Hi guys,

Recently, I flushed out my radiator and now my car has developed an odd sound. First off, I used the following method when flushing the system out:

- Car's front was jacked up and on stands.
- Used drain bolt on the block.
- Refilled with distilled water, start, fill with coolant.
- Get the air out.
- Refill with distilled water as needed.

Anyways, now the car has a slight bubbling or boiling sound whenever I tip-in on acceleration. I've never heard this type of sound before. Leaky radiator cap? That was my only conclusion. But can a cap make that noise so audible that I can hear it from inside while driving?

 

Look around for MIAC references......might have a big air bubble in the heater core....drive the car nose up on a steep hill and open the heater to full hot and rev it up and down a bit...might burp it out. Some reference to a heater core restrictor that is supposed to fix the noise. If you didn't have it before...go with the bubble removal and it should be OK again

 

cavication?

 

Or even cavitation......

 

Cavitation usually was an issue north of 6000 rpms.

I'm getting this sound at low rpms usually right after I take off from dead stop using part throttle.

dannobre,

I've read that method (actually from one of your old posts) and have performed it. It doesn't seem like the same air bubble issue.

 

Start your car when everything is cold, and let it idle without the radiator cap, let all the airbubbles out. Then add coolant. then cap it

 

If it started after you did your coolant swap..likely it has something to do with that...

Spontaneous things do happen...but usually a good place to start is the last system you screwed with

 

Yeah.....

I'm thinking it might be the radiator cap. It hasn't been changed and I'm at about 45k miles (I bought the car at 21k miles). I'm going to start with that and work through the rest of the cooling system.

Thanks for the help guys!

 

Try leaving the radiator cap off and let the car warm up, turn on the heater to high for a about a minute or 2, then put the radiator cap back on. This fixed my issue after I did a drain/fill coolant, had your symptoms.

 

youve got air in the system

 

You guys speak as if I don't know how to properly bleed the RX8's cooling system.

Cap off, front end in the air on jack stands, ran the car with the heater on, refilled and bled correctly, and then replaced the cap.

Coolant levels have stayed the same at the same mark I made after bleeding completely. I know that the cooling system is pressurized so my assumption was a faulty radiator cap.

Again, I only get the sound right as I press the accelerator and there is a change in load on the engine. WOT does not reproduce the sound nor can I hear it since the sound isn't ridiculously loud. It's a very faint fast bubbling sound at tip-in throttle only.

I've ordered a new cap so we'll see if that takes the issue away. I have no reported power loss and the car has several modifications - all of which shouldn't affect this issue.

Quick question for some of the technical guys here......

When you introduce load on your motor, does the cooling system pressurize according to load? Would this pressure at low rpms be enough to create a sound if the cap was faulty and not sealing correctly?

 

Cooling system pressurizes due to temperature of coolant on a closed system....the rpm change from stepping on the gas would only increase the water pump RPM in relation to the engine speed

Drive it with the heater on full for a few days and see if it goes away

 

it doesn't matter if you run the heater on high or at all, there is no control or bypass valve in that particular side of the cooling system, it always has whatever flow rate is coming out of the rear iron and going back into the water pump inlet area on the front cover. The heater control is via air diversion over the HVAC and cabin air flow paths, not the coolant side of the system. Funny thing is, if the AC is removed or non-functional the system blows hot air continuously. I never did figure that one out.

diagram #3 in this thread: https://www.rx8club.com/showpost.php...30&postcount=7

EDIT: just noticed there is a fixed flow control orifice in that loop, apparently in the hose right before the cover/pump inlet connection #61-E09. Thanks for letting me learn something new but all of the above still applies


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