Rings or head gasket ?

7ponies

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Hey folks new to this forum and need some advice on next steps. Back in Jan , I bought a 05 mineral grey GT and drove it from Pittsburgh to Philly where I live. Car had a few owners but only 53 k miles. The seller seemed like a trustworthy guy, but since then I'm convinced this private pilot was a lying s.o.s. knew there was an issue and lied about health of the motor. Incidentally the car ran pretty good for stock. Regardless karma usually catches up with people like that. Once home the next day I checked the oil and it was down almost 1/2 quart , so I figured I misread the level the day before since it's only about 320 miles. So I changed the oil and within a week or or so lost a quart, no leaks no bad smoke out the exhaust that I could see. Another week and I picked up a misfire on #6, started poking around and found a new coil pack on 6 and decided to pull the plug, which was badly coked up. Pulled the rest of the plugs and did a compression check. All are around 190-210 except 6 which was at 55-65 psi. Added teaspoon of oil no big change. Rotated the motor until all three valves were closed put some air pressure in the cylinder and really couldn't hear any leaks out the exhaust or through the intake. I'm thinking bad rings or maybe hopefully a head gasket? do theses motors have an oil passage to the cam followers between the cylinders? Btw have not seen any oil in the coolant...thoughts ? thnx for any ideas.
 

86GT351

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Welcome. The proper way besides listening for air is to do or have a leak down test done to see the percentage of drop in that cylinder. If you put some oil in and saw no improvement, it is probably NOT rings.
 
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To be honest it very much sounds like a ring, if there is no oil in coolant and none on the ground considering the compression, where else would it go except being burned off passed the ring. Hole in the piston also can explain a lot of things, but thats too severe, never seen one in person
 

GlassTop09

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Hi 7ponies,
Question I have is how did you determine that all 3 valves were closed on #6 cyl w\ piston up at TDC? Did you have B2 valve cover pulled so you can definitively determine this (you did not mention anything about this)? Now if you did have B2 valve cover removed to verify this then Ok, but if you haven't done this then I would highly recommend that you pull B2 valve cover & verify all valve train components on B2 are OK before coming to a final analysis as I agree w\ 86GT351's analysis concerning the rings......this looks more like the head is more suspect & since you're not seeing oil in coolant I'll also assume that you're not loosing coolant AND not over pressuring the coolant system which makes the head even more suspect.

Hope this helps & welcome to the forums.
 

7ponies

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Gents thnx for the discussion.
@Andrey I'm thinking a hole in a piston would give 0 psi on the compression check?
@GlassTop09, yes valve cover pulled on drivers side, 3x lobes are somewhere on base circle although not sure #6 was at TDC , not sure it would matter either. If piston is mid-stroke and valves are closed air leak through valves would still be evident if valve are closed but faulty , just takes more air to fill the cylinder. Before doing leak down will probably check results where piston is now then take it to TDC and check again, that way if bottom of cylinder is scored i should have different readings. The assumption here is if car has 53 k , and a) plugs weren't pulled until recently and b) #6 plug broke possible bits went in, c) motor was run and d) cylinder wall scored? Wouldn't scored cylinder wall give the same compression results as bad rings except adding teaspoon of oil wouldn't make a difference? As for coolant just checked- level is ok, no way of checking over pressurization at this point. Also I eyeballed valve train component looked ok , cam looks pretty good too . If I pull the head ( likely next step) I'll also pick up the valvetrain kit from AM and replace followers, lash adjusters and seals.
 

redfirepearlgt

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You obviously have an issue with 6. Just for purpose of knowing, when a compression test is performed on a 4.6L-3V the highest and lowest pressure reading of all 8 cylinders cannot greater than 75%. IOW - If you read 200 psi on the strongest cylinder, the weakest cylinder can read no less than 150psi according to the Ford Shop manual pg 303-00-7. The chart Ford provides gives a range from 134psi (101 being the minimum) to as high as 250 psi (187 the min). Consistency is apparently the more important concern than a minimum pressure overall.

Rerun the test on cyl 6 after placing a teaspoon of oil in the piston. The manual says that if the compression on that cylinder improves over the dry value it is ring related. If it stays at or near the same value it is valve related...sticking or not seating.

This is straight from the 12/2004 edition of the 2005 Mustang Ford shop manual.
 

