D chunk cylinder failure- early signs?
Discussion
It depends on the failure, very often there is pressurisation of the cylinder block first (showing as coolant discharging from the overflow pipe and a slightly increased running temperature).
There can also be an increase in the oil level (as coolant seeps into the engine over night) and a corresponding misfire.
We have had a few that were running around with the fault before it was fixed. The problem is that if the car comes in with the D chumk missing we often don't know if that might have had symptoms or not by then as the owners are often in shock anyway and not very communicative.
If it is a D chunk - usually the piston is still OK so it is not such a serious fault especially if the engine is getting up to a mileage where a rebuild may be considered to prolong it's life for owners wishing to keep the cars.
However a cracked cylinder head may have similar initial symptoms - although after while you get oil in the coolant whreas with a cracked cylinder - it is usually the other way around.
Baz
There can also be an increase in the oil level (as coolant seeps into the engine over night) and a corresponding misfire.
We have had a few that were running around with the fault before it was fixed. The problem is that if the car comes in with the D chumk missing we often don't know if that might have had symptoms or not by then as the owners are often in shock anyway and not very communicative.
If it is a D chunk - usually the piston is still OK so it is not such a serious fault especially if the engine is getting up to a mileage where a rebuild may be considered to prolong it's life for owners wishing to keep the cars.
However a cracked cylinder head may have similar initial symptoms - although after while you get oil in the coolant whreas with a cracked cylinder - it is usually the other way around.
Baz
911Fiddler said:
Thanks for the insights baz. Water is clean. No over pressure symptoms but think I will pop on a pressure gauge for interests sake. my coolant loss ( minor ) is probably a weak joint, one out of sight I reckon.
Pressure test the cooling system. (Don't over pressure it either. There's a callout but I forget what it is, on the order of 1.3 or 1.4 bar IIRC, but do some research and learn the max. pressure for sure.)But test the cap too. Early caps (the two stage versions) leak a bit and over time this allows water vapor to escape and the coolant level to drop. In several cases (my cars) I've seen the level drop enough to cause the low coolant light to come on.
In fact, if the cap part number ends in '00' or '01' see if you can find a new cap that ends in part number '02' or higher. (I think the number is up to '04' now.)
Also, if you suspect a D-chunk failure is coming your way, have the engine oil analyzed for any signs of anti-freeze in the oil. There should not be any.
Sincerely,
Rockster.
Why not run a carbon monoxide test on the cooling system to see if there are any combustion gasses present? That would let you know if there was a head gasket or liner issue.
I have to say we haven't had to do it for donkey's years but in the good old days it was a fairly regular test.
Henry
I have to say we haven't had to do it for donkey's years but in the good old days it was a fairly regular test.
Henry
Am now running with a pressure gauge installed on the cooling system so will be checking running values, normal run, high speed/power run etc. Anybody know what pressure values to expect as normal? Am thinking if it says well under the pressure relief value of the reservoir cap, then it's normal?
911Fiddler said:
Am now running with a pressure gauge installed on the cooling system so will be checking running values, normal run, high speed/power run etc. Anybody know what pressure values to expect as normal? Am thinking if it says well under the pressure relief value of the reservoir cap, then it's normal?
My info is the cooling system should be pressure tested with the engine cold.To test the system the system is pressurized to 1.3 bar. If the pressure decreases there's a leak.
To check the cap screw the pressure tester, adapter and cap together. For single state caps, part number 443.121.321, verify the pressure relief opens and the pressure remains constant at an excess pressure of 1.3 bar.
If the pressure decreases replace the cap. The two stage cap is the preferred cap.
To test the two stage cap, part number 996.106.447.00 (though newer versions of caps are available: '02', '03' maybe even '04).
Generate excess pressure to test the 1st stage of the cap. The pressure relief valve opens at approx. 1.4 bar; the pressure slowly decreases again and the valve closes at 1.0 bar. If the pressure descreases further, replace the cap.
If the test pressure at stage 1 is maintained test stage 2. Apply excess pressure to the pressure relief valve of stage 1 by pumping rapidly. The pressure relief valve of stage 2 must open at an excess pressure of approx. 1.8 bar. If the valve does not open replace the cap.
Sincerely,
Rockster.
911Fiddler said:
Like that idea, co test on coolant, do I just go to my MOT centre an pop the probe in the open header tank, then Bobs your unc....or not....?
