Soo… I was driving back from a long journey the other day and got to within 5 mins of my house and suddenly the air in the cabin didnt smell normal… I thought nothing of it and then got to my drive and saw a load of smoke coming from the passenger wing under the bonnet! I had a look and there was quite a lot of coolant everywhere…
So that night i got the plastic pan under the car off and had a good look around, the only hose that seems wet is the upper bottom (i think thats right…) hose, but i couldnt feel any cracks or see anything wrong… so i drained off the remaining coolant, flushed the system twice and then let it run up to temperature with just water in the system and hey presto, no leak! Drained water out and refilled with coolant…
I thought i had just gone through a puddle or something, but then after coming back from a 40 mile round round trip a had a looky under the bonnet and the smell was there again, as was the moisture around the same hose! In the 40 miles ive done, I have lost around a litre of coolant.
Have since ordered a new silicon hose from mx5parts, but im really not sure its going to fix the problem… Anyone had the same problem or have any ideas? The problem only seems to occur if you drive the car, if you just leave it running up to temp at idle its fine…
I’m not sure what an “upper bottom” hose is; sounds like something from Carry On Doctor.[:O] Are we talking about the bottom radiator hose, or the next section which returns to the water pump inlet?
Anyway, it sounds as if you’ve identified the problem - a degraded hose with a leak which only opens at fairly high pressure. I’m sure if you change it, it’ll be fine.
Curious if it’s a lower hose that’s gone - I thought it was generally the upper radiator hose that failed as it has the extra stress of carrying hot coolant to the rad. (That’s what happened to mine - the upper rad hose developed a split on the inside which only went as far as the woven reinforcement. So coolant wicked along the weave to the ends and, under pressure, beads of liquid would bleed out of both ends of the hose. Very odd effect.)
If the hose is starting to crack then it will leak when it is under maximum pressure - so when it’s hot and at higher revs (water pump speed increases with engine revs). The failure mode you are describing is normal.
Thats the part I ordered and im pretty sure its the one I need… I also got the MX5 enthusiasts book as the reviews seemed a little better than Mr. Haynes…
Thanks for the advise - Part arriving tomorrow with any luck, so I will let you know how it goes when I fit it!
OK, that makes sense - the return hose from the bottom of the radiator goes to a short pipe that’s fixed to the left* side of the engine compartment, then there’s another hose joining that to the engine, and that’s the hose that’s failed. It meets up with the return pipe from the cabin heater before they feed back into the water pump.
*Left as in UK passenger side. “Stage left” if you like, or right as you look at the engine from the front.[:)]
Thanks for the advise - I have replaced the coolant hose and the leak seems to have stopped I can say that I highly recommend the silicone hoses on offer from mx5parts - they are really good and look pretty decent too
Okay - the issue isnt actually resolved sigh Although the replacement pipe has slowed the leaking coolant a lot (im not losing 500ml every 4 miles anymore!) its still leaking at a rate of roughly 500 mls to a litre every 100 - 130 miles. Anyone else got any ideas? I ordered the full on hose kit for my car just in case it was a combination of hoses that were leaking, that and one blue hose by itself just looked dumb! But im not convinced its going to solve the problem…
Take a look at the water pump. Looking from the front of the car it’s on the right hand side about half way down the block. There’s a small tube comes out of it. Slightly smaller dia. than a pencil. It has a 90 degree joint, not bend, in it where two 45 degree cut joints are soldered or welded to gether. That gives way and you’ll start off with a very small leak that will get bigger as the joint opens up, then it will just empty itself quite rapidly.
It’s not easy to find or spot but under pressure it does spray water onto other hoses to give a misleading impression of where the leak is coming from.
May not be that - but it was the one and only problem I’ve had on my red car in 7 years of ownership - and was tricky to find.
Hi mate, thanks for that, ive got the hose kit so all hoses are getting replaced… I started out tonight and got 4 done in 4 hours… Sounds like slow progress, but I had to break half way through to get jubilee clips from frauds! 4 more to go tomorrow night and hopefully a bone dry car again… Will post up some pics when im done, all nice and blued out
In the end I fixed it yeah - it seemed to be a combination of the upper bottom hose going as well as the rad cap not sealing right. I bought a real cheap nasty replacement cap off ebay which just wasnt worth it. the cheaper of the two replacements available on mx5parts works just fine. I replaced all the other hoses whilst i was at it just because they were so badly worn. (one fell apart in my hands as i was pulling it off!)
The hose kit that MX5parts do is incredible value for money, looks great and is probably cheaper than sfs. Id go with them if i were you
Reading your reply regarding your water leak that you had - seems like I have the same problem as well.
It seems there is what feels like a 90degree bend coming out of the block which has a hose connected to it and this fits onto the bottom of the thermostat housing.
It is leaking from what seems like the bottom of this 90degree bend, but it is hard to see where exactly.
Just wondered if it was the same problem that you had and how you overcome it ??
I’ve got this same leak too from what I now realise is the water pump. Can you get the 90 deg pipe off without having to take the whole water pump off? If you take it off is it new water pump time or can the pipe be changed without the rest of the pump?
The pipe is cast into the pump. I had my pump replaced but afterwards thought, why not cut the 90 degree end off and put the hose onto the straight pipe that’s left?
It would need a longer bit of hose and you’d have to make sure the hose cleared all the pulleys and belts but I don’t see why that wouldn’t work, at least as a temporary fix. Got to be worth a try anyway.
Well, my slight leak has now escalated into a full blown loss of coolant… My water pump has been growling for a few months now, and as I dont do many miles in the old MX, I left it, and turned up the radio… I’ve been topping the system up as I drive, and had only noticed a few drops round the bottom of the timing belt cover… I was hoping the water pump would hold out till June, so I could spend a whole weekend, with my spanners and several cups of tea, replacing the pump and timing belt…
Today, after picking my lad up, and after adding a pint of water to the system, I smelt steam from the front of the car… Pulling onto the drive it was a full gusher… Saw that the small metal pipe leading off the lower thermostat housing had corroded clean off…!! Ordered cam belt,water pump, lower housing etc off mx5 parts last night…over £150 …
Looks like my weekend is now full…
“The pipe is cast into the pump.”
Im under the impression its a seperate casting bolted onto the waterpump… Looks like I might have to order that as well…
Well, jobs going well. Only problem is I cant find my half inch ratchet… As you can see, the rust is because the coolant was sprayed out by a rusting pipe.
One worrying issue, is that the cambelt, although still under tension, appears to be very stretched, and loops out between the two cam pulleys. This will make the timings slightly out when running, as the belt stretches taught. Good job I bought the whole cam belt replacement kit. as well as the waterpump and thermostat housing. The waterpump bearings are shot as the shaft can be wiggled about. It was squeeking and leaking, so off it goes to the scrapyard.
Can anyone tell me … do I need to take off the crankshaft sprocket, or can I take off the pully set ? I have a 21mm nut on the centre of the pulley, and 4 smaller bolts. Will the pulley come off with the 4 bolts removed ?
I can say that I highly recommend the silicone hoses on offer from mx5parts - they are really good and look pretty decent too 
I’ve been topping the system up as I drive, and had only noticed a few drops round the bottom of the timing belt cover… I was hoping the water pump would hold out till June, so I could spend a whole weekend, with my spanners and several cups of tea, replacing the pump and timing belt…
