Losing my coolant, and my mind

I am hoping someone here can give me ideas. I am continuing to lose coolant, and I cannot figure out why. Here is the history of the issue. One of my coolant pipes cracked in August, and I got it replaced. They did a dye test at the time, and it came back fine. It was just the coolant pipe. Things were good for a bit, about 2 weeks, but I again noticed water disappearing, about 250 ml per 250 miles. The water seemed to disappear when the car was under load, basically, it was fine when it was at slower speeds, but if I got it over 70, it got bad. There was no issue with overheating at all, both the coolant temperature and the oil temp were rock solid in the lower end categories on both.

Then I had another crisis, with the shifter cable snapping, so back to the shop it went, and I asked them to look at why I was losing water. They found a leak at the water pump and replaced it. They also replaced the cap on the coolant tank. However, there was no sign of water leaking anywhere else. Again everything seemed fine for about 2 weeks, but yesterday, I again noticed that coolant was missing, at essentially the same rate. I drove 125 miles, and it was down 125 mil, which is almost identical to the previous time. Again, the temp is perfect, and everything seems to be running just fine, other than the disappearing coolant.

I am almost to the point of just doing the head gasket to rule that out, that that is major surgery if it isn't the cause. If anyone has any ideas, or places I could look for this, it would be really helpful.

I would add a dye to the coolant, run the car as normal and then, using a blacklight, look for signs of glowing coolant. It could be that the gasket on the inlet manifold is leaking, the engine to heater coolant rail or the head gasket on the exhaust side, which can be very difficult to see except for from under the car.

Thanks. They did a dye test when the pipe blew, are you saying that it should be repeated? Is so, what dye would I use?

If it is an MGF with the plastic inlet manifold, check under the nearside of the engine for coolant coloured staining. The plastic manifold tends to warp and cause a leak when hot. It evaporates on the engine block and so doesn't reveal itself by dripping. You can replace the plastic manifold with an alloy one off a 135 TF.

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M

Thank you. I will see if that is it.