Diesel vs Petrol - Either more or less prone to this overhea

[dave_aber]

Still trying to make my mind up as to which of the many variants of Bongo to try to buy.

I recently hired a petrol v6, which was excellent, but I also have a bit of a preference for 4WD.

So, to help (or confuse?) me - is there any evidence to suggest that the 2.0, 2.5 v6 or 2.5TD are more or less prone to overheating / cracked head(s) / etc?

Still trying to fathom out if the overheating thing is a) the most common fault, which happens to a small minority of otherwise reliable bongos, or b) loads of these are overheating. Hopefully a) !!

Cheers
Dave

[apole]

Hi Dave,

It's hard to say for sure.

Things I know are:

Less V6 petrols round than the diesel ones so there are bound to be more instances of overheating in the diesel ones due to the numbers.

I haven't heard of a petrol one overheating as yet.

The cooling systems are pretty much the same in terms of pipework etc to block/fail.

Do diesels create more heat than petrol engines (I'm not sure on that).

Personally I would look out for a good bongo that fits your remit and feels the right one, then look after it and protect yourself with a low coolant alarm and maybe a temp alarm too.

Andy

[scanner]

Do diesels create more heat than petrol engines (I'm not sure on that).

No less, as they are more thermodynaically efficient.

More of the heat they produce is converted into useful energy/work done.

So far as I can see overheating is more a result of poor maintenance/mixing of incompatible coolants/lack of use leading to sludging up/grotty hoses that leak etc. than anything else.

[g8dhe]

I understood that the temperature was higher, checking with Wikipedia it suggests that the cylinder temperature is higher hence greater efficiency (see second paragraph). But I don't claim any great knowledge of either type of engine - give me electronics any day!

[Alison01326]

Not speaking technically, as I will leave that to others, don't forget that more people post about problems than will just put up a message saying my Bongo has been running without a hitch for the last two years (not least because that sort of thing tempts fate).

If you read the Buying a Bongo information along with the FAQS, both of which are on the www.bongofury.co.uk home page, there will be information on there which may help.

[Ian]

We have only ever heard of 2 xV6 overheating problems. One where a radiator cap was left off. The other when a pipe was loosened during a cam belt change.

[dave_aber]

Alison,

That's just the issue I'm trying to get my head round - what is the genuine proportion of TD's which suffer overheating 'episodes' compared to v6's / 2l's.

It's always the same problem on fora such as these, that few people post when there is no problem, and almost everyone posts when they have a problem - so the 'problems' seem to be really common.

Interesting to hear Ian's comment that so few v6's have been reported with issues, and for clear accidental reasons. Might start thinking about v6 and LPG more again!! But I still 'think' I want 4WD! Damn, too many choices.

Andy's probably right - find a good un, and look after it.

[waycar8]

We have only ever heard of 2 xV6 overheating problems. One where a radiator cap was left off. The other when a pipe was loosened during a cam belt change.

But when you consider the amount of V6 petrol compared to 2.5TD's in the UK, i suppose that the ratio could be something to do with that figure

Also, I have seen at least 1 V6 bongo for sale on ebay with a cracked head for sale, thats not counting the 2l petrols that have had same problems, allthoe I havent seen or heard of any with that type of engine with issues

[scanner]

I understood that the temperature was higher, checking with Wikipedia it suggests that the cylinder temperature is higher hence greater efficiency (see second paragraph). But I don't claim any great knowledge of either type of engine - give me electronics any day!

Yes temperature is higher, but also lower - greater difference so less is lost to cooling.

It's why some diesels are now fitted with auxiliary cabin heaters because they can be so slow to warm up.

[mikeonb4c]

I understood that the temperature was higher, checking with Wikipedia it suggests that the cylinder temperature is higher hence greater efficiency (see second paragraph). But I don't claim any great knowledge of either type of engine - give me electronics any day!

Yes temperature is higher, but also lower - greater difference so less is lost to cooling.

It's why some diesels are now fitted with auxiliary cabin heaters because they can be so slow to warm up.

Putting all this together, might it be then that the heads of diesels are at higher risk due to higher temp gradients (hot bits -> cold bits) and attendant thermal stresses. And does the higher compression add to the hammering the material gets or is that an irrelevance. And is an alloy head a less robust thing than a cast iron head (or are these a thing of the past anyway)?

So many questions

[dave_aber]

higher compression

The head gaskets in diesel's are certainly under more stress generally due to the higher pressures involved. Lots of wee air-cooled petrol engines don't even have head gaskets (2CV, GS etc)

[BongoMTBer]

Cast iron heads are certainly more durable. The material has a much longer fatigue life than aluminium, both thermal and mechanical.

I cooked my old A-series mini engine twice to the extent that the oil was starting to boil. After an oil change etc it was all fine again and is still running!

I would say don't let the overheating issue worry you. Buy what you want, splash the cash at the start on flushing, good quality pipes, thermostat and new rad if it is all looking a bit tired and it should be fine. Factor in that cost into your budget and you will get what you want and hopefully many years of use out of the new parts.

[dave_aber]

Sound advice.

Some ally heads are surprisingly solid - I cooked a Passat TD once, to the extent that I had a partial seize, followed by a 30 min cool down, drove to a nearby garage, accompanied by thick white smoke coming out of the wheelarches (!). When I put oil in it (it was empty!), it sounded like a chip shop. After another 30 min cool down, the cold water going in just boiled immediately, and came gurgling out.

Once it had all cooled down, and the water and oil were full again, I drove home. Changed the split hose the next day, topped the water up again and it was OK for another year.

To say I was amazed would be an understatement. Doubt a Bongo would stand up to such abuse. Not how I normally treat cars, but it was a 'needs must' situation. I had to get home or to a train station to carry on regardless.

[Alison01326]

As a total non-expert, I am completely unqualified to add anything further to that which I have already posted but I think you may have hit the nail on the head.

From other posts which I have read (or rather studied, as I have an irrational paranoia about overheating) a Bongo engine will not survive as the Mini and the Passat (and doubtless many other vehicles) did. Hence the popularity of alarms (hi and lo coolant alarms plus a Mason alarm which effectively makes your temperature gauge tell the truth as well as sounding an alarm when the temperature goes above your Bongo's normal). Once the warning signs of overheating have started, if you don't take heed immediately, the chances are the damage will have been done.

This is a summary of how I understand the situation from everything I have read and if I have understood it wrongly (and I appreciate that I will have oversimplified it) please put me right someone.

As has already been said, don't concentrate too much on the overheating issue when you are choosing your Bongo - find the right one for you, check for signs that it hasn't overheated before (if all the documentation is in Japanese you may be hard pushed to find out what repairs have been done) and look after it well. And forget your incident with the Passat - the Bongo will lose hands down in a similar situation.

[scanner]

All alloy engines are often OK - everything expands and contracts at the same rate.

All iron engines are often OK - everything expands and contracts at the same rate.

Alloy head on Iron block? - hmmmm two things expanding and contracting at different rates......... maybe not so OK