Burping a bongo... Mine behaves differently....

[langtoftnick]

In the videos showing a bongo being burped, towards the end the engine is revved and the fluid level in the funnel goes down. Mine does the opposite. When it's revved the level in the funnel goes up dramatically, to the extent that a previously full header empties enough for the alarm to go off. This is alarming to say the least when you are holding a brimming full funnel of scalding water, even with gloves on.

My pipes have been butchered to a certain extent, the rear heater has been removed avd the pipes blanked off. The thermostat had been removed and the alarm shorted out to prevent it sounding so someone in the past has been messing with it, presumably as a result of cooling problems. I have found and fixed (I hope) a few leaks with the aid of a brilliant UV torch and fluorescent dye from ebay, but cannot find anything else seriously wrong unless there's something awry with the water ducts in the head.

Does anyone know enough about the dynamics of a bongos innards to suggest why mine does what it does?

[Simon Jones]

You say rear heater pipes have been blanked off. When I did mine I made a loop such that it retains the circulation rather than having stopped-off pipes that can trap air.

Have you refitted the correct Mazda thermostat now? It's the opening of the thermostat that tends to cause the 'burp'.

This is my 'bypass' hose which is made from the U-shaped one over the starter motor on the diesel engine.

[langtoftnick]

Fitted an oem 82degree thermostat which opens ok, lower rad hose is cold until engine is hot then it gets hot. I have connected the rear end of the passenger side heater metal pipe to the thermostat, and blanked off the tee where the original was fitted. May be better to take a rubber hose across tonthe blank on the drivers side?

Will have to refer to me engine with your pic to see what you have done.

Thanks

[Simon Jones]

That photo is taken from under the drivers side of the van approx just behind the door looking forward. Difficult to describe it but it makes sense from underneath. It can also be done with a new piece of hose from under the passenger seat, round and down the back of the engine. Mines a V6 but the process is the same.

[mantaJim]

Is yours a V6 ?

Mine (a V6) is the same as yours in that the level in the funnel rises with revs - I read elsewhere on here that someone else with a V6 reported likewise

Cheers Jim

[billymansell]

Is yours a V6 ?

Mine (a V6) is the same as yours in that the level in the funnel rises with revs - I read elsewhere on here that someone else with a V6 reported likewise

Cheers Jim

Yep, my V6 does the same.

[langtoftnick]

No its a 2.5 TD and its doing my head in.

Ran it up and bled it yesterday, then kept it topped to the brim as it cooled down, until late last night so I could see if it was still leaking. This morning it still needed about 250ml to bring it back up. No idea where it is going. No leaks visible with the UV.

Can only think it's going internally somewhere, but the oil isn't foamed up and a dye test shows no combustion gases in the water system. Must be the exhaust I suppose *sigh*

Any more ideas would be very welcome.

[langtoftnick]

I thought that maybe the return to the rad wasn't flowing properly which meant that an increase in revs generates more pressure as it can't just flow back to the rad - causing the level to rise in the funnel.

I am guessing that the level should fall due to bernoulli effect of the faster flow across the end of the bleed pipe in the the thermostat, reducing the pressure there, but if it's not flowing it will increase pressure instead.

Maybe the thermostat isn't opening properly - which would have the same effect I suppose.

[Simon Jones]

It is normal for level to drop following a bleed once its cooled down as the remaining air is purged via the expansion tank. May even take a couple of runs before it finally stabilises.

[langtoftnick]

hey wanna know something dumb? Thermal expansion coefficient of water is higher than that of water/antifreeze. I was testing with water so as to avoid the expense of maybe dumping expensive glycol. This means I was underestimating how much it would expand in the tank when hot, so a full expansion tank when hot shrinks quite a bit when it cools off. Over 13 litres its the best part of 1/2 a litre between 10 and 90 degrees.

Level has now stabilised after 12 hours of cooling. Maybe the leaks have gone after all?

[Northern Bongolow]

in the initial stages the coolant level in the funnel drops when the revs are applied.
bottom hose cold.

as the temps rise during bleeding the stat opens, bottom hose hot, the level in the funnel raises when revved this is when the burp is seen in the funnel.
the stat is a 2 part stat, the final stage of the stat opening is when the flow is diverted via the the bypass hose, this changes the flow so the funnel fills when the revs are applied.

look at page 4 of this link for good animation by steve widdowson.
http://www.igmaynard.co.uk/bongo/forum/ ... at#p511661

this one is also helpful.
http://www.igmaynard.co.uk/bongo/forum/ ... ng#p353190

[langtoftnick]

That is EXACTLY the sort of information I was looking for, fantastic, thank you. I was worried that something was blocked or piped in reverse or something.

The graphics will take a little working out, but, again, a really useful resource. Maybe these should be in the factsheet section of the site somewhere. The coolant system does seem to be a constant bone of contention!