recommended rpm

It should carbon up, use more fuel and possibly overheat. Oil won't pump with enough pressure for the work being asked of the motor, so it won't last as long. But it's hard to prove all that to someone who doesn't understand and God protects fools, women and drunks.

I usually try to keep it under 2000 RPM cruising, though that's not always possible. It's best to just drive it by feel, if it's lugging or vibrating excessively then downshift to raise the RPM.

It does go into the yellow zone on the turbo dial, which worries me because I've heard overuse of the turbo can wreck the engine. The previous owner says his teenage kids blew two motors! But what's the difference between a teenaged boy driving it hard, and my wife low-rpming it up the hills with the turbo in yellow?

Boy Racers (of whatever age) tend to rev the engine high and long, and this is harder on turbos than having to operate at low speeds and higher pressures. Do these engines even increase the turbo pressure that much under low-speed load...?

How could reving high be hard on the turbo if the turbo dial is showing a lower reading for the same speed? I assume the turbo dial is pressure, but I don't know.

The particular circumstance is driving on the highway around 90km per hour, in OD, around 1800 rpm, then not gearing down for hills, and the turbo going way into the yellow until back on the flat.

When I drive, I gear down for hills, the engine revs are higher (2500ish) but the turbo reading is much lower, well below the yellow.

Using the turbo a lot will consume more fuel and cause more wear on the turbo, but you really have to try in order to blow a Volvo motor. I don't know what the teenagers could have been doing other than possibly constant redlining the RPM or messing with the boost. I drive mine fairly hard and have yet to damage even a high mileage motor.

Generally you want to keep the needle in the black unless you need the power, boost won't hurt it but it won't help the economy any since the ECU richens the mixture under boost.

The turbo pressure will increase to the full 8.5 PSI at any speed if you give it enough gas. The pressure is always whatever the guage shows regardless of RPM, though the guage is not calibrated. The difference is that the turbo will be spinning faster to maintain any given pressure at a higher RPM as more air will be flowing through the motor.

For a given pressure, higher revs result in more heat and more wear on the turbo. I doubt it glows dull red when run under load at low speeds like it can at high speeds.

As noted elsewhere, if it isn't pinging, she probably isn't damaging it. You may want to see if you can adjust the wastegate to limit the boost.

FWIW, the 740 series water cooled turbos are remarkably robust. I couldn't convince my wife (who was the primary driver of our '85 765T for more than a decade) not to rev the engine when she started it or to let the turbo cool down when pulling off the freeway into a gas station. I could hear the turbo spinning down as she got out of the car. At nearly 240K miles it is still going, and the engine has never been apart beyond timing belt replacements.

Your wife is more valuable than the car, so relax and enjoy the ride.

Mike

Because the boost guage is showing just that, pressure. If the engine is revving higher the turbo has to spin faster to maintain the same boost. Really though either scenario will not hurt the turbo, it should last a long time regardless of how it's driven as long as it's well maintained and doesn't get extreme abuse.

Maybe she needs this:

Regards,

Boris Mohar

Got Knock? - see: Viatrack Printed Circuit Designs (among other things)

void _-void-_ in the obvious place

In general high revs wear the top end of the engine (rings, cams and valves) whereas low revs wear the bottom end of the engine (bearings). As long as the engine isn't lugging it should be ok although personally I tend to keep the revs between 2000-3000 for general driving (S70 T5).