Overheating: The Statistics

[Ian]

Bit of context

5000 forum members of which 1280 responded. A 25% response rate ain't too bad!, if you pro-rata the stats back against those people that could have responded but didn't then it ain't all bad news

I think the response rate is actually better than that. Of those who responded, 44% are not registered on the Bongo Forum, but 90% are paid up members of the club. There are currently 3,790 members of the club, but 499 of these are postal members who did not have access to the survey. So the response rate is closer to 35% I reckon.

[dobby]

Bit of context

5000 forum members of which 1280 responded. A 25% response rate ain't too bad!, if you pro-rata the stats back against those people that could have responded but didn't then it ain't all bad news

I think the response rate is actually better than that. Of those who responded, 44% are not registered on the Bongo Forum, but 90% are paid up members of the club. There are currently 3,790 members of the club, but 499 of these are postal members who did not have access to the survey. So the response rate is closer to 35% I reckon.

That's healthy

Thanks - couldn't remember if it was forum or email based.

I do a fair bit of work on housing condition surveys, it's easier on those as you pick the survey sample and extrapolate out. Maybe you could relate the survey back against membership profiles and then compare Or have a glass of wine instead!

[dvisor]

Bit of context

5000 forum members of which 1280 responded. A 25% response rate ain't too bad!, if you apply the stats back against those people that could have responded but didn't then it ain't all bad news. i.e. assume that if people didn't respond then they are less likely to have had major issues?

Is that really the case though? There seems to be a lot of assumptions being made. I've had no problems with the van (touch wood), but still responded to the survey. It's also probably the only survey I've done in years. The questions regarding coolant problems and head replacement were just a couple out of many. Its true that people often only respond to surveys when they have an axe to grind, but in this case I can't really see it. Don't get me wrong, maybe 18.3% isn't that bad considering the age of the vehicle etc, and we all know there are steps that can be taken to help prevent being one of these statistics, but there seems to be a reluctance in actually accepting these figures. Not trying to stir anything up, but I think its very useful to put all this in perspective, and get a better idea of the extent of the problem.

[dobby]

Bit of context

5000 forum members of which 1280 responded. A 25% response rate ain't too bad!, if you apply the stats back against those people that could have responded but didn't then it ain't all bad news. i.e. assume that if people didn't respond then they are less likely to have had major issues?

Is that really the case though? There seems to be a lot of assumptions being made. I've had no problems with the van (touch wood), but still responded to the survey. It's also probably the only survey I've done in years. The questions regarding coolant problems and head replacement were just a couple out of many. Its true that people often only respond to surveys when they have an axe to grind, but in this case I can't really see it. Don't get me wrong, maybe 18.3% isn't that bad considering the age of the vehicle etc, and we all know there are steps that can be taken to help prevent being one of these statistics, but there seems to be a reluctance in actually accepting these figures. Not trying to stir anything up, but I think its very useful to put all this in perspective, and get a better idea of the extent of the problem.

Ian's reply to my post sets it straight and supports your point though, the survey had a good response so the answers will hopefully be more representative.

[missfixit70]

What the figures show, is what has been said by some of us on the forum for some time ( & been accused of scaremongering for doing so ) the diesel engine is susceptible to coolant leaks/overheating with a fairly high chance of expensive consequences - IF YOU'RE NOT CAREFUL.
It would be interesting to be able to break down the why's & wherefore's of what happened, but it should highlight the need for sensible precautions in ensuring the system is working as it should, by making sure incompatible coolants aren't mixed, components are replaced (they don't go on for ever), proper & regular servicing & my opinion is that sensible monitoring & alarms are fitted. Most importantly if it leaks or gets hot, don't try & "just get it home" that last 20 minutes unless you've got £1500 to burn.

[Glenda]

Again, the "Don't Knows" have been excluded. The actual number of replacement heads was 119; 86 replaced by current owners, 33 replaced by previous owner or dealer.

Good work stato. Numerically that adds up. It means 42% (491) of diesel respondents do not know if they have had a head replacement and 58% (651) do know.

But from 1142 diesel respondents you have excluded 42% (whom we can assume most have not had a new head) to come up with a figure of 18.3%. A figure nearer to 10% could be obtained from your survey and be nearer the truth (119 from 1142). But that's why statistics are brilliant.

However, as your subject title states this is an example of overheating the statistics.

[bigdaddycain]

I'm not gonna dispute the stats (geddit?) Figures are figures, and there is nothing more clinically crisply clear than a number.

I'm of the opinion though that in the real world, maybe 10 out of 20 people would have bothered with the survey had they suffered a head gasket problem, whereas, perhaps 2 out of 20 people would have bothered with the survey if they hadn't experienced a head issue.

Like i said at the beginning of this post, figures are just that, here's the reality in MY experience... I probably know of a hundred or so bongo owners, out of that 100 or so bongo's i've known of less than 5 head gasket failures... That doesn't tally with the official statistic...So which is the closest to reality? (footnote: associated cooling issues always preceded C/H failures) I'm not trying to paint the bongo as a 100% reliable,sun shines out of it's tailgate machine, i'm really not. But i have no reason to falsely sing it's praises neither. If i'd formed the opinion that my bongo wasn't reliable, nor was it within the realms of affordability to "keep it on the road" then i wouldn't still have it six years down the line.

I wonder how many failed cylinder heads of which were reported in the survey had the wrong type of coolant fitted/or (more likely) a mismatch of incompatible coolants at some stage? This is VERY relevant, yet hard to gauge with any degree of accuracy.