GlassTop09

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Gents thnx for the discussion.
@Andrey I'm thinking a hole in a piston would give 0 psi on the compression check?
@GlassTop09, yes valve cover pulled on drivers side, 3x lobes are somewhere on base circle although not sure #6 was at TDC , not sure it would matter either. If piston is mid-stroke and valves are closed air leak through valves would still be evident if valve are closed but faulty , just takes more air to fill the cylinder. Before doing leak down will probably check results where piston is now then take it to TDC and check again, that way if bottom of cylinder is scored i should have different readings. The assumption here is if car has 53 k , and a) plugs weren't pulled until recently and b) #6 plug broke possible bits went in, c) motor was run and d) cylinder wall scored? Wouldn't scored cylinder wall give the same compression results as bad rings except adding teaspoon of oil wouldn't make a difference? As for coolant just checked- level is ok, no way of checking over pressurization at this point. Also I eyeballed valve train component looked ok , cam looks pretty good too . If I pull the head ( likely next step) I'll also pick up the valvetrain kit from AM and replace followers, lash adjusters and seals.
Ok, good deal you physically checked valve train to verify valve position & verify upper valve train wasn't suspect.
As 86GT351 posted, this is why doing a full cyl leakdown test w\ leakdown test manifold will give much better indication than just using pressurized air alone.

If you don't have 1 then you gotta go w\ what you have, but you also could perform same air test on adjacent B2 cyls to #6 cyl & compare results to #6 for further analysis.

In my experiences, for piston\rings to lose that much compression they have to be really bad (broken) thus IMHO would've shown up much earlier in CKP sensor variation on #6 cyl which should've been felt thru engine balancing during rotation (cyl acting like a dead miss scenario) thus should've shown up in #6 cyl misfire last counts as a very high count number vs the rest. The lack of compression response from adding oil to cyl gives this much worse indication of broke rings\popped piston ring land but also gives indication of bad valve sealing in head, especially exhaust side (H\X pipes make exhaust valve leaks much harder to hear distinctly due to exhaust air going into both sides of exhaust thru midpipe).

Just got a thought, do you have a smoke leak detector on hand? If so, you can use it to send smoke into #6 cyl then see where it comes out instead of listening for it........

Hope this helps.
 

7ponies

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Ok then , just dug out the leak down tester from the bottom of the tool chest ( long time since I used it) . Quick check show 35 % leakage or per the gauge on the edge of "low " almost "moderate". Also listening- the hissing is coming through the dipstick tube and oil fill neck i.e. crankcase not intake or tailpipe .Recall I'm chasing a oil fouled plug on #6 , bad compression on same cylinder so it's not valves or valve seals. Oil in the cylinder didn't change the compression test , which I'm convincing myself only works if you have worn rings not broken rings. Also I'm trying to see if this in any way can still be the head gasket ? Does anyone know for sure if there are oil passages in the gasket between the cylinders for the top end valvetrain? Anyone following what I'm thinking?
 

Flusher

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...Anyone following what I'm thinking?

I've had that happen on OHV engines, where there is a path available from the combustion chamber to the crankcase via the lifter valley.

I don't see a direct path to the crankcase.

https://images.app.goo.gl/mBscwx86ReDUFA7EA

It looks like the oil supply is in front of the front two cylinders and the oil returns are outside of the water jackets. Of course there is no sealed lifter valley.

Do you still have the valve cover off? Did you see or hear anything from the driver side while pressurizing #6?

I have also had rings lose tension and result in almost zero compression. I think that was the result of overheating the rings and killing the heat treating.
 

Midlife Crises

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There are oil return passages that allow oil to drain from the cam area back to the oil pan. There are coolant passages surrounding the cylinder sealing surface that are much closer to the cylinder wall. If you pop a head gasket it will push compression gasses into the coolant. It would have to be really bed to reach the oil drain passage and would probably bring coolant with it. Overheating and coolant in the oil would show up.
It’s a very good bet you have a cracked or broken piston. Ring land failing perhaps.
 

Dino Dino Bambino

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Hey folks new to this forum and need some advice on next steps. Back in Jan , I bought a 05 mineral grey GT and drove it from Pittsburgh to Philly where I live. Car had a few owners but only 53 k miles. The seller seemed like a trustworthy guy, but since then I'm convinced this private pilot was a lying s.o.s. knew there was an issue and lied about health of the motor. Incidentally the car ran pretty good for stock. Regardless karma usually catches up with people like that. Once home the next day I checked the oil and it was down almost 1/2 quart , so I figured I misread the level the day before since it's only about 320 miles. So I changed the oil and within a week or or so lost a quart, no leaks no bad smoke out the exhaust that I could see. Another week and I picked up a misfire on #6, started poking around and found a new coil pack on 6 and decided to pull the plug, which was badly coked up. Pulled the rest of the plugs and did a compression check. All are around 190-210 except 6 which was at 55-65 psi. Added teaspoon of oil no big change. Rotated the motor until all three valves were closed put some air pressure in the cylinder and really couldn't hear any leaks out the exhaust or through the intake. I'm thinking bad rings or maybe hopefully a head gasket? do theses motors have an oil passage to the cam followers between the cylinders? Btw have not seen any oil in the coolant...thoughts ? thnx for any ideas.

