Oil fouled plugs - What is the thickest oil I can run in a stock 67 200 six cylinder?

I have what I think are bad valve guides on my 67 Mustang with 200 six. The engine has about 20,000 on the rebuilt engine. I have had the car for many years so pretty good at fixing it but this one has me stumped.

I have done full tune up, compression test (good numbers) and rebuilt the carb. I also pulled the valve cover and confirmed the rubber seals are in good shape and not cracked and made sure PVC is functioning properly and not sucking up oil.

The car oil fouls #1 and #3 cylinders quickly like in about 30 miles of driving. Yikes! Will develop a miss and rough idle. Otherwise runs great with no smoke that I can see. I see no oil in the coolant or coolant in the oil so don't suspect head gasket. Wish it was as that would be a relatively easy fix.

Pretty much convinced at this point that my valve guides are shot / worn on those cylinders. Maybe not done right during the rebuild? I'm in the CA bay area were it doesn't get to hot or to cold. Can I run straight SAE 40 in my car without causing problems? Want to see if it will help and if it does it may further confirm that it is the guides. Could also be stuck oil rings I guess.

Having a hard time finding a mechanic in my area that will actually work on an old car believe it or not. Hate to pull the head but will try and budget for that.

I thought of one other thing to ad to this. While the engine is decelerating from higher speeds it will have some backfires in the mufflers. A pop, pop, pop sound and not one loud bang. From researching online it seems that on deceleration would be when oil would be sucked past bad valve guides?

Actually I'm probably using the wrong terminology -

I may need new valve rods that go into the guides to adjust when the valve opens and seats etc?

How'd Back:

Yes, you can safely use straight 40 weight oil. No problem.

Is this an auto trans rig? Vacuum modulator?

If the valve seals are there and working valve guides should not be the problem. Rings?

Keep it coming.

Adios,David

Thanks for the reply David. Definitely appreciate any help solving this problem.

The car is a 1967 Mustang convertible with no power brakes or steering and has a manual trans. I have sprayed carb cleaner around and looked for vacuum leaks but non to be found.

The valve seals look good. I actually took pics of them and posted on here a while back to confirm they looked ok. The car has less than 20k since a rebuild so not surprised the seals look good. I'm thinking my problem is related to the push rod that goes through the valve guide? I'm pretty sure the only way to adjust the valves is to change out the length of the push rods right?

I know oil is getting into the cylinder somehow. I should mention I have made sure there is no leaking from the valve cover. I cleaned the area above the plugs and it remains clean. I did a compression test last week and 185 to 190 on all cylinders.

Any other ideas how oil can get in and foul out plugs so quickly? Stumped. Has to be oil control rings, seals or guides right?

Attached are pics of oil fouled plug. It used to only foul out #3 but now #1 gets oils soaked and fouled also. The oil on the paper in the first pic I wiped off the threads.

install the vintron (spelling ?) non - umbrella stile seals (if so machined)?
Check our "Locally recommended mechanics & machinests" forum?

I have the stock type of valve seals that worked good for a long time so pretty sure they are correct for my car. I checked the recommended shops section but did not see any for my area. I'm in the Santa Cruz CA area. Thanks for the ideas though!

U Go, bra!

Reweb67,

I read your post with great interest as I am working on nearly the same problems! I combed this forum for clues (this my first post). Let's keep this thread going to document the answers.

My issue: rough idle and miss, slight backfire in the exhaust during deceleration. Oil-fouling plug in the #4 cylinder. However, not burning oil (that I can tell)

What I started with:

-65 Mustang 200, 128K miles
-Carb: Holley 1940 (1V)
-Trans: 3-sp manual
-All else: stock/original
-Rebuilt 20K miles (and 30 years) ago. Replaced rings but not valve guides (in good shape at the time)
-Compression: 180-190 all cylinders except #5 at 155 (but this is not the oil-fouling cylinder)
-Leak-down test: 5-10% through the rings (hear/feel air through oil fill opening)

Work done, so far:

-Rebuilt carb, check for leaks
-Replaced ignition (Pertronix), coil, plugs (gap 0.040), wires, distributor cap and rotor
-Tuned for max vacuum, advance; idle mixture
-Inspected valve seals, valve cover and rocker assembly for wear, damage, leaks (no major issue observed)

All this helped but not the full answer. Problems went from very annoying to slightly annoying.

Plans for next 2-3 yrs:

-Replace exhaust with headers and 2" line, muffler. There is a leak and suspect this contributes to the backfire
-Pull head and inspect/fix/upgrade valve train
-Replace carb (upgrade)
-If problem still exists, pull the block and replace rings (possibly cam, timing chain, and so on)

Did thicker oil help? I'm using 10W30. Good luck and keep posting!

