Hello all,

I am just about at my wit's end; after six pretty solid years of service, for the past year, my '71 225 Slant Six has been plagued by a mystery issue(s) I can't seem to solve. To top it all off, it seems to be getting worse after the most recent fix instead of better, with billowing plumes of whitish smoke and some spit coming out of the tailpipe.

To catch up on what's been happening so far:

1. Last October I took it to a rad shop for a re-core, new thermostat and an A/C leak fix; on the drive back home, the car began stalling when it got down to idle
2. We tried a bunch of small fixes in the electrical vein, including a new distributor rotor and cap, coil, new wires, and new PCV valves and oil breather
3. At some point we realized part of the problem was it was fouling the spark plugs – black, dry – so we swapped in a set of NGK UR5GPs and tightened down the valve cover; we'd replaced that gasket in the summer, and must not have tightened it properly and oil was getting everywhere
4. The fix works briefly before it goes back to stalling at idle again and not even starting; vacuum readings are abysmal
5. An expert friend replaces the vacuum line from the distributor and adjusts the carb and timing; I replace the plugs with gapped NFK ZF5RNs with the crush washer removed—it's still fouling the plugs
6. I take it to a shop, and they find the diaphragm in the vacuum advance has busted and needs replacement; and that the A/C compressor had been over-charged by about two times, adding significant draw on the A/C belt, likely enough resistance to stall it at idle—they fix both issues, but it's still fouling plugs
7. I try to drive it to a carburetor expert in case it's running rich, but stall en route and just take it to the same nearby shop that fixed the last issues
8. I decide my cracked exhaust manifold can't be helping, so the shop replaces the intake manifold with a junkyard unit I'd had cleaned up and powdercoated; and an exhaust manifold they'd sourced
9. The car runs great—for 15 minutes, and then starts emitting an incredible amount of white smoke and some kind of droplets of something from the tailpipe, and gradually also fouls the plugs, a new set of NFK ZF5RNs with the washers cut

I looked at it today, saw the incredible amount of smoke myself; the shop figures it's head-gasket-related, but also notes the oil and coolant don't seem to be mixing. We agreed they'd try a pressure-test of the coolant system (to 9 lbs—is that correct?) to see if it shows a leak.

So I guess my question is:
a) What could be causing excessive white smoke besides coolant, or how could swapping the manifolds cause a coolant leak?
b) After all of those fixes, what could still be fouling the plugs? Could it still just be a rich mixture?

Sorry if some of these questions are dumb, if I've messed up some terminology or if I'm missing something obvious; despite having had this car for a while, I still feel a novice mechanically, and am very, very tired as I'm writing this.

Any help anyone can provide is much appreciated; thanks in advance!

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"We put a Dodge in our garage!" —old lady in older Dodge ad

Proud 1971 Plymouth Scamp owner

Nothing. It's burning coolant. Almost certainly head gasket. Depending on the size of the leak, you can also tend to get enough exhaust in the cooling system to create overheat/boilover types of symptoms.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I wonder if they original shop put the thermostat in wrong and it overheated, causing a toasted head gasket or maybe cracked head or block. Have your shop do the pressure test. So, you see no whiteness on any of the plugs?

Hmmm,
Lou

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Home of Slant6-powered fun machines since 1988

I'm wondering if there might be a coolant leak into the exhaust manifold from a intake/exhaust stud, since you mentioned the manifolds were changed. I have seen this in the past, if a stud was removed and replaced without sealant. Usually the upper rear stud.
Of course this has nothing to do with the sooted plugs.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

Yeah, if you're fuel-foulling your spark plugs, that's a rich mixture condition, a separate issue.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

You stated that the vacuum reading was abysmal. Has timing chain stretch been checked? In my experience, a timing chain with enough stretch causes what appears to be a rich condition.

If the plugs are black but you are getting copious amounts of steam out the back, I would agree there's coolant being pushed into the exhaust manifold from the swap.

~THOR~

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1984 D100 Shorty Custom
Certified Auto Appraiser - RevItUp Classic Appraisals
President - Cherry City Bombers CC
Part of Tyrde-Browne Racing

I agree, you have a pathway between the combustion chamber and water passage. Probably a head gasket but could be other things. Me? I'd be thankful that I had been given an opportunity to rebuild the entire engine....

Maybe do a valve lash adjustment (can cause rich condition and stalling, and is easy/cheap to fix) and look for an intake/exh stud leaking (as Charlie said) before going deep into the engine.

