QUESTION: I have an '07 CTS that from the start has used synthetic oil. On my last oil change they put in regular oil (at half the price) by mistake. Will this cause damage and should I change back right away or is it okay to use regular oil? Thanks
ANSWER: Synthetic oils are often used in engines for a few reasons. They flow easily when cold, so they help with easier engine starting. The lighter or thinner oil creates less internal engine friction, so fuel economy is better, and synthetic oils protect moving parts well under high heat and load conditions.
Conventional oils have provided similar protection for decades, but they are always a compromise between easy flow during cold weather and protection during hot weather. That is why many older cars specified different oil viscosity ranges for winter and summer driving, ie: 5W-20 for winter and 10W-30 for summer.
The use of conventional oil in your CTS will not cause any damage, especially during the cooler winter months, but may not provide the protection if you are travelling during hot summer weather at higher speeds or hauling heavy loads. If it were my vehicle, I would keep the conventional oil in the engine for the winter and then change back to synthetic as temperatures warm up at the end of spring. Be sure to change the oil filter at the same time so most of the old oil is removed.
QUESTION: I recently purchased a used 2007 GMC Z71 with 60,000 kilometres. The problem is the transmission cooler lines are leaking at the rubber-to-metal connections. The dealer where I purchased the vehicle said he would replace them with original GM hoses but they would probably leak again in the cold weather. Is there a solution to this problem? Thank you.
ANSWER: This has been an ongoing problem for several years, not only with GM but other manufacturers as well. The problem is the with the crimp where the rubber hose connects to the metal pipes. Vehicle manufacturers constantly attempt to lower vehicle weight and save manufacturing costs. One of these areas is by using aluminum crimps at the hose connections. For most of North America, these work fine. For colder climates such as we see in Canada, a problem develops.
The aluminum expands and contracts about twice as much as steel does during temperature changes. The crimps on the hose ends are subject to these hot and cold extremes and eventually loosen just enough to allow oil to seep from the connections. I haven't seen examples of hoses coming completely off, but the seeping oil does make a mess of both the vehicle and your driveway. If you don't check oil levels on a regular basis, you could potentially run low on oil over a longer period.
This seeping/leaking problem always appears in abundance during the first real cold snap of winter. New hoses will work for awhile but the problem returns and many times there is such a demand for hoses that there is a back-order situation and you have to wait weeks for the new ones to arrive.
Many shops are using remanufactured hoses, where they take your original metal pipes and have a new rubber hose crimped on using steel crimps. Industrial hose and rubber supply businesses in larger centres usually perform this type of repair or know of shops that do. You could have your automotive repair shop take the hoses off and send them out to be refitted with new hose and crimps. But typically a dealership will provide only original replacement parts so you may need to find an aftermarket repair shop.
Jim Kerr is an experienced mechanic, instructor of automotive technology, freelance journalist and member of the Automobile Journalists' Association of Canada.