Hi, since the compression is good I have a feeling the valve guides in a couple of cylinders are worn. If they were knurled when the head was done they may be too loose. Too bad the only way I know of to check the valve to guide clearence is to pull the head and remove the valves. The better way to repair the head is to drill out the guides and install new guides.
As for the oil I have been a Castrol GTX 10W 40 guy my whole life, except when I had an engine with oil pressure that would disappear at idle. That engine got 20W 50. Good luck

OP, What type of ignition system are you running? I'm going to go out on a limb and suggest you might have an ignition problem. Maybe bad wires on those cylinders. The fact that you are misfiring and ignition in the exhaust could be a couple fouled plugs b/c of guides or it could be fouled plugs b/c of faulty ignition. It's a chicken and egg thing. Always verify if bronze guides were installed if guides are worn and need attn on a rebuild. I find it hard to believe anyone is knurling guides at this point. The machinists I know take a lot of pride in what they do and don't like band aid type fixes unless it's discussed. They can charge more for installing new guides and no fall back down the line. For oil I'd recommend delo 15-40 diesel oil if you want to run thick oil. In the long run you are better off addressing the problem though, esp with a fairly fresh engine. You should be running 10-30w. Thicker oil will just wear things out faster on start up and pushing it around imo.

Cincinnati, I'd dbl check the pertronix set up and maybe swap coils, regap lower. I don't know what coil you are running but 35 gap is a safe bet and won't cause a misfire. Ensure that you are running full 12v to the pertronix. Doesn't hurt to run a new wire battery supplied to the ignition and thrown by a relay. That takes the ignition off of anything else that's running off the ignition switch. Outside of that when you do a valve job have it done well and bronze guides installed.

Even though the compression is good, I believe you need to pull the head & have another machine shop install new guides & seals.
In addition you need to pull the pistons & hone the cylinders for what type of rings you plan to use. For example cast rings will seat on any cylinder walls. If you go with plasma moly they require a 500 grit & a real plus would be to have the bores plasma honed to remove all the high areas.
If you do it right you will never have to pull it apart again.
Sure you can put 50W oil in it but that is a band aid fix.

CincinnatiRed":2oumh88x said:

Reweb67,

I read your post with great interest as I am working on nearly the same problems! I combed this forum for clues (this my first post). Let's keep this thread going to document the answers.

My issue: rough idle and miss, slight backfire in the exhaust during deceleration. Oil-fouling plug in the #4 cylinder. However, not burning oil (that I can tell)

What I started with:

-65 Mustang 200, 128K miles
-Carb: Holley 1940 (1V)
-Trans: 3-sp manual
-All else: stock/original
-Rebuilt 20K miles (and 30 years) ago. Replaced rings but not valve guides (in good shape at the time)
-Compression: 180-190 all cylinders except #5 at 155 (but this is not the oil-fouling cylinder)
-Leak-down test: 5-10% through the rings (hear/feel air through oil fill opening)

Work done, so far:

-Rebuilt carb, check for leaks
-Replaced ignition (Pertronix), coil, plugs (gap 0.040), wires, distributor cap and rotor
-Tuned for max vacuum, advance; idle mixture
-Inspected valve seals, valve cover and rocker assembly for wear, damage, leaks (no major issue observed)

All this helped but not the full answer. Problems went from very annoying to slightly annoying.

Plans for next 2-3 yrs:

-Replace exhaust with headers and 2" line, muffler. There is a leak and suspect this contributes to the backfire
-Pull head and inspect/fix/upgrade valve train
-Replace carb (upgrade)
-If problem still exists, pull the block and replace rings (possibly cam, timing chain, and so on)

Did thicker oil help? I'm using 10W30. Good luck and keep posting!

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Cincinnati Red - are you a fan or located in Cincinnati? I'm in Cincinnati myself.

Sorry I have not gotten back to you guys sooner.

I did change the oil to sae 30 and added STP oil treatment. Sadly no help.

I have figured out what I have is weak spark. At this point I do not think my plugs are oil fouling but they are carbon fouled from weak spark not burning off the gas. My plugs look exactly like the picture in the shop manual of a carbon fouled plug. When I pull the coil wire from the distributor cap and check the spark off the block it is yellow and pretty thin. Not fat and blue like it should be.

My car is an all stock ignition 200 six. I have replaced nearly every part associated with the ignition system (most multiple times) and can not get the spark to improve. Have confirmed battery and alternator are good. Cleaned all grounding points. Also spent a lot of time with my voltmeter checking wiring voltage etc. And I can't find anything that seems wrong. Temporarily ran wire directly from battery + to + of coil and spark off block remains weak.

Have spent a ridiculous amount of time with really no results. Love the car but this one has been pretty rough. Planning to buy and install a new distributor hoping that somehow that may be the issue? It and the ignition switch are all that I have not changed in the last few weeks. Both are only 6 or so years old.

reweb67":1x1ekmla said:

Sorry I have not gotten back to you guys sooner.

I did change the oil to sae 30 and added STP oil treatment. Sadly no help.

I have figured out what I have is weak spark. At this point I do not think my plugs are oil fouling but they are carbon fouled from weak spark not burning off the gas. My plugs look exactly like the picture in the shop manual of a carbon fouled plug. When I pull the coil wire from the distributor cap and check the spark off the block it is yellow and pretty thin. Not fat and blue like it should be.

