No coolant light and no DTC means no coolant leak?
 

Will I always see the coolant light or have a DTC if the coolant level is low? I just bought my RX-8 a few days ago, and the previous owner told me it had a slow coolant leak. And you can smell it under the hood (but not in the exhaust).

After I filled up the coolant yesterday I made sure everything around the reservoir was dry, then I took it for a drive. When I got back, there was coolant underneath the reservoir. So I assumed it's a leaky reservoir and I ordered a new one.

But now I'm wondering if the previous owner was just overfilling it, thus causing it to come out of the overflow tube. It's been 9 years since my last RX-8, and I never had any coolant problems with that one, so over the past few days as I've been topping it off, it's possible I've been overfilling it as well. It's pretty much impossible to tell how close it is to the F line, so I've been guestimating. It keeps dropping down after I fill it, but maybe it's coming out of the overflow, and not out of a crack.

The coolant light hasn't shown up, and there has been no DTC relating to the coolant. So maybe I don't actually have a leak.

How dangerous is it for me to not top it off for a few days and then just keep a really close eye on the reservoir? I'm thinking if I do that, and it gets to the point where I can see the bottom of the reservoir, I'll know for sure I have a leak. If not, no leak. Would I be crazy to try that?

A coolant leak will not trip any DTC's. When the coolant runs low in the expansion tank or the coolant level sensor in the expansion tank is faulty a low coolant light will be set on the cluster. The low coolant light is red looks like a little tank of sorts.

When you remove the old expansion tank, check the hoses going to it and check the coolant hoses on the engine. Also, check the water outlet/thermostat housing for leaks.

Thanks. So in theory, there's no way for the coolant level to get dangerously low without me being notified by a light on the cluster.

Thanks for the tip about the hoses and housing.

Correct.

Verify that the coolant level sensor is plugged in ;) They sometimes go bad and give a false low coolant light, and some owners unplug the sensor as a half-ass solution.

Ah! Thanks! I'll check that. I just assumed that if it was unplugged the light would come on or there would be a CEL or something.

It is indeed disconnected! Really glad you pointed that out to me.

To naive me, that seems like a design flaw. If it's not getting a signal from the sensor, it should show the coolant light. What if some sort of fluid got inside the connector and blocked the connection? Seems like a good way to overheat without knowing it.