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Hello Mach V fans! It finally feels like fall in Virginia. We had our first overnight frost recently, the leaves are changing colors, and pumpkins are appearing on front porches. Turbo weather!
When the ambient temperature goes down, your tire pressure is going to decrease. A rough rule of thumb is that for every ten degrees of ambient temperature drop, your tire pressure will go down by 1 psi. So if the outside temp is 30 degrees lower than it has been, your tire pressures will all be low by at least 3 psi. Even if you don't see any TPMS (Tire Pressure Monitor System) warnings in your dash, it's a good idea to check your tire pressures now that lower fall temps have arrived. Use the sticker on the driver side door jamb as a guide to a good starting pressure for your car, but you might want to adjust if your tires and wheels have been changed from their stock size. Generally a lower-profile tire is going to need a slightly higher starting pressure. As a guideline add one psi for each inch of wheel size over stock. So if your car started with 17" wheels, but you have installed 19" wheels instead, figure +2 psi for your starting tire pressures.
Note that you should check your tire pressures when the tires are cold. The air will warm up as you use the car, so checking them after driving for an hour will not give you accurate readings.
Most gas stations have a tire inflation station (which you will likely have to pay for), but you can also use a portable electric tire inflator. Don't rule out an old-fashioned bicycle tire pump, either. It will take a little longer, but it requires no power other than your muscles.
Keeping your tires properly inflated will help get the longest life from the tires, and it will help your car handle and perform it best.
SHOP SUBARU TIRE PRESSURE GAUGE
We imported these thick and fluffy fleece STi jackets from Japan just in time for the cool season. They feature the STi logo embroidered on the chest, plus some nice technical details like wear patches on the forearms, elastic hems to reduce wind intrusion, and nice zippered hand pockets. Sizing is Japanese so they run a little smaller than US standard. Pay attention to the sizing notes on the product page when ordering. In stock now in limited quanitities!
Most modern engines use direct fuel injection, or more simply direct injection (DI), and a side effect of DI fueling is that the intake valves of the engine accumulate carbon deposits. Today we'll talk a little about why that happens, what problems that can cause, and what you can do about it.
Older engines used port fuel injection, where the fuel injector was positioned outside the intake port and fuel was sprayed into the airstream ahead of the intake valve. Although this older technology was inferior in many ways, it did have the benefit of keeping the intake valves clean, since gasoline is a solvent and the constant wash of gasoline over the valves would naturally dissolve away anything that landed on the valves.
With the direct injection fuel injector relocated to spray directly into the combustion chamber, the intake valves accumulate little particles of airborne carbon that are natural byproducts of the car's crankcase ventilation system. Over time, the tiny particles can build up into substantial deposits of carbon material that can seriously obstruct the airflow around the intake valves.
If the deposits get bad enough, the car can suffer from reduced horsepower, unsteady idle, poor starting, and other running problems.
You might think that traditional solvent-based intake system cleaners, like Sea Foam or other similar products, might take care of these intake valve deposits, but from experience the hardened carbon is too resistant to those solvents and the only effective method to clean the valves is physical scrubbing or abrasion.
Our preferred method of cleaning the valves is to use an abrasive media sprayer. Walnut shell media works perfectly because it is hard enough to remove the crusty carbon deposits, but not so hard it will damage the heads, valves or engine internals. This process is commonly known as "walnut blasting."
To access the intake valves requires removal of the intake manifold, and the cleaning itself is time consuming, taking several hours, so this procedure is not inexpensive -- our current rate is a little over $1250. We have seen substantial deposits develop in as little as 40,000 miles.
Customers ask if this problem can be reduced or prevented with either certain behavior (using high-quality gas, driving in a certain way), or using specific aftermarket parts like an air/oil separator. Our experience is none of these will make any substantial change in the buildup on the intake valves.
For what it's worth, almost all modern direct injected gasoline engines have this problem, so Subaru owners aren't alone in having to perform this maintenance. (One exception in the Subaru lineup is the BRZ, which uses a Toyota-developed dual injection system with both direct AND port fuel injectors.)
That's it for today's email update. We hope this has been informative and interesting. Now go for a fall drive!
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