08 Tacoma Overheating planning Head Gasket replacement

Hey Guys , I am new to the website can't believe all the great information here. Here's my deal, 08 has 268k on it all of a sudden it wanted to over heat when I would sit in traffic. Reservoir would overfill and after turning off my top radiator hose would suck in like a straw without drawing fluid back into radiator. Truck runs smooth, no idle issues, no leaking coolant, I can literally siphon my coolant out of my over fill reservoir and refill all of it into my radiator. Why doesn't it get sucked back into my radiator? I replaced the cap blew out the overfill line, and not sure why it does this? Oil is clean no signs of coolant contamination. I've never replaced water pump, can they loose their efficiency and cause overheating issue? No leaks present been reading head gasket, but that's a huge undertaking of labor.
Thank you in advance

 

Have you made sure your fan clutch is working?
If it's not working properly it could cause overheating when the vehicle is not moving, also look at the outside and between the condenser and radiator and make sure they aren't plugged with debris.

 

Is the new cap good?
Is the radiator stopped up at the overflow line?
Does the hose immediately return to “normal” when you remove the cap?

I don’t like anything but OEM caps.
Is the new one OEM?

Something is causing vacuum in to remain in the cooling system.
Typically the radiator cap controls this.

 

Or the port in the overflow tank is plugged.

 

That too.

 

Cap was an after market O'Riley, clutch fan replaced, I blew out the suction line into the overfill. I will check further the radiator for blockage even though none present.

 

Take the cap off.
Blow through the suction line into the radiator.

 

I mean if you want to verify whether or not it's a headgasket you could do a combustion gas test on the cooling system, usually if it's leaking bad enough to cause chronic overheating a combustion gas test will detect it.

 

Did that, it's clear, once I opened it just now there was a vacuum present when I removed the cap, I will go get a OEM cap tomorrow not sure why.

 

Good call on this, do I need to bring to a mechanic to get this done or can I rent the testing equipment? Average cost?
Thank

 

Check for a clogged radiator. That's what happened to my 96 that had an overheating problem. Since coolant wasn't able to pass through, it would build up pressure and come out the overfill reservoir. Sounds like that's what is happening to yours.

 

Are you saying to purge it with a water hose or just replace it? Air passage is free I can shine a light through it.

 

Not sure what a shop would charge to check it but you can buy a

$64 UView 560000 Automotive Combustion Leak Test Kit for Head Gaskets, Cylinder Heads and Engine Block Leaks, Gas/Diesel Engines, Dual-Chamber Tester Filters Alkaline Particles, 16oz Testing Fluid

test kit is around $50 and a

$23 EPAuto Spill Proof Radiator Coolant Filling Funnel Kit

spillproof funnel for around $20.
The method I use is put the spillproof funnel on the radiator, leave the stopper out, and put a plastic bag over it with a rubber band or tie a string around it to hold it and cut a small slit in it.
Start the engine and let it come up to temp while making sure the funnel doesn't overflow, once the engine is hot place the tester end in the opening that you cut in the bag and pump it slowly while being careful not to suck up any coolant, if the test fluid changes color you 100% have combustion gas entering the cooling system.

 

Someone posted a similar problem recently, I think it ended up being a new faulty radiator cap

 

i had head gaskets replaced at 250,000ish miles...
similar symptoms.
radiator cap (Toyota, Amazon) is the simplest cheapest troubleshooting.

autozone will loan the test equipment for pressure testing radiator system for leaks, and the cap...
all i had to buy was the small container of the chemical to test coolant for contamination of gas, exhaust (mine turned just a little yellow, but still failed)

look at the UTube videos, lots of info...