I've been very slowly redoing my interior as time allows and i finally got it all back together this morning. The car has sat without being cranked for about 9 months. The coolant lever low buzzer came on. I checked all the lines and tightened them, they were loose and I suspect some coolant evaporated or... worse. I slapped the good ole Lisle funnel on, mixed 70/30 and filled a bit, left some extra as usual in the funnel.

I crank the car and it starts up perfectly. Stalled twice after a min but the third time it stood on and idled all good. Everything checked out right, no leaks, fans came on at temp. I let it run with the fans on for a minute as usual, turned it off, all good. I saw nothing problematic while it was running.

Once off, I noticed this brownish scum floating on top of the coolant in the funnel. I did the same thing before the car was parked long term when I relocated the radiator and installed new hoses with better shapes for the new routing. I've never seen this in coolant before on any car. The scum can be seen in the picture at the bottom of this post.

2 questions. 1, is this bad? 2, if yes to 1, how bad is this? For context I'm very knowledgeable on electrical work, I can do interior finishing easily, and I do minor mechanical work but I'm by no means well versed in working on the rotary and don't have the time/tools/skills to resolve internal engine issues. So I'm looking to get thoughts on if this is a problem, what it could be, and what work would be needed to resolve it. I'm hoping i still hit my goal of driving it today for the first time in many months. Hopefully y'all have some feedback on a Saturday morning.

 

You should do a coolant flush and put some fresh coolant in it. Some corrosion in the iron can happen for 9 month of not running the engine.
Just change the coolant and check again.

 

Thanks @Red94fd , I got impatient and went for a 10 mile drive. All was well, so I guess it's not catastrophic. Still going to flush as you suggested to be on the safe side.

 

If that's all you noticed, you're good.
You can do a coolant system pressure test to test for and identify any other leaking coolant lines.
Myself and others tend to recommend factory spring style clamps since they are constant tension and provide the right amount of torque and don't loosen up after repeated heat cycles. I've posted about that before if you want to search.