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Mazda MX5 NB, Coolant Change

Yet another part of the car that made me question who worked on it last. I needed to change the coolant as I did not trust what was in it.

When I first got the MX5 I did the usual check over, and checked all the fluid levels. One thing I noticed was that the coolant was a weird color. It wasn’t green, but sort of a yellow color, but smelt like anti-freeze.

The aftermarket aluminium radiator doesn’t appear to be too old, so I suspect the liquid in the cooling system isn’t old either, but I didn’t trust it. My coolant must be green (unless OEM is derp like VW).

After work today I grabbed some more of my favourite coolant. This is the stuff I run in the Rover, and its done me well. Its nice and easy to wipe off the floor when it inevitably leaks/spills out of the Rover too.

Being the little car it is, the radiator is right there and I didn’t have to jack the car up. My spill tray and catch pan fit perfectly under it. I used a 24mm spanner to remove the drain plug on the bottom.

This is what came out

Now normally I would be worried if my coolant came out this color, it could be what is termed “milky” and indicate a blown head gasket, but in this case I actually think it’s the type of coolant used. I suspect it’s something like Nulon One, which is a yellow brown color. There was no typical oily-ness to the coolant (or coolant in the oil), no frothing, no odd smell, no bubbling etc, so not a head gasket.

It kinda looked like banana milk, whilst still being watery and transparent

Being such a small car I used the radiator cap to regulate the flow of coolant into the pan, as my pan wasn’t big enough to contain all the fluid at once. I could have the cap in one hand creating a seal on the top of the radiator, and screw the drain plug in with the other hand. Small car ftw.

When nothing else came out, I plugged the radiator back up and filled it with plain water and ran the engine to cycle it through. I didn’t run it long as I didn’t want the coolant hot, so the thermostat didn’t open, but it seemed to get more of the stuff out, as this is the pan for round two

Once I was happy that I got as much out as I could, I mixed up some 50:50 coolant in another bottle, and using my new funnel, poured it in

I wrapped some insulation tape around the bottom of the funnel so it would create a seal with the neck of the radiator. This increases the coolant height to help remove trapped air bubbles, and gives a small amount of coolant to use when the radiator burps air.

I also needed to clamp off the overflow hose as it filled the overflow bottle from the neck of the radiator

I did take the opportunity when the radiator was draining to remove the overflow bottle and clean that out too

I bled the system by keeping it topped up with coolant, and running the engine until the thermostat opened and the top radiator hose was hot. This did take a while, so not sure if the thermostat is a bit slow, or if its normal. The gauge (which is apparently almost useless) was at operating temp for ages, well before the thermostat opened.

I also tested the fans activated, which they did. After a quick drive I was satisfied that it was keeping its coolant inside, the heater is hot as hell and the temps were good.

Another thing checked off the list. I have the oil and filter for the engine, and the oil for the trans, i’m just waiting on a delivery of parts for the gearbox before I change that oil.

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