Moaning sound at cold start-up

As Dick points out , as rubber gets older it gets harder, as do aged tyres, new ones for Silver this year..... more conforming to track surfaces, makes for faster times ....we hope. .Art

In the 80s GM had a rash of "problem noises" caused by fluid dynamics/harmonics issues. Fuel line thumps and power steering moans, etc. Usually the revised hose/pipe assemblies they offered fixed the problem.

Somtimes just adding a tiny kink or bend...or anything the slightly change the flow characteristics...would do the trick.

I had a 66 Olds where the cooling system moaned. Long story short I introduced a small restriction into one of the heater hoses and it solved the problem.

Weird stuff.....

Cheers
DD

Over the years, I had extensively modified the car. I made and installed quad throttle plates around 1990. Ended up having to modify the AAV system along with a lot of other stuff. Noise did not change. Put in a 6 speed manual. Noise did not change. Oil hoses were hard as a rock though. I do see this noise on hot rodders that use the teflon lined hose for the high side of the power steering hose. No dampening and it howls to beat the band. The long rubber hose is there for a reason. On the XJ6 fuel injected models the rubber hoses can get hard and the injector pulses can cause a tapping sound. Took a while to figure this one out as by the time you can trace it down, it is gone. Once again, hard rubber that cannot asorb the pulses.

I also was thinking perhaps the aav , raise the bonnet next time when cold and have a long piece of wooden dowel or a long tune up screwdriver ready and quickly go over each piece till perhaps you get the moaning sound direct to your favourite ear.......... ps be carefull of spinning things.................. Art

Fairly common on older V12's. It mostly is not the smog pump but rather hardened hoses that are not dampening the pulses of the oil pumps from the transmission and engine. I to had this groaning on cold mornings when the car was left outside and I was not running a smog pump. The power steering can groan when cold for the same hardened hose reason but most likely only when the steering is turned as there is virtually no pump pressure without steering action. The fix is rather expensive and difficult so it depends on how bad it bothers you. I put up with it for years until I sold the car. (not the reason I sold it).

> ...moaning sound ... V-12... upon cold start-up.
> The sound dissipates after a few minutes, .... Could it be the air pump?

There has been much discussion about this V12 moan on many Jag forums. I have it too, regardless of the ambient temps, when the engine is started while cold.

Some have surmised that it was the Auto Trans pump refilling the torque converter and/or pressurizing the trans fluid galleries. However, the moan did not change when I got rid of the trans and torque converter when I installed a 5-speed manual trans.

It's not the EPA air pump; I removed that many years ago with no change to the moan sound.

It's not the AAV valve, I ran without one for a while - no difference in the moan with or without it.

It's not the water pump cavitating - my system has no air in it and both thermostats work fine at proper temps.

My conclusion is that it is the V12 oil pump pressurizing the engine oil galleries.

A few years ago I installed digital gauges. The moan dies out at the same rate the reading on the digital oil gauge increases .

Does the tone change when you move the steering wheel? If so, the fluid level could be low or steering pump is worn and it has the start of what is known as "morning sickness" in the steering system. My 96 v12 air pump makes some noise too at start up, but it is not what I would describe as a "moan" in my case. Open the hood and start the engine and watch the air pump. If the sound stops when you see the clutch released on the front of the air pump, you will know if it is the air pump.

David

I've heard a few other owners mention the same thing. I *think* I read where it was the water pump cavitating. Try bleeding the cooling system and see if anything changes.

Cheers
DD