If you aren't losing coolant as steam out of the tailpipe, and you don't have coolant mixing with oil, and the low compression is in one solitary cylinder, I can confidently rule out the head gasket.
Bad rings would cause a mild loss of compression but not a 70% drop, and a holed piston would result in zero compression. A bent valve would cause some leakdown either into the intake manifold or the exhaust, and you don't seem to have either.
That leaves a cracked piston or broken piston ring land as the most likely culprit, as this would allow oil from the crankcase to enter the combustion chamber. This would also explain why the "wet" compression test revealed no increase in compression. If you have a borescope, you should be able to diagnose the problem pretty quickly. Whatever the cause, the driver's side head will have to come off anyway.
The car history of several owners but only 53k miles suggests to me that it's been abused and each owner just wanted to pass the problems onto the next.
 

7ponies

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Gents , thanks again for the discussion, to clarify the leakdown was 35% that is losing 35% holding at 65% if you're familiar with the typical HF gages I'm still at the edge of the green "low" range, also the piston was probably at BDC , but again all valves on base circle. I've not done the other cylinders on this bank but will.
@dino expect for #6 all were 190 or better and I did borrow a borescope ( again cheap HF version) and surprisingly the piston looks good considering how crappy the plug looked , relatively carbon free no visible chunks missing or cracks. I'll recheck again.
@Flusher no not really most hissing coming from crankcase . This sucks wasn't really looking for this type of project car....next step pilling the head ? is that a major project or just time consuming ? Also if piston ring or land is it worth / can it be replaced assuming cylinder wall ok , ok do I start hunting for a motor?
 

Juice

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Sounds like you have it narrowed down to piston/piston ring issue.
With the piston at the bottom of the bore, how does the bore look? This answer will be the decision as what you are going to do next.
If the bore looks good, with no significant scoring- pull the engine, than pan and head. Remove #6 piston and replace whats needed, reassemble.

If bore is smoked, you have a decision to make: rebuild or replace engine.
Sucks, I know. Ive trashed a few engines...
The only thing that bugs me is what destroyed that spark plug.
 
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Gents thnx for the discussion.
@Andrey I'm thinking a hole in a piston would give 0 psi on the compression check?
@GlassTop09, yes valve cover pulled on drivers side, 3x lobes are somewhere on base circle although not sure #6 was at TDC , not sure it would matter either. If piston is mid-stroke and valves are closed air leak through valves would still be evident if valve are closed but faulty , just takes more air to fill the cylinder. Before doing leak down will probably check results where piston is now then take it to TDC and check again, that way if bottom of cylinder is scored i should have different readings. The assumption here is if car has 53 k , and a) plugs weren't pulled until recently and b) #6 plug broke possible bits went in, c) motor was run and d) cylinder wall scored? Wouldn't scored cylinder wall give the same compression results as bad rings except adding teaspoon of oil wouldn't make a difference? As for coolant just checked- level is ok, no way of checking over pressurization at this point. Also I eyeballed valve train component looked ok , cam looks pretty good too . If I pull the head ( likely next step) I'll also pick up the valvetrain kit from AM and replace followers, lash adjusters and seals.


That is a good point, it would be 0, also if the ring is totally gone like in my case (im going through putting a new motor in right now) it will also be 0, if ring is bad but still there you will have a way lower compression (depending on how bad it is). Since you tried put oil there and saw no difference in reading, its either 1- its not the ring or 2 - it is so bad that it didnt make a difference (cause 55-60 psi is hella low) I think our cars are rated around 210 new if im not mistaken. I feel you its a PITA to figure those things out. You will have to pull the heads and while you there you might as well do everything (assuming block is good) Im sure people have done it without pulling the motor out but it will be way easier if you do honestly. Im going through the same thing right now except i threw a rod (im boosted) cause of oil pump gears that are made of sh** and i have litterally no ring in cyl 1 (0 comp) i decided to go with the used motor, which was way harder to find that i anticipated. People drive those cars and finding good condition low miles motor isnt as easy as i thought (and prices right now are ridiculous), but i got lucky at the end. In your case your motor is very healthy if you read 190 on other cylinders, except this one. Mine wasnt (150-160 on all except 0 on first). So depending on what you plan is on the build, might as well strip everything down and do things like rings, boss 302 rods (like 35 a piece from any ford dealer forged rods from 5.0 coyote that are a direct fit), oil pump gears, pistons and you wont worry about nothing ever and can even go boosted after. Its kind of weird that such a low miles stock 4.6 3v has such problem, they are pretty reliable motors- i wonder what it is so keep us updated!
 
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Also just fyi, pull the oil pan if you haven't done so, cause i had a headgasket problems before and by checking overflow tank i saw no oil in coolant and no coolant on oil cap, dip stick etc. But when i pulled the oil pan i was in shock - that thing was covered inside with a mix of both ( milky looking substance )
 

Midlife Crises

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You can’t see the ring lands from the top of the cylinder. If you have a broken land that has bound the rings from moving that explained your oil migration and low compression. The wet compression test did not improve because the rings are already full of oil. Pull the engine so you can get at it and remove the suspect piston.
 

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