Overheating/coolant boiling after coolant change and bleed

[mikeonb4c]

It would be interesting to mix some old coolant with some new coolant in a bucket to see just how significant this gelling problem is. Has anyone ever done that? It seems incredible that makers of antifreeze could have allowed such a potentially ruinous problem to have got out of the R&D barn.

[Northern Bongolow]

before you try again to bleed the system you must first establish that the system is air /coolant tight, or there is no point.

on the expansion tank there is a little black pipe, fit a car inner tube valve to it via what ever means you need to, then inflate the system with a foot pump with gauge on it, up to 1 bar and let stand for a min or two, if the pressure drops you have a leak. doing it this way gives you time to look round for the leak without the engine running.

your coolant level drop may be explained by the following.

when hot and capped up the system is under pressure, about 9-10 pounds when up to temp, stop the engine and if leaking the pressure pushes out coolant, when the pressure reaches zero it then allows air to be sucked into the leak as the coolant cools and slightly contracts, this depends on ambient temps, a warm night will suck in less air than a real cold night.
NOW THE IMPORTANT BIT.
depending on where the leak is, the amount of air entering the engine and pipework MAY hold up the level of the coolant, so a leak at the top end of the engine may be seen as a big drop in coolant level,as this air can get to the expansion tank, but a low down leak may be trapped in pipework or the head and hold coolant up in the tank.

SO.
maybe in your case, you have a leak, not yet found,that is holding up the level of the coolant that is only found when no coolant flow is established when the cooled bongo is started up the day after.

hope that makes some weird sense.

[Long]

Hi,

that does make some sense, however i would expect even a little drop in the coolant level after a leak. also if air was sucked back in it should also leak out a bit too??? . I will try using a vacuum filler to create a vacuum in the system. This will also show me if there are any leaks under vacuum. If not then i will fill with vacuum hopefully it will solve the bleeding problem. Also i will mix my new coolant with the old to test if there are issues mixing before actually performing the coolant change.

other then draining the radiator and flushing it from the top and bottom. does anyone have instruction on how to flush the heater cores? and rear hoses?

thanks.

[g8dhe]

Vacuum filling won't always locate pin holes, the rubber tends to collapse down with vacuum fillers whilst under pressure the rubber expands and opens the holes!

[Long]

I will try using a hand pump with a gauge and pump air into the bleed hose under the passenger seat to 15psi (1.1 bar). and see if it holds. this should tell me if i have a leak in a system under pressure. I will do it while engine cold.

hoping it will hold. if it does then i'll drain, flush, vacuum fill and hopefully my overheating problem will finally be solved. if a there is a leak.. then i guess i'll be looking for it, it must be a very tiny leak.

Thanks for all the advice.

[cmm303]

Rear heater is easy to flush. Take both rubber hoses off heater (underneath behind driver) and stick a hose on each spigot in turn.

Front is harder to access. From underneath see if you can trace hoses from the heater and remove them from their metal pipes so you can get a hose on them. I did this with a lot else removed so not sure how easy it is. To access the heater spigots from above you'll need to remove the cabin air recycling ducting.

[mikeonb4c]

Be careful with rear heater - vague memory but i think i was told the plastic spigots hoses attached to embrittle with age and musn't have clips overtightened (if you're using jubilee) or otherwise be treated roughly.

Has anyone suggested pressure testing the system?

[haydn callow]

2/3 replies mention pressure testing.....


Problem is, if you have overheated the cylinder head and the temp gauge went across to hot at any time .... You could well have cracked the head and the crack is causing combustion gases to enter the cooling system and chuck the coolant out of the expansion tank.

[Long]

I actually did a pressure test yesterday, with the engine cold. I pumped 15 PSI (1 Bar) into the system. it held up and stayed at 1 Bar and did not go down at all I held it for about 1 min before releasing. it looks like there are no leaks.

if i have a crack in the cylinder head, shouldn't it leak when i pressure test it?

thanks for the info about flushing the rear heater. I will flush this as well when draining everything.

Also with the point about the crack. My system does not overheat/boil over when the A/C is off. it only boils when the AC is turned on.

[haydn callow]

The cracks often only open up when the engine heats up.

[Long]

I do hope it is not a crack given it was working perfectly fine before this coolant change. Also when it did over heat. on the dash temp indicator it only went past the middle by a slight bit before i turned the engine off. as soon as i see it go pass middle, i shut the engine off. also the bongo was driving very slowly less than 25km/ hour, reving less than 2.1 each time.

[haydn callow]

Finger crossed for you!!

[Northern Bongolow]

just have a look at this thread, it shows how you can have a hard to spot leak that only leaks when on neg pressure and cold, the bongo running warm can seal up the leaking seal when it warms up and pressurising.

http://igmaynard.co.uk/bongo/forum/view ... ak#p572203

[Long]

Hi,

i am looking around for coolants. The one at my local auto store. sells asian long life coolant but it is yellow in colour. Also the Prestone antifreeze we have here in canada is yellow in colour. I am having trouble finding green coolant. However the prestone antifreeze does say you can mix with any colour any vehicle. also it says "silicate, borate, nitrite and amine free. Prestone contains trace amounts of phosphates, however they are present in such small quantities the product is effectively phosphate-free."

Would this coolant work for the bongo even though it is yellow, and the original was green? thanks and much appreciated.

[cmm303]

Hi,

i am looking around for coolants. The one at my local auto store. sells asian long life coolant but it is yellow in colour. Also the Prestone antifreeze we have here in canada is yellow in colour. I am having trouble finding green coolant. However the prestone antifreeze does say you can mix with any colour any vehicle. also it says "silicate, borate, nitrite and amine free. Prestone contains trace amounts of phosphates, however they are present in such small quantities the product is effectively phosphate-free."

Would this coolant work for the bongo even though it is yellow, and the original was green? thanks and much appreciated.

There is no hard and fast standard with the colours. In the UK generally red/pink is used for OAT (long life) a/f and green/blue for non-OAT (2 yr) a/f but, as I understand it, without international standards it is up to the manufacturers.

Hopefully a real a/f expert will be along but you would be working along the right lines by checking out the specs, rather than being bound by colour.