2003 XC70 hot start noise

volver wrote:

> I have a 2003 XC70...with 100K miles. Love this car! However, I’ve
> had the car back to the dealer 3 times for a ’hot start’ problem. The
> car makes a noise (knocking/clanging) upon firing ONLY when the engine
> is hot and has sat for 30-45 minutes. The noise stops in about 2
> seconds and will not reocurr upon restarting. It doesn’t make the
> noise at cold start. In the winter, it’s minimal...in the summer,
> it’s horrible. The dealer has
> *replaced exhaust manifold gasket (even I knew that wasn’t the
> problem!)
> *replaced the timing belt and ’tensionor’ which they were sure was the
> cause...NOT!
> *replaced the oil pump seal...I picked the car up today and the noise
> is still there.
>
> It’s obviously caused by heat build up. What on/in the engine could
> be the cause of this mysterious noise? Any ideas? Thanks, Volver

If it starts, it is not a problem, unless it is damaging something, and
I doubt that it is.

My theory is that the heat build up causes the computer sensors to make
the computer choose a bad set of parameters (mixture and timing) but
after the engine starts the parameters correct themselves. It could be
aggravated by a sensor that is bad when hot or improved with a computer
program update.

My '80s vintage 240's would sometimes have trouble starting under the
scenario you mention. My '90s 850's and '01 V70 have never had trouble
starting. Sometimes they run rough after starting. In those cases I
just shut it off to reset the computer and start again and all is good.

Another possibility is water in the gas. The fuel tank would be the
hottest under the scenario you describe, hence the level of water in the
tank would have expanded most. Try 2 cans of dry gas.
--
Cheers, Steve Henning in Reading, PA, USA
Owned '67,'68,'71,'74,'79,'81,'87,'93,'95 & '01 Volvos.
The '67,'74,'79,'87,'95 and '01 through European Delivery.
http://rhodyman.net/homevo.html