Just drained the oil and coolant. Not sure about the colors?
 

https://cimg7.ibsrv.net/gimg/mustang...39d150249a.jpgOil came out lighy brown. Sat overnight and is back to dark brown? Coolant appears to be murky orange. Internal rust or oil mixing?After having my 98 GT sit for a few weeks, I finally drained the oil last night and the coolant guys afternoon and I was concerned about the colors. When the oil drained, it looked light brown which set off alarm bells in my head. However, after sitting overnight, its color is back to dark brown like normal.

On the other hand, I just drained the coolant today and it seems to be turning orangish and maybe a bit murky? Also when I rinsed my bucket I drained into, I noticed a light rainbow sheen on the water. But I don't see any goopy buildup in the coolant reservoir and there was no white smoke the last time I ran the car. Am I just being paranoid and continue with my fluids flush/change? Or am I getting early warnings and should start taking things apart more?

I'll also note that when I drainrd the oil, it finished a lot faster than I was expecting and makes me feel like either it lost oil or whomever changed it last didn't add enough. I don't see any leaks on the garage floor but there certainly was good layer of oily/dirt buildup underneath the oil filter area and the whole K member.

Oil looks like it ran a few thousand miles more than it needed to. The overall lack of oil that drained out suggests that the engine is consuming it, which while some consumption is normal on an older or higher mileage engine its something that moving forward you will want to monitor periodically. You need to do a cooling system flush, badly. Run a flush solution (possibly double-up on the flush solution) with distilled water, drain, refill with distilled water and run it for a day like that, then drain again and refill with 50/50 mix. Should be sufficient anyway. If the second fill using distilled water still comes out heavily discolored then do another with flush solution. Again, make sure to use distilled water. It's only about $1/gallon.

If the engine was consuming oil, would there be smoke out the exhaust? Or is it only a small amount and would be a matter of just periodically adding oil and monitoring the consumption rate? It has over 180k miles on it so it's definitely a high miler but no exhaust smoke. I've just never had a car with this many miles on it before. It's funny though because according to the oil change sticker in the car, I should of still had 1k+ miles before it was due for its next change. But I've only had the car for a month or so so I don't know it's actual maintenance history.

I bought some radiator flush but am waiting until my new brakes come in next week before adding the fluids back. The back rotor is warped and pads are worn so I'm going to attempt a full brake and brake fluid change for safety before I put it on the road again. Is there a risk to letting the radiator sit empty without fluid for the time being? I also need to switch out the plugs and wires so maybe they'll give me insight too.

I've never heard of running the car just on distilled water but I'll give it a go after i work the flush through. Thanks for thr advice.

Also, about how di water/5050 solution should I need to fill the system? I'd prefer to have an approximate amount on hand when I do the fills rather than run back and forth between the store. I'd estimate I drained about 2-2.5 gallons of coolant. Is that about right?

If the engine is consuming oil then it's a very slow sort of thing, given the lack of smoke emitting from the exhaust. Just keep an eye on it.

Leaving the cooling system empty while you're waiting on other stuff won't hurt anything. Regarding the rear brakes, go to your local parts store and "rent" the brake caliper tool, you'll need it. The rear caliper pistons on these cars (and many other Fords) do not simply just compress back into their bores, they must also be rotated CW at the same time as compression is applied. The caliper tool makes it an easy 5 minute job per side, there are other methods but trust me dude just get the tool.

Running the cooling system on just distilled water for a couple days will be fine, especially this time of year. All we're trying to do here is clean out the system, so no need to spend $25 on fluids that are only going to be in there for a day or two before draining and discarding. Plan on about 3 gallons per fill, you should have a little left over. Think the radiator itself holds around 2 gallons, and the overall capacity of the system is about 3 gallons.

I run a slightly less than 50/50 ratio. More like 60/40 (60 is the water), but we don't need to muddy the waters with all that conversation right now, only mentioned that so you are aware that achieving an exact 50/50 ratio is not at all crucial. If you end up using more water than coolant its fine, and to some extent actually preferable. When it comes time for the final refill feel free to use the 50/50 predilluted or get full strength and distilled water and make your own mix.

Each time you drain and refill the radiator you also need to "burp" the cooling system. What often happens when you drain and refill is an air pocket tends to settle in the thermostat housing and cause improper operation of the thermostat and thus overheating. All burping consists of is filling the system and allowing the engine to idle until it reaches operating temperature (t-stat opens and coolant circulates) with the overflow reservoir cap removed. Doing this will save you some headaches.

Thanks again for the detailed info. I'll be sure to keep an eye on that oil. On the site's How To section it mentions a bleed screw near the water pumo while other posts mention the burping procedure you mentioned. Does my car not have that bleed screw for air in the system?

I really appreciate the patience and effort it takes for your responses. I'm sure they can seem like newby questions but I really want to learn this maintenance correctly so I can keep this car running forever.

I've never used any bleeder screw on the water pump. Actually this is the first Ive heard of it. There is a small hole right on top ususally referred to as a weep hole but the only thing its good for is letting you know that the pumps shaft seal is leaking (because coolant will be coming out from there). Just the above noted process is all I've ever done.