Your MOT test centre do MOT tests and their probe is designed to go in the exhaust pipe. You need to go to a Porsche specialist service garage and let them do the test which comprises drawing a sample of the air in the head tank through a chemical which changes colour when carbon monoxide is present.Henry
911Fiddler said:
Am now running with a pressure gauge installed on the cooling system so will be checking running values, normal run, high speed/power run etc. Anybody know what pressure values to expect as normal? Am thinking if it says well under the pressure relief value of the reservoir cap, then it's normal?
You may find this test unhelpful as you do not know what normal running looks like. You could end up chasing a lot of red herrings this way.Do the test Henry suggests or do the static pressure test.
Bert
Henry-F said:
Why not run a carbon monoxide test on the cooling system to see if there are any combustion gasses present? That would let you know if there was a head gasket or liner issue.
I have to say we haven't had to do it for donkey's years but in the good old days it was a fairly regular test.
Henry
HenryI have to say we haven't had to do it for donkey's years but in the good old days it was a fairly regular test.
Henry
You said yesterday that one of the main reasons you reject 997s is scored bores. How do you know if a car has such a problem? Compression test?
We listen to the engine. The problem with engines and noises is that sometimes noises are quite normal, sometimes they are a relatively easy to change ancillary component and sometimes they are indicative of financially serious issues.
Fortunately I started off my car selling career by repairing cars before selling them and I have always seen it as important to know your product, rather than just it's value. We are able to diagnose pretty much most issues during our pre-purchase look at a car. If there is anything we want confirmation on (we don't want to penalise a car un-necessarily), then we run it down to a workshop and get a specialist to cast their beady eye over it to confirm our thoughts. There are times when several faults give the same symptoms.
I suppose the short answer to your question is experience and knowledge.
Henry
Fortunately I started off my car selling career by repairing cars before selling them and I have always seen it as important to know your product, rather than just it's value. We are able to diagnose pretty much most issues during our pre-purchase look at a car. If there is anything we want confirmation on (we don't want to penalise a car un-necessarily), then we run it down to a workshop and get a specialist to cast their beady eye over it to confirm our thoughts. There are times when several faults give the same symptoms.
I suppose the short answer to your question is experience and knowledge.
Henry
Henry-F said:
I suppose the short answer to your question is experience and knowledge.
Henry
I didn't doubt that for a moment.Henry
In onomatopoeic terms, then, what does an engine with scored bores sound like? Is it a ping, ping, ping noise? Clatter, clatter clatter? Splish, splash, splosh? What?
If it will help, you could always perform an impression of it and post it on Youtube.
Hey, this could be the start of something big: Henry-F's interpretations of common 997 engine problems in D minor. This could eclipse Nigel Kennedy's Four Seasons and possibly challenge the X-Factor for Christmas No.1.
Manks
If only it were that simple.
The trouble with noises is that there are many variables. When does the noise occur? Where does it come from within the engine? (and that's not always easy to determine). What speed is the noise and then the noise it's self. An engine is noisy, so it's not like you're listening for something in silence.
It's the same as asking someone how to determine if a banknote is forged or not. The problem in this case is that we are talking a £30,000 or £40,000 bank note. You could be ultra cautious with everything you see but you don't want to miss out on a good car for the wrong reasons.
It's a funny thing diagnosing problems. The difference between symptoms can often be miniscule but you know exactly what something is and what it isn't. As I mentioned previously though there are times when the different faults give identical symptoms so you need to explore further.
A good example of this was a car we bought recently which had a drive-train noise. Likely candidates were a diff, a wheel bearing or, as it turned out tyres. Each could have made the same noise and reacted the same to some driving style changes used to remove possible issues from the equation. The diff was put to one side for a while for various reasons but I was convinced it was a wheel bearing. In the end whilst rolling the wheel manually to look for bearing noise (which wasn't there annoyingly) we felt every third or fourth tread block on the tyre was chamfered. Not a particularly common occurance but something we've seen before a few times. Sure enough another set of wheels on the car and the noise was gone. This was an easy one to get to the bottom of, engine noises are rarely as friendly because you can't easily swap out parts to eliminate them. You have to be pretty sure before you start spending 40 hours pulling an engine apart. That said there are some ancillary parts which can be eliminated from your enquiry.
Keep smiling
Henry
The trouble with noises is that there are many variables. When does the noise occur? Where does it come from within the engine? (and that's not always easy to determine). What speed is the noise and then the noise it's self. An engine is noisy, so it's not like you're listening for something in silence.
