Weird coolant issues, I'm stumped

Please help me figure out what's going on, my Taco ('95, 200K miles) is sick.

Clue #1: new radiator about 6 months ago
Clue #2: hissing, bubbling sounds coming from behind the dash upon acceleration
Clue #3: reddish brown goo accumulating under the radiator cap and in the overflow tank.
Clue #4: previously green coolant is now the color of piss or flat beer
Clue #5: I am not losing coolant, at least not noticeably
Clue #6: Assuming from Clues 1-5 that I have a head gasket leak of some sort, just today I ran a combustion gas test (the fluid type) of the coolant. But the fluid stayed blue, indicating no exhaust gases in the coolant.

Huh? What could be happening here?

 

It sounds like you still have air in your cooling system from the radiator replacement.

 

The hissing bubbling behind the dash sounds to me like you didn't have your heater on when you burped the air from the coolant system when refilling and now have air trapped.

Reddish brown goo sounds like your transmission cooler from the old radiator was starting to leak.

Look up pink milkshake.

Toyota should never have green coolant and if you switch to red with a simple drain and fill and no water flush and block draining your getting a chemical reaction of the two mixing, not good.

It's still possible you have a small head gasket leak.

Miles on truck?
What Motor?
Manual or automatic?

 

You mentioned green coolant. Did you THOROUGHLY flush the coolant system of the Toyota red coolant before adding the green coolant?

Toyota coolant does not mix well with any other coolant. The mixture will cause a lot of the symptoms you're talking about. It will turn to a light reddish brown mud looking crap. If it is backing up in the heater core, that would be why you are hearing things go on under the dash.

Flush your system. I would add a flush agent and drive it a few days. Then drain. Put a flush in again fill with distilled water. Run the engine to operating temp and then let it idle for a few minutes... then shut it off and let that sit overnight.

Then I would flush the heater core opposite of the normal flow of the coolant till the water running through runs clear... then flip the flush and run it the normal direction of flow, till the water runs clear. Put it all back together and flush the system again.

You need to get as much of that red out as you can if you want to run green.

 

I'm 99.9999999% sure that reddish goo you're seeing is the Toyota red mixed with the green.

That is the cheapest and easiest thing to fix (and the most likely cause). I would eliminate that as a possibility before freaking out and tearing off cylider heads.

The pink milkshake is not as common a problem as people make it out to be... yet it seems to be the very first thing some people want to suggest as the problem.

 

It amazes me that Prestone can claim on the front of their 1-gallon jugs that it mixes with all color antifreeze. I'm surprised someone has challenged that claim for causing damage yet.

 

NO DOUBT! +1000

 

do you have heat in the truck and is it over heating and do you see white smoke

 

Why I say that is I came from a 1988 Nissan truck and used Prestone for all 18 years and still had some down cellar, so according to their claim I did just that and I'm 100% sure it's what caused my water pump to leak at 30,000 miles. I ran a flush/cleaner through while doing multiple distilled water flushes too, to get all the green out and went back to the factory recommended coolant.

 

I was totally agreeing with you. Prestone should not make the claim they mix with ALL coolants... They aren't the only ones that make that claim though, NAPA makes the same claim with their coolant and others do so as well.

Green coolant WILL NOT mix properly with Toyota red... ever.

I run Prestone in my coolant system, because it cools better than Toyota red. I just made sure to get all the Toyota red out before putting in the Prestone.

 

OK, I really don't think it's the Toyota red anti-freeze mixing with green, because I've never used Toyota red anti-freeze! And yes, I did use a flush agent before I replaced the radiator.

 

Pretty bold statement. Got any proof to back that up?

 

Well... Whether you used red or not, Toyota did. So at some point there was red in your cooling system. And if you didn't flush ALL of it out, before using green the sludge is what happens.

When I say flush the system, I'm not just saying flush it once and you are done. You have to flush the entire system. Even when you completely "drain" the system, there is still residual coolant in the heater core and all throughout the block. You have to flush and then flush and then flush again etc to get it clean enough.

 

I have personal experience. When I bought the truck (a 2 year old lease return) 14 years ago, It was having problems with over heating. I flushed the system thoroughly and changed to Prestone. It ran cooler immediately... not as cool as I would have liked but cooler, without doing anything else in the cooling system. Now that I have replaced most of the cooling system and I'm still running Prestone, the truck runs the way I think it should.

Which is more proof than anyone can provide that says otherwise.