Wierd overheating issue, any ideas?

[mp3oplecarrier]

Hi, I took a quick trip out to asda this afternoon, no dramas, spent an hour in the shop then jumped back in the bongo, put the aircon and heater on to clear the screen and waited about5-6 mins for someone to be considerate enough to let me reverse out of my space.

I drove no more than 1/4 mile and the mason alarm went loopy, I pulled into a layby and jumped out expecting to see water pouring out of a burst hose as usual, but no drips, no odd smells or noises. I opened the bonnet and felt the top of the rad was warm and the expansion tank was warm. Mine's too discoloured to see the level through the plastic so I left it a little while and opened the lid. First time I tried that the water boiled and splashed a little out, when I'd left it another 10 mins I opened again and could see that the level was normal.

Not being able to see any problems that I could fix, and with no facilities to bleed the system I thought I'd risk driving home with my eyes on the temp guage, when I turned on the ignition the needle went to the normal 12 o'clock position and it never went past 12:30 in the 2 miles home...

Any ideas? It's been running fine since my last hose went a few months ago with several long motorway trips with no problems. I've not topped up the water since bleeding it back then and the level looks the same....

Themostat?

Blocked Rad?

Water pump?


Thanks
Steve

[stilldesperate]

Hi Steve,

If you've enough water in the system, and the engines overheating, I would look at coolant not circulating that's the prob.

With it being cold out, and having been parked up, I don't think the stat would need to be opening so soon.
The flow (before the stat needs to open) just goes in and out of the top of the rad, and doesn't flow through the matrix, so I'd be doubtful this was the cause.

Water pump not pumping - I've no experience of, but if water couldn't be moved away from the head, then I guess temperatures will rise.

Could it be that the Mason Alarm just had a "Wobbly" ? (I've got one, and it's a well made piece of kit)

As there were no more signs to back it up, mebbe it was just having a bad day?

Now it's been stood a while, have you tried to repeat the fault?

SD

[The Great Pretender]

Try bleeding the head Steve there could be some air floating about in there, maybe the fast decompression when you took the cap off popped the air out.

[MondoBongo]

Very similar incident happened to us a few years back, a month or two after we'd had the head replaced. (had been driving quite a bit with no problems between head replacement and the incident). Ours just seemed to overheat on the motorway, we stopped, gave it time to cool down, no coolant loss to speak of.

Think it was an airlock.. apparently they can be prone to it after cooling system works if not bled properly. Though our mechanic, who's very good, said he did bleed it properly, so maybe just prone to it after coolant system works in any event !

Best of luck ...

[mp3oplecarrier]

Thanks for the input guys, I've done about 40 miles today with no problems at all.....

Steve