Coolant issue!
 

Ok so my 90 Na recently has been starting hard hot almost like its ingesting coolant, sometimes the gauge will say its starting to overheat but then shoots back down to normal. Its pushing coolant into the overflow and sometimes wont draw it back in yet sometimes it will. I've done the champagne test multiple times and every time there are no bubbles! It will start cold fine but hot it does not and there will be some white smoke but none on cold start. Just tonight I stopped to get gas, then fired it up and there was a decent cloud of white smoke and then it started to say it was overheating so I pulled over and the overflow was full, yet the radiator was full of coolant. When I started it back up after emptying the overflow and topping off the radiator the idle shot to 3000 and was a BUNCH of white smoke. The idle would not go back down and the gauge was starting to say it was overheating but I was about 30 seconds to my house when the gauge then shot back down to normal and when I pulled in the idle was normal. I have changed the radiator cap, the line from the radiator to the overflow and the thermostat. Is it possible the thermostat is not any good or was installed wrong? I am getting really fed up with this engine! It runs well once its going and makes a lot of power but I'm just getting tired of it acting up like this. Oh and at first it would do this, then I changed the exhaust and for about 2 weeks it was good for whatever reason and about a week ago it started doing this again. Thanks!

It sounds to me like you have an air bubble in your system somewhere.

What colour was the coolant, as in was it mixed with oil?

I thought it could be an air bubble but im not sure if it would be doing this kind of stuff, from what I've searched I havent seen anyone saying it doing this to their car. As for oil in the coolant theres none, its a nice green color.

I'd start with a thorough coolant flush. Typical symptoms of blown coolant seals is noticeable coolant consumption and oil in the coolant resevoir

Can the coolant seals be going though and not be pushing any bubbles into the coolant when I run it cold? Because I only ever have this problem when its hot and when hot starting. When its cold its perfect.

Anyone else have any other ideas?

Rent a coolant system pressure tester from a parts store. Attach it, warm the engine up, then shut it off and remove the spark plugs. Keep pressure on the system, and rotate the engine over while maintaining pressure. If you get coolant out of the spark plug holes, you have found the culprit. I have a suspicion it's a blown coolant seal. A very good suspicion, that is.

Alright I will give that a try when I get paid in a few days. When a seal goes does it always pool coolant in the housing once you let it sit? Because I've let it sit for a few days and when I went to start it, it fired right up zero hesitation and is now not losing coolant and draws it back in from the overflow.

Well still waiting on getting the pressure tester but I've found if I start the car completely cold I can drive with zero issue for as long as I feel like. But if I shut it off and say go to drive it again in an hour while its still a little warm it will start saying its overheating but then after 30 seconds the gauge goes down to normal, then a few mins later it repeats the same thing. The add coolant buzzer will go off then 10-30 secs later turn off and during it my idle will go to 2000-3000 then after the same amount of time go back to normal. After it does this and I let it sit for a few hours and go to run it it is 100% fine again. During all that it will push coolant into the overflow but wont push it all the way out and if I let it sit for a long period of time it will suck all the coolant back in as well. Will a blown coolant seal really do this as I cant find any other info or thread about this same issue???

Ok, your indication of overheat, as well as the low coolant buzzer going off is a pretty good indication that your car is ACTUALLY overheating. There are a number of things that could cause this. A faulty thermostat, a water pump shear (seen it happen before where the shaft spins somewhat freely inside the impeller), a clogged radiator, a clogged something somewhere not in the radiator, a fan malfunction, a ducting issue (missing the under tray?), or anything else like that. It's really hard to say based on your description of the issue, so try the pressure tester thing first. If it's not conclusive, then start with replacing the thermostat and radiator cap(s).

The S5 temperature gauge has a dead band built in to it. So it essentially has 3 areas.
1) Up to 1/2 way, which means it's STONE cold.
2) Exactly 1/2 way, which should be the normal operating temperature, but will still indicate 1/2 even if it's beginning to overheat.
3) Over halfway, which means you're already past overheating, and you're screwed.

So it will go off even if its full of coolant? Yes the under tray has been missing since I bought the car but had no issues until just recently but I will do the test then see what happens!

Well, I figure I should update as I fixed the issue. It ended up being a faulty coolant cap even though it was brand new, I have now changed it again and have zero issues. The stock coolant temp gauge is also faulty and found it started not reading the temp at all until it would suddenly shoot up from stone cold to operating temp after driving for 5-10 mins.

What branded rad cap were you using? New coolant temp sensors are $65 from Mazda. Mine made a difference, and the gauge operates as it did when it was new (I assume). The sensor I'm talking about is the one behind the water pump housing.

The sensor on the pump housing is used by the ECU and is not connected in any way to the gauge.

Well this is embarrassing.

I cant recall the brand but I got it from mazdatrix, I think it was just faulty to begin with. Im not too concerned about the stock gauge as I have an aftermarket now anyway haha.