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I have a gen III 98 24dohc with 187k. My parents have a 2002 gen IV with 135k and the motor now has a stumble and they took it to the dealership and it sounds like a compression test was done and the tech says it has two burnt valves. They say it is not worth taking apart the motor to confirm and that this is a common problem with this motor. Is my 98 the same as the 2002 motor and is this problem common?
 

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I have a gen III 98 24dohc with 187k. My parents have a 2002 gen IV with 135k and the motor now has a stumble and they took it to the dealership and it sounds like a compression test was done and the tech says it has two burnt valves. They say it is not worth taking apart the motor to confirm and that this is a common problem with this motor. Is my 98 the same as the 2002 motor and is this problem common?

Piston Slap: Escaping A Duratec Headache? | The Truth About Cars

Rebuilding the Ford 3.0L: Engine Builder
 

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Valves are cooled by content with the valve seat. The valve seats are usually made from steal inserts that are designed to be harder than the rest of the head. When the engine leans out or overheats, it puts added stress on these parts. If the valve or the seat gets too hot, they both start to fail, its hard to say which fails first. I would imagine the valve warps first. Once it warps, it no longer makes full contact with the seat, which causes two things to happen. One, the valve can now get hotter, because it no longer has full contact and cannot dissipate its heat, and two, the warped valve focuses all its spring force against a smaller portion of the seat, which damages the seat. The hot exhaust leaking past overheats both the valve and the seat, softening the metal and accelerating the damage.

Some engines are more prone to this than others. I wouldn't doubt that the Duratec is more prone to this than some other engines, it's 4 valve per cylinder design produces more volumetric efficiency, and more efficiency can result in higher burn temps, all it takes is something going wrong like a vacuum leak or a slightly restricted injector to lean one or more cylinders out, which can increase the burn temperature to the point where an exhaust valve starts to warp.

Duratecs are kinda complicated motors to have major repairs like valve jobs done on, they are hard to disassemble, especially in the car, and there are more moving parts than a vulcan would have. Lots of other automakers have similar designs, especially among the newer models, so complexity is all in perspective.

The problem can be corrected. A machine shop could use higher grade valves, and could use even harder seats. This would correct the underlying problem that makes these prone to this type of failure, and would give you a more reliable engine than either a new head or a new factory engine. The main flaw is the valves themselves. I'm not sure if anyone makes a performance valve of these motors, but any valve made from stainless steel, hardened alloys, or sodium filled, would be ideal.

Unless they are really attached to the car, its probably not worth it. You can easy spend $5000 or more to get this fixed. However such an engine makes an excellent starting point for a built Duratec, run new seats, better valves, stiffer springs, run forged turbo pistons, redone the cylinders (unless they need to be rebored for whatever reason), and replace the bearings while your in there, you basically get a like new motor that is performance ready.
 

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Used Duratecs are on ebay all the time for 400-600 + shipping
 

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Used Duratecs are on ebay all the time for 400-600 + shipping
Pretty much what I was going to say. Also check out www.car-part.com and see if you can find something local that you can hear run before they pull it. You might spend a little more, but you save in shipping and the headache of dealing with a "sight unseen" engine. Still cheaper than buying a new car.........


Doing a quick search, there's a 2002 duratec with 18K miles on it for $650 in PA. Not a bad deal on that at all!!
 

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I would say a burned valves with a 2002 engine is a fluke. There hasn't been any historical data that indicates the Duratec burns valves.
However, I would a agree a lean condition could burn a valve given enough time.

Has the engine ever been in an overheat condition?

The other possibility (thinking outside the box) is poor quality of fuel that causes an abnormally high temperature.

You have to find the root cause why the valves burn. The other question here is only one cylinder has burned valves? Are the remaining valves on their way out as well? Or are the 2-valves just a fluke?

I've got 205K miles on my 'Tec with no issues.

Monsoon
 

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^^^^^ +1

The Tec is definitely not known for burned valves. This is the first time I have ever heard of such as case (ASSuming the diagnosis is in fact correct about the burned valve). If a cylinder or 2 in the engine were running lean due to a vac leak with the CEL on, or even CEL off and high positive fuel trims on one bank due to a UIM / LIM vac leak in just one cyl causing that cyl to run very lean, valves on that cyl could be fried.

