Published October 06. 2012 4:00AM
Q: You have recommended changing coolant every 30,000 miles or three years. How does universal coolant compare to green, orange, etc., types of coolant?
A: As coolants and engine technology continue to improve, I've softened my position on coolant changes. Assuming a long-life coolant and 15,000-25,000 annual mileage, I'm willing to go five years now - a huge step for me.
There are basically two technologies for corrosion protection in engine coolants - inorganic and organic. The conventional antifreeze used for decades, which is usually green in color, utilizes silicates and/or phosphates to protect the various metals used in engines and radiators.
The so-called long-life coolants - often orange in color - introduced in the mid-1990s utilize organic compounds to provide anti-corrosion protection. The benefit is these compounds last longer, thus the extended-life concept. There are also several hybrid coolants used by several carmakers that combine both organic and inorganic compounds.
Universal coolants typically use organic compounds like long-life coolants and claim to be compatible with any coolant.
As confusing as the different coolants can be, remember three important things: You own and are responsible for the vehicle; if the cooling system contains any conventional antifreeze, change it every three years; and, finally, no coolant is permanent, or capable of lasting for the life of the vehicle.
Q: I have 2006 Jeep Grand Cherokee SRT8. I took it to the dealer, and they said I have a No. 1 cylinder misfire. They checked the compression and leak down on all cylinders and everything was OK. Now they want to pull the cylinder head and check for carbon deposits on the valve and the valve possibly not rotating. The miss occurs while idling. Can you come up with any more possibilities?
A: There are several steps in the diagnostic process before deciding to remove the cylinder head for inspection. First, decarbonize the induction system to remove any carbon buildups. Next, connect the engine to an electronic engine analyzer to determine if the misfire is electrical rather than mechanical. This can show the actual voltage required to fire the spark plugs. Comparing this information to the performance of the other cylinders might well identify an ignition problem with the spark plug, coils or harness. The 6.1-liter Hemi V-8 in this vehicle features twin plugs per cylinder and coil-on-plug ignition coils.
If the misfire is electrical, it may be possible to swap coil packs between different cylinders to see if the misfire follows the coils. A new pair of spark plugs in the misfiring cylinder might also help.
If the misfire is not electrical, try the same thing with the fuel injector from the misfiring cylinder. Does the misfire follow the injector?
If the misfire is neither electrical nor fuel-related, it may - and not having tried this on a dual-plug engine, I emphasize "may" - be possible to remove and disable the coil pack from that cylinder, disable the injector, remove one of the two spark plugs, and install a compression gauge with the Schrader valve stem removed so that the gauge will not hold pressure. Starting the engine momentarily will show the actual running compression in that cylinder. If airflow into or out of that cylinder is restricted by carbon deposits or a valve problem, the running compression will be low.
Paul Brand is an automotive troubleshooter, driving instructor and former race-car driver. Readers may write to him at: at firstname.lastname@example.org. Please explain the problem in detail and include a daytime phone number. Because of the volume of mail, we cannot provide personal replies.