Weak radiator cap?

Have you bled all the air from the engine coolant passages? There may be a couple of bleeder plugs to facilitate this. Hot air expands a lot.

John

^^^^^^^^^^^^^^^

I think that's your problem. You shouldn't need to fill it to the max mark. Where does all that coolant go when it gets hot and expands ;-) ?

Out the pipe of course....

Leave the level somewhere between min and max - (i'd go nearer min if it were me) and you should see that when the engine is hot it is much nearer max. That's how it should work. So, if the level is already at max, the expanded coolant has to go somewhere when hit, so it goes out the expansion tank vent pipe. Then when it cools, it goes back down near min. This is also why it never drops below min, as it's working as it should.

hth

Mike

There should be plenty of capacity above the MAX mark on the expansion tank to allow for expansion. Filling below the MAX is not curing the cause of the problem but, at best, simply avoiding the sypmtom.

Mathew

No, although i did feel all the pipes to see if any were cold (just in case an air lock had developed somehow). All of them were hot ... very hot :)

Unless i've sprung a leak, i can't see how one would develop though. The coolant has been in for nearly three years, and i haven't done any work on the coolant system since then. The coolant level doesn't drop in the filler neck under the radiator cap, so i don't think i have a leak.

Couldn't find any mention of them in the handbook, or Haynes. I'll check this out some more though just in case air has got in somehow, thanks.

...Nick.

Thanks chaps. I must admit i was thinking along the same lines as Mathew - i.e. the space above the max mark should take care of any expansion. The handbook states to top it up to max when cold, which is what i've been doing. *However*, the handbook also suggests that it will need topping up periodically, suggesting that they expect it to dump coolant occasionally (presumably when really hot). Seems a bit silly not to allow a little more room in the expansion tank though, but it does fit it with what Mike is saying. I've seen a Mk1 MR2 with a well fettled cooling system dump a little coolant overboard when really hot too (same kind of system with unpressurised expansion tank

- although a rather more convoluted layout due to the mid-engined layout!).

As i mentioned elsewhere on the thread, i'll look into the possibility of there being air in the system, although i suspect there isn't any. I'll also buy a new filler cap, and then see how it behaves on any really hot days we may have left this summer. I'll post an update then, if anybody is interested :)

...Nick.

Different engine I expect then, but my '97 Nissan with a GA16DE engine has two, and there's instructions for purging the air in the handbook's section on changing the coolant.

I filled mine to the "full" mark in the coolant overflow bottle when I changed the coolant (cold). The level gets about half-way from there to the very top with the engine hot, but always return to "full" when it cools.

John

Just a little story from the past (1976) that may be worth bearing in mind:

A work colleague was having a problem with loss of coolant from his (then) elderly Vauxhall. He asked what we all thought and a new radiator cap was suggested as this was the cheapest starting point. The following day he reported no change and so we suggested the next step (can't remember what that was, now).

Anyway, nothing was stopping this water loss and he ended up with the engine out and stripped down, everything tested and then rebuilt. He was still losing water.

We then suggested that, as he had tried everything that could have caused the problem, he start again and buy another new radiator cap.

It worked. The first new radiator cap must have had a weak spring for some reason.

It's a CA16S engine in mine. There's no direct mention of purging air in the handbook, although it does say run it to normal operating temp, then let it cool and top back up to max (i guess they think that's all that's required to purge air).

That's what mine does most of the time. It's just when it gets really hot on a really hot day - then the level rises all the way to the cap and a little is dumped out of the overflow tube.

As i mentioned elsewhere, i'm inclined to think it's supposed to be like that from the wording in the manual. I'll buy a new cap anyway (or perhaps two with your 1976 Vauxhall story in mind!).

...Nick.