Another coolant issue? Please advise

2007 with 2.7l and 205k miles. Runs strong but been battling an occasional overheating problem since summer. Changed out water pump, t stat, fan clutch, radiator, and cap...still occasionaly overheats! Fresh coolant twice now.

Ive checked for blown head gasket 3 times and all negative...(blue die that turns yellow type test).

Recently now im getting the typical plumes of white smoke on a cold start and a miss while it quickly clears up and stumbles back to life...then runs great again. I know this is the tell-tale head gasket scenario but i tested again and still no change and does not indicate exhaust gasses in the coolant. Exhaust even has a hint of sweet smell- but again, test comes back negative. Im at a loss what to do next? Boils from upper hose into overflow reservoir at about 185 so I will get another oem rad cap, but if not head gasket where else can coolant get into the cylinders? Any suggestions greatly appreciated, Thanks!

 

There’s a few things to look at. Depending what tools you already have, one easy way is to look at the motor oil. Looking at what’s on the dip stick it can’t be easy to tell. Drain the oil and look at it. It might be light brown to white, indicating coolant mixed with oil. If you have a cooling system pressure tester you want to see it hold pressure.

https://mechanicbase.com/engine/how-to-test-if-your-head-gasket-is-blown/

 

Toyotas don't always seem to work with the HG chemical testers. No idea why.

https://www.youtube.com/shorts/_oWXDmrs96c

This is how I confirm combustion, works on all Toyotas as long as it correlates to the symptoms. I've changed loads of HG's due to cold start misfire, smoke, and coolant loss.

 

There are seven ways a head gasket can go bad. It appears you’ve checked for #7 on the list below. You can probably rule out # 1 & 6 if you have no leaks. Start with a compression test.


1) Coolant to outside leak
2) Compression leak to oil galleries
3) Water to oil leak
4) Compression leak between cylinders
5) Compression to outside leak
6) Oil to outside leak
7) Compression leak to coolant

 

Thanks for the replies guys...oil is clean/blackish, no indication of water at all in the oil *except for just the slightest bit of milkshake under the filler cap- which i assumed was just condensation. Just color really..
Like I'd have to clean it out the corners with a q tip. I know everything points to head gasket but was hoping I may get lucky by some off chance! Changed the valve cover gasket aswell and no milkshake underneath either. Has been taking about a quart of coolant per month or so...but some of that gets burned and some overflows the overflow!

 

Trucks doesn't leak a drop anywhere except the occasional overheat...overflow of the overflow.
Bottom radiator hose always seems cooler than it should be and top hose always hot. Often both hoses seem under pressure and very firm to where cannot squeeze with the radiator cap on?
Heat output is great like it's always been but I've tried to burp any air just in case on an incline with funnel half full on top of radiator. It's difficult to get hot enough and seems like the lower hose is always cold....thermostat is new also so I believe this is all normal?
Thanks for the ideas, I really appreciate it!
I suppose it could be number 4 on the list above but I'm definitely burning coolant aswell. Plumes of sweet swelling exhaust with a miss. When the exhaust cleens up same time as I'm hearing the miss go away and the engine runs smooth as silk on all 4 cylinders again?...

 

The chemical block tester did not work for me when I was trying to determine if I had a head gasket issue. I had no visible leaks anywhere on the truck. I ended up pressurizing the cooling system while using an inspection camera to look into the cylinders starting with #6. While under pressure, I was able to see a single drop of coolant drip from the head gasket down the cylinder wall and onto the piston. Both cylinders #6 and #4 were leaking.

 

Its a head gasket. The tell is the white smoke, smell and running rough for a minute as it chokes on the liquid coolant in the cylinder.

The block tester isn't always going to pick up the gases. It'll never give a false positive but you can get false negatives all day long

 

Yes, agreed I'm sure it's the head gasket aswell...just had a false sense of hope after repeated negative tests!!