It's the same as asking someone how to determine if a banknote is forged or not. The problem in this case is that we are talking a £30,000 or £40,000 bank note. You could be ultra cautious with everything you see but you don't want to miss out on a good car for the wrong reasons.
It's a funny thing diagnosing problems. The difference between symptoms can often be miniscule but you know exactly what something is and what it isn't. As I mentioned previously though there are times when the different faults give identical symptoms so you need to explore further.
A good example of this was a car we bought recently which had a drive-train noise. Likely candidates were a diff, a wheel bearing or, as it turned out tyres. Each could have made the same noise and reacted the same to some driving style changes used to remove possible issues from the equation. The diff was put to one side for a while for various reasons but I was convinced it was a wheel bearing. In the end whilst rolling the wheel manually to look for bearing noise (which wasn't there annoyingly) we felt every third or fourth tread block on the tyre was chamfered. Not a particularly common occurance but something we've seen before a few times. Sure enough another set of wheels on the car and the noise was gone. This was an easy one to get to the bottom of, engine noises are rarely as friendly because you can't easily swap out parts to eliminate them. You have to be pretty sure before you start spending 40 hours pulling an engine apart. That said there are some ancillary parts which can be eliminated from your enquiry.
Keep smiling
Henry
You can buy a block tester from eBay.
Instructions ;
"To do the test, add the blue detector fluid to the (block-tester) plastic container according to the directions, and place it onto the radiator filler neck. The squeeze bulb is placed on top of the reservoir and squeezed repeatedly (Some block testers, have a tube that connects to a vacuum line instead of a squeeze bulb). Squeezing the bulb will draw air from the radiator through the test fluid. Block tester fluid is normally blue. Exhaust gases in the cooling system will change the colour of the fluid to yellow, indicating a combustion leak. If the fluid remains blue, exhaust gases were not present during the test. The vehicle should be started and at operating temperature before performing the test."
Instructions ;
"To do the test, add the blue detector fluid to the (block-tester) plastic container according to the directions, and place it onto the radiator filler neck. The squeeze bulb is placed on top of the reservoir and squeezed repeatedly (Some block testers, have a tube that connects to a vacuum line instead of a squeeze bulb). Squeezing the bulb will draw air from the radiator through the test fluid. Block tester fluid is normally blue. Exhaust gases in the cooling system will change the colour of the fluid to yellow, indicating a combustion leak. If the fluid remains blue, exhaust gases were not present during the test. The vehicle should be started and at operating temperature before performing the test."
Henry-F said:
If only it were that simple.
The trouble with noises is that there are many variables. When does the noise occur? Where does it come from within the engine? (and that's not always easy to determine). What speed is the noise and then the noise it's self. An engine is noisy, so it's not like you're listening for something in silence.
It's the same as asking someone how to determine if a banknote is forged or not. The problem in this case is that we are talking a £30,000 or £40,000 bank note. You could be ultra cautious with everything you see but you don't want to miss out on a good car for the wrong reasons.
It's a funny thing diagnosing problems. The difference between symptoms can often be miniscule but you know exactly what something is and what it isn't. As I mentioned previously though there are times when the different faults give identical symptoms so you need to explore further.
A good example of this was a car we bought recently which had a drive-train noise. Likely candidates were a diff, a wheel bearing or, as it turned out tyres. Each could have made the same noise and reacted the same to some driving style changes used to remove possible issues from the equation. The diff was put to one side for a while for various reasons but I was convinced it was a wheel bearing. In the end whilst rolling the wheel manually to look for bearing noise (which wasn't there annoyingly) we felt every third or fourth tread block on the tyre was chamfered. Not a particularly common occurance but something we've seen before a few times. Sure enough another set of wheels on the car and the noise was gone. This was an easy one to get to the bottom of, engine noises are rarely as friendly because you can't easily swap out parts to eliminate them. You have to be pretty sure before you start spending 40 hours pulling an engine apart. That said there are some ancillary parts which can be eliminated from your enquiry.
Keep smiling
Henry
Good answer, though probably not as amusing as an attempt to describe the noise in words.The trouble with noises is that there are many variables. When does the noise occur? Where does it come from within the engine? (and that's not always easy to determine). What speed is the noise and then the noise it's self. An engine is noisy, so it's not like you're listening for something in silence.