Lou

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Home of Slant6-powered fun machines since 1988

That makes sense, and I do believe they mentioned replacing the studs. Will ask them to look at this first before pulling the head off. I like that hypothesis better than head gasket, since it just seems weird to me the head gasket/head itself would have gone from perfectly fine to billowing clouds in a snap, when the only change was the manifolds. Of course, I understand a hypothesis isn't more or less true just because I like it—

Dan, definitely think the fouling – which seems to be the ongoing issue, well before the white smoke – is a separate issue from this new one. Hopefully just rich mixture, but we'll see once I can get it to a carb guy.

THOR, the vacuum issue thankfully went away after the diaphragm fix and other associated repairs, now reading a healthy 20 inches, they tell me. When I had it in my garage, I was seeing lower than 10 at times—

Thanks for the help, guys, will keep you posted on what I find out!

_________________
"We put a Dodge in our garage!" —old lady in older Dodge ad

Proud 1971 Plymouth Scamp owner

Tight valve lash will cause stalling and rich mixture, so I would try that before you do any carb work.

Best,
Lou

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Home of Slant6-powered fun machines since 1988

Wanted to thank everyone who chimed in with advice. I thought you all deserved an update: I ended up taking it to a professional who – I now know correctly – surmised the engine is, after 110,000 miles, essentially just very tired, specifically tired of eating unleaded fuel and low-zinc oil.

I also thought some of you might be happy to hear I am, as a result, putting the Six through a complete top-flight engine rebuild!

Met with the blueprinter yesterday to do some disassembly; we came across issues like (and forgive me if I bungle some terminology, here, my engine expertise is a little rudimentary) worn valves/valve stems shimmying in their guides; oil pooling on the back side of the valves through the guides; eccentric, excessive wear on the fuel pump lobe on the camshaft; concave surfaces on the valve lifters; a very slack timing chain; hard ridges in the top of the cylinder; completely glazed cylinder walls; and a cracked top piston ring with a chunk missing (on #2 cylinder; we only did the one while I was there).

The engine will be getting a no-expense-barred as-close-to-factory-spec-as-possible rebuild with the goal of keeping it original-appearing. To make it extra-difficult, we've even decided to keep the engine patina. The crew I've hired is accustomed to refreshing survivor (mostly Hemi and AAR or T/A) cars, so enjoys a challenge like this. Suffice it to say, at the end of the day, the cost of the rebuild will be roughly that of some complete Slant Six cars But I am a loon, love my car and plan to drive it 50 years on top of the 50 it's already been through, so I figure it's earned it.

I plan to put together an article chronicling the rebuild when it's all done, and will be sure to share it here once it's written.

Thanks again, all, for your help and support! It's much appreciated.

_________________
"We put a Dodge in our garage!" —old lady in older Dodge ad

Proud 1971 Plymouth Scamp owner

Awesome!! Keep us updated!

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Rob

I’m Mater
The Kentucky Poser

Update: just got the car back Sunday following the rebuild that started Hallowe'en! The engine is running smooth and strong, but, at extra cost, I kept the original paint, patina and engine markings on it, so it looks just like it did before. The rebuild I commissioned went generally pretty smoothly, and I opted to swap in a new exhaust pipe at the same time, too, besides a new uncracked exhaust manifold.

The only big catches were the carburetor, even after a rebuild of its own, wasn't delivering fuel properly; and the distributor (someone had added an electronic ignition system at some point) wasn't taking any timing, so they replaced both pieces with equivalents from a '69 Satellite's six while we bench-test the originals.

The A904 trans may need some adjustment, I think, just because it offers some resistance at low idle when, for example, making lefts at stop signs. But I guess that's part of the break-in process, seeing what little tweaks still need to be adjusted!

I hope to get started on the article detailing the process soon, but the car is driving finally! Thanks so much for your help, everyone!

_________________
"We put a Dodge in our garage!" —old lady in older Dodge ad

Proud 1971 Plymouth Scamp owner

Great to hear. Enjoy the drive...

Lou

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Home of Slant6-powered fun machines since 1988

Hello all,

Want to thank you all again so much for your help; it was much appreciated.

The article on the rebuild went live yesterday, and runs down part of the litany of problems the engine was dealing with.

https://driving.ca/plymouth/features/fe ... ooking-old

So satisfied with how it starts, idles and drives now, it's like a whole different engine. Cheers!

_________________
"We put a Dodge in our garage!" —old lady in older Dodge ad

Proud 1971 Plymouth Scamp owner