My car is an all stock ignition 200 six. I have replaced nearly every part associated with the ignition system (most multiple times) and can not get the spark to improve. Have confirmed battery and alternator are good. Cleaned all grounding points. Also spent a lot of time with my voltmeter checking wiring voltage etc. And I can't find anything that seems wrong. Temporarily ran wire directly from battery + to + of coil and spark off block remains weak.

Have spent a ridiculous amount of time with really no results. Love the car but this one has been pretty rough. Planning to buy and install a new distributor hoping that somehow that may be the issue? It and the ignition switch are all that I have not changed in the last few weeks. Both are only 6 or so years old.

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the resistor wire from the ignition switch may have increased resistance with age...

Seth, thanks for the help. I'll try re-gapping #4 plug and check it this weekend. I've already run a separate lead and checked voltage.

Matthew68, yes, I'm in Cincinnati and a Reds fan and the car is red (and so was my hair at one point). So it all seems to fit.

OP, putting in Pertronix (including new coil, wires) was cheaper and easier than other options. It made a significant improvement, just not 100% there yet.

Hi, for reweb67, I would consider putting a pertronix 2 and pertronix flamethrower coil (hooked up to 12 volts) before just buying a new distributor. Many of the replacement tune up parts leave much to be desired. Any of your replacement parts could be adding to your weak spark issue. I think you said you are sure the polarity on the coil is correct. I would worry about imported points and condenser working properly. Good luck

What kind of valve cover do you have on your engine???
You need to make sure the power valve is free in its bore if you have a 1100 carb.
I would scrap the loadamatic carb & distributor & install a DS11 with a MSD6-AL & a MSD Blaster 2-3 coil with spiral wound plug wires. Or go with an HEI module or a HEI distributor. All of the above require a full 12V to the coil or distributor.
Your 1100 carb can be modified for another distributor. See our tech section of the forum.
You need to run an A/F test to see if your carb is pig rich??
The rich A/F mixture may have washed the cylinder walls.
The oil rings in those cylinders may be frozen in the ring lands of the pistons. Best of luck.

Thanks for the help.

The resistor wire from the ignition switch may have increased resistance with age. - Good tip but I did have to replace the resistance wire about 5 years ago. I have checked the voltage both hot and cold and seems to be correct at + side of coil.

What kind of valve cover do you have on your engine??? - I have the stock valve cover and baffle is in there properly. Also a good tip but I did check that.

I would consider putting a pertronix 2 and pertronix flamethrower coil (hooked up to 12 volts) before just buying a new distributor. Many of the replacement tune up parts leave much to be desired. - Good idea but I have had this car for about 17 years and have had it running great all stock so kinda stuck on getting it right as is. I know the new parts are junk but I have tried many different ones. They can't all be bad right? Or can they?

The oil rings in those cylinders may be frozen in the ring lands of the pistons. - Freakin hope not! But possible I'm sure

Even though the compression is good, I believe you need to pull the head & have another machine shop install new guides & seals. - Yikes! Hope to not go there.

I should mention that all of the plugs are getting fouled out. The others just take longer for some reason.

Basically I'm pretty sure I have weak spark and my carb is possibly flooding too.

Anybody know how much fuel should be in the bowl when you take the top off an autolite 1100?

I have 7/8 of an inch of fuel in there. Looks to be roughly half full. To much? Don't know. I have the float set properly, actually a little lower than spec. It is a plastic float if that makes any difference.

reweb67":3fwaducs said:

Thanks for the help.

The resistor wire from the ignition switch may have increased resistance with age. - Good tip but I did have to replace the resistance wire about 5 years ago. I have checked the voltage both hot and cold and seems to be correct at + side of coil.

What kind of valve cover do you have on your engine??? - I have the stock valve cover and baffle is in there properly. Also a good tip but I did check that.

I would consider putting a pertronix 2 and pertronix flamethrower coil (hooked up to 12 volts) before just buying a new distributor. Many of the replacement tune up parts leave much to be desired. - Good idea but I have had this car for about 17 years and have had it running great all stock so kinda stuck on getting it right as is. I know the new parts are junk but I have tried many different ones. They can't all be bad right? Or can they?

The oil rings in those cylinders may be frozen in the ring lands of the pistons. - Freakin hope not! But possible I'm sure

Even though the compression is good, I believe you need to pull the head & have another machine shop install new guides & seals. - Yikes! Hope to not go there.

Basically I'm pretty sure I have weak spark and my carb is possibly flooding too.

Anybody know how much fuel should be in the bowl when you take the top off an autolite 1100?

I have 7/8 of an inch of fuel in there. Looks to be roughly half full. To much? Don't know. I have the float set properly, actually a little lower than spec. It is a plastic float if that makes any difference.

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I agree that you have a weak spark! It dose sound like you might have enough of a wet fuel level in the float bowl. You can try unhooking the float and placing it in the fuel bowl and then remeasuring the fuel height again for a bit more accuracy. As for finding good ignistion parts NAPA has some of the very best in their Echlin line. Sadly many of the discount auto parts versions are not of very good quality and not worth even trying to use. Have you tested out or replace your ignistion switch yet? If it's not all worn out and sloppy so that's it's still in good usable condistion then you may still have poor engine grounding from an undersized or dirty, croded, high resistance, ground wire going to your engine. Good luck