Over-heating

[Stanstead]

I have just got back from a trip to Spain and Portugal.

My bongo (2.5 petrol) over heated and boiled up three times in the intense heat and mountains of Portugal. I replaced lost water and everything was all right when the weather cooled. However, a similar thing happened in this country on a very hot day in July this year. My mechanic checked everything before I left for Spain and Portugal (fan, hoses, pressure) and could find no problems. I intend to get him to have another look but in the meantime wonder if anybody has any suggestions about what might be wrong.

Thank you

Robert
Brighton

[Simon Jones]

Presumably the system was bleed after replacing lost coolant & the correct mix of coolant / water used? I would suggest there may be a problem with the thermostat being stuck or lazy (genuine Mazda replacement is about £45) or party clogged up radiator matrix. While the V6 engine does not tend to suffer overheating issues, they are just as prone to problems elsewhere in the cooling system.

What do you have fitted in terms of low coolant or temperature alarms?

[mikeonb4c]

I have just got back from a trip to Spain and Portugal.

My bongo (2.5 petrol) over heated and boiled up three times in the intense heat and mountains of Portugal. I replaced lost water and everything was all right when the weather cooled. However, a similar thing happened in this country on a very hot day in July this year. My mechanic checked everything before I left for Spain and Portugal (fan, hoses, pressure) and could find no problems. I intend to get him to have another look but in the meantime wonder if anybody has any suggestions about what might be wrong.

Thank you

Robert
Brighton

Did they check the temp sensor that activates the fans is working properly? Did it lose water because the system boiled or because there was a leak? If it lost coolant, was the overheating as a result of that? Is thermostat operating properly? When you say the mechanic tested pressure, do you mean he pressurised the cooling system looking for leaks? Where are you based, as it might be worth visiting a specialist Bongo mechanic like Discount Trucks at Newbury. You might also consider fitting alarms (low coolant and engine block temp alarm) to give you early warning of trouble.

P.S. Simon's point above about clogged radiator matrix is another definite possibility - is there any sign of crud or staining in the header tank as this might hint at this.

[Stanstead]

Hello Simon, hello Mike.

Thanks to you both for taking the trouble to reply to my post.

The bongo lost coolant because of overheating, rather than the other way round. Also, I have a coolant alarm.

I'm not sure of the answers to your other questions - I'm not very technical. But, the header tank does look a bit stained brown. However, I've made a note of your suggestions and will put them to the mechanic when I take the bongo to him. By the way, he's a bongo specialist.

You've been very helpful.

Best wishes to you both

Robert

[Gasy]

If the header tank has ever dropped to empty
The system require bleeding after refilling
To release trapped air
If this is not done it will overheat again
There are 3 vids to watch on you tube
Which explains how to bleed them with the bleed hose under passenger seat
Make sure he knows this
There seems to be a few bongo specialist garage that arnt really specialists

[mikeonb4c]

Hello Simon, hello Mike.

Thanks to you both for taking the trouble to reply to my post.

The bongo lost coolant because of overheating, rather than the other way round. Also, I have a coolant alarm.

I'm not sure of the answers to your other questions - I'm not very technical. But, the header tank does look a bit stained brown. However, I've made a note of your suggestions and will put them to the mechanic when I take the bongo to him. By the way, he's a bongo specialist.

You've been very helpful.

Best wishes to you both

Robert

V6 seems to survive overheats better than diesel but somethings clearly wrong with the cooling system as this shouldn't happen. A thorough inspection and overhaul would seem to be on the cards. Good luck, keep us posted.

[Simon Jones]

Really there's only 3 reasons why the coolant can 'boil up' from the header tank:

1) Air has got into the system as a result of a leak that has either allowed coolant out (so the level in header tank has dropped too low) or air has got drawn in to the system. The hot air pockets then expand and the extra pressure forces coolant from the overflow.

2) Combustion gases are getting into the coolant either from a cracked head, leaking head gasket or in very rare cases, a crack in the engine block. The V6 is not known to suffer these problems. I can only recall reading of one person who's had to replace a head due to a problem.

3) The cooling system is in poor condition and not capable of taking the heat away fast enough. This could be due to a blocked radiator, thermostat stuck in the closed position, use of too weak coolant mix or failure to hold the correct pressure such as if the header cap is left off. By running the system under pressure, it increases the boiling point of water from 100C which reduces the likelihood of it boiling up. Good quality anti-freeze of th correct mix will also help increase the boiling point as well as be more thermally efficient at taking the heat out of the system.

Unfortunately, these 3 factors often combine together to produce disasterous results. A small leak can cause the level to drop, air gets into the system so there is a hot-spot and the head overheats and cracks which allows combustion gases into the system which then force out more coolant, and the cycle continues.

My guess would be that in your instance, the level has dropped so air has got into the system and even though you've topped it back up again, if it's not been bleed then the system will tend to boil up when put under the extra load of driving up mountains in a hot climate. The V6 requires to be bled in the same way as a diesel so the YouTube videos will give you a good idea of the process. The only engine that does not require bleeding is the 2 litre petrol as it has a different arrangement on the header tank.

[Northern Bongolow]

just to firm up on simons post above,
the cooling system natural produces hot temperatures when working correctly, with this heat comes pressure, the system needs this pressure to raise the boiling point of the coolant you have in your bongo. if you have a leak in your plumbing somewhere this pressure is lost so the coolant can boil early. the same can be said if at altitude as the unpressurised coolant boils at a lower temperature the higher you go up.

[mikeonb4c]

just to firm up on simons post above,
the cooling system natural produces hot temperatures when working correctly, with this heat comes pressure, the system needs this pressure to raise the boiling point of the coolant you have in your bongo. if you have a leak in your plumbing somewhere this pressure is lost so the coolant can boil early. the same can be said if at altitude as the unpressurised coolant boils at a lower temperature the higher you go up.

Very valid point there Ady.