Mk1 1.8 Eunos - steam pouring into cabin

[NorthernSky]

Evening all,

Had a problem with my Eunos a few days ago which has been temporarily solved by turning all heating to 'off', but the problem is still there.

When directing the fans to body or feet after the car has been run hot for 30 mins or so, I can hear a hissing sound and steam is coming into the cabin through the heater vents. When stopped and with the bonnet up, I can see a lot of water settled near the rubber pipes leading from the radiator into the cabin.

Has anyone had this problem before & what's the fix like? Hoping it won't be a cabin panel removal job... The car is nearly 20 so issues were to be expected

TIA!

[Gilhooligan]

The coolant hose from the back of the engine block to the heater matrix is well known to fail. Mines burst and emitted steam everywhere. Worth checking that. Pretty easy fix if it is.

[MX-5 Lazza]

As above, check the coolant hoses to the heater matrix. If the CAS has been dripping oil onto it that will cause it to fail and is a very common fault. But as you are getting steam into the cabin I suspect it might be the heater matrix itself that is leaking which is a much bigger job.
For now though, make sure your coolant levels aren't dropping too far. A coolant leak in that area has boiled a lot of MX5 engines and the coolant gauge is next to useless.

[snotrag]

I'll back both of those up -

Its either a holed coolant hose at the back of the head, of the matrix.

The 2 small coolant hoses are very common failures, and cheap - I would suggest you need to order those two first off anyway.

Get the car hot, and check under bonnet. You'll need to squeeze the hoses as often its just a pinhole that might not show up. Make sure you turn heating on/off. If it doesn't appear to be the hoses it could well be the heater matrix.

This means dashboard out - but I promises its not as hard as it sounds.

And if you need to replace the matrix, you'll need the two hoses anyway as you have to cut them off to get the matrix out anyway.

So I suggest you order the hoses first, and in the meantime keep a very close eye on your coolant level!

[MX-5 Lazza]

Not sure but I think the coolant is routed through the heater matrix whether the heater is set to hot or cold. It just redirects the air around the matrix for cold. Pretty sure there isn't a coolant "tap" to stop the coolant flow through the matrix.

[Rickyy]

Not sure where the air is taken from for the heating, but is it possible that the coolant hoses are split and the steam is entering the air intake for the heaters?

[NorthernSky]

Thanks guys, your replies have been an enormous help. Going to look at it over the next few days and sort it out, i'll post back when it's fixed up! Suspect it's just the hoses as they look old and probably where the failure happened. If not it'll be the dash cover out I think...

[Rickyy]

Be careful when you remove them from the bulk head, the connections for the heater matrix deform easily, so try not to use excessive force.