2004 Sounds Like Teapot

My 2004 has 47K miles. Springtime has arrived in southern CA and the weather has turned warm (high 70's to low 80's F ambient temp.)

I notice that after driving for a while and then turning the car IG-OFF, I can hear a continuous sound from the engine compartment, almost like a teapot whistle. After several minutes, the sound stops momentarily, resumes, stops, resumes, stops, resumes, then finally stops.

This is a different sound than produced by the engine coolant heat recovery pump or the brake pressure accumulator pump. The sound does not happen in colder weather.

I tried to localize the source of the sound within the engine compartment, but that is not easy. It seems to be coming from the engine.

This happened last spring as well, and continued into summer. I replaced the radiator cap. The engine coolant level in the reservoir stays at full.

The presence of the sound seems to imply that higher pressure is venting to lower pressure. Can anyone think of a cooling system location where high pressure & low pressure exist - maybe the electric coolant pump for the cabin heater? The overall system appears to remain sealed since the reservoir coolant level does not drop.

Has anyone experienced this problem before; if so what was the resolution?
Thanks!

 

Hi Galaxee,

Thanks for your reply & for consulting with DH. The sound probably lasts a couple of minutes; I'll time it next time it happens.

I don't have instrumentation on my 2004 but there's no obvious sign of engine overheating.

I posted to one of the Yahoo Prius groups and heard from a Nevada poster w/ a 2004 who noticed a similar issue.

 

Thanks, Galaxee.

I am planning a drive to San Diego today. When I return home the engine should be nice & hot and I expect to hear the sound again. I am planning the following:

1. Use a length of rubber hose as a make-shift stethoscope to see if I can localize the sound. Maybe the sound is just coming from the radiator cap allowing pressure release into the overflow container.

2. Slightly turn the radiator cap to allow the pressure to vent into the overflow container (doing so without injuring myself). When I vent the pressure, I believe the sound will go away which would prove that the sound is coming from the hot engine coolant system.

IIRC the radiator tank opening for the cap is black plastic. When I replaced the radiator cap last year it seemed that the fit was not as tight compared to my 2001 that had an aluminum tank opening for the cap.

Have you ever been in a motel or apartment where the plumbing was cheaply constructed? When someone is taking a shower, you may have heard the high-pitched sound that the pipes make as water flows through. This is what the Prius sounds like.

 

The sound does not seem to be due to engine coolant system pressure. While hearing the sound this afternoon I opened the radiator cap and the sound continued.

My next move will be to disconnect the wire connector to the positive jump start terminal in the main relay fuse box, to see whether the sound is produced by a 12V-powered device.