Bongo Fury

Hi all, I have just had an eventful return trip from a night away in my V6 petrol.

10 miles from home I filled up with fuel, noticed a bit of steam and thought I could smell coolant. 5 miles later I was watching the temperature guage fluctuate up and down and then go too high for comfort so I pulled over and looked underneath. I could see coolant dripping from the plastic engine cover thing underneath. I shut off the engine and carefully opened the expansion tank which overflowed for quite some time spilling boiling coolant onto the road. After it had subsided I used the fresh water from my water tank to top up the expansion tank so I could get home. It took about 3 litres.

On the way home the temp gauge stayed where it should and I looked underneath and could not see any dripping but as I was concerned that tonight could be another big freeze and that I had put a load of fresh water in I have just drained the system from the rad drain valve with the expansion tank lid removed.

The problem that I have now is that I dont know where the leak came from. From what I can see of the hoses they look ok but I cant see them all or the full length of them. I can see where they join with clips to the metal pipes there is a load of crusty crud. What I can see from the passenger side under the passenger seat is some coolant on the electric fan thing that points at the engine and what also looks like some on a round thing with a black cap that says "TANK" on it on the passenger side.

Does anyone have any idea how I find the point of failure? Do I need to refill the system again and run it until I see where it is escaping from?

The bongo has done 75K miles and is pretty much rust free looking at the steel pipes etc,

Any advice would be welcome. I am tempted to just fill it as best I can with tap water and try to get it to a Bongo friendly garage to sort but I dont know if this will be possible if it is leaking.

Can anyone recommend a garage near Knutsford (Cheshire) that are Bongo experts? I think there is one in Wigan which is about 30-40 mins away.

Thanks, Ian

dont drive it at all until you have found and fixed it. find ian taylor in the potteries somewhere he will advice and maybe pick it up etc.

ive sent you a personal message about how to pressure test the system.

The black plastic cylinder under the passenger seat is part of the petrol fume vent system. There is at least one metal coolant pipe that runs along the chassis member at point. Towards the front of the compartment is a rubber pipe that goes to the engine by the A/C compressor, and theres another rubber pipe towards the rear of the compartment that links to more metal pipe work that goes off to the rear heater. None of these pipes are particularly known to fail, so it may be you have a pin hole in a pipe elsewhere which is spraying coolant around.

Other pipe that is in that area is the bleed pipe which should be clipped to the rocker cover.

There is one nasty area of pipe work at the very front of the engine approx under where the gear selector is. There is an aluminium casting that joints the top of the head to the thermostat and the bleed pipe. Mine had a slight leak from the joint from the pipe at the front where the aluminium had corroded under the rubber. Don't have a photo to hand unfortunately.

Whatever you do, follow the same bleeding proceedure as with the diesel engine to get rid of the air in the system. The V6 seems a little easier to bleed, but I find it takes longer to get it up to temperature to open the thermostat which is when the level in the expansion tank is most likely to drop as the air is expelled.

Many thanks for the replies. Hopefully there has been no lasting damage caused already - how do I tell if there has though? Will there be gunk in the oil on the dipstick?

Anyway, my current thoughts are to refill the system with fresh water (the weather is milder now too) and run the engine on the drive to try to see where the point of failure is. I have watched the youtube videos on how to bleed the system so I will try to incorporate that as best I can without the custom built funnel that they seem to use. Hopefully I wont get scalded!

Its a shame its winter nights now as all this has to be done in the dark after work.

Hi guys,

Now its the weekend and I have had some daylight I have filled up the coolant system just with water to try to find the leak and give the system a wash out at the same time. I followed the instructions off the site and I think I am right being able to leave the lid off the expansion tank while testing? However it got to the point when the coolant(water) boiled and it errupted out of the expansion tank in quite an spectacular fashion, all over the leisure battery etc.

At the same time the radiator fan kicked in. Would you expect the water to get to boiling point or is something else wrong? I expect this may be a dumb question!

I let the boiling water spill out until it was safe to fit the lid on the tank and ran the engine for a bit longer looking for leaks now the system was under pressure but I could not find the one that caused me the issue last Sunday.

Thanks for your help.

Ian

Why leave the lid off ? Its a pressurised system so you want it up to pressure to help find the leak ...

I'm not far from Knutsford and I take mine to Adrian at Japan Direct in Bury because if I have to leave I car I can get the tram straight back to altrincham (and you take the knutsford train from there). Otherwise, I have a lovely time in Bury market whistle he does the car.

U/v dye and lamp would identify where leak is, assuming you have one. Odd its boiling over, even though it will do so easier with cap off and system unpressurised. You don't want it doing that if you're doing a dye test!

Hi, I left the lid off as that seemed to be what the instructions said for refilling and bleeding the system and as far as I could tell from the Youtube video was going on but its not that clear to me at what point the lid gets put back on - I thought it was after the thermostat had let the coolant flow through as it may need topping up at this point.

It was a very short time after the bottom pipe to the radiator had begun to get warm that it errupted with boiling water. I had to wait for the erruption to end to get the cap on.

Should it not reach boiling point then?

If it does, what do you think the problem is - the Thermostat?

Thanks,

Ian

You leave the cap off while bleeding, then refit it once done. The thermostat opens somewhere mid 80 degrees which should be about when the fans come on. It takes a while for it to open, when it does, the bottom hose on the radiator (passenger side) will get noticeably warmer. On mine, the pipe coming out the thermostat housing to the radiator doesn't get much above 20 degrees in this weather, but when it does it will go up to about 80 degrees, although it will be cooler at the radiator end of things.

The cap needs to be on during normal use to allow the pressure to build up which will increase the boiling point. Personally, I would stick the cap on and then in the morning you will probably find the level in the expansion tank will have dropped by a cm or so, so top it back up to the maximum line, replace the cap and let it warm up again. The level will probably rise by 1 - 2 cm in the tank which is normal.

If you have a leak in the system it can allow air to get in which causes an airlock which prevents the coolant circulating correctly which is when you start to get hot spots which can then start to boil the water.

Get the van up on ramps or axle stands so you can remove the plastic engine trays. There are about 10 bolts on the main one and then once that's off, you will have a good view of all the main hoses and pipes.

It should be possible to find the leak with a torch and following all the pipe work around the engine, gearbox and rear heater. If you can't see anything obvious external, then you have to consider the possibility of a problem within the engine or one of the heater matrices.

Hi Simon,

Many thanks for the reply. I will have another go at filling it, maybe just with water again to practice/allow me to get to a garage.

I am wondering now if there is a problem with the Thermostat due to the boiling issue?

Thanks,

Ian

Personally I would change it anyway with a genuine Mazda part (available from club shop). To change it:

-Stick front end up on ramps
-Drain coolant from tap on bottom of rad
-Undo engine undertray
-Undo 3x 12mm (?) bolts on the thermostat housing. Prepare to get a load more coolant pouring out as you loosen the bolts
-Clean out the mating surfaces of the thermostat housing. There is no gasket as such, but the 'stat is fitted with a rubber O-ring around the circumference which forms a seal when two halves bolted together
-When re-fitting, 'stat can only go back in one way up & you want the little bead at the highest point

You can see the thermostat housing here:



Test both 'stats in a pan of near boiling water. The new one should open slightly earlier, slightly wider & close slower than the old one.

Simon once again thanks for your help. I am planning to take it to my local garage tomorrow for them to assess. I would like to get the thermostat changed no matter what. Its the ideal opportunity.

I just don't have time to attempt the thermostat myself with work and family commitments along with the short nights.

Thanks, Ian