STICKING THERMOSTAT

[playnotwork]

Having troble with overheating recently.
On short journeys she quickly heats up on hills, I stop and allow to cool. Changed the stat for an aftermarket one. Initially ok and bleed well. But the next day overheated, thinking the stat was not opening.
Bought a mazda one to try and whilst exchanging, found the lower coolant hose had a hole so replaced.
Now she bleeds up ok, runs well. The next day she takes a concerning high heat to open the stat and then runs ok.
I tendto watch the dial to about 3/4, then back of the throttle and this seems to open the stat.
when she cool the coolant hoses apper loose any pressure in them.
Any ideas apperciated mlt due tuesday!

[mikeonb4c]

Could your radiator(s) be clogged. Sounds like circulation is poor. Is water pump belt and water pump working ok. Are radiator fans cutting in ok as engine gets hot? A general overhaul might be in order and fingers crossed head not yet damaged.

[Markas]

If you had a new stat on order you've probably got it sorted by now, but worth mentioning that Mazda Bobgo temperature gauges are heavily damped to avoid small fluctuations and only start to move upwards with excessively high coolant temperatures. My temperature gauge's normal reading is at about the 11 o'clock position, with the needle pointing at the thermometer logo.

[playnotwork]

Ran van down for mot today. And gues what she overheated. Has ran well for 2 weeks, I have no idea what has changed. Before the stat opens does the water circulate in a smaller loop heating up until the stat opens, or does the water pump against the head until cconduction of heat through water finally opens the head?

[Northern Bongolow]

the info supplied above would suggest you have a small leak on the system somewhere low down on the system, this is sucking in a little air each time the bongo cools down, this can take several days to build up to a good sized airlock that stops flow enough to overheat. this often hides a reduction in coolant volume as the level stays the same, as the air is holding up the level.
if the leak was high up it may force the air out through to the front tank, but would then show a drop in coolant level.
do a pressure test.