Why would an engine "gurgle" only after turning it off (and spill coolant?)

[Bram van den Heuvel]

What diagnostics can I do to figure out why the coolant gurgles after shutting down?

This happened twice over the past two days on a 30 mile trip each way, both days of which were pretty hot at around 90 degrees.

Temperature gauge is working as it goes from cold to middle & stays in middle so the car is not overheating.

Yet, when I shut down the engine, it "gurgles" a bubbly sound.

I can simulate the gurgling sound by squeezing the upper hose, where I can hear the air and fluid moving about.

I had filled the coolant tank to the Full level, but it spilled out a cup or two onto the ground when it gurgled.

The fluid is "watery" and "brown" so it hasn't been changed in a super long time so that will be the first thing after a flush that I do.

I will borrow a pressure tester at the local auto parts store, but that won't tell me if the water pump is working. The belts are intact and the fan spins, so, that doesn't tell me much either.

What diagnostics can I do to figure out why the coolant gurgles after shutting down?

[Dick Schmutz]

Maybe combustion chamber gasses leaking into the cooling system? Bad gasket or something cracked/warped?

[Stormin' Norman]

Sounds to me like you might have some partially blocked passages in the engine cooling jacket which is resulting in some trapped air. I suggest you get a reverse power flush of the cooling system and refill it with a high quality coolant / distilled or demineralized water mixture. I suspect your gurgling engine will settle down after that.

[micky]

I think when the engine is on and the coolant is circulating, it never gets that hot. The heat from the hottest parts of the engine is transferred to a stream** of coolant, but when the coolant stops moving, that which is next to the hottest parts of the engine get hotter than ever.

Why this doesn't happen all the time I don't know.

**This is similar to the mistake they make in cowboy and adventure movies where they are pulling someone up with a rope that is rubbing against a rock where the rope bends over the edge of the cliff. In the movies, there is a close-up of the rope gooing over the rock, getting more and more frayed. But in reality every moment it's a different part of the rope rubbing the rock so the rock won't ruin the rope.

[Bram van den Heuvel]

I ordered a new radiator and hoses and thermostat and gasket after finding this pinhole hairline crack in the plastic neck of the radiator when running a pressure test with the oreilly pressure testing kit.

ng_tool.jpg

This is the pinhole crack

I tried thick expoxy to hold me out until the new radiator arrives

But it was too thick. So I tried thinner epoxy.

After sanding and cleaning with MAF cleaner, this thinner stuff stuck.

I will pressure test it tomorrow after it has cured for 24 hours

Is there any way to test the water pump action better than just watching water go into the upper hose?

[Bram van den Heuvel]

I think the engine has never been "cleaned and flushed". This is what the Toyota red fluid looks like

Trying to think of an intelligent way to flush the cooling system, how does

this sound as a plan?

-1 Open a petcock or block drain bolt and leave it open

-2 Remove the thermostat & replace the thermomstat cover loosely

-3 Remove the radiator cap & run a garden hose in the radiator neck

-4 Run the engine until the fluid draining is clear

Does that sound like a workable plan for flushing? What did I miss or what should I do different?

[Bram van den Heuvel]

This is the color of the fluid which is supposed to be Toyota red.

I saw water moving when the engine was running and the radiator cap was removed but is there a good way to test the operation of the water pump?

[Bram van den Heuvel]

et or something cracked/warped?

The radiator cap has 0.9 embossed on it which I guess means 0.9 bar, which I guess means 0.9 times 14.7 which is about 13-1/4 PSI above atmospheric pressure.

The problem was that the pressure tester from oreillys doesn't seem to come

with an adaptor that fits my cap so I couldn't test the cap.

pg

[Bram van den Heuvel]

I found the problem by borrowing a pressure tester from oreillys!

It was a hairline crack at the plastic neck of the radiator.

[Jess Guessing]

What caused it to crack? Excess pressure, flexing or just old age?

[Bram van den Heuvel]

The radiator is the OEM radiator on a 1990's vintage Toyota.

If they didn't make the top plastic, it would still be working, but two decades is a decent amount of time for a $200 radiator.

Unfortunately, the whack-a-mole game failed in that it still lost pressure this morning when I tested the epoxy temporary repair (until the parts arrive).

The question is how far can you drive on an unpressurized system?

[Bram van den Heuvel]

Thank you for that helpful link which discussed . Water rinse Not effective in electrolysis, aluminum oxide, or oil contamination . Tee flush Introduces a weakness into the system that will leak. . Sodium citrate flush Doesn't really do much. . Garden hose into lower hose & thermostat removed Works well on the engine but crud remains in the radiator . L-11 oil milkshake emulsifying flush Works well for oil contamination. . Engine flush by driving 100 miles over 3 days with a cleaning mix Works well but requires a drivable vehicle Use 420CF for Electrolysis, Rust, Dexcool muck, or Silicate Drop-out. . Lowerhose drop flush (remove lower hose on a hot engine) Dangerous to getting burned . Sump-pump flush Takes Time, Temperature, Chemistry, Agitation and Settling into account.

One non-flush question I have for those who are experienced with cars is what are the ramifications of driving with an unpressurized system?

I tested it this morning and it still leaked around the neck in a different spot, which I duly epoxied but I have no illusions about playing whackamole.

What I just don't know is how much danger there is in driving an unpressurized system?

[trader_4]

If they made it of metal it probably would have corroded and failed sooner. Plus it and it's replacement would have costed more.

Depends on ambient temperature, how hard the drive, and percent antifreeze.

[Jon Doe]

There are too many factors (vehicle speed, engine load, ambient air temperature) to determine if it's safe. The overheat risk and resultant engine damage may not be worth it. YMMV

[trader_4]

+1

If it's a minor leak and local, easy driving, I would do it. Crossing Death Valley pulling a trailer, probably not.

[Bram van den Heuvel]

I agree that going up a mountain or crossing a desert or a long 100 mile trip might be pushing my luck, but I'm asking technically what happens if we drive, essentially, with the radiator cap off.

Assuming everything else is working fine, the only difference I can think of is that the pressure of the system above ambient is zero psi compared to about 1 atmosphere.

That lowers the boiling point of pure water to 212 degrees, where a 50:50 mixture of coolant would be something higher than 212 degrees.

But how hot does an engine typically get? Isn't an engine coolant generally around 200 degrees F?

[Bram van den Heuvel]

But that doesn't answer the question. The question is what happens when you drive unpressurized.

All I can think of is that the boiling point is lowered.

Most engines keep the temperature around the 200 F degree mark, I think, where even plain water wouldn't boil.

What's the boiling point of unpressurized 50:50 coolant?

[trader_4]

Modern engines run hotter, I'd say they can easily be close to 212F. That's why you need 50 50 antifreeze. And that's the overall average temp, not the localized temp in the hottest spots in the engine.

[Ed Pawlowski]

223 degrees

Thermostat is usually 195 degrees but they will run hotter in summer with AC on. That is why they are pressurized. With 50-50 mix and pressure you can go to 250 before boiling.

[Dean Hoffman]

Irrigation power units sometimes had a cooling coil instead of a radiator. The cooling coils had caps but weren't really intentionally pressurized. They worked fine as long as they had coolant. The thermostats were probably in the 185 degree range. Picture here:

The cooling coils are one pipe inside of another. The cold irrigation water runs through the center pipe. (not visible) The engine coolant circulates through the outside pipe then back to the engine.