Happy memorial day weekend!

Our 210 RX 350 awd with 137k miles started making a rapid thumping noise from the back, and it sounds like it's coming from the fuel tank, drivers side under rear seat. Used mechanic stethoscope on it. Can only hear it when car is pointed uphill , engine on, in gear or parked doesn't matter. Cannot hear it when moving probably because of road noise. Are our fuel pumps an electric piston type motor? It sounds like piston slap on a smaller scale. I thought our fuel pumps would be a propeller type like a water pump? Anyone know type of fuel pump we have or if my diagnosis fits the noise? Tried posting the sound but m4a is not an acceptable file type. Thanks

 

I have not dissected an RX fuel pump [last pump that gave me an issue was on an Accord]. As you mention there are two types of common pumps .. pistons and centrifugal. The centrifugal have to have a relatively larger diameter while the piston types can be elongated .... this makes it idle for a rod like structure ... ideal for servicing in a tank of a vehicle.

These pumps make a rapid clicking sound. tick, tick,tick,tick. They come on as soon as the vehicle realizes there is going to be a need. With modern electronics .. it be turned on the second the key is detected inside the vehicle [don't leave the keys in the cabin] and there is an elaborate mechanism to cut the pump in case of accident, Normally it shuts off once the line pressure is detected over a threshold.

Ideally you should try to keep the fuel level above the 1/2 mark.

Just making a noise, does not mean there is a problem. If it is abnormal then investigate. I would worry if sound is not regular.

Salim

 

Thanks for chiming in. It makes sense then that this uses a piston setup given the shape of the pump. I'm concerned that it's not a tick tick, but a thump thump. Actually sounded like a drive line thump like a ujoint going, except car is stationary. Tank was full when I noticed. It was after driving it a few miles. Not happening this morning just driving it up on ramps in my driveway. Dang, I hate crawling under there with a fully warmed up exhaust.

 

Try the trunk or the back seat. Underneath is just the bottom of the tank and the pump and level sensors are dropped in from the top.

Salim