Now there is one more piece to this puzzle I should disclose...somewhat embarrassing, but here's what I did. The very first chemical hg test I did I underestimated my vacuum source. I bought the tester the draws off engine vacuum rather than the squeeze bulb type. Well, before I knew it, it sucked coolant hard enough to fill the tube completely and drew it into the intake...similar like you've seen on the seafoam tutorials. Truck spit and sputtered and cleared out when I realized what I'd done and pulled it off. Engine never stalled, but barely kept running. I regrouped and did the test again- negative. Then a ran about 2 cups of bulk wd40 through that same vacuum line into the intake. (Slowly...kinda a slurp at a time) thinking it could only help clear out the coolant id ingested. Everything appeared back to normal and i took about a 20 minute hard drive. All seemed as usual after. Well, the truck started with the miss and smoke the next morning but I figured was residuals. Then it stopped and cleared up for awhile and now it's back. I've prob put 500 miles on since this mishap and I did changed plugs and oil soon after. Anyways that's the whole story for what it's worth...not sure if it did any damage but it certainly couldn't help!
Seems like my next move is to buy a coolant system pressure tester just to confirm its the head gasket. 80 bucks on Amazon for a universal mishimoto set seems reasonable I suppose to find out for sure. Thanks for all the feedback good or bad...ive got thick skin, haha!

 

You can also get it roaring hot and park it, then pull all plugs. Sometimes when they're really bad you can see the mist entering the cylinders with a simple pen light.

 

Don't buy a coolant tester, rent one from Autozone. You get 100% of your money back once you return it.

PowerBuilt Cooling System Pressure Testing Kit 22 Piece

 

The first thing I need to note is that those blown gasket chemical testers are useless.

The main issue here is that everything you stated in your main post is indicative of your typical blown head gasket. The metal is causing the coolant to leak into the combustion chamber when the vehicle is hot. If you have had to periodically fill the coolant reservoir bottle then this only solidifies what I stated above.

To inspect, a typical cylinder leakage test will need to be performed, but note that this test will be invalidated when the vehicle is cold and needs to be done with a hot engine. However, you can't keep it as hot as it needs to be to test, so good luck testing while the engine is fully hot.

The gasket in essence is shrunken and sealing properly with the engine when cold, once it expands, it's causing a leak somewhere in the gasket.

The only other thing which you can do to really inspect what the heck is going on without having to do that sort of testing is to physically inspect the cylinders with a camera or a light (and mirror if needed) and inspect the piston tops. If one or several look shiny then that would indicate they are the ones leaking, as the piston tops will be getting "steam cleaned" by the coolant escaping into them.

 

or, @>200K mi..



you could just dump some $10 leak sealer in, say a little prayer and run it ‘til it goes boom.



(then buy a new motor)

 

+1 on inspecting the cylinders. There are only 4 of them, hopefully not all of them have coolant leaking into them. The steam-cleaning effect is real (see various youtube videos on this,) & if some cylinders look much cleaner than others those are probably the leaking ones. Could avoid the trouble of having to try to do hot compression tests.

Decent-quality flex-neck fiber optic cameras with dual-view end & side lenses fairly affordable these days on A mazon. I bought

DEPSTECH 5.0MP Dual Lens Borescope, 5" IPS Screen Endoscope with Light, Industrial Video Inspection Tool, 10ft Gooseneck Snake Camera, Waterproof for Wall, Pipe, Automotive

one of these to replace my old ExTech 240 flex-neck camera.

 

Light-colored 'cream' under the oil filler cap can come from other causes, such as humidity-related condensation. It tends to accumulate on my oil cap in winter weather when I do only very short in-town drives & the engine doesn't get up to temperature. The 'cream' disappears after some spirited freeway driving up moderate grades at high rpms heats up the oil enough to boil off the small amt. of residual moisture.

 

Those kind of suggestions are the kind that wind up costing folks more money then they need to spend down the stretch, because if he replaces his entire engine then he better be prepared to buy an entirely new cooling system as well if he runs this stuff on his current engine. This includes the heater core (not replaced but not currently bad either), radiator (replaced), water pump (replaced), T-stat (replaced) and all hoses (not replaced). That stop leak crap is the absolute worst and wreaks havoc on cooling passages with all the gunk it produces.