Cylinder Deactivation Systems And Transmission Fuel Change

This week I thought I would expand on two frequently asked questions I get from listeners across the country.



Dear Tom,

How reliable and effective are the cylinder management systems today? I am considering a new Honda Accord V6 sedan. Years ago, I had a Cadillac with the 8-6-4 system and it was a nightmare to keep running so I am apprehensive of this technology. What are your thoughts?

Samuel from Chicago


Cylinder deactivation systems are much more reliable then past systems and operate efficiently. Honda uses the technology in both their cars and motorcycles. Go for it!


How does cylinder deactivation work?

When not needed, the system shuts down fuel supply to the cylinders not being used and closes the valves. There are two ways to accomplish this: 1) rocker arm control mechanically or 2) collapsing the valve lifters via oil pressure control through the ECM (Engine Control Module). The remaining exhaust gas from the previous combustion explosion in the deactivated cylinders act as an “air spring,” bouncing the piston back down after traveling to TDC (Top Dead Center) on compression and exhaust strokes. This causes no undue stress or pressure on the engine. Fuel, ignition, lifter collapse, and rocker arm control are managed via the computer.

The problem with Cadillac’s 8-6-4 cylinder deactivation system

Years ago, cylinder deactivation was very unreliable because computer systems were so primitive. Today’s systems control the valvetrain via oil pressure to the lifters or rocker arm system. In contrast, the older Cadillac system used electromagnetic solenoids to mechanically disengage the rocker arms and thus close the valves during cylinder deactivation. The major problems that Cadillac had with these systems stemmed from poor control of fuel through the throttle body. It continued to pump fuel into all the cylinders even when some cylinders were deactivated, causing drivability problems. Also it didn’t help that the ECU (Engine Control Unit) only updated 10 times per second, which is entirely too slow to efficiently operate the engine in deactivation mode. Today carmakers employ computer systems that update hundreds of times per second, managing cylinder deactivation systems efficiently and effectively, thus keeping up with the rigorous demands of on-the-road operation.

What fuel mileage savings are realized with such systems?

It’s sketchy but carmakers claim an average of 20 percent fuel savings with cylinder deactivation. GM’s 8-6-4 system for Cadillac claimed 30 percent savings in highway mileage.

Is there anything I have to do to activate cylinder deactivation?

No, the system monitors engine demand via the computer and deactivated cylinders when not needed, all quite seamlessly.

Can I install an aftermarket cylinder deactivation system on my car?

Yes, Delphi makes an aftermarket kit that will work on most 6- and 8-cylinder pushrod overhead valve engines. There are other companies out there that make aftermarket kits for cylinder deactivation, but I like the Delphi offering because of their extensive research and development.

What carmakers offer cylinder deactivation technology today?

Mercedes, VW, Chrysler, Jeep, GM, and Honda cars and motorcycles. As gas prices continue to rise, look for more cylinder deactivation offerings from more carmakers.


Dear Tom,

I own a 2005 4-Runner with 88,000 miles and I had no problems with this truck. Do I need to change the transmission oil? Should I have a complete fluid exchange done?

Mr. Max

Mr. Max,

Toyota recommends to change the transmission fluid and filter on your truck every 60,000 miles. Check it before changing it to make sure its red and clean before doing a complete fluid exchange. If the fluid is dark red or brown and smells burned, just change the fluid in the pan along with the filter. Make sure you use the fluid that Toyota recommends as well as a high quality filter (Toyota, if possible).


Mr. Max asks a good question regarding transmission service. Let’s break it out a bit.

When to change transmission fluid and filter

In this case, Toyota recommends to change the trans fluid & filter every 60,000 miles, the Automatic Transmission Rebuilder’s Association (ATRA) recommend transmission oil and filter replacement every 30 – 40,000 miles (I subscribe to this suggestion as trans oil is subject to a harsh environment and should not be left in the unit longer than 30-40,000 miles). Check your owner’s manual for specific guidelines.

What to look for when checking transmission fluid

Transmission fluid tells quite a story about the condition of the unit. Observe its color, consistency, and smell. If it’s red, clear, clean of gritty material, and does not smell burned, then a simple maintenance is all that is required. The procedure includes dropping the pan, replacing the filter, and doing a complete fluid exchange. Should the fluid smell burned, is dark in color, and there’s material in the pan, then I would seek the advice of a transmission specialist before performing a complete transmission fluid exchange because, at this point, it can cause catastrophic failure on a transmission that is internally burned up.

Dark-colored gritty fluid

Dark colored, gritty transmission fluid means that there’s internal wear inside the transmission. Friction clutches have worn out and the material is ground up and circulating through the unit. Also, if there are bits of metal present, then hard parts are worn. The dark colored fluid means that the unit has overheated and burnt the fluid, rendering it unable to lubricate, cool, and protect internal parts. Depending on how much wear material and how burnt the fluid is, the shop might opt to change just the fluid and filter in the pan rather than a complete fluid exchange, which can cause the unit to fail.

Use the correct fluid and filter

Compared to transmissions made years ago, today’s transmissions are very sensitive. They require filters with defined flow and filtration rate. Fluid is engineered specifically for transaxles. Carmakers work together with petroleum companies to develop trans fluids that address problems and idiosyncrasies of a particular transmission. If the recommended fluid and filter is not used, erratic shift patterns and internal problems can ensue. The best advice here is to use the recommended fluid and filter for your particular vehicle. Aftermarket products that are endorsed by the carmaker are also acceptable.

When to change the lubricants in transfer cases and differentials

No rule of thumb here. Carmakers use special fluids for transfer cases and a few different differential lubricants, so the best advice is to consult your owner’s manual.

‘Til next time … Keep Rollin’

Tom Torbjornsen is an automotive expert of 38 years. An automotive journalist in good standing with the nternational Motor Press Association and Motor Press Guild, Torbjornsen has been the Repair and Maintenance editor for AOL Autos, At Home Portals, and many other websites. Hear his radio show AMERICA’S CAR SHOW, locally on AM1340 WKSN via the SSI Radio Network Saturday mornings at 8. See Tom’s television show, “America’s Car Show” on Buffalo’s all new WBBZ TV, Channel 5 on Dish, channel 67 over-the-air and on Direct TV. The show airs weekly Wednsday nights 6:30-7. It is re-aired on Thursday mornings at 9 and Saturday mornings at 11. For more info on Tom Torbjornsen, visit AMERICA’S CAR SHOW website at: You can send Tom your car questions and TV show topic suggestions at: Find Tom’s book, “How To Make Your Car Last Forever” in local Barnes & Nobel booksellers and online at