Toyota's Mysterious Grumbling Noise at Shut Off



I bought the car new in '92 and have taken very good car with oil changes and required maintenance. The vehicle just turned 200 K miles, although mechanics have said they have seen these cars top 300 K miles. Noise started about a month ago and was initially noticed after turning off the engine after a 15 mile drive. Started happening more frequently after 10-15 mile drives. Now it happens on short drives (5-6 miles), but not every time, and not when I brought to my mechanic to examine (figures!). Water was put through the radiator hose to flush out any trapped air, so that is not it. The noise is a cross between a grumbling of both air and water and it goes on for quite awhile. I stayed in the car about 3-4 minutes after shut off and it was still acting up. Any Ideas? Thank you for your input.


Noise is under the hood.


Could this be the sound of nucleate boiling? With the mileage on this car, it is possible that coolant is boiling next to hot parts of the engine (exhaust seats, exhaust passages, cylinder domes. etc.). The boiling bubbles expand into cooler water and collapse so there is expansion and contraction in short time span. The coolant in the radiator will not be boiling but due to the cessation of coolant flow the coolant is boiling inside the engine.

A way to tell if this is occuring is to touch the upper radiator hose-- carefully as it will be hot. If you feel vibration in the hose, you may have nucleate boiling in the engine. The cure is to check the mix ratio of the coolant and/or delime the cooling system.

Hope this helps.


How old is the radiator cap?
If it’s not holding pressure you can get nucleate, er, hot spot boiling.