Cooling Conundrum

[wittyname]

My Freda which I have owned for almost a year now has started behaving oddly. On a trip of 25 mins dual carriageway at a fairly constant 60mph+, towards the end of the trip the Temp Gauge starts to move slowly to the wrong side of vertical. Panic ensues and a steadying of the throttle to 40-50mph gradually causes a reduction to One O'Clock. Coming off the dual carriageway onto B roads a steep hill causing high revs and reduced forward speed sends it towards the dreaded H. Again reduction of revs and continued steady progress causes it to fall back towards the vertical. arrive at destination and bonnet up shows coolant level way up above the full marker but not overflowing. After an hour and a half's rest, coolant level is back to normal and the return journey is incident free if slightly slower. Van has been recently serviced and cooling system pressure tested to relieve my paranoia. No leaks were found.
I am due to go to Wales in three weeks and would like to have confidence that the old bus
will make it. Firstly I need to try and work out what may be causing it and secondly what should I do when the gauge starts heading up to the H zone - apart from panic !!

[Ian]

Sticking thermostat? Scavenging fan not operating correctly?

[helen&tony]

Hi
I tend to agree with Ian on thermostat, or maybe the cap on the clear coolant tank is faulty, causing pressure loss
Cheers
Helen

[paul9]

possibly an underperforming radiator,could be clogged.

[Aethelric]

My Freda which I have owned for almost a year now has started behaving oddly. On a trip of 25 mins dual carriageway at a fairly constant 60mph+, towards the end of the trip the Temp Gauge starts to move slowly to the wrong side of vertical. Panic ensues and a steadying of the throttle to 40-50mph gradually causes a reduction to One O'Clock. Coming off the dual carriageway onto B roads a steep hill causing high revs and reduced forward speed sends it towards the dreaded H. Again reduction of revs and continued steady progress causes it to fall back towards the vertical. arrive at destination and bonnet up shows coolant level way up above the full marker but not overflowing. After an hour and a half's rest, coolant level is back to normal and the return journey is incident free if slightly slower. Van has been recently serviced and cooling system pressure tested to relieve my paranoia. No leaks were found.
I am due to go to Wales in three weeks and would like to have confidence that the old bus
will make it. Firstly I need to try and work out what may be causing it and secondly what should I do when the gauge starts heading up to the H zone - apart from panic !!

Hi Wittyname
If the coolant level is going up and down you must have trapped gas in the system somewhere. It is expanding when it is hot to push the water higher up the header tank and then as it cools down the water drops back to the usual level. It could be air or it may be that the water is boiling somewhere and producing a steam pocket. It would boil if the system were not pressurised, for example if the cap on the header tank was defective??

Dave