[The Great Pretender]

Well said BDC, also I would think the majority of owners would rely on a garage if they had a coolant loss/ overheat problem and we know that can lead to head problems don't we?

[Glenda]

I am 100% for the Bongo Survey.

The results would be better presented without percentages as the strength of the survey stands alone. We can then ignore the lack of correlation coefficients and the sample not being random.

So from 1142 Diesel Bongo respondents 651 knew if they had a new or original head. Of that number 119 of them had new heads and 532 had the original.

That's probably it for me until the Bar Charts are ready.

[mikexgough]

I wonder how many failed cylinder heads of which were reported in the survey had the wrong type of coolant fitted/or (more likely) a mismatch of incompatible coolants at some stage? This is VERY relevant, yet hard to gauge with any degree of accuracy.

[mikeonb4c]

I'm not gonna dispute the stats (geddit?) Figures are figures, and there is nothing more clinically crisply clear than a number.

I'm of the opinion though that in the real world, maybe 10 out of 20 people would have bothered with the survey had they suffered a head gasket problem, whereas, perhaps 2 out of 20 people would have bothered with the survey if they hadn't experienced a head issue.

Like i said at the beginning of this post, figures are just that, here's the reality in MY experience... I probably know of a hundred or so bongo owners, out of that 100 or so bongo's i've known of less than 5 head gasket failures... That doesn't tally with the official statistic...So which is the closest to reality? (footnote: associated cooling issues always preceded C/H failures) I'm not trying to paint the bongo as a 100% reliable,sun shines out of it's tailgate machine, i'm really not. But i have no reason to falsely sing it's praises neither. If i'd formed the opinion that my bongo wasn't reliable, nor was it within the realms of affordability to "keep it on the road" then i wouldn't still have it six years down the line.

I wonder how many failed cylinder heads of which were reported in the survey had the wrong type of coolant fitted/or (more likely) a mismatch of incompatible coolants at some stage? This is VERY relevant, yet hard to gauge with any degree of accuracy.

Excellent post BDC

And like Glenda says, the survey is a great idea (with a spectacular response rate) so not wasted. But the interpretation of the figures needs to be done with plenty of circumspection. Your point about knowing 100 Bongos etc. rings the truest to me - it just makes sense. I believe Previas, Hiaces (is it?) and some other ageing (diesel?) cars with complex plumbing, owners who may more not be enthusiastic DIY car maintenance people etc. are also known to end up having to have heads replaced?

[Doone]

So from 1142 Diesel Bongo respondents 651 knew if they had a new or original head. Of that number 119 of them had new heads and 532 had the original.

I'm reading this with interest, but know absolutely nothing about statistics.

Does the above mean that what we know for certain is that 651 people knew if they had a new or original head...
And 119 of the 651 had a new head?
I'm probably not working this out right... But if we use what we know for certain, does it mean that 5.47 people in a 100, had new heads?

If that's right (and bearing in mind that forums often attract those with problems), it's fairly close to BDC's observation of "...I probably know of a hundred or so bongo owners, out of that 100 or so bongo's i've known of less than 5 head gasket failures..."

But I've probably worked it out wrong, as I'm learning, statistics can mean all sorts.

[dvisor]

So from 1142 Diesel Bongo respondents 651 knew if they had a new or original head. Of that number 119 of them had new heads and 532 had the original.

I'm reading this with interest, but know absolutely nothing about statistics.

Does the above mean that what we know for certain is that 651 people knew if they had a new or original head...
And 119 of the 651 had a new head?
I'm probably not working this out right... But if we use what we know for certain, does it mean that 5.47 people in a 100, had new heads?

If that's right, it's fairly close to BDC's observation of "...I probably know of a hundred or so bongo owners, out of that 100 or so bongo's i've known of less than 5 head gasket failures..."

But I've probably worked it out wrong, as I'm learning, statistics can mean all sorts.

'fraid not. It means that 18.3% (i.e. 18.3 in a hundred) of those that know they whether or not they have had a new head have had a new one. The percentage of those with a new head that don't know they've had a new head is unknown - but it's likely to be lower IMHO. If that's true, this would bring down the figure lower than 18.3%.

[Glenda]

So from 1142 Diesel Bongo respondents 651 knew if they had a new or original head. Of that number 119 of them had new heads and 532 had the original.

I'm reading this with interest, but know absolutely nothing about statistics.

Does the above mean that what we know for certain is that 651 people knew if they had a new or original head...
And 119 of the 651 had a new head?
I'm probably not working this out right... But if we use what we know for certain, does it mean that 5.47 people in a 100, had new heads?

If that's right (and bearing in mind that forums often attract those with problems), it's fairly close to BDC's observation of "...I probably know of a hundred or so bongo owners, out of that 100 or so bongo's i've known of less than 5 head gasket failures..."

But I've probably worked it out wrong, as I'm learning, statistics can mean all sorts.

No Allan,

These figures show 18.3% if done with the do knows, 10% if done as a result of the survey. If the survey was done randomly, we would presumably get nearer to the 5%. But it wasn't and can still be usefull.

What I do know is that you probably see more than the average head job as they would be making a bee line for your garage. What are your statistics? I mean in terms of Bongos rather
than bodywise.
Bet your glad to get some sun down there this week. Cheers

[missfixit70]

Doone is Lorna, not Allan