Overheating conundrum

[bongomonkey]

Symptoms are :- high temp gauge, bubbling expansion tank and leaking out through expansion tank exit hose via the cap (due to pressure)

Have changed the thermostat and refilled coolant (as per Bongo service manual!). Bongo ran fine for 2 days. Then overheating again.

When it did overheat, I waited tilll it sufficiently cooled down and took off the air duct, then the radiator cap. Water rushed into the radiator from the expansion tank (This hose joining the expansion tank to the radiator become instantly red hot ). This got me home (5 miles). The temp gauge fell to half, rose slightly and fell back (as per normal). However, this must only be a temp solution - something is causing this pressure and inability to fill the radiator.

Any help would be more than welcome.

[westonwarrior]

unfortunatly it sounds like a blown gasket or cracked head best bet is to get a garage to test it for you

It could be a blocked radiator causing the coolant to boil

does it give off smoke when starting

just an amateur guess

[Dolly1]

Hi B,M
Go for the cheapest option first.
Could be your rad needs flushing.
Also the easiest option.Best of luck

[mikeonb4c]

there was some good advice recently on here about how to quickly to a flow test on your radiator to see if it is flowing freely. Its a shame we can't find out what the weight of a healthy radiator is as that too would allow identification of radiators carrying a lot of crud. Ou of interest, what is the colour of the coolant (i.e. is it clear or dirty/cloudy at all).

Might it be best to get the coolant tested for exhaust trace gasses before draining and flushing radiator as otherwise you'll be putting clean coolant in (we all think its OK to use water to save money over 50/50 antifreeze PROVIDED its left there only short term and of course there is no risk of freezing) and it might not immediately show exhaust gas contamination.

Good luck - keep us posted.

[bongomonkey]

coolant (after putting just water in it) leaking out a very light brown - not clear

[bongomonkey]

also does not give off any smoke during starting.

[mikeonb4c]

The light brown does suggest the system has got some kack in it. In my (modest - I'm not a mechanical guru) opinion the radiator then has to be suspect No.1. My feeling is that precipitation and trapping of crud is most likely to occur there first (and anyway there's not much you can do about it IF the engine cooling bores themselves have crudded up apart from flush and hope). I'd not waste too much time before trying a new radiator (and thermostat while I was doing it although did you say you'd already done that - cant read the thread now I'm writing). And then pray it sorts it. The other thing, as suggested, is get the coolant tested for exhaust gas traces, but I would imagine that's best done once the coolant has been in place for a while as I don't know long it takes for levels to build up to those easily measured (might actually be quite quick, in which case do it before refilling with 50/50 and possibly wasting £s).

Mike

[Aethelric]

Symptoms are :- high temp gauge, bubbling expansion tank and leaking out through expansion tank exit hose via the cap (due to pressure)

Have changed the thermostat and refilled coolant (as per Bongo service manual!). Bongo ran fine for 2 days. Then overheating again.

When it did overheat, I waited tilll it sufficiently cooled down and took off the air duct, then the radiator cap. Water rushed into the radiator from the expansion tank (This hose joining the expansion tank to the radiator become instantly red hot ). This got me home (5 miles). The temp gauge fell to half, rose slightly and fell back (as per normal). However, this must only be a temp solution - something is causing this pressure and inability to fill the radiator.

Any help would be more than welcome.

You should never take the cap of the radiator first. Always remove the cap from the header tank first, and very carefully. When you do this, the pressure in the system is released by the air coming out - what you did was to releases it by forcing the water out.

The system works under pressure when it is hot, this is quite normal. Its a sealed system and when hot the coolant expands and compresses the air in the header tank. This air gets hot which increases the pressure even more.

That said, the system should not normally leak via the header tank unless the pressure is too high. The simple answer could be that you overfilled the system in which case without enough air in the header tank you would get leakage through the hose. But the temperature guage should be OK.
The most likely answer is that the system was not bled properly when the stat was changed. Air gets trapped in the bottom hose and if the bleeding is done properly, then this get into the engine and out of the bleed hose. If the bleeding was not done properly than the air stays trapped and when the stat opened under running condititions it would get into the engine, get very hot, expand a lot and give the symptoms you have.

When you say it ran fine for two days, over what mileage? If you are driving "easy" then it may take 5-10 miles for the stat to open from cold.

Another possible answer is that the stat was not fitted properly and is jammed shut.

Why were you changing the stat in the first place, was there a cooling problem?

Dave

[westonwarrior]

Do I remember some where the stat can be put in backwards???

[Peg leg Pete]

I do not think it can be fit in the wrong way round.

[Simon Jones]

PLP is correct - it physically cannot be fitted backwards in the housing.