steam - split rad or spilt water?

[NiceCupOfTea]

I've been doing a little surgery on the neglected cooling system of my MX-5 - temp guage always shows fine (except for once in very heavy traffic on a hot day when it crept up) but the expansion tank has been bubbling regularly.

Replaced a couple of hoses, new genuine stat, new genuine rad cap, reverse flushed the radiator which is original but looks in OK condition, no blue stains.

Have used some flushing stuff on the cooling system, and it came out black! Flushed, filled with water, ran up to temp, drained again - brown. Have flushed, filled with water and run up to temp again.

This time I noticed a bit of steam from around the rad cap - pretty sure I fitted it properly but too hot to check atm! A lot of water spilt down the rad while topping up/burping/bleeding. Was still doing it after a couple of minutes though...

Is this normal behaviour for water boiling off or do I have a cracked rad on my hands after all that?

[Steve_D]

Most likely just your spilt water.
You will pretty soon know if it is leaking as the temp will shoot up because you have no system pressure allowing the water to boil at a lower temp.

Steve

[NiceCupOfTea]

Cheers Steve.

I think I will run with water for a couple of weeks and see how it goes - if it's OK I'll drain and fill with coolant.

[109 Bob]

NiceCupOfTea said:

but the expansion tank has been bubbling regularly.

Leaking head gasket pressurising the cooling system possibly.

[NiceCupOfTea]

109 Bob said:

NiceCupOfTea said:

but the expansion tank has been bubbling regularly.

Leaking head gasket pressurising the cooling system possibly.

Now that's the sort of thing I really don't want to hear! I know what you're saying and it has been at the back of my mind - coolant was filthy and still coming out yellow/brown after 2 or 3 flushes, but otherwise it runs fine, no steam from the exhaust, not using any coolant, and my mechanic hasn't noticed anything untoward.

[109 Bob]

I hope it isn't & they are very easy to check nowadays. They use a tester tube with a blue liquid connected to the header tank, if the liquid changes to a green/brown colour the gasket has gone. Easy, cheap & will put your mind at rest.

[NiceCupOfTea]

Yes, I've used one before. I think this is unlikely (no bubbling in the rad while I've been flushing the system, no steam, no mayo, just some sludge in the cooling system (but on a 16 year old car that has not been looked after)) but if I still have problems then I'll get one of those ebay block tester kits.