Chasing the elusive coolant leak
Entry posted by Dommo
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Ever since the car was built (and technically before whilst the engine was in the MX5) there's always been a coolant leak of some sort. I fixed most of them whilst the engine was out during the build but one remained - just above the oil pressure sender. I'd originally caught this leak and 'fixed' it by replacing the head gasket. Here's the leak from last time:
As we're in a spell of cold weather with the roads once again salty, it seemed like a good time to strip it down and take a look. As opposed to the rest of the Winter, where I've done sweet FA 
The oil pressure sender definitely had coolant on it, and the oil cooler had marks too. I poked the camera down for a better look:
There's signs of coolant 'spray' all over the place, mostly to the left of the oil cooler. However, there wasn't any tell tale marks above the oil cooler, which suggests the head gasket isn't at fault. I needed a better look so I set about removing the inlet manifold. I think it would have been easier to remove the engine than faff about in there. I look like I've been self harming!
Still, several hours later, most of which spent wondering where I've put the spanner now and the inlet manifold was split from the head,
Certainly doesn't look like it's coming from the head. However, there's not a lot of coolant connections around there. I took off the oil cooler outlet pipe which looked a little worse for wear.
It doesn't look happy, but there's no obvious cracks or splits. Back to the oil cooler:
My suspicions are that there's a tiny crack forming in that pipe. As the coolant heats up and the pressure increases it will open up and spray out towards the back of the engine. Once the coolant is up to temperature the thermostat will have opened and so the pressure in that area will reduce and so it won't leak. That's why it's been difficult to catch and why it doesn't leak much. It's like you have to top it up every x journeys rather than x miles.
I've ordered replacement inlet and outlet hoses and new hose clips for good measure. Hopefully the solution is that simple!
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