It's the same as asking someone how to determine if a banknote is forged or not. The problem in this case is that we are talking a £30,000 or £40,000 bank note. You could be ultra cautious with everything you see but you don't want to miss out on a good car for the wrong reasons.
It's a funny thing diagnosing problems. The difference between symptoms can often be miniscule but you know exactly what something is and what it isn't. As I mentioned previously though there are times when the different faults give identical symptoms so you need to explore further.
A good example of this was a car we bought recently which had a drive-train noise. Likely candidates were a diff, a wheel bearing or, as it turned out tyres. Each could have made the same noise and reacted the same to some driving style changes used to remove possible issues from the equation. The diff was put to one side for a while for various reasons but I was convinced it was a wheel bearing. In the end whilst rolling the wheel manually to look for bearing noise (which wasn't there annoyingly) we felt every third or fourth tread block on the tyre was chamfered. Not a particularly common occurance but something we've seen before a few times. Sure enough another set of wheels on the car and the noise was gone. This was an easy one to get to the bottom of, engine noises are rarely as friendly because you can't easily swap out parts to eliminate them. You have to be pretty sure before you start spending 40 hours pulling an engine apart. That said there are some ancillary parts which can be eliminated from your enquiry.
Keep smiling
Henry
I shall nonetheless keep smiling
Having repaired dozens of scored bore engines and now looking inside every car in for our top service (to check for signs before going on our Maintenance Plan) it has become clear that the detereoration of the piston coating is more gradual than we first thought.
So some cars with no symptoms may already have the first signs, others with minor symptoms may be well on their way while those making noises are well past it.
I now think it may take around 15 or 20K to go from one extreme to the other and most engines we look into after 40K have signs.
Obviously it will take many more months before those engines we spotted the first signs in will deteriorate to a recogniseable point where the higher oil consumption, general performance and noises appear - before we know exactly how long that period of deterioration actually is and I can think of no way around just waiting to see.
I aso think those driven the hardest will suffer first.
When the 944 S, S2 and 968 camshaft teeth started falling off (many years ago now) we recorded the tooth wear and chain stretch early on and soon were able to simply give the technician a chart on which to record the results of checking a customer's engine against previous experience - showing up straight away if the customers parts were of a size that we found still ok for "X" K miles more, or already at a size where several had failed (so needed replacing) or at a size when they were compeltely knackered - and this gave a fool proof scientific way of advising cusomers (and better than just looking at the teeth like others did and giving a visual opinion).
In a similar way - as well as keeping these records we are also recording photographic microscopic analysis of the various engines Lokasil cylinder walls surfaces and the surface finish to gradually create a picture that will enable us eventually to check condition and predict the exact state of play (see photo) - but again - building up these background records takes time (and a considerable amount if investment in equipment) and those answers will inevitably take a while to show clear results - but at least we started this process long enough ago to be ahead with the answers and a reliable investigative system.
This is the only way I know to create an accurate analysis of the state of play.
Baz
So some cars with no symptoms may already have the first signs, others with minor symptoms may be well on their way while those making noises are well past it.
I now think it may take around 15 or 20K to go from one extreme to the other and most engines we look into after 40K have signs.
Obviously it will take many more months before those engines we spotted the first signs in will deteriorate to a recogniseable point where the higher oil consumption, general performance and noises appear - before we know exactly how long that period of deterioration actually is and I can think of no way around just waiting to see.
I aso think those driven the hardest will suffer first.
When the 944 S, S2 and 968 camshaft teeth started falling off (many years ago now) we recorded the tooth wear and chain stretch early on and soon were able to simply give the technician a chart on which to record the results of checking a customer's engine against previous experience - showing up straight away if the customers parts were of a size that we found still ok for "X" K miles more, or already at a size where several had failed (so needed replacing) or at a size when they were compeltely knackered - and this gave a fool proof scientific way of advising cusomers (and better than just looking at the teeth like others did and giving a visual opinion).
In a similar way - as well as keeping these records we are also recording photographic microscopic analysis of the various engines Lokasil cylinder walls surfaces and the surface finish to gradually create a picture that will enable us eventually to check condition and predict the exact state of play (see photo) - but again - building up these background records takes time (and a considerable amount if investment in equipment) and those answers will inevitably take a while to show clear results - but at least we started this process long enough ago to be ahead with the answers and a reliable investigative system.
This is the only way I know to create an accurate analysis of the state of play.
Baz
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