Stuff like that is why I check fuel trims, 02 switch rates, fuel pressure, etc on all my OBDII cars every few months even if they seem to be running fine and the CEL is off. Preventative maintenance.
 

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Here is a relevant question on this: Is it 'preventive maintenance' to replace both co sensors say after 10 years and/or 100K miles?

(My 'tecs have @ 85K, no CEL and run perfect but have original sensors)
 

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DWK, What sensors are you referring to?

I am betting his parents car had a UIM/LIM leak just for the 1 cylinder causing it to be lean, but over all the ECU was able to correct for the over all bank AF levels without triggering a code.

I would get a low mileage JK motor and swap it.

http://www.taurusclub.com/forum/2904-clydesdale.html
 

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Outside all other factors, if the burnt valves are exhaust valves, check for cracks in the exhaust manifold nearest the valves. You can usually hear a click click click click when the manifold cracks, but not always. That can lead to burned exhaust valves. Also leads to premature failure of the o2 sensor causing it to run rich, washing out the cylinders, ruining spark plugs, ruining the catalytic converter. Easy to overlook a cracked manifold but they can cause trouble.

If you do hear a clicking under the hood take a piece of hose and put one end to your ear, move the other end around the engine compartment. You should be able to locate the source fairly quickly.

Also, only use regular unleaded gas in low compression engines. Using "premium" high octane fuel in a low compression engine will lead to quicker carbon deposit buildup, which can heat up and cause detonation and also carbonize your valves pretty good, leading to a burn. It's because the high octane fuel will burn slower than normal in a low compression engine, leaving a lot of unburned fuel behind to carbonize (also provide a slightly false reading to the o2 sensor and destroy the catalyst), not to mention decreased performance compared to regular octane. It's not "premium" in any way, shape or form. It's for high compression and forced induction engines only.
 

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Yes, I was looking his problem up on TCCA 'Topic Finder' Then scrolled down to 'Engine' then clicked on 'Oxygen Sensor Terminology'. There is a wealth of info there and the sensors come up frequently on here as trouble makers. My concern was for the upstream and downstream sensors and how this may be related to this problem.
 

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Thats what I was looking for. What gave me a scare was codes can come after the sensors start giving a problem. I thought this could possibly be related to his problem.
 

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^^^^ Yup, exactly what I am thinking.
 

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And yes, O2 sensors are maintenance items, and should be replaced every 80-100k miles. If they fail, they tend to cause other problems long before a sensor related code will ever be set.
I would go for 120K miles. That's when I replaced mine.

Monsoon
 

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The main problems with putting it off till that kind of mileage is severalfold. Firstly, as the sensors deteriorate, the voltage they generate decreases, which causes the computer to interpret the signal as a lean condition. The computer will add more fuel, which will cause it to see the signal it wants, but you are now running rich. Running rich doesn't just waste fuel, it causes carbon build up, which can cause all sorts of other problems. It plugs up the EGR system (I think that most EGR faults actually begin life as carbon deposits in the sensor and lines from rich operation). The second problem is the longer the sensors are left in, the greater the risk that they will seize in place, making removal and replacement much more difficult. This makes the removal more labor intensive, and there is always the chance that the may not be removable.

Putting it off may be tempting, but remember, todays cars are actually much cheaper to maintain in consideration of how long parts last and how infrequent major failures are. So having to replace a part every 100,000 miles should not be considered a big deal. We should gladly replace maintenance items such as spark plugs and O2 sensors.

I would find it unlikely that a bad O2 sensor could cause burnt valves though, the lean reading causes a richer mixture, which actually cools and slows the combustion down, which would make burnt valves less likely. However, enough carbon deposits might cause knocking or pinging, which in theory could cause valve damage, so I wouldn't rule it out, though I think you'd have to have an awful lot of pinging going on to cause that.

