Bubbling in expansion tank
Discussion
Hello,
I took the '5 out yesterday (a '95 1.8) to Box Hill, which is about twenty minutes away. It was quite hot out and I noticed when we got to the top that there was boiling water in the expansion tank. At no point did the fan come on and I don't know what the temperature sensor in the car said. Overall, we lost about 200ml of water, dropping it down to the minimum line.
Driving home in clear air and low-revs, the temperature gauge didn't stray from the centre, there was no boiling and the water level remained constant.
Checking the car over this evening, the oil is clean and the water in the expansion tank looks fine - just like it always has. I also checked the radiator, and the water was to the top of that. If I'm being picky it did look a little rusty, but that's consistent with the water in the expansion tank.
The car had a new waterpump last year, though the coolant was not refreshed at this time, but recycled.
From looking at the forums, it looks like it could be the fan, a blocked rad or the rad cap. Any ideas?
Thanks!
I took the '5 out yesterday (a '95 1.8) to Box Hill, which is about twenty minutes away. It was quite hot out and I noticed when we got to the top that there was boiling water in the expansion tank. At no point did the fan come on and I don't know what the temperature sensor in the car said. Overall, we lost about 200ml of water, dropping it down to the minimum line.
Driving home in clear air and low-revs, the temperature gauge didn't stray from the centre, there was no boiling and the water level remained constant.
Checking the car over this evening, the oil is clean and the water in the expansion tank looks fine - just like it always has. I also checked the radiator, and the water was to the top of that. If I'm being picky it did look a little rusty, but that's consistent with the water in the expansion tank.
The car had a new waterpump last year, though the coolant was not refreshed at this time, but recycled.
From looking at the forums, it looks like it could be the fan, a blocked rad or the rad cap. Any ideas?
Thanks!
According to this page you can test the fan by shorting 2 terminals in the diagnostic connector, I've never done this so not 100% sure this is accurate.
http://forum.miata.net/vb/showthread.php?t=281249
When my 1992 1.6 blew the HG it would bubble through the expansion tank at idle, and overflow or empty the tank when hot, despite running just fine and showing no mayo in the oil or oil in the coolant. Just after blowing the HG (in a massive cloud of steam from the exhaust) it drove a further 5 miles with no issues, then I topped it up and drove it 15 miles home, again with no issues or temp gauge indication of the fault, so it's not always obvious what is up.
I would test the fan, buy a new genuine Mazda rad cap and fit a new thermostat (cheap enough and easy to do), then see what happens while keeping a very close eye on the water level and temp gauge.
http://forum.miata.net/vb/showthread.php?t=281249
When my 1992 1.6 blew the HG it would bubble through the expansion tank at idle, and overflow or empty the tank when hot, despite running just fine and showing no mayo in the oil or oil in the coolant. Just after blowing the HG (in a massive cloud of steam from the exhaust) it drove a further 5 miles with no issues, then I topped it up and drove it 15 miles home, again with no issues or temp gauge indication of the fault, so it's not always obvious what is up.
I would test the fan, buy a new genuine Mazda rad cap and fit a new thermostat (cheap enough and easy to do), then see what happens while keeping a very close eye on the water level and temp gauge.
I had this, and it was a sign of air in the system due to a holed radiator. Check your fluid levels when the car is cool. Water will be forced into the expansion tank if the car gets very hot, but bubbling like a percolator means air is being blown into the tank. This does happen with radiator caps going funny too, but can also be a symptom of other problems such as HGF. Did you check your water levels when the car cooled down?
It'll boil because it's at over 100C when it's expelled from the cooling system under pressure, so it'll immediately boil in the tank. The idea is that as the car cools and the water in the cooling system contracts the vacuum with suck the water back in from the expansion tank. If there is a net loss from radiator+tank when it's all cooled downthen you have a problem with the cooling system somewhere.
Gassing Station | Mazda MX5/Roadster/Miata | Top of Page | What's New | My Stuff