Dirty Coolant / Poor Heating

The coolant in my spirit is very dirty, brown in color, there is a blank buildup on the radiator cap. The oil looks fine and I don't see any bubbles in the radiator when idling. It doesn't use any coolant to speak of. The engine gets relatively hot when driving. The radiator doesn't seem to be removing much heat and the heater doesn't blow very hot. The return on the heater core is hot after running for 5 minutes so there is flow just not much heat. Same with the return from the radiator. The radiator has been cooling poorly for a while so I know that needs fixing. I flushed the cooling system and replaced the coolant. Also installed a new water pump. Still getting poor heat in the car and running warm even though it's pretty cold out. I think I'm going to change out the radiator with a spare I have this weekend and try back flushing the heater core. Any other suggestions? I'm not sure how the coolant is getting so bad. It was only about 2 years old. I'm going to check the compression also just to see how that is. The motor was refreshed 5 years ago with new seals, gaskets, turned crank and bearings. It has about 50,000 miles on it since then. Maybe lifted a head gasket at one point in time?

New radiator and new heatercore is what I would do, if I want good cooling and good heat.
After 20+ years, the radiator/heatercore is pretty much junk.

There is only so much flushing can do.

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So here is what I found. First after running the radiator flush through the system as directed and then draining and flushing with clean water 6 time some of the cleaner must have still been in the system because the coolant was slightly foamy when drained. I'm guessing it may have been cavitating the pump causing poor coolant flow. I drained the coolant again and removed the heater hoses and back flushed with water, then forward flushed, back flushed ect. Filled the system with water again and started the car and let it idle. The heat in the car is good now. I let the car idle up to temp and topped the radiator off with water. Every once in a while I see a small bubble come up into the radiator. I'm guessing the head gasket is on it's way out and pushing exhaust into the cooling system? Could the black crud in the cooling system be carbon from the exhaust? I'm going to pick up a new gasket and change it out tonight or tomorrow. I may just do a slip and slide replacement and see how far it gets me. I'm planning on finding a different car next year as the Wisconsin winters are starting to get to this car and it has over 300,000 on it. Let me know what you think.

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Every once in a while I see a small bubble come up into the radiator.

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Drive it for a few days then check for bubbles again.

Agreed, just drive it for a few days. I like to use CLR to clean out heater cores, had to do mine every year for 8 years otherwise no heat in winter.

I wouldn't go by bubbles in the radiator. I've had perfectly good vehicles have bubble come up to the filler cap. Get a block tester and test it that way. Doing a headgasket on a "hunch" is a lot of work for possibly nothing.

Are you using tap water or distilled water in your 50/50 mix? I've seen tap water turn coolant faster than it should have.

To check the radiator for flow, start with a cold car (first thing in the morning), take the fan off so you have access to the radiator core, and once the thermostat opens feel the radiator for cold spots. If part of the radiator is too hot to touch and another part is okay to touch you have a partially plugged radiator. Replace it, you can't flush it. Unless it's all copper you can get a shop to "dip" it.

You can flush a 20 year old radiator/heater core all you want sometimes. What I have found 9 times out of ten is the heat is not transferring thru the fins anymore and they are falling out most of the time. 20 years is alot of heating a cooling cycles. Just my 02 cents.

If it gets hot driving at speed but then is ok while the fan is on in traffic this is probably your problem.

Ended up changing the head gasket. Found one spot where carbon was traced across the fire ring and pushing exhaust into the cooling system. The radiator is partially plugged, been getting worse and worse the last few years. Currently using a Spirit R/T rad/IC. I think next year will be time for a new or different car for a DD. This one has served me well for 12+ years so it's time.

My Spirit has had terrible heat for the last 10 years at least. Flow seems fine through the core when directly flushing it. Maybe its the aforementioned disappearance of internal fins. I changed back to a 192 and even a 195 thermostat trying to get more heat and it didn't help. Wife's same year spirit never had this problem. Mine has always had the rusty coolant since 2005.

IMO, coolant, like brake fluid, should be changed annually.

Coolant is similar to a sacrificial anode on a boat. The components of the additive package are what is sacrificed. That's why they sell the different colored coolants. IIRC, green is for systems that expose the coolant to brass/copper/iron while red/orange is for all aluminum systems. The color also indicates a different PH for iron vs aluminum systems.

The color on the coolant is more for manufacturers. They can put whatever dye they want in it to make it any color they want. The current Dodge factory coolant is purple. BMW uses blue.

On any system that has aluminum in it, the coolant should be flushed and replaced every year or two. Aluminum reacts with coolant, causing it to turn "toxic" and form the nasty white crud that accumulates over time. Luckily my truck gets a flush every few monts, since it likes to eat all the plastic couplers used throughout it.