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So we have brown gunk in our 93 FD cooling system, and I’d like to know what it is, and if we have a problem.
Symptoms:
1) When we got the car a few months ago the coolant system was full of brown water. It took about seven changes to get the water to come out much less brown.
2) When we pull off the coolant hose by the throttle body thermowax thing, nothing comes out at idle, and only a slow stream when revving. I’ll try to attach a video of that.
3) When we put actual coolant in the engine it blows sweet white smoke out the tail pipe - I’m guessing this is why the previous owner was running water, and maybe why he sold it.
4) Given the white smoke we tore down the engine (for new water jacket seals among other things) and all the coolant passages in the housings are coated and stained with the brown gunk. No amount of scrubbing or chemicals (carb cleaner, brake cleaner, penetrating oil) seems to get back to a metal color.
My guess is someone mixed coolants at some point and made super goo which then stained everything and maybe clogged the radiator. Good guess? If so, should we worry about the engine passages (hoses will all be swapped) and should I swap out the radiator, or god forbid even the water pump? What sort of water flow should we be expecting?
Typical if you never change your coolant over many years, especially if people use just water (no anti rust/corrosion properties). You most likely will have to replace an iron due to the cooling jacket wall between the combustion chamber being rusted through and failing if you were blowing coolant out the exhaust.
Brown is also caused by coolant additves like Water Wetter so that could be a reason for the color of the coolant. I wouldn't worry too much about it. Maybe hit it with a wire brush like those engine cleaning brushes they sell at Harbor Freight to get any loose stuff out. https://www.harborfreight.com/engine...id=21901271240
One other suspect for the color would be stop-leak additive by the PO trying to deal with a seal failure. Asian coolant is also brownish-red.
Regardless, as mentioned, check the walls around a coolant seal for any pitting or wall failure. If all is good there, you might try submerging the irons and housings in some white vinegar. Then following with a rinse and alot of WD-40 on the iron. IIRc there’s also specs in the FSM for the plate surfaces
That looks like rust and corrosion to me. Leaving the cooling system sit with tap water will make it worse, and leaving it sit open to the air will also make it worse. Evaporust is worth a try on the bare metal parts, it will chemically convert the rust and help remove it. Some local auto parts stores should carry it, I think it was at Napa or Autozone near me. After you remove the rust, coat the metal parts with something like WD40 before letting them sit or they can begin rusting again in just a few hours. If the car still had the engine installed and cooling system intact, Thermo-Cure mixed with water would do a similar job of converting the rust. Depending how much crud is in the radiator (and heater core), it might be wise to replace it.
At this point I’ve just degreased, pressure washed, scrapped gaskets, and wiped down with WD40. I’m also working through the FsM inspections. I checked the water gasket channels really carefully and couldn’t find anything that looked suspicious in terms of rusting through or damage which is good news. I’ll be taking the hard parts to MazdaTrix on Friday and see if Dave has an opinion. After that I can set up some experiments with Evaporust, white vinegar, and the Harbor Freight wire brushes and follow up here. I’m a bit nervous about the housings given they’re aluminum, so I’ll focus on an area that doesn’t mater as much there.
Still curious if anyone know if the waterflow through the thermowax pipe is reasonable, and if there’s a way to check for restriction in the radiator.
Following up on the thread here in case someone refers back to this.
So I took the parts to Mazdatrix and they thought that someone had dumped some leak stopper in the radiator. That kind of makes sense given that the water jacket was leaking into the engine, and the PO had started running water in the radiator. I tried evaporust but it had no effect on the brown material - definitely not rust (and it's on aluminum which won't rust). With the metal it dry, I could scrape it away the brown gunk to an extent with wire brushes, but couldn't fully remove it as it had seemed to stain the metal, and I obviously can't reach the internal galleries. I swapped all the water hoses, the radiator, and scrubbed out the inside of the water pump as best I could, so other than some stained metal in the engine I should be back to a healthy cooling system (assuming I didn't goof up the engine build!).
