S5 GTU Muddy Radiator
 

Hey guys, I just picked up a 1989 GTU. It runs & drives well. The limited slip is strong & it's got light suspension mods. The engine is bone stock. Compression sounds fine but I've yet to test it. Once warm, the engine pulls strong through the gears. It does no overheat at all. Have done about 100 miles of mixed driving. All fluid are level and in fair condition except coolant. The coolant was a bit low when I first got the car. I topped it off & it seemed normal. No leaks & the car doesn't smoke at all. Even under hard acceleration. There seems to be some type of mud build up in the radiator after a few days of driving. Is it time for new coolant seals or what? Any insight would be greatly appreciated.

Flush and fill the coolant with a good mix of coolant/water.Use that Prestone flush stuff(small yellow bottle.)
I like ratios above 50/50 myself.I go about 60/40 or so.Use Distilled water,not tap water.
It's most likely rust and corrosion that have been sitting in the engine.Get that out and you should have a nice,clean,well operating cooling system.
Changing the thermostat with a OEM( no other brand) thermostat would be a bonus too.

Sweet, legit info. Its ok to use even in high mileage engines like mine? I have 180,000 miles. Will flushing it with a machine likely destroy the coolant seals? Thanks.

machine flushing any coolant system with high miles can produce a leak, though not too sure about the rotary. Does the coolant get thicker and look like mud or does it just change color. What type of coolant are you using? Easily said, is it the average green stuff, or the "long life" orange?

It's regular green. The majority of the coolant is still normal green but, when i open the cap there is brown/slate grey sludge on the coolant cap spring & rubber as well as the uppe inside of the neck.