The Duratec is a lot less likely to have burnt valves than the older OHV 3.0L engine. That engine had lousy valve seats, and when they wore out, the head would crack and that would cause a leak past the valves, which would chew up the valve and cause it to warp. The Vulcan is a pretty good engine all around, but the heads are lousy. Few high mileage Vulcans can be found with good exhaust valves. They will still seem to run fine, but the performance will be down, and the economy suffers a little. The Duratec is however, more likely to have a valve seat issue than some other DOHC engines. I think this problems is far more common on the Escape than on a Taurus, the Escape is heavier, and is under more load more of the time, so that means it burns hotter too, and it doesn't get the best cooling due to the extra crowded engine compartment of the Escape (its more crowded than a Taurus).
 

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The main problems with putting it off till that kind of mileage is severalfold. Firstly, as the sensors deteriorate, the voltage they generate decreases, which causes the computer to interpret the signal as a lean condition. The computer will add more fuel, which will cause it to see the signal it wants, but you are now running rich. Running rich doesn't just waste fuel, it causes carbon build up, which can cause all sorts of other problems. It plugs up the EGR system (I think that most EGR faults actually begin life as carbon deposits in the sensor and lines from rich operation). The second problem is the longer the sensors are left in, the greater the risk that they will seize in place, making removal and replacement much more difficult. This makes the removal more labor intensive, and there is always the chance that the may not be removable.

Putting it off may be tempting, but remember, todays cars are actually much cheaper to maintain in consideration of how long parts last and how infrequent major failures are. So having to replace a part every 100,000 miles should not be considered a big deal. We should gladly replace maintenance items such as spark plugs and O2 sensors.

I would find it unlikely that a bad O2 sensor could cause burnt valves though, the lean reading causes a richer mixture, which actually cools and slows the combustion down, which would make burnt valves less likely. However, enough carbon deposits might cause knocking or pinging, which in theory could cause valve damage, so I wouldn't rule it out, though I think you'd have to have an awful lot of pinging going on to cause that.

The Duratec is a lot less likely to have burnt valves than the older OHV 3.0L engine. That engine had lousy valve seats, and when they wore out, the head would crack and that would cause a leak past the valves, which would chew up the valve and cause it to warp. The Vulcan is a pretty good engine all around, but the heads are lousy. Few high mileage Vulcans can be found with good exhaust valves. They will still seem to run fine, but the performance will be down, and the economy suffers a little. The Duratec is however, more likely to have a valve seat issue than some other DOHC engines. I think this problems is far more common on the Escape than on a Taurus, the Escape is heavier, and is under more load more of the time, so that means it burns hotter too, and it doesn't get the best cooling due to the extra crowded engine compartment of the Escape (its more crowded than a Taurus).
The Duratec is more likely to have vacuum leaks from PCV and clean air inlet ells to the valve covers resulting in lean conditions. IMHO.

Run hard lean it makes exhaust get hot, valves and manifolds. Lean flame propogation rate is slower causing the flame to go out arouond the valve and into the exhaust manifold. A piston airplane pilot can explain what happens if they select a lean mix to try to stretch fuel. I have only read about it.

-chart-
 

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A lean mixture might propagate slower, but it is more prone to spontaneous detonation. A lean mixture also burns hotter (this is why vehicles enrich the mixture under acceleration and by turbo cars enrich the mixture under boost). Vacuum leaks are just as likely on Vulcans, so this is not more likely on a Duratec. Hot exhaust is flowing around the valve whether the mixture is lean or not, if you believe the mature burns entirely inside the engine, you are mislead. The exhaust valve opens towards the end of the power stroke, and the fuel is very much still burning and expanding as it exits through the valve. Its the temperature of the gas, that determines whether a valve warps. A lean mix burns hotter, and if it detonates, it strips away the boundary layers, which makes the metal parts get much hotter. This in turn will make the metal softer, and under the severe stresses it has to undergo anyway, can cause failure.

The older 3.0L Vulcan is much more prone to this type of problem, a flame hardened cast iron seat is nowhere near as durable or long lasting as the hardened steel alloy seats used in the Duratec. That cast iron seat is only a couple hundredths of an inch thick, and once it wears through, the valve will quickly wear in to the head. A hardened steel seat is not only much harder, but much thicker.
 
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