Coolant bubbling, overflowing out of overflow tank

I've had this truck for over a year. On a long trip from CO to Wyoming(about 500 miles) i noticed my temp gauge starting to go up on highway hill climbs. I pulled over at a rest area, and my coolant was bubbling/boiling, out of the coolant overflow tank, onto the ground.
After about 60 seconds of being off, still off, the coolant was gulped(not even kidding) in two moderately loud gulp noises, back into the radiator, leaving me with the coolant I had in overflow before, minus what bubbled over onto the ground.
I topped it off to the full line on the overflow, and kept driving.
I drove another 350 miles to Jackson, WY, and 500 back, with no sign of temp gauge getting higher at all. No bubbling, no boiling, nothing. I chalked it up to a steam bubble.
Fast forward a month, I hear my coolant bubbling one day. A week later it actually overflows a little bit. No signs of overheating, but clearly the problem isn't going away.

I monitor my cold radiator level(normally full to top), and overflow level, which sits right on the full line, on a regular basis.
I've replaced water pump, thermostat, and radiator cap, as well as replaced all coolant. It had green when I bought it so that's what I used. I read a lot of stuff that says pink, so I plan to flush cooling system and replace with pink. I noticed some cooper colored small metallic stuff floating in the rop of rad cap last time i looked. Not a lot. Also a bit of orange buildup is seen under rad cap. Kinda like a goopy clay type material, again very little.
The coolant tank is stained brown but existing coolant is green. I wonder if someone previously mixed dexcool(orange) with green.
I've read a lot of threads that say HEAD GASKET and I am just not sold on it. Especially with this being a first-gen. I understand many 2nd gen's have a head gasket issue around 150-200k.
I have no white tailpipe smoke, no coolant(white) in oil(i change my own), no oil in coolant, no power loss in motor, and the engine idles smoothly.
Additionally, this coolant boiling issue is very inconsistent. I can drive around all day with no problems and the next day I drive 20 minutes and hear it. Typically on longer drives with hills on freeway brings it on though. If it was head gasket, wouldn't the problem be consistent?

I've put on another rad cap, and I'm going to do another thermostat just for grins. Fan clutch works fine, I hear it spinning on acceleration. Never overheats while idling(even for an hour, i tried as a test). I plan to have a mechanic flush the cooling system and refill with pink, maybe something is plugged somewhere.

No visible eaks other than overflow tank overflowing over the top. I do sometimes smell a bit of coolant however, maybe I've got a tiny leak somewhere that's letting air in the system.

Anyone got any experience with this issue?

 

Denial is the first part of the process.

 

I knew someone that has a 98' 4 runner that had the same problem. Fixed it without replacing head gasket. Too much logic against it being a head gasket.

Does anyone have any suggestions that are NOT just the jump to conclusion of head gasket? Please read my thread before responding, it will make sense that it is NOT a head gasket.

 

Had the same problem with an old Chevy. Had to keep the Chevy moving but keep the speed below 65. Dreaded long traffic signals, I would turn the AC off at stops. Radiator/cooling system was on its last legs, but luckily the transmission gave out first. Donated it to the Disabled Vets.

 

Specs call for pink coolant only because it does not contain silicate which is not compatible with yota metal alloys. Drain and flush with fresh water only then fill with 50/50 non silicate pink coolant. The only copper colored stuff is the thermostat which should be OEM toyota only which are cupric nickel alloy.

 

Yeah, I'm pretty sure it takes pink coolant. Whoever doofus put it before you got it must have not known the difference. Don't take out word though, check your manual, I believe you can get a free online one on Toyota owners site. The green stuff probably clogged something.

 

If you put silicate, aluminum phosphate and cupric sulphate in ethelyne glycol solution and mix under pressure at 200+degrees it seperates H from 2o converting your liquid coolant to a gaseous state. This is how a hydrogen generator works.

 

That sounds smart

 

Hows your oil pressure?

 

You dont have to use Toyota coolant just be sure its pink/red extended life silica free. Gallon bottles will be marked ASIAN for Toyotas 1980 and newer. Premix 50/50 cost is about $18 gal. Specs say cooling system holds 4 gal. but ive never been able to put more than 2 gal in after flush and fill but hygrometer still reads 50/50 good to 30+below 0.

 

i havent checked oil pressure. I don't have any indicator lights going off though. Although, last time jiffy lube changed my oil they showed me that oil leaked out the valve cover gasket right after pouring it in. Maybe that has something to do with it. Annoying part is I paid to have valve cover gaskets changed about a year ago.

 

You can stop valve cover seepage by torquing tha bolts to 53 inch pounds or just a smug fit. Your over heating is caused by WRONG COOLANT and possibly aftermarket copper thermostat.

 

Have you checked inside the radiator? You probably have 20 years of gunk built up inside the radiator not to mention bugs imbedded on the outside. Hill climbs are worse since engine is at max power but reduced vehicle speed so less ram airflow through radiator. Mixing different type coolants never advised because different additives between different brands can react with each other and precipitate out as gunk inside the radiator tubes.

Suggest you find a competent radiator show, and ask them to do a system pressure check to rule out the head gasket and then have them do a proper power flush of the radiator.

 

I wonder if the clay-type substance is a radiator stop-leak material the PO used to plug a radiator leak before selling it to you.

 

Thats what silaca does. Green coolant.

 

If your radiator is old with lots of miles they tend to plug up inside and outside.

Radiators are a throw away item now because you can buy them for 100.00.

I would replace the radiator if it looks at all plugged inside or in the fins in front.

Check your fan clutch, water pump

 

Desert Dog gave the correct answer. An old and dirty radiator can't transfer heat as well as a new clean radiator.

No way. All coolants use ethylene glycol as the main ingredient and they all have the same ability to transfer heat. The only real difference in colors is the corrosion inhibitors.

If you mixed more coolant than 50/50 it would have less cooling capacity since ethylene glycol has half the specific heat capacity of water. This could explain overheating.

Can someone post where it says red or pink coolant must be used? The 1996 repair manual just says "Use a good brand of ethylene-glycol base coolant and mix it according to the manufacturer's directions."

 

Change your radiator/ flush well or change water pump and thermostat if you wish and hope the copper stuff isn't from someone trying to patch a headgasket with leak stop. that's why the radiator is plugged though.

Use whatever coolant you want but make sure it's flushed out well before changing. Green isn't great for aluminum but it doesn't kill it either. They don't want you to use it anymore because it's poison and needs to be changed often, new coolant sloughs more than old also. Really, red or pink is better, just not necessary.

 

Correct AND the stock tacoma core is less than an 1” thick too, very thin actually

 

That's plenty to keep one cool though unless it's full of stalactites.

edit for actually more likely mites.