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350matt
350matt, Engineer
Category: Mazda
Satisfied Customers: 20811
Experience:  Mechanical Engineer BEng Hons22 years experience
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My 2005 Mazda RX8 makes a rattling sound when under load.

Customer Question

Customer: My 2005 Mazda RX8 makes a rattling sound when under load. Doesn't do it all the time but sounds likd something is coming apart in the engine
JA: Thanks. Can you give me any more details about your issue?
Customer: Car has about 108K miles on it. I've changed the spark plugs and wires recent and replaced he EGR vacuum valve. Ford/Mazda claimed that was the problem. This did get rid of an issue I had with stalling under initial acceleration from stopped position. However, when I accelerate a loud rattling noise comes from the engine compartment as it is changing gears.
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Customer: Can't right now. I'll log in later
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Submitted: 1 year ago.
Category: Mazda
Expert:  350matt replied 1 year ago.

Hello

I'd first try removing the auxiliary drive belt and turning every pulley and ancillary ( power steering pump , alternator etc) by hand. All should turn easily (with the exception of the AC pump) with no grittyness or wobbly pulleys- If you do find a sticky pump / alternator then it should be replaced or repaired

If the engine is stone cold you can briefly run it with no belts to see if the noise changes or has gone away, this will help show if an ancillary is the issue

Examine carefully the condition of the bottom / crank pulley as these are composite construction with a rubber element and its possible this rubber is breaking up and allowing the two metal portions to move.

Customer: replied 1 year ago.
Not sure why your suggestion would be useful in diagnosing the rattling noise from the engine compartment. This noise does not occur when the engine is idling. The noise occurs when the engine is in gear when being accelerated and shifting through gears. Do you have any other suggestions?
Expert:  350matt replied 1 year ago.

hello

ok thanks for highlighting that

in that case I'd say that this could be a faulty clutch release bearing?

if the noise changes when you press the clutch pedal then this would bear this out

sorry to say that the transmission will have to be removed as the next step

Customer: replied 1 year ago.
My mazda rx8 has an automatic transmission so can't depress the clutch. The rattling sound does diminish when I let off the gas when the rattling starts.
Expert:  350matt replied 1 year ago.

Hello

Ok in that case I'd check over the propshaft for wear

you can easily check for for any slack in the propshaft joints by twisting either half by hand and feeling for any play as there should be virtually none

the centre bearing is quite loosely mounted so this can be moved normally but if you can run the car in gear with the wheels off the ground and then feel the centre bearing housing for vibration if there's any then consider replacing the unit

and then look along the propshaft for any signs of a missing balance weight as these take the form of little 3/4" squares that are welded onto the shaft - as they are only tacked on they can sometimes come loose and be lost resulting in the shaft being out of balance - if a joint is worn this can also shake them loose

so if a joint is replaced its good practice to have the shaft re-balanced afterwards

Expert:  350matt replied 1 year ago.

Hi

do you still need help?

Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! Thank you

Customer: replied 1 year ago.
I haven't had a chance to check the propshaft for wear. I'll rate you after I've done so as I may have more questions.
Expert:  350matt replied 1 year ago.

no problem

just get back to me on this post with your other questions

Expert:  350matt replied 1 year ago.

Hi

do you still need help?

Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! Thank you