which was at the time a 20-year-old 1965 Dodge Polara) had
a slant-6 and I rebuilt it once or twice during the 10 years that it was
my daily driver.

I know that the theory was that leaded gas helped lubricate the valve
seats, and unless you did a valve job and had the valve seats hardened,
that the use of unleaded was supposed to wear out the valve seats on
these engines.

So I'm wondering if anyone knows if a 1974-vintage slant-6 could run on
unleaded gas (or what-ever passes for gasoline today).

I looked through the manual for this combine - and it says absolutely
nothing about the recommended gasoline - not even the octane.

I seem to recall that in the 1990's that you could get a can of additive
to throw into your tank to substitute for leaded gas - I have no idea if
that stuff is still available.

Joe Pfeiffer

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Jun 24, 2012, 1:11:50 AM6/24/12

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Don't worry about it. The valve seats will wear somewhat faster than
they would have, but you're still talking many tens of thousands of
miles (at least); wait until you're rebuilding the engine anyway to
replace the seats.

Bob Grimes

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Jun 24, 2012, 8:41:29 PM6/24/12

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I have a 41 Windsor, flathead "6", and the WPC has always said that
Chrysler used hardened valve seats from the '30s till today. Also, did't
Amoco sell "white gas"(unleaded) for years in the '30s on up?

Joe Pfeiffer

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Jun 25, 2012, 12:34:28 AM6/25/12

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I pretty consistently see the claim that Chrysler went to hardened seats
in the early 1970s...

Steve Stone

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Jun 25, 2012, 2:30:15 PM6/25/12

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My family had a couple of Dodge Darts with slant 6's from 1964 (190 CI
with pushbutton automatic) thru 1974 225 CI that could not get out of
its own way because of all the smog bolt ons. You should have no trouble
running a 1974 vintage slant six meant for automotive use on unleaded
gas. 1973 was the first year for catalytic convertors. You can't run
leaded gas with a convertor in the exhaust. (well you can but you will
kill it in short order.)

Steve

Bob Grimes

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Jun 27, 2012, 9:41:45 AM6/27/12

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Steve,
I hope you are speaking of the 74 Dart? My mother and grandfather both had
new 64 Dart GT's, with the 225/Slant Six, pushbutton auto/Torque-Flite, and
never had any, except PCV valves, emission equipment. My 70 Dart only had a
PCV valve also. These were OK cars.

Steve Stone

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Jun 29, 2012, 9:47:19 AM6/29/12

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Yes, the 1974 Dart had a catalytic convertor and took unleaded, and was
a slug compared to our 1970 225 slant 6 Dart, which had only a PCV
valve. It seemed to take them a few years to improve smog control.

MoPar Man

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Jun 29, 2012, 10:25:53 AM6/29/12

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Steve Stone wrote:

> Yes, the 1974 Dart had a catalytic convertor and took unleaded,

I can't find clear information on the web when US cars were supposed to
have catalytic convertors - I've seen some mention of 1975.

It's also not clear if 1974/75 was supposed to be the year in California
- with a possibly later date in other states.

Since the combine (and engine) in question is Canadian, it's quite
possible that cat-convertors weren't required in Canada until years
later than in the USA.

And given that this is a piece of farm equipment, there's no telling
when it was supposed to have a cat convertor in either the US or Canada.

Steve Stone

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Jun 29, 2012, 12:48:47 PM6/29/12

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> Since the combine (and engine) in question is Canadian, it's quite
> possible that cat-convertors weren't required in Canada until years
> later than in the USA.
>
> And given that this is a piece of farm equipment, there's no telling
> when it was supposed to have a cat convertor in either the US or Canada.
>

I agree, all very true.