A definitive TEST: How to check for a blown Head Gasket without any tools and zero costs...
I have a 2005 SR5 V6 with 150,000 miles. After reading all the HG threads full of HG failure paranoia, I did the following.
First. Checked the overfill canister and filled it up to the top "see through" line with fresh antifreeze. My canister was down 1/4 inch when I started this maintenance, and there were no coolant leaks.
Every day I open the hood and look at the coolant level to see if it has changed. I sometimes do this twice or three times a day.
Every day (after a 10 minute drive or a 2 hour drive) I check the overflow canister for a change in level, and not once has it moved up or down - and I've done this 30 times. AND.. I've never had to add coolant!
I also have had no overheats since I bought the car new in 2005. The gauge for temperature on the dash works fine, and I've concluded I do not have a blown HG (or any other coolant issues - thermostat, radiator, WP, hoses, etc., etc.).
Yes. Coolant leaking into your cylinders via the HG is a serious thing, but why worry about it if your coolant level is right where it's supposed to be (unchanged), the car doesn't miss at start up, doesn't smoke white water fumes out the tailpipe, and you get no "codes"?
BTW.. I changed the radiator cap with a new OEM cap about a week before I decided to run this "test". The original radiator cap was 14 years old. The old radiator cap was worn, and needed replacing.
Head Gasket Sealer | Head Gasket Sealant | BlueDevil
BTW Toyota 4runners on the road are upwards of 1 million or more, and probably less than 1% have a HG issue IMO.
UPDATE: Checked the coolant level in canister this Dec 6 2019 for any change. It has stayed exactly at the same height in the overflow canister. I tread the day I hear the gurgling behind the dash; a coolant level drop in the overfill canister, coolant smell out the exhaust, miss on startup. My 4runner has never had an overheat in 15 years and 145,000 miles.